We’re all going to be putting food in our bodies just about every day for the rest of our lives. Most of us will do it several times a day. We’ll chew it, send it down the esophagus into our stomach, and expose it to gastric juices and digestive enzymes. We’ll strip it of nutrients and send the excess down to the colon for dismissal, feeding resident gut bacteria along the way. The whole process should go smoothly. There shouldn’t be any pain or discomfort, bloating or constipation. Oh sure, nobody’s perfect, and there will be slow-downs or speed-ups from time to time, but in general a vital, fundamental process like digestion shouldn’t even register in our waking, conscious lives.
Sometimes digestion can be downright unpleasant, or even unproductive. The symptoms are familiar:
Bloating. Distended belly. Feeling overly full and unwieldy. Same weight but the pants don’t fit.
Excessive gas. No need to define it. You just know it when you see (hear) it.
Diarrhea. Acute (occasional) diarrhea that goes away immediately doesn’t indicate poor digestion, but protracted or chronic diarrhea is a warning sign.
Constipation. Same deal with constipation: acute normal, chronic not.
Stomach pain. Persistent gut pain should never be ignored.
Bleeding or pain on the toilet. Elimination should be painless.
Heartburn, or acid reflux. Although most people assume heartburn and acid reflux are caused by too much stomach acid, it’s actually the opposite: inadequate stomach acid is usually the culprit.
The Digestive Process: Troubleshooting Top to Bottom
To get to the bottom of these symptoms and hopefully fix them, let’s look at the actual process of digestion. We’ll go step by step down the line to identify and offer solutions for various issues that can arise at each.
What happens when you eat something?
The stops along the digestive route involve:
Sensing and signaling
Oral digestion, or chewing
Mechanical digestion, in the stomach
Small intestine digestion
Here’s how it works.
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Sensing and Signaling
You start digesting before you’ve even taken your first bite. Have you ever smelled burgers grilling, and you mouth started to water? Certain aromas can signal to your body that food is coming, and you begin to salivate and secrete digestive enzymes.
Even thinking about food can trigger a response.
Oral Digestion, or Chewing
Now, you’ve taken a bite.
First, you chew your food. Chewing is the first step in digestion. You physically break it up with your teeth into smaller pieces, increasing the surface area for digestive enzymes to access. Most of those enzymes appear later in the gut, but some appear in the saliva and start working immediately in the mouth during the chewing process.
Your taste buds communicate what you’re eating so that your body starts getting the right digestive juices flowing. For example, if you ate something sweet, you’ll make insulin. If you’re eating a fatty food, you’ll start secreting bile and enzymes.
Salivary amylase begins converting starch into sugar for easier digestion. Chew a potato for long enough and it’ll start tasting sweet.
Lingual lipase begins digesting the fats you eat. This is more important in babies, who express very high levels of lingual lipase in order to optimize their calorie intake from breastmilk. It still has an effect in adult fat digestion.
How to optimize oral digestion
Chew more: The longer you chew, the better you digest your food. In one study, healthy adults who chewed 50 times for each bite ended up eating fewer calories than those who chewed 15 times per bite, a strong indication of more efficient digestion and nutrient extraction.1 They were getting “more” out of their food simply by chewing it up more.
Heed your salivary amylase levels: How much salivary amylase you produce is determined by your genetics, with historically agricultural (and thus starch-consuming) populations tending to possess more copies of the salivary amylase gene than other populations. There’s no good way to test salivary amylase gene status because the commercial genetic analysis sites don’t cover it. You’d need a more specific (and expensive) test for that. Ancestry can be a rough proxy; try to match your carb intake with the carb intake (and thus amylase copies) of your recent ancestors. But whatever number of amylase copies you (might) carry, chewing more times per bite will increase the efficacy of the salivary amylase you do produce.
As for meat and other animal foods which salivary amylase doesn’t affect, chewing is still important because it breaks apart the fibers and makes the nutrients contained therein more accessible to protein-digesting enzymes (proteases) in the stomach.
Mechanical Digestion, in the Stomach
Leaving the mouth, the food travels down the esophagus on into the stomach, where hydrochloric acid and a protein-degrading enzyme called pepsin break the food down into a big semifluid mass of partially-digested food components, water, enzymes, and acid known as chyme. The stomach walls undulate (move up and down) and mix the chyme,
How to Optimize Stomach Digestion?
Get your thiamine. Thiamine is a B-vitamin involved in hydrochloric acid production. If you want optimal stomach acidity—and you definitely do want it—you need to be replete in thiamine. The best source of thiamine is pork.
Watch the antacids. While heartburn meds can make a person feel better in an acute case of heartburn, they do so by inhibiting production of hydrochloric acid, which makes the stomach more alkaline and worsens your digestion in the long run. Pepsin cannot work without adequate acidity.
Try bitters. Post-meal bitters stimulate production of hydrochloric acid and assist many of the digestive organs, making the whole operation run more smoothly. But they must be bitter. Covering up the bitter flavor with something sweet mitigates the beneficial effect on digestion.
Get enough sodium. Low sodium levels reduce hydrochloric acid production. Make sure you’re salting your food to taste, as our moment-to-moment desire for salt is a good marker for sodium requirements. As long as you’re not eating packaged junk food, you won’t crave too much salt.
Try supplemental hydrochloric acid. A little betaine HCl, especially with protein meals, can really help if your acid production is too low. If you take betaine HCl and you feel a burn, you probably don’t need it.
Since the stomach is too acidic for amylase to work, the chyme migrates down to the duodenum, the first section of the small intestine immediately after the stomach where the pH is more alkaline. The pancreas produces protein-digesting enzymes as well as amylase and delivers them to the duodenum, where the full range of digestive enzymes can get to work liberating nutrients for absorption down the line. This is also where bile is introduced to assist in fat digestion.
Eat meals rather than graze. The human digestive system operates best when it encounters whole meals with plenty of time between subsequent meals, rather than a steady stream of incoming food. It even tries to enforce this; when a bolus of chyme enters the duodenum, the opening leading from the stomach to the duodenum tightens up to prevent more food from coming in. Overriding this with constant snacking will only impair your digestion and back things up.
Go for a walk. A short walk after eating speeds up the transition of food from the stomach through the duodenum into the small intestine. It “gets things moving,” in a good, beneficial way.
Small Intestine Digestion
After softening up in the duodenum, the chyme passes on into the small intestine where the bulk of nutrient absorption occurs. All along the intestinal walls lie villi — microscopic finger-like projections that increase the surface area of the intestinal lining and pluck nutrients from the passing slurry to be absorbed and assimilated. (You may have heard of villi in the context of gluten. Gluten can wipe out the villi in some people, leading to nutritional malabsorption.)
Optimize your serotonin. 95% of the serotonin in our body occurs in the gut; it’s one of the primary regulators of intestinal peristalsis — the muscular contractions that move and mix food through the digestive tract.2 I’ll have a much more in-depth post in the near future on this topic.
Fix leaky gut: Leaky gut isn’t just about allowing in pathogens and unwanted, allergenic food components into your bloodstream. It also impairs nutrient absorption and digestion in the small intestine. Go through this post and make sure you’re practicing excellent tight junction hygiene.
Pay attention to FODMAPs: Not everyone with digestive issues has to do this, but anyone who gets bloating, belly pain, excessive gas, and many of the other symptoms of poor digestion after eating should analyze their diet for FODMAPs and do an elimination trial. FODMAP foods include a wide range of fermentable fibers, sugars, vegetables, and fruits that have been shown to provoke uncontrollable and uncomfortable gut issues. These are often foods we consider to be healthy. Read the posts I’ve done on FODMAPs and follow the advice listed therein if you suspect you may have a problem with them.
You can also get tested for SIBO to see whether eliminating FODMAPs will benefit you.
You don’t actually “digest” anything in the colon. Rather, you gather and expel the waste — mostly fiber — that’s left over from digestion. Some of that “waste” is food for the gut bacteria who live in your colon. So someone’s digesting the stuff, just not you.
Eat some prebiotic fiber. Ironically, sometimes you need to eat stuff you can’t digest in order to improve your digestion over the longterm. Fermentable, prebiotic fibers like inulin and resistant starch are some of the best-studied examples. They feed the (mostly) good gut bacteria, who in turn produce short chain fatty acids that power your colonic cells and improve your metabolic health.
Take probiotics. Certain probiotics have been shown to reduce bloating and belly pain, improve GI symptoms, improve IBS symptoms, reduce leaky gut, and reduce antibiotic-related diarrhea.34567 I created Primal Probiotics with precisely these probiotics to tip the balance in your favor.
Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.