45 Timeless Recommendations for Bulletproofing Your Gut Against Wrong Food and Bad Habits

I won’t pretend to be modest, and I’ll say it as it is: this may be one of the most important health-related texts you’ll read in your lifetime. And it’s not important for me that you read it. It’s important for you. The price of ignoring it is pain, lost opportunities, large medical bills, and a shortened life.

Here, you will learn (or relearn) how human digestion actually works and gain a clear understanding of its physiology. You will grasp the timeline of digestive processes and what happens to food en route to the toilet bowl. Understanding it firsthand is your best defense against the misinformation about health and nutrition that has contributed to the following tragic outcomes in the United States:

None of the conditions above are preordained or particularly related to old age. Without exception, all of them are an outcome of the lifestyle and diet of most Americans, poor and rich alike.

Medical professionals and their families are affected by all of the same conditions at the same or greater rate than the general population because most of them sincerely believe in their own propaganda of a healthy diet and lifestyle. In most communities, the hospitals are now the largest employers.

When I moved in 1982 to Bergen County in Northern New Jersey, the Hackensack Medical Center was occupying a single brick building in the leafy residential area and employed approximately 2,000 people.

Today, it occupies a large campus with five high-rise buildings and has become the largest employer in the county with approximately 9,000 employees, a 350% increase over the original figure.

Between the same 1982 to 2025, the population of Bergen County increased from 844,419 to 957,736, or only 13%.

In 1982, the average life expectancy at birth in the United States was 74.6 years. Today, in 2025, the projected average life expectancy is approximately 79.3 years, or only a 6% increase.

So while the Bergen County population barely grew and life expectancy crept up by a mere five years, our local hospital staff expanded 350% over its original size to accommodate increasing demand for its services.

And all of this is happening in one of the wealthiest and most educated counties in the United States, east of the Hudson River and a spit away from Manhattan. The health attainment situation in less affluent areas is far worse.

So, by now, do you believe me when I say that the text on this page is as important as I claim? Or would you rather become fodder for the medical-industrial complex in your own state? If not, please read on!

Digestion's Timeline

In the next six sections, I will describe the ins and outs of each major digestive organ along the gastrointestinal tract (proverbially "the gut"). Respectively, they are the mouth, stomach, duodenum, jejunum, ileum, and the large intestine. 

The minutes and hours displayed in the parenthesis next to each indicate approximate minimum and maximum food transit times in healthy individuals in their twenties and thirties who DO NOT take drugs, drink alcohol, do the hard or stressful work after meals, snack every few hours, and gulp cups of cold or hot beverages (water, soda, coffee, tea, juices, beer, smoothies, etc.) between meals.

Add 5% to 10% to that time for each decade after 40. More if you are taking systemic or illicit drugs that can affect muscular function, including cardiovascular agents, central nervous system and psychiatric medications, endocrine and metabolic drugs, neurological and pain treatments, chemotherapeutics and immunosuppressants, and certain antibiotics.

By mechanism of action, the drug classes that slow down or inhibit digestion include beta-blockers, calcium channel blockers, statins, antipsychotics, sleep aids, SSRIs, SNRIs, corticosteroids, thyroid hormone replacements, antiepileptics, muscle relaxants, opioids, stimulants for ADHD, PPIs and H2 blockers, local antacids, immunosuppressants, chemotherapy agents, broad-spectrum antibiotics, antidiabetic drugs such as metformin, diuretics, cholinergic and anticholinergic agents, dietary fiber, and fiber-based laxatives as well as any other pharmaceutical agent that lists dry mouth, constipation, bloating, abdominal pain, cramping, irritable bowel syndrome, or other gastrointestinal symptoms among its known side effects, however minor they may appear.

After describing the function of each organ along the digestive path, I’ll outline 45 detailed recommendations for protecting it from avoidable harm and bulletproofing its performance. These recommendations form the foundation of ageless nutrition, good health, and life-long vitality.

Let’s start the journey:

Mouth (15 to 30 minutes, the longer the better)

Digestion starts with the first bite inside the mouth, not the stomach. Chewing breaks down foods into smaller particles and mixes them up with saliva. This process is called mastication.

Saliva contains the enzyme salivary amylase (also known as ptyalin), which begins breaking down carbohydrates into shorter polysaccharides and maltose. Lingual lipase, another enzyme secreted from glands on the tongue, initiates the slow breakdown of fats. Its activity becomes more pronounced in the acidic environment of the stomach.

The combined action of the teeth and tongue forms the bolus, a soft, round lump of chewed food. Saliva also contains mucins, which lubricate the bolus for smooth passage through the esophagus.

Thorough mastication reduces the burden on the stomach, speeds up gastric processing, and triggers anticipatory digestive signals via the vagus nerve, including the stimulation of gastric acid production. In other words, the longer and the better you chew, the better and faster your digestion and assimilation of nutrients.

Incomplete chewing, on the other hand, delays digestion further down the line, while excessive fluid intake with a meal can dilute saliva and impair the initial enzymatic breakdown of starches. What happens in the mouth sets the pace and quality for the digestion that follows.

I use the term fluids instead of water not to sound academic, but because wine, beer, juices, soups, sauces, and anything else containing mostly water, all count. I also use precise descriptions of digestive substances and processes (like salivary amylase, lingual lipase, or mastication) not to impress or intimidate you, but to ensure the text is accurate and useful to both the general audience and medical professionals alike.

Takeaways for a healthy mouth

The following rules — some already familiar but worth repeating, others lesser-known or often overlooked — will extend the useful life of your teeth and mouth and protect your gut from premature wear-and-tear. They form the foundation of not only a healthy gut, but also a longer and more functional life. The older you are, the more critical it becomes to follow these rules, because digestion after age 50 to 60 is a completely different kettle of tea than it was before:

• Hydrate in advance, not during meals or after meals. Drinking a glass or two of mineral water 30 to 60 minutes before eating primes your digestive system by promoting saliva production, supporting enzyme secretion, and ensuring optimal hydration for the mucus lining and gastric juice output. Arriving at the table already hydrated allows your mouth and stomach to do their jobs without getting flooded.

• How much water should you drink? The amount of water you need varies based on multiple factors: meal composition (protein-heavy meals require more), time of day, body weight, ambient temperature, hydration status, and even stress levels. There’s no one-size-fits-all rule. As a guideline, drink enough so that your mouth doesn’t feel dry a few hours after eating, but not so much that you're urinating excessively throughout the day. Yes, beer and wine technically count toward hydration, though they also come with diuretic effects. I prefer lager-style non-alcoholic beers for hydration with a flavor kick and without sweetness. Among the health-conscious in urban Europe, particularly in France, Italy, and Spain, it’s common to dilute wine with mineral water, creating a light “spitzer” that hydrates and refreshes without overloading the system with alcohol.

• Do not consume hard liquor before or after meals. Strong alcohol — vodka, whiskey, scotch, brandy, and the like — acts as an irritant to the mucosal lining of the mouth, esophagus, and stomach. Taken on an empty stomach, alcohol suppresses salivary and gastric secretions, disrupts the pacing of digestion, and blunts your natural appetite signals. After meals, it interferes with absorption and can provoke reflux, particularly if your lower esophageal sphincter is already compromised. While a shot of hard liquor may be marketed as a “digestif,” it does little to improve digestion and much to impair it, especially in people with underlying GI issues. If alcohol is part of your routine, keep it light, diluted, and moderate.

• Limit fluids during meals to preserve saliva concentration. Large volumes of water or other fluids during meals dilute saliva and its enzymes, weakening the initial breakdown of carbohydrates and fats. Sipping is fine, but gulping your way through a meal suppresses enzyme activity and slows down the formation of a cohesive bolus, leading to inefficient swallowing and delayed gastric processing.

• Chew well and slow. The longer you chew, the more your food breaks down mechanically and mixes with saliva, kickstarting digestion before anything reaches the stomach. A good rule of thumb is 15 to 30 minutes per meal. It allows salivary amylase to begin converting complex carbohydrates into digestible sugars and gives lingual lipase a head start on fat digestion. Rushing meals short-circuit this phase and shift the entire burden on the stomach, which, alas, doesn't have teeth to help itself with chunks of poorly chewed steak.

• Eat with intention, not distraction. Mindless eating in front of screens suppresses the salivary response and reduces chewing efficiency. Conscious chewing activates the vagus nerve, which stimulates the production of gastric acid and digestive enzymes in the stomach. When you eat in a distracted state, the brain doesn't fully register the incoming food, leaving the digestive system unprepared. This makes even a well-balanced meal harder to process. You're also more likely to overeat and gain weight because the body and brain fail to register satiety properly.

• Protect your salivary glands by managing stress and dehydration. Chronic stress and poor hydration reduce saliva production, which weakens the mouth’s digestive role and raises the risk of oral infections, cavities, and indigestion. Dry mouth signals a deeper disruption in the parasympathetic control of digestion. Stay hydrated, avoid unnecessary medications that reduce saliva (like certain antihistamines), and keep stress in check during meals.

• Don’t brush your teeth right after eating to protect enamel. Acidic conditions after meals temporarily soften enamel. Brushing too soon can wear it down, increasing sensitivity and long-term erosion. Instead, rinse your mouth with water or use a water flosser to remove food debris and neutralize acidity. Wait at least 30 minutes before brushing with a soft-bristle toothbrush without toothpaste because most of them are abrasive.

• Treat your teeth and gums like vital digestive organs. Dental health is digestive health. Poor oral hygiene leads to gum disease, which increases systemic inflammation and introduces harmful bacteria into the gut. Cracked, missing, or sensitive teeth also force you to chew less, which shortens oral-phase digestion and increases the chance of poorly digested food causing all kinds of harm downstream.

• Avoid ultraprocessed food that doesn't require much chewing. Soft, slippery, pre-digested food like shakes, white bread, and refined cereals require little to no chewing. That may seem convenient, but it deprives your body of the mechanical and enzymatic preparation that real digestion depends on. Meals that you must chew give your mouth a reason to work, and that work pays dividends all the way down the GI tract.

• Avoid food and drinks that are too hot or too cold. Extreme temperatures inflame oral tissues, weaken the mucosal lining, and dull the sensory receptors that trigger digestion. Ice-cold beverages suppress saliva production and temporarily numb taste buds, reducing both flavor perception and enzyme release. Scalding beverages, soups, and stews may feel comforting, but over time, they cause chronic microtrauma of the tongue, gums, and throat. Lukewarm is best, especially when digestion and oral health are priorities. Extreme temperatures are also damaging to teeth and dental work, particularly when alternating between very hot and very cold items, because thermal stress causes expansion and contraction that weaken the bond between fillings and tooth structure, and creates micro-fissures that trap bacteria and gradually degrade the tooth.

• Be cautious with overly spicy foods. Spices stimulate appetite and circulation, but in excess or when combined with common food allergens (like nuts or certain peppers), they can inflame the oral mucosa, trigger histamine release, and disrupt salivary balance. Frequent irritation also raises the risk of tissue sensitivity or ulceration. So drinking Tabasco may prove your manhood, but it won’t do your mucosal lining any favors. Chronic exposure to intense spices can desensitize taste receptors, strain your esophageal lining, and worsen conditions like acid reflux or gastritis. Use spices to enhance taste, not to assault your digestive and respiratory organs.

• Don’t overload your bites and limit food volume per swallow. Stuffing the mouth with large chunks of food overwhelms your ability to chew thoroughly and mix food with saliva. It also leads to large, poorly masticated boluses passing into the stomach and increases the risk of reflux, choking, or downstream fermentation. Smaller bites, chewed slowly, make digestion smoother and more efficient. Don’t swallow food until you chew it properly because your stomach isn’t designed to pick up the slack.

• Eat slowly to manage weight and improve digestion. Satiety isn’t instant! It takes 15 to 30 minutes for your brain to register fullness. Eating slowly gives your body time to prevent overeating by letting internal signals catch up with food intake. It also extends the oral digestive phase, improving nutrient absorption and reducing the chance of post-meal fatigue or bloating. Fast eaters eat more, digest less, and feel worse.

• Favor solid, chewable proteins over ground or processed meats. Solid cuts of meat (like steak, chicken breast, or fish fillet) require more chewing, which improves saliva mixing and slows down intake. Ground meats, meatloaf, franks, and pulverized protein blends are easy to swallow too quickly, which increases the risk of under-chewing and overloads the stomach. They’re also more likely to ferment in the gut and produce gas.

Stomach (4 to 6 hours)

Gastric digestion (inside the stomach) begins when the specialized cells in the stomach’s wall secrete ions of hydrogen (H⁺) and chloride (Cl⁻) into the stomach’s cavity, where they combine to form hydrochloric acid (HCl).

If necessary, the stomach will also secrete water derived from the blood's plasma that is essential for diluting acid and enzymes to the required concentration. There is no spigot there to shower the chew with 'gastric juices' as many incorrectly think. Those juices are formed on the fly from the saliva, consumed fluids, and the water content of most food.

Hydrochloric acid lowers the stomach’s pH to between 1 and 2—an extremely acidic environment that denatures (unravels their structure) proteins, activates pepsinogen into pepsin (the stomach’s main protein-digesting enzyme), and initiates a cascade of digestive activity.

Acid also serves as a disinfectant, killing bacteria, viruses, and fungi (molds and yeasts) present in food and saliva before they reach the intestines.

Gastrin, a hormone released in response to stomach stretching and the presence of protein, intensifies acid secretion and promotes muscular contractions of the stomach walls to mix food with digestive juices.

In healthy individuals, this phase of gastric digestion typically lasts between 4 and 6 hours, though the duration can vary significantly. The total time depends on how much food was consumed, how thoroughly it was chewed, the types of macronutrients involved (fat and protein slow digestion), and the volume and timing of fluid intake. Too many fluids reduce acidity and extend the length of digestion.

The stomach gradually churns food into a semi-liquid mixture called chyme, and only when the contents are sufficiently acidified and liquefied does the pyloric sphincter, located between the stomach and duodenum, begin releasing it into the small intestine in small bursts.

Gastric acidity decreases as digestion progresses because the flow of acidic chyme into the duodenum triggers the release of bicarbonate-rich fluids from the pancreas, which neutralize the acid in the upper small intestine.

This process is precise and tightly regulated unless disrupted by ingesting more food or fluids within a few hours after eating, intense physical activity, acute stress, or certain sitting positions that constrict the stomach and prevent it from churning.

In such cases, digestion may extend to 7, 8, or more hours, regardless of one’s age or overall health, and even longer for older people. Please pay attention to this aside, because this quirk of human digestion plays a major role in the development of heartburn and GERD.

Takeaways for a healthy stomach

• Respect the stomach’s timeline—4 to 6 hours means hands off. Once food enters your stomach, digestion becomes a time- and acid-intensive process. For most meals, especially those containing protein or fat, the stomach needs at least 4 to 6 hours to do its job. Adding more food, snacks, or even water during this phase dilutes acidity, disrupts enzyme activity, and extends digestion well past the 6-hour mark. This isn't just inefficient—it’s a setup for fermentation, gas, reflux, and long-term gastric dysfunction. Let the stomach work in peace.

• Digestion of proteins requires fluids. Depending on the composition of the meal, you do need fluids (soup, water, beer, wine) to provide a base for the formation of gastric juices. This is especially important when consuming protein-rich meals because they require more fluids for proper digestion. There’s no fixed formula, but typically 200 to 350 ml is enough, assuming you had the same amount 30 to 60 minutes before the meal.

• Avoid largea amount of fluids with meals to avoid acid dilution. Drinking water or other fluids above and beyond the amount mentioned in the previous bullet) during meals may sound harmless, but it dilutes gastric acid and enzymes, weakens the stomach’s ability to break down protein and destroy pathogens, and extends digestion time.

• Avoid drinking fluids after a meal. Adding a lot of water or other liquids after eating will dilute the acid concentration, slow digestion, and interfere with the proper breakdown of proteins. Let your body complete this critical phase undisturbed. The length of the wait depends on the meal. If you ate mostly carbohydrates, where little gastric acidity is involved, an hour or two is usually enough. But if your meal included proteins, wait at least 5 to 6 hours.

  Even if you're thirsty and drink a lot of water, it will remain in the stomach, won’t be absorbed right away, and won’t satisfy your thirst. But as soon as the meal starts leaving the stomach and entering the intestines, water absorption resumes quickly, and so does relief from thirst.

• Don’t lean forward, slouch, or constrict your midsection after eating. Compression of the stomach, whether from tight clothing, sitting hunched over, or lying down, limits the stomach’s ability to churn food effectively. It also increases the risk of gastric contents pushing upward into the esophagus, triggering heartburn or reflux. After eating, stay upright and allow the stomach its natural mobility. If you’re working or relaxing, use positions that open, not cramp, your abdomen.

• Don’t eat on top of undigested food. If your previous meal hasn’t cleared the stomach, typically 4 to 6 hours, longer for heavier meals, adding more food forces the stomach to dilute acid further and reheat partially digested matter. This leads to poor breakdown, fermentation, bloating, and eventually chronic gastric stagnation. If you’re unsure whether your stomach has finished, err on the side of more time, not less. Skipping a meal is less harmful than stacking one.

• Avoid intense physical activity for 2 to 3 hours after meals. Exercise shunts blood away from the digestive tract and diverts the body’s energy toward muscles, impairing gastric function and increasing the risk of nausea, cramping, and reflux. Even walking or bending excessively during the peak of digestion can compromise acid distribution and muscular churning. Let digestion finish before resuming activity that competes with it.

• Don’t suppress acid unless your life depends on it. Low stomach acid isn’t a minor inconvenience—it’s a root cause of poor digestion, nutrient malabsorption, bacterial overgrowth, and downstream GI dysfunction. Using PPIs or other acid-suppressing drugs out of habit, fear, or convenience turns off the system responsible for sterilizing food and breaking down proteins. If you have to suppress acid short-term, do so strategically. If it’s long-term, you need a second opinion—and a plan.

• Think before you medicate for heartburn and reflux. Heartburn is often a sign of delayed gastric emptying, not excess acid. Taking antacids or PPIs may offer symptom relief, but they worsen the underlying issue by slowing digestion further and impairing the stomach’s ability to empty itself. Instead of masking the reflux, investigate the timing, posture, volume, and composition of your meals, and give your stomach a chance to finish its job before judging its performance.

• Protein needs acid—don’t neutralize the only thing that digests it. Pepsin, the stomach’s main protein-digesting enzyme, is only activated in highly acidic environments. If your pH isn’t low enough, pepsin stays inactive, and your steak, chicken, or eggs sit undigested, leading to stagnation, gas, and downstream inflammation. Skimping on acid means your protein doesn’t get broken down properly, and the consequences can show up as muscle loss, fatigue, food sensitivities, and skin issues.

• Mixed meals are fine if you don’t overdo it. The idea that proteins and carbohydrates shouldn’t be eaten together is more dogma than physiology. In healthy people with adequate gastric acid and motility, the stomach is fully capable of handling mixed meals. The key is moderation: large volumes, poor chewing, and excessive fluids create the overload, not the macronutrient mix itself. Unless you’re on a specific therapeutic diet, there’s no need to separate foods by class—just keep portions reasonable and digestion on pace.

• Fat in moderation is not the enemy, but an appetite reducer and regulator. Dietary fat delays gastric emptying, triggers satiety hormones, and provides sustained energy—all essential for avoiding overeating. A meal too low in fat may leave you hungry again in an hour, prompting snacking that interrupts digestion. Conversely, a modest amount of healthy fat (like olive oil, egg yolks, fatty fish, or butter) helps calm the nervous system, prolong satiety, and support fat-soluble nutrient absorption. Don’t fear fat—fear its absence.

• Chronic indigestion? Enzymes can help, but choose wisely. If you're no longer using antacids but still struggling with sluggish digestion, bloating, or heaviness after meals, consider short-term use of digestive enzyme supplements. Look for products containing protease, lipase, amylase, and possibly ox bile or HCl (if tolerated). These aren’t crutches—they’re support tools, especially helpful in people over 50, or anyone recovering from long-term PPI use. Just don’t treat them like candy. Use them strategically to recondition the gut, not to bypass it.

• Your stomach only recovers when it’s empty. Digestion is a physically demanding process, and your stomach can’t rest, heal, or regenerate while it’s still working. Snacking between meals, grazing out of boredom, or eating late into the evening keeps the acid pumps firing and the mucosal lining under stress. Aim for three solid meals a day if under 50, and two meals a day after 50 if you’re not underweight. This gives your digestive organs time to clean up, repair, and reset for the next cycle.

• Stick to your eating schedule—your stomach expects it. As Pavlov’s dogs proved, the digestive system runs on anticipation. The sight, smell, and even the timing of a meal trigger acid, enzyme, and hormone release. Eating erratically confuses that rhythm. When food arrives off-schedule, the stomach isn’t prepared, and digestion suffers. Train your stomach like you’d train a pet: be consistent, reward good behavior, and don’t give it surprises it can’t handle.

• Jet lag disrupts more than sleep—it derails digestion. Crossing time zones throws off your circadian rhythm, and your stomach clock is no exception. If you start eating on the schedule of your new location too soon, before your body has adjusted, you may develop indigestion, nausea, or even mild food poisoning-like symptoms. Unless you’re staying more than two weeks, stick to your home eating schedule as much as possible. If relocating for longer, start shifting meal timing gradually a few days before departure to ease the transition.

• The aging stomach is slower, quieter, and more fragile. After age 50, your stomach doesn't behave like it used to. Acid production declines, pepsin activity drops, and muscular contractions that once churned food effortlessly now slow down. You may not feel it, but that “heavy” sensation after meals is your stomach struggling to liquefy food with fewer tools. Large or late meals become harder to handle, and protein digestion, already acid-dependent, suffers the most. In practice, it means smaller portions, longer gaps between meals, and fewer ingredients per plate. Aging digestion isn’t a disease, but a natural shift in capacity. Work with it, not against it.

To conclude, never forget that digestion starts in the mouth. The stomach doesn’t have teeth. If you rush through meals, skip chewing, or wash down half-chewed food with drinks, your stomach is left to clean up the mess, and over time, it breaks down. Chewing thoroughly reduces the stomach’s workload, triggers acid production at the right time, and ensures that food arrives in a form the stomach can process efficiently. Honor the rules of the mouth every time you eat. It’s not just polite or traditional—it’s how you protect your stomach from wear and tear before it starts showing symptoms.

Duodenum (2 to 3 hours)

The duodenum is the first and shortest segment of the small intestine, and just as critically important as the stomach. Once the chyme passes through the pyloric sphincter into the duodenum, digestion enters its most complex phase.

To do this job, its walls are lined with highly sensitive receptors that monitor pH, concentration, volume, and temperature of the incoming liquefied chyme.

Unlike the stomach, which slowly processes food over many hours, the duodenum must instantly coordinate responses from the pancreas, gallbladder, and intestinal wall to analyze and neutralize it.

In response to the acidic chyme, the duodenum triggers the release of two key hormones: secretin and cholecystokinin (CCK). Secretin stimulates the pancreas to release sodium bicarbonate to neutralize stomach acid and create a neutral environment for the enzymes that follow.

The hormone cholecystokinin (CCK)  instructs the pancreas to secrete lipase, proteases, and amylase enzymes, and signals the gallbladder to release bile, which emulsifies fats and makes them easier to digest and absorb.

When hydrochloric acid (HCl) mixes with sodium bicarbonate (NaHCO₃, the same substance as baking soda), it breaks down into NaCl (table salt), H₂O (water), and CO₂ (carbon dioxide—the same gas we exhale):

HCl + NaHCO₃ → NaCl + H₂O + CO₂

This reaction protects the lining of the small intestine from getting burned by hydrochloric acid.

The release of CO₂ is rapid and effervescent, similar to what you see when mixing vinegar with baking soda. It is immediately dispersed into the small intestine but may also reflux upward into the stomach.

As the gas moves through the narrow, fluid-filled space of the duodenum, it can create soft gurgling or bubbling sounds that people sometimes hear or feel after eating. These internal sounds are normal and part of a healthy, well-coordinated process.

All three components of the reaction—salt, water, and gas—are later absorbed back into the bloodstream through the small and large intestines. Nothing is left to waste.

The duodenal phase of digestion typically lasts 2 to 3 hours in healthy individuals, though this timing varies based on meal composition, food volume, gastric acid volume, motility, enzymatic efficiency, and other situation-specific factors:

• High-fat and high-protein meals slow the process because fats require emulsification, and proteins demand more enzymatic action.

• If the chyme is insufficiently acidified or not properly liquefied, the duodenum sends feedback to delay further release from the stomach.

• Larger meals prolong gastric emptying and, in turn, extend the duodenal phase.

• Age, medication, stress, inflammation, physical activity, constrained posture, or any other factor that interferes with digestive coordination can slow transit and processing.

All of this takes place within the first 10 to 12 inches of the small intestine. By the time chyme leaves the duodenum, it has become a nutrient-rich soup, ready for the jejunum, where absorption becomes the primary task.

Takeaways for a healthy duodenum

This list is decidedly shorter because the duodenal health is the function of what, when, and how much food passes your mouth and what happens with it in the stomach. So the ‘control’ over this organ is mostly indirect, but with a few caveats:

• Duodenum functionality is age-dependent. The pancreas contributes key enzymes for digesting protein, fat, and carbs, but it can’t keep up if you're throwing dense, unchewed, or excessive meals at it three or more times a day. Over time, it starts dialing down output, especially in older adults or those with chronic inflammation. If digestion is sluggish, consider taking digestive enzymes for support, but don’t treat them like a replacement plan. Train your gut to recover its own secretions by spacing out meals and chewing properly.

• Bile flow is essential for fat digestion. Bile is a biological detergent that breaks fat into droplets that your enzymes can actually digest. If bile isn’t flowing, fat lingers in the gut undigested, causing fullness, nausea, greasy stools, and even gallbladder attacks. Keep bile moving by eating moderate amounts of fat regularly to prevent bile stagnation in the gallbladder and the formation of gallstones.

• Avoid starting a new meal while the duodenum is still clearing the last one. It takes 2 to 3 hours to process a normal meal through the duodenum. If you snack or eat again before that window closes, you interrupt hormone signaling, overload the system with fresh chyme, and dilute enzyme and bile concentrations. It leads to fermentation, incomplete digestion, and inflammation downstream. Respect the gap between meals.

• Duodenal ulcer risk. The stomach’s thick mucus lining safeguards it from its own acidic environment. In contrast, the duodenum is more susceptible to damage when exposed to excessive acid. Consequently, duodenal ulcers may develop earlier than gastric ulcers.

• Post-meal bloating and discomfort. A sudden sensation of abdominal distension or tightness may occur shortly after eating, often within 15 to 30 minutes. It happens when consuming food and fluids atop an incompletely digested previous meal. This sudden influx of acidic fluids prompts the pancreas to release sodium bicarbonate to neutralize them. The neutralization process produces gases that, in turn, cause intestinal expansion and bloating.

• Duodenal inflammation and ductal obstruction. The common bile duct and pancreatic duct converge and empty into the duodenum through the ampulla of Vater. Inflammation of the duodenal wall, due to infections, ulcers, or chronic pancreatitis, can lead to swelling or fibrosis that compresses these ducts, causing stenosis (narrowing). Such obstruction impedes the flow of bile and pancreatic enzymes, potentially resulting in acute cholecystitis (gallbladder inflammation) or pancreatitis (pancreas inflammation). These conditions are severe and may necessitate immediate medical intervention.

• Acute pancreatitis is particularly dangerous because it can damage the insulin-producing regions of the pancreas, potentially leading to irreversible type 1 diabetes. In situations where immediate medical intervention isn't available, a person may die from untreated diabetic ketoacidosis (DKA). Another reason to pay respect to what’s happening with and around the duodenum.

Jejunum (1.5 to 2.5 hours)

The jejunum is the middle and longest portion of the small intestine that is responsible for the absorption of nutrients, fluids, and gases. It measures about 8 to 9 feet (2.5 to 3 meters) in length and occupies the central segment of the small intestine.

Chyme is propelled through the jejunum by a coordinated series of muscular contractions called peristalsis. These wave-like movements are generated by smooth muscle layers in the intestinal wall and are regulated by both the enteric nervous system and hormonal feedback.

Between peristaltic waves, the intestine performs segmentation contractions, which rhythmically mix the chyme back and forth. This action slows transit just enough to maximize contact with the absorptive surface of the lining.

The speed of propulsion is finely tuned. If chyme moves too quickly, nutrients pass through unabsorbed; if too slowly, it can lead to fermentation, gas, and bloating. In a healthy gut, peristalsis and segmentation keep the contents moving at just the right pace—silent, smooth, and unnoticed.

By this stage, carbohydrates have been broken down into simple sugars, proteins into amino acids and peptides (short chains of amino acids), and fats into fatty acids and monoglycerides. The jejunum’s task is to transfer these nutrients into the bloodstream and lymph.

The inner lining of the jejunum is covered with tiny, finger-like projections called villi, and an even finer layer of microvilli, collectively known as the brush border. This anatomy greatly increases surface area for absorption and contains enzymes that finish breaking down any remaining disaccharides, peptides, and other small molecules.

Capillaries inside each villus absorb sugars and amino acids directly into the bloodstream, while lacteals (small lymphatic vessels) transport emulsified fats into the lymphatic system, temporarily bypassing the liver.

The jejunum also plays a role in absorbing digestive gases, primarily carbon dioxide, nitrogen, and small amounts of hydrogen and methane produced during digestion and fermentation.

Its thin, permeable mucosal lining — richly supplied with capillaries—allows for passive diffusion of gases. As gas bubbles come into contact with the moist intestinal surface, their contents diffuse into the bloodstream along concentration gradients. These gases are then carried to the lungs and exhaled.

In healthy individuals, this process prevents most gases from reaching the large intestine. But when the intestinal lining is inflamed or damaged, gas absorption is impaired. That’s when bloating, cramping, and abdominal distention begin to appear—not because of excess gas production, but because the normal absorption mechanism has been disrupted.

In healthy individuals, transit time through the jejunum ranges from 1.5 to 2.5 hours, depending on the same factors that affect the stomach and duodenum: meal composition, gastric emptying rate, motility, hydration, physical activity, stress, body posture, and the overall health of the jejunal lining.

This timing allows for thorough nutrient absorption without stagnation. If transit is too fast, nutrients are lost; if too slow, gas and fermentation increase. The jejunum doesn’t just absorb nutrients and gases — it also regulates their flow.

Takeaways for a healthy Jejunum

The jejunum is a continuation of the small intestine that starts with the duodenum. There are no specific takeaways for this organ that are distinctly different from the ones for the mouth, stomach, and duodenum.

Ileum (2 to 4 hours)

After the jejunum, digestion enters its final phase in the ileum — the last and longest section of the small intestine, measuring about 10 to 12 feet (3 to 3.6 meters). While most nutrient absorption occurs upstream, the ileum plays a critical role in absorbing what remains, especially substances that require more time or specialized transport mechanisms.

The ileum is responsible for the absorption of vitamin B-12, bile salts, and residual nutrients not fully processed in the jejunum. Bile salts, released earlier in the duodenum to emulsify fats, are reabsorbed in the ileum and recycled back to the liver through what’s known as enterohepatic circulation. Without this recycling, the body would lose bile with every meal and struggle to digest fats efficiently.

Vitamin B-12, meanwhile, is absorbed only when intrinsic factor—a glycoprotein secreted by the stomach—is present. The ileum contains specialized receptors that recognize and absorb the B-12-intrinsic factor complex. If this mechanism fails due to acid suppression, inflammation, or surgical resection, B-12 deficiency can eventually lead to anemia, neuropathy, and cognitive decline.

The ileum also absorbs residual fatty acids and electrolytes (especially sodium and chloride), helping to regulate the body’s overall balance of water and minerals. Though slower and less forceful than in the upper segments, peristalsis continues in the ileum, gently propelling the remaining chyme toward the large intestine.

By the time the contents move from the ileum to the large intestine through the ileocecal valve, most nutrients and digestible material have been extracted. What remains is mostly water, some bile, residual fat, intestinal bacteria, undigested soluble and insoluble fiber, cellular debris, and inorganic minerals (often referred to as ash).

Transit through the ileum typically takes between 2 to 4 hours in healthy individuals. The duration depends on meal composition, hydration status, neural and hormonal signaling, and the resistance of the ileocecal valve. If the large intestine is already full, the ileum will temporarily retain the chyme to avoid overloading the colon.

Takeaways for a Healthy Ileum

The ileum is the final leg of the food journey through the small intestine. Just like the jejunum, the takeaways are largely the same, except for one major issue: SIBO, or Small Intestine Bacterial Overgrowth.

SIBO occurs when the ileum is exposed to a backflow of fecal matter from the large intestine. This retrograde reflux allows dense populations of colonic bacteria to invade the normally sterile environment of the small intestine. Once there, these bacteria ferment carbohydrates and other undigested food components, producing gas, bloating, and discomfort.

Over time, this condition can disrupt nutrient absorption, damage the mucosal lining, and lead to chronic inflammation or motility disorders. The ileocecal valve, which separates the small and large intestines, is designed to prevent this reflux. But when it weakens or malfunctions, SIBO often follows.

The only way to prevent SIBO is to ask one simple question: What causes feces to flood back into the ileum? There’s only one answer: persistent constipation that leads to stool accumulation in the large intestine. When stools aren’t fully evacuated, they have only one direction left to go: back up the “tube,” where they remain until the constipation is resolved. That’s the primary challenge most people face when it comes to the next organ in line.

The true SIBO has a very prominent telltale sign: the smell of stool in the breath. In cases of advanced or severe SIBO, hydrogen sulfide, methane, and other fermentation gases produced by colonic-type bacteria in the small intestine can be absorbed into the bloodstream and exhaled.

These compounds can produce a fecal or sulfur-like odor on the breath, though it's rare and typically indicates significant bacterial overgrowth. This is, in fact, the physiological basis of hydrogen/methane breath testing for SIBO.

If you are bloated, but there is no smell, that’s not SIBO, but ordinary enteritis, the inflammation of the small intestine that prevents the absorption of gases into the blood.

Large Intestine (12 to 48 hours)

Finally, finally, finally, after an 8.5-hour journey through the mouth, stomach, and small intestine in the best of all worlds, or up to 16 hours under less-than-ideal circumstances, our first bite of food has reached the almighty colon (same as large intestine), where it will be turned into... crap. Oh, Lord, what a journey.

The colon reclaims what it can from the remaining chyme and discards the rest. Measuring about 5 feet (1.5 meters) in length, it starts at the cecum and ends at the anus. By the time the chyme enters, most nutrients have been absorbed. What remains is a slurry of water, electrolytes, fiber, bacteria, dead intestinal cells, inorganic minerals, and metabolic byproducts, all of it waste the body needs to discard.

The colon’s main job is to reabsorb remaining water and mineral salts back into the blood. As water is removed, the slurry thickens, is impregnated with mucus, and gradually forms stool. This process is slow and deliberate, taking anywhere from 12 to 48 hours, depending on motility, individual physiology, and the presence or absence of latent or obvious constipation.

Meanwhile, trillions of bacteria in the colon go to work fermenting soluble and insoluble fiber and mucins, the glycoproteins produced by epithelial tissues. This microbial fermentation produces gases (hydrogen, methane, carbon dioxide) and short-chain fatty acids like butyrate, which help nourish colon cells and modulate inflammation.

During fermentation, certain gut bacteria also synthesize small amounts of B-complex and other vitamins. Although absorption in the colon is negligible, microbial synthesis may still help maintain systemic levels of vitamin K2 and biotin (B7).

Fermentation also yields ethanol, methanol, isopropanol, and butanol—the same alcohols as in beer, wine, or whiskey making. These alcohols are normally produced in physiologically insignificant amounts, but in cases of excessive fiber intake, they can accumulate and trigger bloating, fatigue, brain fog, or even pseudo-intoxication in sensitive individuals.

Anatomically, the colon is divided into six distinct sections, each with its own orientation and role:

• The cecum is a pouch-like organ that receives chyme from the ileum. It plays a role in absorbing fluids and salts that remain after digestion and houses the appendix, a narrow, finger-shaped tube that supports certain immune functions and microbiome balance.

• The ascending colon runs up on the right side of the abdomen. It receives semi-liquid material from the cecum and continuous the slow process of absorbing water and minerals. Gravity helps here, but so does time — the content lingers for thorough extraction.

• The transverse colon crosses the abdomen from right to left, suspended horizontally just below the stomach. This is where fermentation intensifies. Gases and byproducts build up, often leading to abdominal distention and audible rumbling from the bursting gas bubbles, especially if prior meals were poorly digested.

• The descending colon travels down the left side. At this stage, the stool begins to solidify. Water absorption is nearly complete, and motility slows to compact and hold the stool for release.

• The sigmoid colon is an S-shaped curve that connects the descending colon to the rectum. It accumulates and holds stool until it's time to go. It’s muscular, responsive to stretch, and highly sensitive to both internal and external stimulation.

• The rectum is the final reservoir. Its walls stretch as stool accumulates, signaling the brain to initiate the urge to defecate. It coordinates with pelvic floor muscles and internal sphincters to control timing.

  In healthy people, the rectum remains empty. In those with chronic constipation, it’s often filled with hardened, compressed stool. Over time, the pressure desensitizes the rectal wall, making it harder to feel or respond to the urge.

• Finally, the anus serves as the body’s exit valve. It consists of two sphincters: the internal sphincter, which is involuntary and keeps things sealed under normal conditions, and the external sphincter, which is under conscious control. Together, they regulate stool release during bowel movements.

  The anus also prevents gas (flatus) from escaping on its own volition. When the pressure becomes too strong, we consciously release it, preferably when no one is around. The accompanying sound effect depends on how tight or relaxed the anus is during expulsion.

Sounds pretty amazing, doesn’t it?

After learning and understanding how the large intestine actually works, I stopped believing in evolution. This organ is just too damn complex to be the product of random chance or the whims of natural selection.

And unfortunately, it’s also very prone to an endless functional and organic (permanent) colorectal disoders, many of which I describe in exceptional detail on my website and in my books. The best way to avoid them is never to suppress (or teach children to suppress) an urge to move bowels when the bathroom is available, and here is why:

One of the colon’s most important regulatory mechanisms is the gastrocolic reflex, which is triggered when food enters the stomach. This reflex stimulates the colon to initiate mass peristaltic movements — waves of strong contraction that move fecal matter toward the rectum and trigger the unmistakable urge to move the bowels.

These movements typically occur shortly after meals and are most active in the morning, which is why the urge to defecate often follows the first meal of the day. If you don’t eat a meal before leaving for work, you can still activate the gastrocolic reflex by drinking a glass of any liquid—warm or room temperature—relatively quickly, though not in a single gulp.

The stretch receptors in the stomach respond to volume, not just food, so this simple act can trigger the same reaction as eating: increased motility in the colon and the urge to evacuate. It’s an effective way to maintain regularity without forcing a meal when you're not hungry or don’t have time for one.

Disruption of the gastrocolic reflex — whether from irregular eating patterns, not having access to a bathroom when it kicks in, or consciously retaining the urge — contributes to fecal retention, bloating, enlarged stools, straining, the onset of chronic constipation, enlarged hemorrhoids from straining, irritable bowel syndrome from excess gas and incomplete emptying, diverticular disease from large stools, inflammatory bowel disease from all of the above, and, for the unlucky ones, polyps and colorectal cancers driven by chronic inflammation.

Now that you understand how the entire process works, you’ll hopefully pay closer attention to the journey your food takes from mouth to anus.

I skipped a few critical organs along the way—namely, the pancreas, gallbladder, and liver. While they don’t come into direct contact with food, they, too, play major roles in digestion. I’ll describe their functions (and dysfunctions) in more detail as we move through this cycle.

Takeaways for a healthy large intestine

For that, I have a ton of takeaways to share with you that are already covered on this website:

• How to reverse chronic or sporadic constipation. Moving bowels is an intrinsic instinct, not an acquired trait. You don't need to teach newborns to move their bowels — it comes to them just as naturally as breathing or crying. Similarly, some seniors have never had a problem moving their bowels regularly and are free from common colorectal disorders, such as enlarged hemorrhoids, diverticular disease, or incontinence. So, why, then, are so many other people aren't as lucky? Read..

• Irritable Bowel Syndrome. This guide debunks the universally accepted view that the causes of irritable bowel syndrome are unknown, describes them one by one, and explains how to eliminate each one safely and permanently. This information is vital for persons in the high-risk group for ulcerative colitis, Crohn's disease, and colon cancer because IBS's conventional diagnostic and treatment raises these risks considerably. Read...

• Hemorrhoids and Anal Fissures. Hemorrhoidal disease and anal fissures start with a little "defect" in human anatomy — the anal canal that is too darn tight for large and/or hard stools to pass through. When these abnormal stools get stuck inside the colon or rectum, you may have no choice but to strain, and gradually causing yourself hemorrhoidal disease, anal fissures, and other complications. Read...

• Diverticulosis and Diverticulitis. A high fiber diet is broadly recommended to prevent diverticular disease based on unconfirmed, unproven, untested, and speculative "theories" that a low fiber diet causes this pathology. It's the complete opposite — a high fiber diet is the primary cause of diverticular disease and related complications. Read...

• How to Revitalize Intestinal Flora. Healthy intestinal flora is vital for forming stools, maintaining immunity, synthesizing essential vitamins, and protecting the colon from cancer. The loss of these functions contributes to impaired immunity, diabetes, obesity, hair loss, eczema, seborrhea, anemia, internal bleeding, ulcers, strokes, cancers, and common gastrointestinal, respiratory, and autoimmune disorders. This page explains how to protect and revitalize intestinal flora. Read...

• How to Restore Anorectal Sensitivity. To preserve lifelong colorectal health and prevent colon cancer, a healthy person should move the bowels after each principal meal or at least twice daily. Because circumstances are rarely ideal, people tend to suppress urges and skip stools. When practiced long enough, this habit causes gradual anorectal nerve damage. Finally, one day, laxatives are needed to initiate a bowel movement because the urge sensation has gone away for good. If this describes you, this page will help you restore anorectal sensitivity without resorting to laxatives. Read...

Our journey ends here. Eat well, and listen to your gut. Don’t fall for hucksters peddling a penny’s worth of bull’s shit that ends in a pound of new problems. The organs we’ve just traveled through are too complex and too smart to be fixed by a miracle cure. Now you’ve got the tools to keep your gut sense sharp and yourself out of the gutter.

Author's note

Family doctors are trained to deliver conveyor-belt-style care. They look you in the eyes, write a prescription, make a referral, and move on to the next patient. They don’t have the time or training to explain digestion or indigestion.

As of early 2025, there were nearly 19,000 active gastroenterologists in the United States, and more than half are near retirement age. Most know only slightly more about nutrition than you do because they’re not trained in it in-depth. Don’t expect them to teach you what they don't know.

Medical textbooks, such as the Merck Manual of Diagnosis and Therapy or Rome IV Functional Gastrointestinal Disorders, reduce nutritional and digestive disorders to surface-level summaries tailored to busy professionals. As useful as they are to specialists, depth for patients isn’t their goal.

That said, if you’re dealing with a bleeding ulcer, a tumor, a perforated intestine, or any other emergency that may require surgery, you’ll be in good hands, especially at a major teaching hospital.

But if you’d rather avoid getting to that point, study this page. Then explore the rest of the site. In the process, you'll learn plenty of smart things you can do to protect your gut health from wrong food, outdated dogmas, medical risks, and bad advice.

Please share this post with your family and friends to support my work!

Thank you!

Konstantin Monastyrsky