This article first appeared in Wise Traditions, the quarterly journal of the Weston A. Price Foundation.

All human cultures cook. In his 1960s book, “The Raw and the Cooked,” Claude Lévi-Strauss, often called the father of modern anthropology, noted: “Not only does cooking mark the transition from nature to culture, but through it and by means of it, the human state can be defined with all its attributes.”

The point of view articulated by Lévi-Strauss implies that humans cook their food for cultural and psychological reasons, and not because of any biological or physiological imperative. Fellow anthropologist Edmund Leach held the same view. “[People] do not have to cook their food, they do so for symbolic reasons to show that they are men and not beasts.” Others proposed that cooking was simply an offshoot of using fire for warmth.

However, a newer school of thought references scientific experiments showing that cooking makes our food easier to digest. These findings lead to the conclusion that the practice of cooking allows humans more time for cultural activities and more energy to power a bigger brain.

A Hole in the Stomach

Basic knowledge about the digestion of raw and cooked food comes to us as the result of an unfortunate accident, in which a Canadian named Alexis St. Martin received a gunshot wound to the stomach. The wound did not fully heal, leaving an opening that allowed the curious to view the workings of his stomach. Fortunately, the doctor who treated him, a U.S. Army surgeon named William Beaumont, was not only curious, but meticulous and thorough.

He performed many experiments by dangling food on a string into St. Martin’s stomach, then pulling it out to observe the extent of digestion; he also recorded how quickly various foods eaten by St. Martin left the stomach. For the next ten years, he performed an estimated two hundred studies on his hapless subject, all published in his book “Experiments and Observations on the Gastric Juice, and the Physiology of Digestion (1838).”1

In his first study, Beaumont introduced “articles of diet, suspended by a silk string, and fastened at proper distances, so as to pass in without pain — viz.: — a piece of highly seasoned a la mode beef; a piece of raw, salted, fat pork; a piece of raw, salted lean beef; a piece of boiled, salted beef; a piece of stale bread; and a bunch of raw, sliced cabbage; each piece weighing about two drachms [drams].”

On the introduction of food, he noted that the stomach (which is a muscle) would begin to churn and its color would brighten (due to increased blood flow to the stomach), followed by a “gradual appearance of innumerable, very fine, lucid specks, rising through the transparent mucous coat, and seeming to burst, and discharge themselves upon the very points of the papillae, diffusing a limpid, thin fluid over the whole interior gastric surface.”2

He discovered that the stomach lining excreted this gastric juice, and he confirmed an earlier theory that these juices contained hydrochloric acid.

Beaumont noted that St. Martin’s stomach digested tender foods as well as foods “finely divided” (by cutting or chopping) more rapidly and completely than foods in large pieces. Potatoes boiled and reduced to a fine powder underwent complete digestion while cooked potatoes in pieces resisted complete digestion. Pieces of raw potato left the stomach largely undigested.

“Pieces of raw potato, when submitted to the operation of this fluid, in the same manner, almost entirely resist its action. Many hours elapse before the slightest appearance of digestion is observable, and this only upon the surface.”

St. Martin’s stomach easily digested boiled beef — a morsel introduced at noon was gone by two in the afternoon — but a piece of raw, salted, lean beef left the stomach largely intact. Beaumont’s experiments also determined that vegetables digested more slowly than meat and that milk coagulated (separated into curds and whey) early in the digestive process.

What Happens in the Small Intestine?

After food leaves the stomach, it enters the small intestine, where the environment is mildly alkaline rather than highly acidic. There, a host of digestive enzymes take over the task of breaking food down into basic components, which can then be absorbed across the gut wall. Bile released into the small intestine from the gallbladder breaks down fats (in the form of triglycerides) into individual fatty acids.

Patients who have undergone surgery to remove the colon have a bag where the small intestine ends (the final segment of the small intestine is called the ileum). Experiments with these ileostomy patients have allowed scientists to examine the contents of the small intestine at the end of its digestive activities.

These studies show that humans digest cooked starch very efficiently. The percentage of cooked starch digested by the time it reaches the ileum is at least 95% for oats, wheat, potatoes, plantains, bananas, cornflakes and white bread. Home-cooked kidney beans and flaked barley have an ileal digestibility of around 84%. For raw starch, analyses show 71% digestion for wheat starch, 51% for potatoes and 48% for plantains.3

In general, we digest raw starch only half as well as cooked starch. Some starch granules eaten raw — called “resistant starch” — pass through the ileum and enter the colon unchanged.

Raw Food Diet Studies

Studies on raw food diets have shed more light on why human beings cook their food. In a 1999 report published in the Annals of Nutrition and Metabolism,4 researchers looked at the results of the Giessen Raw Food Study conducted in Germany in the 1990s. The subjects consisted of a group of about five hundred men and women consuming raw food diets long term (on average, almost four years).

The diet largely consisted of fruits and vegetables, but also raw honey and cold-pressed oils, dried fruit, dried or smoked meat and fish, fermented vegetables and certain types of nuts. Even though they included high-caloric foods like honey and oils in the diet, the subjects lost weight and ended up with a body mass index (BMI) below the normal weight range.

Women lost an average of 26.5 pounds and men lost 21.8 pounds — something an overweight person might welcome, but not a good idea if you are a hunter-gatherer relying on a robust physique for hunting and gathering activities. In fact, the volunteers reported always feeling hungry.

About 30% of the women under 45 years of age had partial to complete amenorrhea; subjects eating high amounts of raw food (more than 90% of the diet) were affected more frequently than moderate raw food dieters. Men reported decreased interest in sex.

The researchers noted that “a strict raw food diet cannot guarantee an adequate energy supply” and concluded that the consumption of a raw food diet is associated with a high loss of body weight. They warned: “Since many raw food dieters exhibited underweight and amenorrhea, a very strict raw food diet cannot be recommended on a long-term basis.”

Other risks of an all-raw diet include low bone mass, low B12, low HDL-cholesterol (the so-called “good” cholesterol) and elevated homocysteine.5

The Cooking Theory

These and other observations led to the formulation of the cooking hypothesis, first published in a 1999 article entitled, “The Raw and the Stolen: Cooking and the Ecology of Human Origins.”6

Lead author Richard Wrangham, a primatologist, noted that cooking is a universal human activity and suggested that the practice of using fire to cook our food led to other behaviors considered uniquely human, including greater cooperation and sociability (needed to keep fires going), division of labor between males (who did the hunting) and females (who did the cooking) and the tendency to form male-female bonds “embedded within multifemale, multimale communities.”

More to the point, cooked food provides humans with more energy than enjoyed by other species, allowing selection for a smaller digestive tract, smaller mouth and teeth and a larger brain.

In 2009, Wrangham published the book “Catching Fire: How Cooking Made Us Human,” which expanded on his original thesis. Wrangham notes that digestion is a costly process, requiring between 15% to 30% of our calories, so anything that makes digestion easier provides human beings with greater energy and allows them more time for other activities — from weapon production to ritual.

Human mouths, lips, teeth and jaws are smaller than those of apes and chimpanzees. The human stomach, small intestine and colon are smaller than those of a primate of the same height. Wrangham notes that the “volume of the whole gut is about 60% of what is expected for a primate of our size.”7 The more gut tissue in the body, the more energy must be spent on its metabolism.8

Thus, the reduced size of the human gut “increases efficiency and saves us from wasting unnecessary metabolic costs on features whose only purpose would be to allow us to digest large amounts of high-fiber food.”9 According to physical anthropologists Leslie Aiello and Peter Wheeler, compared to great apes, the reduction in human gut size saves humans at least 10% of daily energy expenditure.10

a gorilla and a man

A gorilla and a man of the same height; the gorilla has much greater digestive capacity while man has a larger brain.

Another difficulty with raw food is that it takes a long time to chew. Wrangham notes that chimpanzees spend more than six hours per day chewing; he estimates that humans living on a raw primate diet would need just over five hours per day for chewing.

As Wrangham puts it, “The unnaturally, atypically soft foods that compose the human diet have given our species an energetic edge, sparing us much of the hard work of digestion. Fire does a job our bodies would otherwise have to do … Cooking gives calories.”11

Why Cook?

These studies of digestion in the stomach and small intestine indicate that for humans, starchy food, fibrous food and most meats require cooking.

Starch inside plant cells occurs as granules — dense packages of stored glucose so small that they may remain even after milling. These starch granules are very stable and can persist in a dry environment for thousands of years. But with warmth and water, they start to swell at around 136 degrees F. In the presence of a liquid at 194 degrees F, the granules break into fragments and lose their structure. The starch “gelatinizes,” meaning that it dissolves in water.

The more starch gelatinizes, the more easily enzymes can reach it and the more completely it is digested. This is why cooked starch yields more energy than raw.

Beaumont’s experiments indicate that vegetables take longer to leave the stomach than starchy food or meat. In addition to starch, plant foods contain dietary fiber or roughage — nonstarch polysaccharides (glucose or fructose chains) such as cellulose, inulin, lignins, chitins, pectins, beta-glucans and oligosaccharides.

Levels will be especially high in certain rough vegetables like cabbage, kale and collard greens. These components are especially resistant to digestive enzymes, and cellulose is indigestible for humans. But cooking — as well as chopping — help break down dietary fiber into more digestible elements.

Fiber that resists digestion in the small intestine becomes food for bacteria in the colon. These beneficial flora break the fiber molecules into short-chain fatty acids, which can provide health benefits. On the other hand, some fiber-rich foods, such as beans and other legumes, can lead to flatulence and gas as the digestive apparatus tries to break down the tough molecules by fermentation.

Cooked Meat

Cooked meat is easier to digest than raw for two reasons. First, cooking melts away the connective tissue that wraps around muscle fibers.

Meat contains several kinds of connective tissue, including tendons (which connect muscles to bones), ligaments (which connect bones to each other) and sheets of white fibrous tissue called silverskin (which surround whole muscles). These are obviously tough and hard to digest when raw, and ligaments and silverskin remain as tough gristle even when cooked; however, the collagen in tendons melts into a broth when cooked in a liquid.

Connective tissue in the form of collagen also encases individual muscle fibers, and a collagen sheath encases individual fibers grouped into bundles — we see these bundles as the “grain” of the meat. It’s these collagen wrappings that make raw meat chewy and tough. Cooking, especially long, slow cooking in liquid, turns the tough collagen into soft gelatin.

Steaks and filets contain relatively little collagen and are most tender when cooked quickly to about 140 degrees F — if cooked longer or at too high a temperature, the muscle fibers themselves become tough. Meat that we eat raw is either sliced very thinly across the grain (carpaccio), ground up (steak tartare) or pounded. All of these techniques make these dishes easier to chew and digest.

Secondly, as the collagen webbing in meat melts away during cooking, the tightly wound muscle fibers begin to relax, providing more surface area for gastric juices in the stomach and digestive enzymes in the small intestine to do their work. For example, digestion of cooked beef by the enzyme trypsin increases four times compared to that for uncooked beef.12

Thus, cooking partially denatures meat proteins, and this denaturation process continues in the digestive tract.

Enhancing the Benefits of Cooking

In addition to cooking, anything that reduces particle size — such as chopping, crushing and grinding — makes our food easier to digest.13 Acidity, salt and drying also promote protein denaturation — think marinated, salted or dried meat.14 Animals contain glycogen in their muscles, and during the process of aging meat, the glycogen is converted to lactic acid, which promotes denaturation.

Hanging makes meat more tender because proteins are partly broken down by lactic acid and enzymes. Kalahari San hunter-gatherers cook their meat until it is so tender that the sinews fall apart and ensure complete digestibility by then crushing it in a mortar.15

Of course, raw foodists can point to many examples of raw food consumption — and in particular, raw meat consumption — among human beings; nevertheless, all human societies cook some or even most of their food, including some or even most of their meat. According to Marco Polo, Mongol warriors could ride for days without lighting a fire.

They ate the raw blood of their horses or put slabs of raw meat under their saddles to consume at the end of their ride, but they looked forward to cooked food at the end of a campaign. Maasai warriors relished fermented raw milk and blood but still cooked their meat.

The Inuit consumed raw meat on a hunt, or raw fish (frozen or fermented) as a snack, but expected a cooked meal waiting for them when they returned in the evening. South Sea Islanders do not need to light fires for warmth but nevertheless cook most of their food, most often in underground pits. They even light small fires in their canoes to steam fish wrapped in leaves.

Typically, hunter-gatherers consume the soft parts of the animal raw immediately after the kill — brain, marrow, tongue and liver — and then subject the muscle meats to cooking, drying or pounding. According to Dr. Price, African hunters ate liver both raw and cooked.16

One argument against cooking concerns the loss of vitamins and enzymes. Vitamin C disappears with cooking, while thiamine (B1), pantothenic acid (B5) and vitamin B6 decline. We need raw foods to obtain these nutrients — occasional raw meat or raw organ meat (especially for B6), raw dairy products and carefully chosen raw fruits and vegetables for vitamin C and B vitamins. Even better are super-raw foods — lacto-fermented foods in which these vitamins increase many-fold.

Vitamin C levels in cabbage can increase up to tenfold when we use lacto-fermentation to transform raw cabbage into raw sauerkraut; B vitamins also increase. Enzyme-rich lacto-fermented foods provide generous compensation for whatever enzymes are lost during cooking. The practice of consuming small amounts of super-raw lacto-fermented food with cooked food finds confirmation in both tradition and science.

The Observations of William Beaumont

In his book “Experiments and Observations on the Gastric Juice, and the Physiology of Digestion,” which describes the experiments performed on Alexis St. Martin, Dr. William Beaumont made the following observations:

The inner coating of the stomach is pale pink when food is absent. The color becomes redder (due to the infusion of blood) during digestion. In health, a mucous coat lines the stomach.

The normal temperature of the stomach is 100 degrees Fahrenheit. When the temperature of the stomach becomes too low, as with the introduction of cold food or cold fluids, digestion almost ceases.

Gastric juice is clear, transparent, without odor, slightly salty and acid. Since Beaumont’s time, we have learned that gastric juice contains a combination of hydrochloric acid (HCl), potassium chloride (KCl) and sodium chloride (NaCl). An empty stomach never contains gastric juice, which only appears when food enters the stomach.

Gastric juice acts as a solvent of food, becoming intimately mixed and blended by the churning motion of the stomach.

The stomach is capable of producing only a fixed quantity of gastric juice. If too much food enters the stomach, there will not be enough gastric juice to digest it all. Taking in too much food “if persevered in, generally produces, not only functional aberration, but disease of the coats of the stomach.”

Bile (for digesting fats) does not occur in the stomach, but in the small intestine.

Food is readily digested when it enters the stomach in a “finely divided” state, because this allows the gastric juice to act on a large surface area.

Raw foods, such as raw beef and raw potato, leave the stomach largely undigested.

Most food leaves the stomach after about three or three and one-half hours. Milk, both boiled and raw, leaves the stomach in about two hours. Tough cuts of meat — such as heart, tendon and salt pork — take around four hours for full digestion.

Surprisingly, soup also takes about four hours for full digestion. In fact, Beaumont observed that “solid food, of a certain texture, is easier of digestion than fluid.” However, soup taken with bread leaves the stomach after the normal time of three to three and one-half hours.

Beaumont observed that animal foods and “farinaceous aliments” (such as bread and porridge) are easier to digest than vegetables. Fats and oils leave the stomach unchanged.

Excesses in eating or drinking, fatigue, anger or excitement, illness and damp weather impair the quantity and quality of gastric juices. When St. Martin had a fever, the stomach appeared dry and inflamed, and the secretion of gastric juice was minimal. When he was angry, the stomach remained contracted, greatly hampering digestion.

The Expensive Tissue Hypothesis

The relative size of the human brain compared to body size is higher than for other mammals. Compared to the chimpanzee brain, the human brain is about three times as large, and the human digestive tract is smaller than would be expected for a primate of our body size.

In 1995, scientists Leslie Aiello and Peter Wheeler formulated the Expensive-Tissue Hypothesis (ETH), noting that when the brain is large, the organism must use less energy on other expensive tissues, such as the digestive tract.

The ETH proposes that humans can get by with a smaller gut by eating an easy-todigest diet. The primary way to make our diet easy to digest is to cook our food.

The original paper introducing the ETH sought to explain how humans manage to have energy for their large and metabolically expensive brains while still maintaining a basal metabolic rate comparable to other primates with smaller brains. The hypothesis holds that the higher energy expenditure of vertebrates with larger brains has to balance out with a decrease in the size of other energy-consuming organs, particularly the gut.

Optimizing Digestion

Milk products — Milk provides exquisite nourishment as a raw food, straight from the breast or the udder. The myriad proteins in milk are fragile three-dimensional objects, not tightly coiled and bound as are meat proteins. They do not require heat to render them digestible.

In fact, heat causes milk proteins to lose function rapidly — whether to provide nourishment as proteins, enhance immune function, eliminate pathogens or act as carrier proteins for the vitamins and minerals in milk. Fermentation further increases the nutritional value of raw milk. Raw cheese, yogurt and kefir are super-nourishing, super-raw foods.

Eggs — Studies with ileostomy patients show that cooking increases the protein value of egg whites by around 40%. Heat denatures proteins and renders them more digestible, a finding reflected in the habits of traditional peoples. The Aborigines of Australia threw emu eggs into the air to scramble them, then put them in hot sand or ashes and turned them regularly to cook them evenly, taking about twenty minutes.

Yaghan hunter-gatherers of Tierra del Fuego “would never eat half-cooked much less raw eggs.” They bored holes in egg shells to prevent bursting and buried them on the edge of a fire, until quite hard inside.17 But we also have traditions of consuming the yolks raw — such as raw egg yolk mixed with rice in Iran.

Meat — Meat requires gentle cooking to melt the collagen it contains and to gently relax tightly bound muscle fibers. Overcooking makes meat tough and harder to digest. Very rapid heating, as in microwaving (see page 46), renders the proteins in meat toxic. However, most cultures also consume raw meat, which provides vitamins B6 and B12 in undenatured form. Grinding, pounding and thinly slicing make raw meat more digestible.

Seafood — Traditional cultures consume fish and shellfish both raw and cooked. Marinating raw fish in an acid medium, as in ceviche, makes the muscle proteins easier to digest.

Grains — Grains require cooking in a liquid to soften them and gelatinize the starch, but cooking alone will not neutralize the many antinutrients in grains, particularly whole grains; these anti-nutrients include phytates, lectins and enzyme inhibitors. All grain-consuming populations throughout the world subject whole grains to soaking, sour leavening and other fermentation processes before cooking, and sometimes even after cooking.

Eating raw muesli (soaked but not cooked) and granola (not soaked and not cooked in water, only baked) is a recipe for digestive problems. A diet of grains that have been rapidly heated or subjected to pressure, such as breakfast cereals and rice cakes, causes rapid death in test animals.18

Beans — Beans are indigestible unless soaked and then cooked a long time. Some cultures then ferment cooked legumes to make a sour porridge.

Vegetables — Beaumont’s experiments revealed that vegetables are harder to digest than meat or starches. Most vegetables should be cooked until tender; those with good digestion can eat salads of tender vegetables cut small, or raw fermented vegetables. The common practice of consuming raw rough vegetables as juices, in salads or as chips poses a real challenge to our digestive apparatus.

Fruit — When St. Martin consumed nine ounces of raw, ripe sour apples, the contents of the stomach became “sharp and acrid,” irritating the aperture; the “morbid appearance of the gastric surface considerably increased.”19 Apples are high in pectin, and studies with rats indicate that compared to other types of dietary fiber, pectin produces lesions in the stomach20 and pathological structural changes of the villi in the small intestine.21

High-pectin fruits such as apples, pears, apricots, cherries, peaches and plums are best cooked; Asian cultures always cook these fruits. If you plan to eat these foods raw, at least remove the skin and make sure the fruit is very ripe and sweet. Citrus fruits also contain pectin, especially in the membranes — so best to section citrus fruit and remove the membranes. Interestingly, in non-obese diabetic mice, eating pectin increases the incidence of diabetes.22

Soups — Beaumont’s surprising finding — that soup takes longer to leave the stomach than meat or starches, unless eaten with bread — indicates that bread or croutons are a natural with soup!

Salt — The digestive juices — hydrochloric acid (HCl) and potassium chloride (KCl) — require chloride, which we get from salt (NaCl). Sodium in salt activates enzymes that help break down starches. Salt is essential for digestion!

Broth — The work of Francis Pottenger, MD indicates that broth taken with meals (in soups, sauces, gravies and stews) acts as an aid to digestion of other foods, especially if these foods are processed to reduce particle size.

Observations of Nutritionist Chris Sandel

In a recent survey, I found that two issues many people seem to be suffering from are low energy and poor digestion. Here are some tips for how to improve both these areas through diet and lifestyle changes.

The first suggestion is to focus on easy-to-digest food. I see countless clients who suffer with IBS and digestive issues, and when I go through their food diary, I am hardly surprised. Their diet consists of lots of salad, spinach, kale, sweet corn, beans, lentils, quinoa, bread, pasta, oat cakes, rice cakes, protein bars, popcorn and so on.

All these foods are really difficult to digest, and yet they are the cornerstones of their diet. If you are unable to digest the food you are eating, this will not only cause digestive issues, it will also mean you get a lot less nutrients and therefore less energy.

On top of being difficult to digest, a lot of these foods are very low in calories. I know “calories” is a dirty word in the mind of the general public, but it is a measure of the energy available to power your body. We use anywhere between 15% to 30% of our calories just to run our digestive system.

If people are eating foods that are difficult to digest and give little in return, then it is no wonder they have low energy. With less energy, the body has fewer resources, and so digestion is turned down further, which then makes the situation worse. It’s a vicious cycle resulting in more digestive upset and less energy.

So instead of low-calorie, hard-to-digest foods, I want people to eat things that are going to give them the biggest bang for their buck. I mean foods that are high in calories, high in macronutrients (carbohydrates, protein and fat), high in vitamins, minerals, enzymes, etc. and are easy to digest so you can get access to all these nutrients.

The foods that generally fall into this category are: carbohydrates, including root vegetables (must be well cooked) and fruit (particularly tropical fruit); protein, including white fish, shellfish, broth, meat (how much and which cuts depends on the person), eggs and dairy (if you can digest it); fat, mainly saturated fat such as butter and coconut oil (but also lard, tallow, suet, ghee and bone marrow). Olive oil is fine as long as it is not heated above 180 degrees C.

The final piece of advice to help with energy and digestion is to eat in a relaxed environment. I know it sounds simple and most people know it in a theoretical sense, but no one is doing it.

People eat meals while rushing around or eat their lunch while sitting in front of their computer working. Every meal doesn’t have to be a long drawn-out affair but giving yourself time to eat where your only focus is the food in front of you makes a huge difference. Even if it is just five to ten minutes, it helps.

We have two sides of the autonomic nervous system, sympathetic (fight or flight) and parasympathetic (rest and digest). You need to be in a relaxed state to digest your food properly, and if you are rushing around and not giving your body a chance to slow down, your ability to digest your food is minimized.

About the Author

Sally Fallon Morell is author of the best-selling cookbook “Nourishing Traditions” and many other books on diet and health. She is the founding president of the Weston A. Price Foundation ( and a founder of A Campaign for Real Milk ( Visit her blog at

A Brief Commentary by Dr. Mercola

The devil is in the details, as they say, so I’d like to add a word of caution with regard to olive oil. While traditionally lauded for its health benefits, olive oil is frequently adulterated with harmful seed oils, so making sure you’re sourcing your olive oil from a reputable seller is paramount.

But even then, olive oil contains high amounts of the monounsaturated fat (MUFA) oleic acid, which, while being less potent than polyunsaturated fats (PUFAs) in terms of harmful effects, still inhibits mitochondrial energy production.

In excessive amounts, MUFAs, like PUFAs, can impair mitochondrial function in several ways. To mention just one, oleic acid controls the expression of delta 5 and delta 6 desaturase (D5D and D6D), enzymes that are crucial in converting LA into arachidonic acid, a precursor to pro-inflammatory molecules.

High intake of oleic acid has been linked to an increase in these enzymes, particularly D6D, suggesting a potential exacerbation of lipogenic (fat-creating) activities. Oleic acid also creates oleoylethanolamide (OEA),23 which activates a nuclear receptor called PPAR-alpha, which directly turns off glucose metabolism. So, every time you eat monounsaturated fat, PPAR-alpha is activated and turns off your ability to break down glucose.24

All of that is to say that using olive oil for cooking is not nearly as ideal as butter or ghee. So, when it comes to olive oil, I recommend limiting your intake to avoid undermining your mitochondrial energy production.

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