Everyone knows that it is important to count calories in order to maintain or lose weight. An important, recent study by Harvard public health and nutrition experts published in the New England Journal of Medicine (June 23, 2011) concludes that simply eating the right type of foods may be the key to controlling weight. In the study, increased physical activity, as expected, helped control weight; however, specific dietary choices, combined with physical activity, contributed to even better weight control.

Many studies about weight control involve small numbers of obese individuals who are followed for short time periods; these studies require extrapolation of results to a healthy, non-obese population. The value of the recent Harvard study is that it assessed long-term weight of healthy, non-obese participants who themselves were all health care professionals. In the study, nearly 120,000 women and men were evaluated every four years over a 12- to-20-year period to assess their habits and current weight. The analysis involved the effects on weight of dietary choices as well as several lifestyle behaviors including exercise, sleep, television viewing, smoking, and alcohol intake. This is the largest and longest-running study of its kind, including well-educated people who are concerned about their own health, and it provides some fascinating information about the impact of different types of food on long-term weight.

Even in healthy, non-obese people, weight gain occurs slowly over a long period of time; in this large study the average gain was 1 pound per year. An extra 50-100 calories a day is enough to account for this gradual weight gain. The most interesting results of this study were the effects of specific foods on weight. Some of the foods associated with weight gain were not surprising as culprits. Potatoes in various forms were high on the weight gain list. The single food item most associated with weight gain was French fries. A daily serving of French fries was calculated to add (all by itself!) nearly 1 pound a year. Potato chips and other forms of potatoes were also high on the “gain” list. In decreasing order of weight gain effect were sugar-sweetened beverages, processed and unprocessed red meats, sweets and desserts, refined grains, 100 percent fruit juice, and butter. In the nearly neutral effect (on weight gain or loss) category were cheese (regardless of fat content) and milk (whether skim, low fat, or whole).

On the list of foods associated strongly with long-term weight loss, the clear winner (with the strongest effect) was yogurt. In decreasing order of weight loss effect were nuts (all nuts are “high fat”), fruits, whole grains and vegetables. Please see page 3 of our recent newsletter (Looking and Feeling Your Best, Volume 3, Number 2) for a table of all the foods that were evaluated in the Harvard study.

This study (as well as several other recent studies) strongly suggests that not all calories are equivalent. As always, diet and exercise are essential to maintaining a healthy weight, but eating the right foods (and avoiding the wrong foods) may, over the long run, make the difference between success and failure.