By Margaret Badore for DietsInReview.com
The raw food trend is getting a lot of media attention lately, both on DietsInReview and in the wider health community. The raw diet tied for the second best diet for weight loss in U.S. News‘ assessment, and raw cleanses are a hot trend that’s gaining popularity both for its promises of detoxification and weight loss.
Supporters of the raw diet believe that raw fruits, vegetables and nuts are the richest sources of vitamins, minerals, enzymes and other nutrients. Some people who follow the raw food diet also include meat and dairy, but many are strict vegans. While a plant-based raw diet is certainly very healthy, cooking some plants actually increases some nutrients and can make others more bio-available.
Once you start into the question of raw vs. cooked foods, it immediately becomes a complex matter. Nutrition science has become quite sophisticated, yet there’s still only a limited amount of research available on this subject. Some vitamins may be lost during the cooking process yet other nutrients are enriched by cooking and exposure to heat. However, there are still many gray areas when it comes to the importance of many vitamins, minerals and other phytochemicals, and even more uncertainly when you want to compare their values before and after cooking. Below are some of the facts that we do have about raw and cooked foods, organized by nutrient.
“Heat readily destroys thiamine (B-1) and vitamin C,” says Mary Hartley, RD, MPH Nutritionist for Calorie Count. Scientific American reports that cooking tomatoes for just two minutes decreases their vitamin C content by 10 percent. Vitamin C is a highly unstable compound that is quickly degraded through oxidization and cooking. “Foods high in thiamin include whole grain and enriched grain foods, fortified cereals, lean pork, wheat germ, legumes, and organ meats,” says Hartley. “Vitamin C is found in many fruits and vegetables, especially red and green peppers, oranges, cantaloupe, broccoli, Brussels sprouts, baked potato, and cabbage.” She suggests eating a raw source of vitamin C every day.
Lycopene is an essential nutrient found in tomatoes and other red berries and fruits. A diet rich in lycopene is associated with lower rates of cancer. One study published in the British Journal of Nutrition found that one kind of lycopene is made more bioavailable by cooking. “Lycopene is a carotenoid, and all carotenoids, along with phenolic acids and flavonoids, are enhanced by cooking,” says Hartley. She adds that studies have shown that carotenoid-rich foods are best eaten in the presence of fat or oil.
Vitamins A, D, E and K
These vitamins appear to be unchanged by cooking. “Fiber, carbohydrates, protein, fat, minerals, trace minerals, and all of vitamins A, D, E and K, remain when vegetables are cooked,” explains Hartley.
Like vitamin C, B vitamins can be lost through boiling because they are water soluble. To decrease the loss of water soluble vitamins, choose cooking methods that minimize the use of water, such as grilling, roasting and microwaving. Making soups and stews will preserve some of these vitamins in the broth. Raw sources of vitamin B include bananas, oysters, tuna and caviar. Liver is also a rich source of B vitamins, but I don’t recommend it raw!
“It is important to differentiate between enzymes that are needed for digestion and enzymes that naturally occur in foods,” points out Hartley. She says that the enzymes found in food have no bearing on digestion. However, enzymes can have other effects on the body. “For instance, the myrosinase enzyme family and indoles found in cruciferous vegetables contain anti-cancer compounds that are destroyed by heat,” says Hartley. Bok choy, broccoli, Brussel sprouts, kale, cauliflower, cabbage, cress, kohlrabi, mustard, rutabaga and turnips are all cruciferous vegetables. Cooking these vegetables also destroys goitrogenic enzymes that interfere with the formation of thyroid hormone. “It’s always a tradeoff,” Hartley reminds us. “With some nutrients becoming more available and others becoming less available, when food is cooked.”
Although some may swear by the raw food diet, Hartley and I agree that it takes a lot of work and careful planning, not to mention the difficulty of giving up foods like cheese and bread. The bottom line is that it’s good to eat plenty of fruits and vegetables, no matter how they are prepared. Garlic and nuts are also best when eaten raw, along with fruits that are high in vitamin C. Consuming a diet that’s high in raw fruits and vegetables can also help you lose weight, because the fiber can help you feel full while consuming fewer calories.
Not only does cooking make many foods more appealing and enhances some nutrients, it also kills off bacteria, which is particularly important when it comes to meat and animal products. “Cooking (and careful chewing!) generally makes food more digestible by softening the fibers,” says Hartley. She recommends a diet that consists of a variety of cooked and raw foods, with a raw source of vitamin C eaten every day.”