Certainly, there are benefits to consuming plenty of raw fruits and vegetables. These foods supply us with high nutrient levels and are generally low in calories too. Eating lots of raw foods is a key feature of an anti-cancer diet style and a long life. But are there advantages to eating a diet of all raw foods and excluding all cooked foods? The answer is a resounding “No”. In fact, eating an exclusively raw-food diet is a disadvantage. Excluding all steamed vegetables and vegetable soups from your diet narrows your nutrient diversity and has a tendency to reduce the percentage of calories from vegetables in favor of nuts and fruits which are lower in nutrients per calorie.
Raw vegetables are dramatically low in calories and we probably only absorb about 50 calories a pound from raw vegetables. Our caloric needs cannot be met on a raw food diet without consuming large amounts of fruits, avocado, nuts and seeds. This may be an adequate diet for some people, but in my 15 years of medical practice catering to the community of natural food enthusiasts, raw foodists and natural hygienists, I have seen many people who weakened their health on such raw food, vegan diets. Frequent fungal skin and nail infections, poor dentition, hair loss and muscular wasting are common on such fruit-based diets.
Unfortunately, sloppy science prevails in the raw-food movement. Raw food advocates mistakenly conclude that since many cooked foods are not healthy for us, then all cooked foods are bad. This is not true.
The idea that stirs the most enthusiasm for this diet is the contention that cooking both destroys about fifty percent of the nutrients in food, and destroys all or most of the life promoting enzymes. It is true that when food is baked at high temperatures—and especially when it is fried or barbecued—toxic compounds are formed and most important nutrients are lost. Many vitamins are water-soluble, and a significant percent can be lost with cooking, especially overcooking. Similarly, many plant enzymes function as phytochemical nutrients in our body and are useful to maximize health. They, too, can be destroyed by overcooking. However, we cannot paint with this brush of negativity over every form of cooking.
Only small amounts of nutrients are lost with conservative cooking like making a soup, but many more nutrients are made more absorbable. These nutrients would have been lost if those vegetables had been consumed raw. When we heat, soften and moisturize the vegetables and beans we dramatically increase the potential digestibility and absorption of many beneficial and nutritious compounds. We also increase the plant proteins in the diet, especially important for those eating a plant-based diet with limited or no animal products.
In many cases, cooking actually destroys some of the harmful anti-nutrients that bind minerals in the gut and interfere with the utilization of nutrients. Destruction of these anti-nutrients increases absorption. Steaming vegetables and making vegetable soups breaks down cellulose and alters the plants’ cell structures so that fewer of your own enzymes are needed to digest the food, not more. On the other hand, the roasting of nuts and the baking of cereals does reduce availability and absorbability of protein.
When food is steamed or made into a soup, the temperature is fixed at 100 degrees Celsius or 212 Fahrenheit—the temperature of boiling water. This moisture-based cooking prevents food from browning and forming toxic compounds. Acrylamides, the most generally recognized of the heat-created toxins, are not formed with boiling or steaming. They are formed only with dry cooking. Most essential nutrients in vegetables are made more absorbable after being cooked in a soup and water-soluble nutrients are not lost because we eat the liquid portion of the soup too.
Recent studies confirm that the body absorbs much more of the beneficial anti-cancer compounds (carotenoids and phytochemicals—especially lutein and lycopene) from cooked vegetables compared with raw. Scientists speculate that the increase in absorption of antioxidants after cooking may be attributed to the destruction of the cell matrix (connective bands) to which the valuable compounds are bound.
Another fallacy promoted in the raw food movement and on the web is that the fragile heat-sensitive enzymes contained in the plants we eat catalyze chemical reactions that occur in humans and aid in digestion of the food. This is not true. Plant foods do not supply enzymes that aid in their digestion when consumed by animals. Our body supplies exactly the precise amount of enzymes needed for digestion; we are not ill equipped to digest normal food. The plant enzymes are broken down into simpler molecules by our own powerful digestive juices and even those that are absorbed as peptide size pieces (or with some biologic function) do not function to catalyze human functions. So it is not true that eating raw food demands less enzyme production by your body. A healthy body produces the precise amount of enzymes needed to digest the ingested food appropriately and the enzymes our body uses for other processes are unique to our human needs and are not present in plants. We make what we need from the proper materials.
In conclusion, eating lots of raw foods is a feature of a healthy diet. I always encourage people to eat more raw food. One of my common statements is—the salad is the main dish. Raw food is necessary for digestive efficiency, proper peristalsis and normal bowel function. Certain foods, especially fruit, avocado and nuts undergo significant change with cooking and are best eaten raw. Baking, frying, barbecuing and other high heat cooking methods that brown and damage food form acrylamides, which are carcinogenic. Browning and other high heat cooking methods should be avoided. Cooking techniques like steaming vegetables, stewing foods in a pressure cooker and soup making, do not have these drawbacks. They do not brown foods or form acrylamides.
Eating raw food is necessary for good health and is an important feature of a healthy diet. But that does not mean that one’s entire diet has to be raw to be in excellent health. It also does not mean eating an all raw diet is the healthiest way to eat. It is healthier to expand your nutrient density, your absorption of plant protein and your nutrient diversity with the inclusion of some conservatively cooked food in your diet.
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Ismail A ; Lee WY. Influence of cooking practice on antioxidant properties and phenolic content of selected vegetables. Asia Pac J Clin Nutr. 2004; 13(Suppl):S162.