Joe Schwarcz, a nutrition expert and chemistry professor at Canada's prestigious McGill University and author of "An Apple A Day," offers his take on the world of food and nutrition:

Q. What are the most common myths about nutrition?

A. Perhaps the most common myth is that there are "healthy" foods and "unhealthy" foods. It is the overall composition of the diet that matters. That being said, there are, of course, foods we should try to incorporate into a healthy diet and ones that should be curbed. It is a good idea to strive for seven to 10 servings of fruits, vegetables and whole grains a day and to cut down on fatty meats and soft drinks. A second widespread myth is that if something is "natural" it is superior to "artificial." There is no such relationship. Nature is not benign; botulin, for example, possibly the most toxic substance known, is produced by the perfectly natural Clostridium botulinum bacterium.

Q. What would you say is the biggest misconception about organic food and pesticides?

A. The belief that organic producers do not use pesticides. There are a number of pesticides approved for organic use, and all come from "natural" sources. That has little meaning. Rotenone, for example, a pesticide derived from the derris plant, is allowed in organic agriculture and has been linked with Parkinson's disease. There is also the belief that organic foods are more nutritious, which is not necessarily so.

Q. What about enhanced foods (e.g., added vitamins, DHA, etc.)?

A. To a large extent, this is marketing hype — with the exception of probiotics. Certain bacterial cultures, when added to food, may help control disease-causing bacteria.

Q. Antioxidants?

A. Again, the benefits have been overhyped. The free-radical theory of disease and aging is interesting and plausible, but there is less evidence than consumers think. This is not to say that antioxidants that can neutralize free radicals are not important, but they appear to work effectively only when they are part of the food itself, not as isolated supplements.

Q. Artificial sweeteners?

A. Artificial sweeteners have to jump over a variety of hurdles before they can be approved. In fact, the regulations for additives are much more stringent than for the natural components of foods. My problem with sweeteners is that they encourage the consumption of soft drinks and snacks that have no redeeming nutritional value.

Charles Stuart Platkin is a nutrition and public-health advocate, and author of "Breaking the FAT Pattern" (Plume, 2006). Sign up for the free Diet Detective newsletter at www.dietdetective.com.