nutrient -- except for sugar. no one knows how much is too much. i can make a guess based on the analogy that i've made with ethanol, with alcohol, that probably 50 grams of fructose a day is probably the maximum. the american heart association put out a paper two years ago that i was an author on that suggested that it was more like 35 grams to 40 grams per day. >> help us understand here. the sugar association which represents members of the sugar industry, they say on its website that sugar is a healthy part of the diet. carbohydrates, including sugar, are the preferred sources of the body's fuel for brain power, muscle energy, and every natural process that goes in every functioning cell. so how do you respond to -- >> that could not be further from the truth. >> why is that? >> because you don't need fructose. there is not one reaction in the body that requires fructose. the only place in your body that has fructose is your semen and your body makes that de novo.