From Scientific American:
Although we are what we eat, we are by no means only what we eat. Some people, for instance, can consume all the fatty foods they want—meat, cheese, butter, ice cream—but somehow manage to stay rail-thin and enjoy low blood triglyceride levels, whereas others living on the same rich fare would soon develop potbellies and clogged arteries. The significant genetic and metabolic variation among individuals makes it almost impossible for experts to prescribe detailed nutritional recommendations that work optimally for everybody. As nutritionist Marion Nestle recommends in her article “Eating Made Simple,” beginning on page 60, the best we can do today is to adhere to the time-honored advice to eat less; exercise more; eat mostly fruits, vegetables and grains; and avoid junk foods.
But this basic regimen leaves many concerned Americans with unresolved issues about dietary choices, especially those regarding specific foods promoted by food companies and their lobbyists: Is milk bad for adults? Should I eat more fish? Are organic foods better? More specific guidance regarding food selection would help.
More here.