For several decades now, Harvard researchers have tracked the effect of various “lifestyle factors”—that’s diet and physical activity to you and me—on the health and well-being of more than 120,000 volunteer doctors and nurses from around the U.S. Their latest report is just out in the New England Journal of Medicine and it tells us in no uncertain terms to lay off French fries and potato chips if we don’t want to get fat. But it’s apparently ok to eat cheese and drink diet soda.
The researchers determined this by looking at the interaction between diet, exercise, sleep, television watching habits and weight gain (or, occasionally, loss). Discouragingly, they found that the average study participant gained 3.35 pounds over every four-year period. But the good news is that the study also points the way to salvation, because some foods actually were associated with weight loss.
First, the bad guys. For every additional daily serving of these foods, here’s how many pounds people gained, on average, over four years:
French fries—3.35 pounds
Potato chips—1.69 pounds
Sugar-sweetened beverages—1 pound
Unprocessed red meat—0.95 pounds
Processed meats—0.93 pounds
Foods containing trans fat—0.65 pounds
Boiled, baked or mashed potatoes—0.57 pounds
Now, the good guys. For every additional daily serving of these foods, people LOST this amount of weight:
Some foods that you’d think would make people fat, apparently didn’t. Butter was the only full-fat dairy food associated with significant weight gain (0.30 pounds per four years for each added daily serving). Cheese and whole milk were not.
And, while some research suggests that diet sodas somehow make you gain weight even though they have zero calories, in this study they didn’t.
Exercise also helped, but not as much as you might hope. The one-fifth of participants who exercised the least gained 1.76 pounds more per four years than the fifth who exercised the most. Adding exercise to a less fattening diet helped a lot, though: people who ate the most fattening foods and exercised the least gained nearly 6 pounds more every four years than people who did the opposite.
As for sleep, it turns out that the optimal amount, weight-gain-wise, is between six and eight hours a night. And every extra daily hour spent in front of the TV added 0.31 pounds of weight every four years.
Changes in Diet and Lifestyle and Long-Term Weight Gain in Women and Men [New England Journal of Medicine]