The study question: What effects do diet and lifestyle changes have on long-term weight gain? Most weight gain happens slowly over time, at the rate of roughly 1 pound a year, and few studies have previously examined what factors can affect weight gain over the long haul in healthy individuals.
This study investigated the relationship of several diet and lifestyle changes such as beverage choices and amount of sleep in nonobese men and women living in the United States. The study combined data from three different, long-term cohort studies—the Nurses' Health Study I and II, and the Health Professionals Follow-up Study—conducted from 1986 to 2006, with more than 280,000 participants. After people with chronic health problems were excluded, data from 120,877 participants were analyzed. Once participants reached age 65, they were excluded from further analysis to avoid confounding due to the loss of lean muscle mass that commonly occurs with age.
Changes in diet and lifestyle factors were measured at four-year intervals. Adjustments were made to take age, baseline body mass and lifestyle factors including physical activity, television watching, alcohol use, sleep duration, and cigarette smoking in account. Dietary factors examined included the amounts of fruits, vegetables, whole and refined grains, potatoes, nuts, dairy products, sweets and desserts, meats, fried foods, alcohol drinks, and trans fat. Several categories were broken down further: boiled and mashed potatoes, french fries, and potato chips; whole-fat and low-fat dairy products; processed and unprocessed meats; sugar-sweetened beverages, diet sodas, and 100% fruit juices; and different types of alcoholic drinks.The relationships between dietary choices and lifestyle factors were analyzed both separately and together.
The results: Small changes in individual behaviors make a big difference in long term weight. The average difference between those with the largest amount of weight gain over the study period and those with the smallest gain or actual weight loss was only 3.1 servings of vegetables per day and 25.3 metabolic equivalents of physical activity per week. Metabolic equivalents (METs) are a practical way to express the intensity of energy expended during various physical activities in a way
that is comparable among different levels of physical activities performed by people of different weights. For example, brisk walking at 3 miles per hour, a moderate intensity activity, is roughly equal to 9-10 METs.
While eating more or less of any one food would change the number of calories consumed, the magnitude of weight gain was associated with specific foods and beverages. These show a strong positive association with increased weight gain. Per serving per day, potato chips resulted in a 1.69 pound gain and french fries resulted in 3.35 pounds gained. Refined grains (.39 lb) increased weight gain almost as much as sweets and desserts (.41 lb) per daily serving. Sugared sweetened beverages (1 lb), processed meats (.93 lb) and unprocessed red meats (.95 lb) all showed a similar pattern. The relationship between alcohol consumption and weight gain was not clear and requires more investigation. However, liquid carbohydrates, including alcohol, were associated with increased weight gain.
Less weight gain was robustly associated with increased consumption of other categories of foods. Per serving per day, vegetables resulted in -.22 lb, whole grains in -37 lb, fruits in -.49 lb, and nuts in -.57 lb. Dairy foods overall appear to be neutral. A surprising result was that a daily serving of yogurt was associated with -.82 lb. The authors speculate that the probiotic bacteria in yogurt may alter gut bacteria in such a way that influences weight. Increased consumption of these foods likely means less
consumption of those foods associated with increased weight gain.
Physical activities such as sleep and television watching are also associated with long term weight. Weight gain was lowest among those who slept 6-8 hours a night, and was higher for those sleeping less than 6 or more than 8 hours a night. More hours of television watching appears to influence weight gain, and this may due to the opportunity for increased snacking and reduced physical activity. Smoking appears to result in a small initial weight gain, but little weight change afterwards, and the health benefits of smoking cessation far outweigh the associated risks of continuing to smoke as a means of weight management.
Is this study relevant to me? Yes. Anyone interested in maintaining a healthy weight as they age can benefit from the information contained in this study. Eating more nuts, fruits, vegetables, and yogurt appear to reduce weight gain over time, while consuming starches such as potatoes and processed foods high in fat and sugar can increase weight gain. A habitual imbalance of 50-100 calories a day may be enough to result in the gradual weight gain observed in most people.
Limitations of the study: Although this is one of the largest and most comprehensive studies to date on this issue, the study does have some limitations. Portion sizes and lifestyle behaviors were estimated, and could have resulted in some degree of error. The authors note that the true relationship with weight change is likely to be an underestimate. Participants in the study were largely white, educated adults in the United States, which may limit the generalizability of its findings to other populations.
Find this study in PubMed:
Changes in diet and lifestyle and long-term weight gain in women and men.
Mozaffarian D, Hao T, Rimm EB, Willett WC, Hu FB.
N Engl J Med. 2011 Jun 23;364(25):2392-404.