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Is cooked food “toxic”?

June 12, 2011


Specific evidence needed rather than vague claims

This part is sometimes fairly technical, but since the raw-foodist claims that cooked food is toxic are so often assertions lacking in specific support, it is necessary that we first examine in detail whether claims about toxicity of cooked food are justified by specific evidence. In particular:


  • Maillard moleculeshave been accused by Guy-Claude Burger (founder of Instinctive Nutrition) of all evils. Below, we show that they do have some (mild) antinutritional properties, but on the other hand are anticarcinogenic. 
  • Natural and non-natural carcinogens. It has been said that cooking results in the formation of carcinogens. We review the literature on the subject, and observe that these carcinogens are only formed in meat and fish cooked at high temperatures, and that by themselves they do not explain all incidences of cancers related to food consumption. In particular, there are many other natural and non-natural carcinogens, and the potency of a carcinogen can be affected, positively or negatively, by numerous dietary factors. 
  • Toxins in raw foods.We review some of the toxins found naturally in raw foods, and the effect (or absence of effect) of cookingon them. 
  • Other common claims about cooking. Then, we investigate other effects of cooking, such as how heating affects fats, and discuss two standard raw-foodist arguments: “Pottenger’s Cats” and digestive leukocytosis. 

Maillard molecules and heterocyclic amines

The Maillard reaction was discovered in 1916, and typically occurs in all forms of cooking. Our objective here is to examine one by one all the effects of these molecules, and determine whether they have a significant impact on our health or not. We will see that, at least when gentle methods of cooking are used, the effects of Maillard molecules on food quality are minimal.

How the Maillard reaction(s) occur


The Maillard reaction is not a single, but in fact a series, of reactions between proteins and carbohydrates. The reactions occur during storage at room temperature, as well as during cooking, with the rate of reaction accelerating as temperature increases. It should be pointed out that virtually all foods contain both proteins and carbohydrates. Even meat contains very small amounts of carbohydrate, i.e., glycogen (muscles store energy in the form of glycogen) and glucose (blood contains some glucose). Cooked meat contains less Maillard molecules than foods high in protein and carbohydrate, such as milk, that have been heated under the same conditions, but we’ll see below that Maillard molecules are the precursor of carcinogenic compounds called “heterocyclic amines” in high-temperature grilled meat and fish.

Browning, aromas, and flavors. So-called “Amadori products” are the result of early Maillard reactions. Then, brown pigments are created, giving the characteristic color of some cooked foods like bread crust, as well as volatile compounds which give various odors such as roasting aromas. More than 2,000 volatile compounds have been identified (and certainly many more exist) [Finotet al. 1990]. (Note: It may be that Maillard reactions are not responsible for all browning that occurs during cooking and aging; oxidation may also be responsible. For instance, meat browns quite easily despite the minuscule amounts of carbohydrates present with which to react with proteins.)

Generation of Maillard products depends on variety of factors. The proportions and the amounts of different Maillard products depend on processing time, temperature, water activity, and pH, resulting–in particular–in a variety of flavors and colors. This explains why under- or overcooking can spoil the flavor of a meal. (Note: “Water activity” is a number which reflects the active portion of the moisture content of a product, i.e., the part which generates a vapor pressure at the surface of the product. This quantity is correlated with total moisture content. For pure water, water activity is equal to 1. For more technical details, see

Adaptation and toxicity. One of the main arguments of Instinctive Nutrition is as follows: Since humans have been cooking for only a relatively short period of time, they can’t possibly have adapted (in the Darwinian sense) to so many different chemical by-products which don’t occur naturally. (Side note of interest: Instincto literature typically claims cooking has only been occurring for the last 10,000 years, when in fact it has been practiced regularly for, at the least, roughly the last 40,000 years according to paleontological evidence, and perhaps considerably longer. (See Fire and Cooking in Human Evolution on this site, including the postscript, for a more in-depth discussion of the evidence for prehistoric fire use.) The aim of this section is to give a brief review of what is known about the toxicological consequences of the Maillard browning reaction.

Are Maillard molecules unnatural?


First of all, since there are no known raw-food human cultures, even among hunter-gatherers or other more primitive peoples, and since widespread cooking has been around for at least 40,000 years (perhaps considerably longer), one might legitimately wonder whether eating a 100% raw-food diet is still totally natural for human beings, but that is outside the scope of our discussion here.

Both stored and cooked foods contain Maillard products. The second remark is that, since the reaction can and also does occur at room temperature, certainly many of the Maillard compounds are found in uncooked foods, though in different (usually lower) concentrations than in cooked foods. One may also observe that many raw-fooders are reluctant to consume anything heated above 104°F (40°C), even if for a few minutes, while they will readily use foods preserved for months (like nuts or olives) which contain a substantial amount of Maillard reaction products and, arguably, are thus hardly more natural than cooked foods.

The body’s normal metabolic processes also produce Maillard molecules via non-food pathways. Finally, there has been a recent growing interest in studying the Maillard reaction in vivo (in living organisms as opposed to in vitro, i.e., in “test tubes” or other situations outside the living organism) and more particularly in relation to diabetes and aging. It is thought that the cross-linking between long-lived proteins such as collagen and free sugars (especially fructose, which has a high cross-linking potential) produces Advanced Glycation Endproducts, or AGEs (the products of the Maillard reaction at an advanced stage) which contribute to tissue degeneration [Baynes and Monnier 1989]. For the intrigued reader, fructose is an intermediate product of a chain of reactions called the “sorbitol pathway,” one of the several possible pathways of glucose metabolism. (I would like to point out here that other theories of aging, related to telomere length, exist.)

Production of Maillard molecules via elevated blood sugar (diabetes, high-fruit diets) may be more of a concern for raw-fooders. The point of the above is that there is no reason to fear Maillard molecules excessively, since they are produced naturally inside our body, whether we eat 100% raw or 100% cooked. Moreover, if one of the goals of the raw-fooder is to increase longevity, then it may be more important to regulate blood sugars (since the Maillard reactions that occur among the body’s own tissues are accelerated in diabetics [Baynes and Monnier 1989]) than to worry excessively about avoiding dietary Maillard molecules.

Note again that dietary Maillard molecules involve FOOD proteins, not the BODY’S proteins; there is no reason to believe that Maillard reaction products consumed in food in any way participate in the body’s own internal cross-linking reactions that contribute to aging, since the latter Maillard reaction products are produced as part of normal cellular metabolism, and via a separate biochemical pathway. Given that so many raw-fooders who attempt to entirely avoid cooked foods often tend to eat high-fruit diets (which are higher in sugars), this is a consideration such individuals may want to keep in mind.

Metabolic defenses against AGEs. Furthermore, the body is not defenseless, since AGEs forming on body proteins such as collagen are recognized and endocytosed (engulfed) by macrophages [Vlassara et al. 1989], i.e., destroyed by white blood cells. (Below, however, we’ll see that dietary Maillard molecules can pose risks to the vascular system and kidney in diabetics, but there is no evidence that such toxic effects occur in non-diabetic individuals.)


(How Important is Genetic Adaptation Regarding Cooking?)

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