High heat cooking is problematic because it creates toxic substances as well as causes the loss of nutrients. Virtually all nutrients in food are susceptible to damage from heat. Of course, whether a particular nutrient gets damaged depends on the exact nutrient in question, the degree of heat, and the amount of cooking time. But in general, most of the temperatures we cook at in the over (250-450°F/120-230°C) are temperatures at which substantial nutrient loss occurs, except for roasting turkey because it takes a long time for the heat to penetrate the meat and damage the nutrients. And although very short cooking at 212°F (100°C) in boiling water produces relatively little nutrient loss, once boiling goes on for anything more than a very short period of time (1-3 minutes) the nutrient loss becomes significant. We've researched and searched through the nutrition research and all of the evidence points to the same conclusion: prolonged high-heat cooking is just not the way to go.
While grilling does create foods that have a unique flavor and texture and grilling is pretty synonymous with summertime, we do have some concerns about it.
There are documented health risks associated with the char-broiling and gas grilling of foods. In general, these risk are associated with the formation of heterocyclic amines (HAs). Most HAs are well-documented carcinogens and keeping their levels to a minimum in a diet can decrease our cancer risk. Here are the basic factors involved with HA formation in food.
It is best to grill or broil on an area without a direct flame as the temperatures directly above or below the flame can reach as high as 500°F to 1000°F. HAs form most easily at high temperatures. Under 325°F the formulation of these compounds is very low. As temperatures increase above 400°F the formation of HAs can increase by 700%-1000%. Gas and charcoal grilling often (but not always) involve higher temperatures.
More HAs form when a food is in very close proximity to its heat source. Flame-grilling is perhaps the best example of a food coming into direct contact with a heat source. Less contact with the heating element (whatever heating element is used) lowers the formation of HAs. In deep fat frying, for example, where we might expect high HA formation, there is often very little HA creation due to relatively low temperatures and indirect exposure to the source of heat (although deep frying involves its own set of issues related to health concerns.)
The longer a food is exposed to high heat, the great the HA formation. When a food like a hamburger is grilled for 10 minutes versus 6 minutes, for example, the HA levels in the hamburger may increase by 25-30%.
The so-called "MPF" foods (meat, fish, and poultry) are more likely to give rise to HA formation when prepared in the above fashion because HA formation requires the presence of amino acids (from protein) as well as nitrogen-containing substances creatine or creatinine. Both of these substances are plentiful in most animal foods.
The principles of nutrient loss from charcoaled or gas-grilled foods are very similar to the principles of all cooking: the shorter the time of exposure to heat, the lower the heat, the less nutrient loss. Since this cooking method does not typically involve use of water, there an be less nutrient loss from this method than from boiling or simmering. However, minimal steaming of a food would typically require less total cooking time and for this reason result in decreased loss of nutrients.
As noted above, most of the research on HAs has been done on meat. Therefore, it is uncertain that the grilling of vegetables and fruits have the same level of outcomes, notably because some of the phytonutrients found in vegetables, such as the sulforaphane in broccoli, have been found to reduce the carcinogenic effect of the HAs in research studies..
The bottom line from a health perspective: we would choose other methods of preparing foods rather than grilling, yet if you want to enjoy grilled foods on occasion, given that the the rest of your diet is healthy, it may not be so detrimental. If you do choose to grill foods and use an oil to coat them, we would suggest using an oil that has a high smoke point, such as avocado oil, high-oleic safflower oil, or coconut oil to avoid the formation of oxidative damage to the oil itself. Additionally, there are certain antioxidant-containing foods, such as rosemary, citrus fruits, and green tea, which have been found to reduce HA levels. Therefore, you could consider using these foods in marinades if you are looking for ways to reduce HA formation.