THE RAW DEAL: Why You Should Avoid the Trendy 'All Raw' Diet
By Beatrice Trum Hunter
Photo by Peter Beard
The dietary fad of eating only uncooked foods surfaces repeatedly. Currently, about three dozen haute-cuisine restaurants scattered throughout American cities offer all-raw food. "Living foods" are touted as offering improved nutrition and health, spiritual enlightenment, and inner contentment. Cooked foods are disdained as "dead foods".
What's wrong with a diet consisting of solely raw foods? Plenty. A totally raw food diet seriously limits the broad base of a mixed diet. An all raw diet eliminates quality protein foods, unless one is willing to risk foodborne illness from pathogens that likely contaminate raw high-protein foods, but which are deactivated by heat.
A Leap Forward for Humankind. There was a sudden spread of hearths about 40,000 years ago, indicating that humans added firemaking to their cultural heritage. The universal use of controlled fire made possible both creature comforts and cooking, and, with this development, a greatly expanded and diversified food supply. Cooking was a necessary evolutionary step that preceded the cultivation of cereal grains that require cooking - such as wheat, barley, rice, and corn. The possibility of cooking food gave humans a major revolutionary advantage. The development of cultivated tubers, legumes and vegetables, all requiring cooking, expanded the diversity of foods. Cooking deactivated toxic substances, present in many of these cultivated foods, through accelerated oxidation with heat. Cooking made possible the consumption of many foods that, in a raw state, are undesirable, inedible, or toxic. Many plants produce chemicals that discourage insects, animals, and humans from devouring the plant. In widening the base of food intake, humans were able to obtain needed nutrients from a greater variety of foods.
Some Unjustified Claims for the All-Raw Food Diet.
Raw food enthusiasts claim that cooking destroys nutrients. However, water-soluble vitamins and minerals that leach out in cooking can be retrieved if the nutrient-rich liquid in which the vegetable is cooked is added to soups, stews , or sauces.
All-raw food proponents claim that cooking destroys food enzymes that facilitate digestion, and that in order to utilize cooked foods, the body must use up its own supply of enzymes. This reasoning is flawed. The enzymes in raw food are tailored to meet the specific needs of the plants. The enzymes destroyed in food when it is cooked bear little relationship to human health. The healthy human manufactures needed enzymes for various systems. The only evidence that we have that an external source of enzymes is useful to humans occurs in the reaction of human infants and young animals to extra supplies of phosphatase, as supplied by breast milk or cow's milk. Other food enzymes merely contribute to quicker spoilage of food, or deterioration of flavor. This is the reason that produce needs to be blanched before canning, in order to deactivate nuisance enzymes. Heat destroys thiaminase, an enzyme that destroys thiamine (vitamin B1) in raw fish, shellfish, Brussels sprouts, and red cabbage.
Raw-food boosters claim that uncooked foods are metabolized more efficiently than cooked foods. There is no evidence to support this view. On the contrary, with newer knowledge of phytochemicals (discussed below) it has been found that these beneficial substances are far more available after food is cooked than when it is raw.
Usually raw fooders consume raw nuts and seeds. However, these foods are not tolerated by everyone. Tree nuts are among the major allergens. Peanuts (not a true nut, but a legume) also are a major allergen, and a number of people with severe peanut allergies continues to soar. Cashew nuts contain appreciable amounts of a shell oil, which can contaminate the surface of raw cashews. The oil can cause a generalized skin eruption. Roasted cashews do not produce this reaction. Sesame-seed allergy can be reduced by deactivating the offending allergen in toasting the raw seeds.
In recent years, a popular practice has been to add raw mushrooms to salad greens. Yet many raw mushrooms are indigestible. They become edible through cooking. Some mushrooms contain poisonous substances that are destroyed in cooking. Raw mushrooms contain hydrazines, some of which are carcinogenic. Most hydrazines are destroyed by cooking or drying the mushrooms.
Raw fooders face a very restricted diet. Over time, the all-raw diet, deficient in many essential minerals, inevitably leads to health problems. Some raw fruit, berries and melons in season, and raw salad greens are desirable in a mixed diet; by themselves, these foods are inadequate for health maintenance and body repair. Yet these are the staples of the raw food diet in extreme vegetarianism, "sproutarianism," and "fruitarianism." At the very extreme end are the "breatharians" who try to emulate the ascetic saints who allegedly obtained all of their nutrients from the air.
Cooking Makes Food Safer. Some naturally occurring toxins in foods can be rendered less poisonous by cooking. Some toxins are changed into harmless products by heat. Even the water used in cooking may serve a useful purpose, by diluting the toxins.
Cooking destroys avidin in raw egg white. Otherwise avidin would bind biotin and some iron present in egg yolk, and make these nutrients unavailable.
Cooking increases the bioavailability of niacin (B1), present in a bound form in many cereal grains.
Heat processing increases the digestibility of starch, by gelatinization; and the digestibility of protein, by denaturing.
Many plant foods contain anti-nutrients that make the nutrients unavailable to humans. Cooking improves the digestibility of foods with anti-nutrients.
RETAINING NUTRIENTS IN COOKED VEGETABLES
Cook vegetables only long enough to loosen the fibrous matrix that surrounds nutrients. Use as little water or other cooking liquid as possible. Use a pot with a tight fitting cover. Steam, pressure-cook, or microwave the vegetable only until it is fairly tender, retains its color, and still has a bit of crunch. Stir-frying is another cooking method that works well. Because it is fast and done without water, water-soluble nutrients do not leach out. In fact, the light oil coating helps to retain nutrients. Also, the oil helps us utilize the fat-soluble vitamins present in foods. The tab of butter added to a cooked vegetable achieves the same goal, as well as adding palatability. Beta-carotene is absorbed best in the presence of butter or oil. Thus, stir-frying carrots helps us to absorb this phytochemical.
Similarly, antioxidants in spinach are far better absorbed when spinach is cooked and butter or oil is added.
In a series of tests conducted by Dr. Gertrude Ambruster and colleagues at the Department of Nutritional Sciences at Cornell University, the investigators found that vitamin C (ascorbic acid) in cooked vegetables decreased as the amount of cooking time and amount of water increased. In general, the lowest levels of ascorbic acid were found in boiling vegetables. Steaming was somewhat better; and microwaving, considerably better. For example, broccoli contained about 81 milligrams of ascorbic acid per 100 grams after boiling; 125 mg after steaming; and 162 mg after microwaving. Similar results were achieved with asparagus, Brussels sprouts, cabbage, and cauliflower.
Frequently ascorbic acid is used to test foods for nutrient losses. This vitamin is heat-,light-; and time-sensitive. It is reasoned that if ascorbic acid is lost, other nutrient losses also occur.
Legumes (beans and peas) contain numerous anti-nutrients, most of which can be reduced by long cooking. Legumes contain the trypsin inhibitor. This anti-nutrient prevents action of the enzyme, trypsin, found in the digestive tract of humans and animals, from digesting and assimilating proteins properly. The trypsin inhibitor renders protein virtually worthless. This condition persists, regardless of increased protein intake. In addition, trypsin normally allows vitamin B12 to be assimilated. Thus, by blocking trypsin activity, legumes increase the requirements for B12 and actually can create a deficiency of this vitamin. The trypsin inhibitor in chick peas resists even heat treatment.
Raw beans contain hemagglutinins. These anti-nutrients have the ability to agglutinate (clump together) the red blood cells in humans and other animals and significantly suppress growth. Hemagglutinins combine with the cells that line the intestinal wall, and interfere with intestinal absorption of nutrients. Hemagglutinins in beans are reduced by long cooking.
Raw beans contain a goitrogenic factor, which blocks the uptake of iodine by the thyroid gland, and can lead to the development of goiter.. This factor is reduced by long cooking of beans.
Raw lima beans contain complex glucosides that release hydrocyanic acid, a highly toxic gas. After cooking, cyanogens are oxidized to harmless products.
Raw fava beans are toxic. Eaten in large quantities, raw fava beans can lead to hemolytic anemia, a characteristic of "favism," which is common in some Mediterranean countries.
Raw soy beans contain numerous toxins, including the trypsin inhibitor described above. The raw soybean's anti-coagulant property is attributed to its anti-trypsin activity. Raw soy beans also contain other anti-nutritents, including phytic acid from phytates, which binds and prevents mineral absorption, especially zinc, calcium and magnesium. Raw soy beans contain hemagglutinins, too.
Raw peas contain lathyrogens, substances that can disrupt the structure of collagens in the body. Lathyrism, a disease in humans, is characterized by muscular weakness and paralysis in the lower part of the legs. Lathyrism has been recognized since the time of Hippocrates. Although many people celebrate the new crop of sweet peas by eating them raw, the practice is unwise. The sweet pea contains not only lathyrogens, but also hemagglutinins and trypsin inhibitors. All of these toxins are reduced by cooking the peas.
Cereal grains should never be eaten raw. Minerals and trace minerals in them are bound, chemically, to phytic acid. The human digestive system cannot break down phytic acid and make the minerals available for assimilation until the grains are cooked.
Some healthful vegetables and fruits contain toxic and undesirable substances. Spinach and rhubarb contain high levels of oxalic acid. This toxin blocks calcium absorption and can cause severe liver damage. These foods should be cooked to reduce the oxalic acid. Cooked spinach accompanied by a calcium-rich food , is a good combination. The calcium will buffer the effects of the residual oxalic acid in the cooked spinach. The leaves of the rhubarb should never be eaten, raw or cooked, because they contain high levels of the toxin. Fortunately, rhubarb's appearance in gardens and grocery stores is for a limited time period. It is far from ideal as a year-round food. If eaten, it should be used sparingly.
Red cabbage, broccoli, Brussels sprouts, cauliflower,
and kale ...all nutritious vegetables.....contain goitrogens. By cooking these vegetables, the goitrogens are destroyed or greatly reduced.
In general, hard, cellulose-rich vegetables are better digested after being cooked. Cooking breaks down the cell walls of food, and makes nutrients more readily available. Thus, vegetables such as broccoli, cauliflower, and carrot yield more nutrients when they are cooked than when raw. Such vegetables should be cooked long enough to loosen the fibrous matrix that encases them and locks in nutrients. A common but unwise practice is to add raw carrot sticks, and cauliflower and broccoli florets to appetizer platters with dips.
Generally, the human body has no problem absorbing vitamin C (ascorbic acid) from foods. Although broccoli contains vitamin C, eating it raw was found to be 20% less effective in raising vitamin C levels in human blood than other foods. The study was conducted by the Agricultural Research Service and the National Cancer Institute. It takes alot of chewing to get the maximum benefits from some raw foods such as broccoli.
Cooking increases the palatability of some foods, making them more appealing and increasing their consumption and the nutrient intake from such foods.
Cooking Food Releases Phytochemicals. In recent years, researchers have uncovered newer findings about formerly unknown substances in foods, phytochemicals. Frequently, these valuable substances are bound within foods, and released when foods are cooked. Then, phytochemicals are well utilized. Some examples:
1) Lycopene is a carotenoid that acts as an antioxidant. It protects our cell membranes from free-radical damage and DNA mutations. The tomato is a good source of lycopene,which is absorbed best when the tomato has been heat processed. Cooking releases lycopene. Products such as bottled tomato juice, tomato sauce, tomato paste, and even ketchup, are better lycopene sources than raw tomatoes. Tomato sauce, with olive oil, fat-containing cheese, or fat containing ground meat all yield appreciable amounts of lycopene. Although red-pigmented fruits such as watermelon, pink grapefruit, and guava are good lycopene sources, these fruits are eaten raw, and their lycopene is not as readily absorbed as the lycopene from cooked tomatoes.
2) In raw foods, beta-carotene and other carotenoids are not always released from inside the fibrous walls of plants. They are released when the food is cooked and made more available to the body. According to Dr. John W. Erdman, Jr. Director of Nutritional Sciences at the University of Illinois at Champaign-Urbana, chewing on a raw carrot results in relatively large chunks that cannot be broken down easily by digestive enzymes. As a result, some individuals may absorb as little as 1% of the beta- carotene contained in a carrot.
Raw Food Is Not For Everyone. Although raw fruits and appropriate salad greens should be part of a mixed diet for most people, raw foods are not tolerated by everyone. The digestive tract of some individuals cannot tolerate large quantities of raw foods. Such individuals can tolerate cooked foods, especially if they have consumed mainly cooked foods over the years. Any radical shift to an all-raw food diet can spell disaster.
Cooked foods are less likely to offer allergic reactions than raw foods. Usually, proteins are the allergic constituents in foods. Cooking denatures the offending proteins, and renders the foods less allergenic.
At-risk patients, such as those with severe burns, patients recieving cancer treatment, those with indwelling catheters, and others whose immune systems are impaired and makes them susceptible to infections, should be discouraged from eating raw foods. The most frequent infections result from consumption of raw tomatoes, radishes and celery. Pseudomonas aeruginosa and klebsiella are the most troublesome contaminants affecting debilitated individuals. Some hospitals dealing with cancer patients, all raw food is treated with radiation to kill pathogens on the food.
A Nutritionist's View of the All-Raw Food Diet.
According to Rebecca Reeves of the Nutritional Research Clinic at Baylor University in Houston, Texas, the scientific basis of the all-raw food diet is lacking. "You take some of these principles. Ok, the American diet is lacking in fruits and vegetables, agreed; OK, probably we do overcook vegetables, so we lose some vitamins. Agreed," says Reeves. But, she adds, "You're probably looking at two exact extremes. Neither of them is healthy. We somehow need to moderate it to get it into the middle."
The author, Beatrice Trum Hunter, MA, has written more than 30 books on food and environmental issues, frequently before widespread public awareness. She was food editor of Consumer's Research Magazine for more than two decades. She is an honorary member of The Price Pottenger Nutrition Foundation, as well as an honorary fellow of The International Academy of Preventative Medicine and an honorary member of The American Academy of Environmental Medicine. She has been the recipient of many awards, including The Jonathan Forman Award of The Society for Clinical Ecology, The New Hampshire Society for Preventative Dentistry, and The Donnon Pepper Humanitarian Award. She can be reached at 243 Falls Road, Deering, N.H. 03244
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