So my friends and I were out at a bar having a debate over what would be the worst imaginable lunch to have every day. Options thrown out included corn-syrup Coke with a large order of fries, doughnuts and a whole-milk latte, and fried mozzarella sticks. Some of this seems like common sense. Fried foods, sugary foods, and junk foods should be terrible for you and make you fat if eaten every day. We couldn't figure out if anyone had bothered to actually study this and figure out what are the worst foods to eat every day. Help us out, Science! Which foods are most likely to make you fat if you eat them all the time?
Formulating a Fat Future
Science has been holding on to your question for a while, waiting for a good, scientifically rigorous answer to your question, which is surprisingly tricky. It's not like scientists can go out into the world and force people to eat one food or another for years on end—randomizing some to foods we suspect are healthy and others to unhealthy foods. But finally a study—recently published in the New England Journal of Medicine by Dariush Mozaffarian and others from Harvard—figured out a way to answer your question: Which foods are most likely to cause one to gain weight?
This study group reanalyzed data from three huge surveys (involving 20 to 50,000 people each) that followed the participants over many years—tracking things like their weight and their habits (smoking, exercise, alcohol consumption, and so on), as well as what they ate (as reported by food diaries). All three were observational studies, where the participants reported what they ate, whether they smoked, how much they exercised. The Harvard group then took this data and ran it through a fancy statistical analysis to figure out which foods were associated with weight gain or loss.
Most of the results were as any reasonable person would suspect. Eating lots of fruits, vegetables, and nuts was associated with weight loss. Whole grain consumption was associated with weight loss, refined grain consumption with weight gain. The more fried foods one ate, the fatter one became over time. A few subtle details popped out, however. Eating potatoes—french fried, baked, or made into chips—was tremendously associated with gaining weight, more than just about any other food. Sugary juice was less associated with weight gain than sugary sodas. Processed meats and red meats were associated with weight gain. Low-fat dairy foods (like yogurt) were associated with weight loss, and even full-fat dairy foods (aside from butter), like whole milk and cheeses, were not associated with either weight gain or loss.
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