A reader asks what might be the ideal percentage of protein, fat, and carbohydrate in diets. It’s not an easy question to answer because the percentages could vary a lot, depending on the amounts of good fats (monounsaturated, for example) and good carbohydrates (whole grains). In any case, it’s too hard to have to look up the nutrient composition of every food you eat. But I sometimes have fun using the USDA’s food composition tables. They do require interpretation though as the numbers may or may not reflect what you are actually eating. Carrots grown in California may or may not have the same nutrient composition as those grown in upstate New York. I consider these tables a national treasure and wish the USDA would put more resources into making them even more comprehensive.