Effects on nutritional content of food

Cooking prevents many foodborne illnesses that would otherwise occur if the raw food was eaten. Cooking also increases the digestibility of some foods such as grains. Many foods are inedible raw. For example kidney beans are toxic when raw, due to the chemical phytohaemagglutinin.

Proponents of Raw foodism argue that cooking food increases the risk of some of detrimental effects on food or health. They point out that the cooking of vegetables and fruit containing vitamin c both elutes the vitamin into the cooking water and degrades the vitamin through oxidation.[citation needed] Peeling vegetables can also substantially reduce the vitamin C content, especially in the case of potatoes where most vitamin C is in the skin.[citation needed] However, research has also suggested that a greater proportion of nutrients present in food is absorbed from cooked foods than from uncooked foods.

Baking, grilling or broiling food, especially starchy foods, until a toasted crust is formed generates significant concentrations of acrylamide, a possible carcinogen.[citation needed]

Cooking dairy products may reduce a protective effect against colon cancer. Researchers at the University of Toronto suggest that ingesting uncooked or unpasteurized dairy products (see also Raw milk) may reduce the risk of colon cancer.[citation needed] Mice and rats fed uncooked sucrose, casein, and beef tallow had one-third to one-fifth the incidence of microadenomas as the mice and rats fed the same ingredients cooked. This claim, however, is contentious. According to the Food and Drug Administration of the United States, health benefits claimed by raw milk advocates do not exist."The small quantities of antibodies in milk are not absorbed in the human intestinal tract," says Barbara Ingham, Ph.D., associate professor and extension food scientist at the University of Wisconsin-Madison. "There is no scientific evidence that raw milk contains an anti-arthritis factor or that it enhances resistance to other diseases."

Several studies published since 1990 indicate that cooking muscle meat creates heterocyclic amines (HCAs), which are thought to increase cancer risk in humans. Researchers at the National Cancer Institute found that human subjects who ate beef rare or medium-rare had less than one third the risk of stomach cancer than those who ate beef medium-well or well-done. While eating muscle meat raw may be the only way to avoid HCAs fully, the National Cancer Institute states that cooking meat below 212 °F (100 °C) creates "negligible amounts" of HCAs. Also, microwaving meat before cooking may reduce HCAs by 90%. Nitrosamines, present in processed and cooked foods, have also been noted as being carcinogenic, being linked to colon cancer.

Research has shown that grilling or barbecuing meat and fish increases levels of carcinogenic Polycyclic aromatic hydrocarbons (PAH). However, meat and fish only contribute a small proportion of dietary PAH intake - most intake comes from cereals, oils and fats. German research in 2003 showed significant benefits in reducing breast cancer risk when large amounts of raw vegetable matter are included in the diet. The authors attribute some of this effect to heat-labile phytonutrients.

Heating sugars with proteins or fats can produce Advanced glycation end products ("glycotoxins"). These have been linked to ageing and health conditions such as diabetes.