What is the secret to losing weight and keeping it off? People have asked this question for ages, and many different answers have been proposed. We’re all familiar with various dieting fads that have passed in and out of favor: the high-protein diet, the juice-only diet, and countless others. But what are the actual long-term weight consequences of consuming different types of food?
In an article published this week in NEJM, Mozaffarian et al. report the findings of a large prospective study that sought to answer this question. The study followed the weight changes of more than 120,000 American men and women for up to 20 years. None of the study participants were obese or had chronic diseases at baseline. The study participants were identified through three prospective studies: the Nurses’ Health Study, the Nurses’ Health Study II, and the Health Professionals Follow-up Study. They were evaluated at four-year intervals.
The study found that participants gained on average 3.4 lbs, or 2.4% of body weight, over each four-year period. This translated to a gain of 16.8 lb over 20 years. The foods associated with the greatest weight gain per four-year period were potato products, including a 3.4 lb average gain associated with French fries and a 1.7 lb gain with potato chips. Other foods linked to weight gain included sugar-sweetened beverages, unprocessed red meat, and processed meats; each of these was associated with a gain of about 1 lb. Increases in alcohol consumption were associated with an average weight gain of 0.4 lb.
On the flip side, the study found that some foods were inversely associated with weight gain. Eating more yogurt was linked to a decrease in weight of 0.8 lb over a four-year period. Other foods linked to weight loss over time were vegetables (-0.2 lb), whole grains (-0.4 lb), fruits (-0.5 lb), and nuts (-0.6 lb).
The authors also investigated how various changes in lifestyle affected weight. Smoking cessation was associated with a 5.2 lb weight gain over the first four years following cessation, but only minimal weight gain thereafter. Sleeping less than six hours or more than eight hours were both associated with weight gain, which the authors speculate might be due to changes in the level of hormones that mediate hunger perception. Watching more TV was independently linked to a weight gain of 0.3 lb per additional hour per day, possibly because it encourages snacking and influences food preferences.
An increase in exercise, not surprisingly, was associated with better weight control. Participants were categorized into quintiles based on the degree of change in physical activity. Those in the highest quintile of change gained on average 1.8 fewer pounds over four years than those in the lowest quintile. Interestingly, the absolute level of physical activity was not significantly associated with weight change.
Combining the effects of diet and lifestyle, the authors report that study participants in the bottom quintile of change along both dimensions gained almost 6 lb more weight than those in the top quintile of change.
What does this mean for those who are tired of periods of intense dieting and looking instead to succeed at long-term weight management? The authors suggest that the study results offer both a cautionary tale and a message of hope. They write, “A habitual energy imbalance of about 50 to 100 kcal per day may be sufficient to cause the gradual weight gain seen in most persons. This means that unintended weight gain occurs easily but also that modest, sustained changes in lifestyle could mitigate or reverse such an energy imbalance.”
So the next time you’re deciding between a cup of yogurt and a bag of potato chips, here’s some food for thought. Small changes today may not noticeably alter how you look tomorrow or even in the next 12 months. But years down the road, you may be thanking yourself: every choice, it seems, does count.