Lesson 1: The Science

Cooking and its Byproducts:

If you are cooking, then Wet cooking methods such as slow cooking, water baths, steaming, boiling and blanching and low temperature drying such as food dehydration are the safest methods of food cooking and preservation . These methods minimise loses and minimise toxic byproducts such as Heterocyclic amines (HCAs), Polycyclic aromatic hydrocarbons (PACs), Advanced glycation end products (AGEs) and Acrylamide. Cooking can increase nutrient availability, especially true with legumes and in some cases such as with certain carotenoids. However Cooking can often increase antioxidant levels in certain foods and has no impact on mineral level unless you strain cooking liquid away.

Cooking can (depending on method + length of time)

  1. Reduce nutrient and phytochemical content 
  2. Damage nutrients 
  3. Produce potentially harmful byproducts
  4. Denature Digestive Enzymes and enzymes required to covert phytonutrients into their bioactive form.
  5. Destroy Beneficial Bacteria
  6. Cooked food often seen as dead food, living food is alive full of energy molecules.

Commercially processed foods loose up to 50-80% of nutrients. Boiling foods loose up to 50-80% of nutrients. Steaming loose up to 20% of nutrients. Cooking also diminishes phytochemicals except carotenoids. However, juicing increases carotenoids much more than cooking.


Potentially harmful byproducts of cooking:

  1. Heterocyclic amines (HCAs)
  2. Polycyclic aromatic hydrocarbons (PACs)
  3. Advanced glycation end products (AGEs)
  4. Acrylamide

There are many other harmful compounds but above are the main ones.

1.Heterocyclic amines are formed when creatine or creatinine are exposed to high temperatures. These are only found in animal flesh products. This compound is cancer causing and linked to many cancers.

2.Polycyclic aromatic hydrocarbons are chemicals formed by the incomplete burning of carbon containing substances in food or in fat heated above 392 F such as grilled or charred foods and toast. These compounds damage DNA + produce cancer.

3.Advanced glycation end products are the irreversible final products of the maillard reaction such as toasting, frying and browning food. Grilled meats – even roasting foods such as tofu and seeds.

4.Acrylamide in food is formed when the amino acid asparagine reacts with naturally occurring sugars such as glucose. This generally occurs at the later stages of baking, roasting, or frying when the moisture content falls, and the surface temperature rises.


Digestive Process: Food Enzymes May Help & How Cooking has Unwanted Byproducts. The Raw Advantage :

Food is held in upper part of stomach for between 20 to 60 minutes where pH is between 4,5 to 5,8 – This is the perfect pH for the functioning of enzymes. When food drops to lower part of the stomach the pH goes down to 1,3 to 2,5 and the enzymes are destroyed, broken down into amino acids, however – sometimes enzymes make it through the small intestine, not often but sometimes, most commonly when the enzymes are attached to a viable microorganism such as with fermented foods. There are very few studies on this and little research on whether these enzymes, that make it to small intestines, help with digestion.

Example: (amylase) – enzyme that breaks down starch called amylose into maltotriose and maltose used as energy. Amylase activity in carrot juice= 20-30 units/litre. Amylose activity in unstimulated saliva= 200,000 units/litre

Most digestion occurs in small intestine and it appears that it is our own enzymes that aid digestion and plant enzymes may help but might only be small. When foods are subjected to heat, especially at high temperatures, several by-products can form that are very damaging to human health. Among the most notorious are heterocyclic amines (HCAs), polycyclic aromatic hydrocarbons (PACs), advanced glycation end-products (AGEs), and acrylamide.


Heterocyclic Amines and Polycyclic Aromatic Hydrocarbons

Heterocyclic amines (HCAs) are chemicals that are created when meat, poultry, fish and eggs are subjected to high temperature cooking, such barbequing, frying, or grilling. The formation of these compounds increases with temperature and duration of cooking. Cooking methods that use direct heat (e.g. frying or grilling) produce more HCAs than do indirect-heat methods such as stewing, steaming or poaching. Many vegetarians wonder if HCAs are produced in a similar manner when vegetables are cooked at high temperatures. The answer is no because the formation of these compounds involves the condensation of creatinine with amino acids (the building blocks of protein), and creatinine is found exclusively in muscle tissue. In January, 2005, HCAs were officially added the list of cancer causing agents put out by the National Institutes of Health (NIH).


Polycyclic aromatic hydrocarbons (PAHs) are a group of over a hundred different chemicals that are formed by the incomplete burning of organic substances such as oil, gas, coal, forests, garbage, tobacco and food or the pyrolysis of fat at temperatures in excesses of 392 degrees F. Food accounts for over 90 percent of our PAH exposure. The most concentrated sources of PAHs are grilled or charred meat, poultry and fish, grains, fats and oils, and sweets. Vegetables, fruits, beverages and dairy products also contribute to overall intake. However, PAHs in vegetables and fruits are due largely to environmental contaminations of the air and soil. Where contamination is minimal, produce will contain few PAHs. A host of factors affects PAH formation, apart from environmental contamination. The primary factors include the temperature of cooking, distance from the heat source, duration of cooking, type of fuel used in heating, amount of fat in the food, and whether the fat drips onto the heat source and rises back onto the food. Raw grains tend to be low in PAHs, however levels increase with certain processing techniques, such as direct combustion gas heating and toasting. While sprouted grains are a very minor source of PAHs, ready-to-eat cereal generally contain much higher levels. Processed sweets can also contribute to PAH intake. Fats and oils are a significant source, as the foods from which they are extracted are often contaminated. In addition, direct combustion gases and solvents used in processing can further increase levels.

Heterocyclic amines and polycyclic aromatic hydrocarbons are known to be mutagenic (that is, they damage DNA). Evidence suggests that HCAs increase our risk for a variety of cancers, including colorectal, stomach, pancreatic and breast cancers. Cancers thought to be linked to PAH intake include lung, skin and genitourinary. Most of our exposure to these compounds comes through our food, and the vast majority through high temperature cooking. Vegetarian diets generally contain negligible amounts of HCAs, and moderate amounts of PAHs. Intakes of those eating raw or high-raw diets would be considerably lower.


Advanced Glycation End-Products (AGEs)

Advanced glycation end products (AGEs) are harmful end-products of the Maillard reaction or of fat oxidation, which are formed when food is heated to high temperatures.  They can also be formed within the body when sugar molecules attach to protein, fat or DNA.

What is the Maillard Reaction?

The Maillard reaction is a form of non-enzymatic browning that occurs when sugars, such as glucose or fructose, combines with an amino acid. The chemical reaction, which is called glycation, results in intermediate products of the Maillard reaction. If heating continues, further chemical reactions may result in irreversible bonding of amino acids (protein cross-links), and the formation of advanced glycation end-products (AGEs). The cross-linking of protein may also result in the destruction of essential amino acids or a reduction in their availability. The Maillard reaction begins to escalate when foods are heated to temperatures of 310 degrees F or higher. Products of the Maillard reaction are minimized when foods are boiled or steamed, as temperatures reach only 212 degrees F. The food industry purposefully uses the Maillard reaction to improve the flavor and color of foods. Good examples of this are the production of colas, coffee, caramel and many baked goods. The potential harmful effects of the end-stage products of the Maillard reaction were not well recognized until the 1970’s when products of non-enzymatically glycated hemoglobin where found in diabetic patients.

There is evidence that AGEs impair immune system function, accelerate aging, and contribute to the progression of Alzheimer’s disease, cardiovascular disease, diabetes, eye diseases, kidney disease, nerve diseases and stroke. Research has shown that about 10 percent of the AGEs in food are absorbed into the system. Restricting foods rich in AGEs has been shown to significantly reduce circulating AGE levels in the body, and levels of C-reactive protein,  a marker for inflammation (high levels of C-reactive protein indicate greater inflammation in the body).Foods that are most concentrated in AGEs are broiled, grilled and fried meats. See Table 3.5 for a list of AGEs in common foods. The average daily AGE intake (based on food records) for people eating a standard Western diet has been estimated at approximately 16,000 kilounits (ku). Vegetarian diets tend to contain lesser amounts, unless they are very high in processed and fried foods. Raw food diets contain minimal AGEs.


Acrylamide is a chemical that is used to make polyacrylamide, which is employed in the manufacturing of certain glues, cosmetics, food packaging materials, soil conditioning agents, plastics and grouting agents. It is also used in water treatment. Although polyacrylamide is non-toxic, small quantities of acrylamide residues, which appear to be less benign, remain in finished products. In April 2002, Swedish researchers discovered the presence of acrylamide in some starchy foods. They noted that acrylamide appears to form spontaneously when certain foods, particularly those that are high in carbohydrate and low in protein such as potatoes, are subjected to high cooking temperatures. The higher the cooking temperature and the longer the cooking time, the greater the acrylamide concentration becomes. Canadian scientists discovered that most acrylamide in food is formed when the amino acid asparagine reacts with naturally occurring sugars such as glucose. This generally occurs at the later stages of baking, roasting, or frying when the moisture content falls, and the surface temperature rises.

The most concentrated food sources of acyrlamide are processed foods such as potato chips and other baked or fried salty snacks and French fries, as potatoes are particularly high in asparagine. Other food sources include crackers, crispbreads, pretzels, breads (especially toasted), cold cereals, and other foods processed at high temperatures such as coffee and cocoa. Acrylamide is also formed during the home preparation of starchy foods. Any significant formation of acrylamide requires temperatures of 248 degrees F or higher. Consequently, it is found only in insignificant amounts in steamed or boiled foods. There are a number of potential health concerns associated with acrylamide consumption. Occupational and accidental exposures to high doses have been shown to cause neurotoxicity in humans. Experimental studies suggest that it could also be toxic to genetic material, increasing risk of cancer and reproductive problems, although these findings have not been confirmed in humans. Acrylamide was evaluated by the International Agency for Research on Cancer in 1994 and classified as “probably carcinogenic to humans” on the basis of a positive cancer bioassay result.

Vegetarians are not necessarily at an advantage over non-vegetarians in terms of acrylamide intake. If vegetarians consume large amounts of baked or fried starchy foods, they may be at a disadvantage. On the other hand, vegetarians relying more heavily on raw foods would have significantly lower intakes.


Experts consistently agree that we should keep our intakes of heterocyclic amines, polycyclic aromatic hydrocarbons, advanced glycation end products, and acrylamide as low as possible. Increasing our intake of raw foods, and selecting lower temperature, wet cooking methods will help to minimize the production of these harmful compounds in our food.