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Title: Changes in diet and lifestyle and long-term weight gain in women and men

Authors: D Mozaffarian, T Hao, E Rimm, W Willett, F Hu

Reference: N Engl J Med 2011; 364:2392-404 (open access)
http://bit.ly/rr7fsZ

Reviewer: Robert Goldberg, PhD, Contributing editor, ProCor; Professor of Medicine and Epidemiology, Division of Cardiovascular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, USA

Reviewer comments: The obesity epidemic continues to rage onward in the US, affecting increasing numbers of adults and adolescents. Despite the well acknowledged adverse health effects associated with being overweight, and that most persons, especially those from industrialized countries, gain weight over time, most individuals have a fairly difficult time losing weight, especially during middle-age when other individual and family obligations and changes occur and levels of physical activity often decline.

The results of the present very important study, using data from three large and well conducted prospective epidemiologic studies, suggest that the majority of persons included in these longitudinal studies of health professionals gained a considerable amount of weight over the period of follow-up, averaging nearly 17 pounds over a 20 year period. As expected, a number and variety of factors were associated with weight gain over time including the consumption of potatoes and potato chips, sugar sweetened beverages, and meats. On the other hand, the intake of vegetables, whole grains, fruits, nuts, and yogurt were inversely associated with weight gain. In addition to the important role of several dietary factors, increased physical activity was associated with weight loss, while weight gain was associated with either too much or too little sleep, or the prolonged watching of television.

The present results provide much useful information for practitioners with regards to the amount of weight people gain during their middle years of life and factors associated with weight loss and weight gain. These findings provide considerable fodder for the development of individual and population-based strategies to help men and women consume fewer calories and certain foods and food groups. Moreover, common sense approaches, including increasing one's level of physical activity, decreasing the number of hours spent watching television, and watching what one eats, especially with limiting snacking on potato chips, and consuming less sweetened soft drinks and processed meats, will pay considerable dividends toward reducing the middle-aged bulge which is accompanying an increasing number of men and women in industrialized countries and the adverse health effects of moderate to excessive weight gain. Indeed, no child or adult should be "left behind" in these efforts as there is much work to be done on this extremely potent risk factor for coronary heart disease, diabetes, and other common maladies of contemporary men and women.

Purpose of study: To examine the long-term effects of changes in diet and lifestyle practices on weight gain in American men and women

Location of study: Boston, MA, US

Study design: Secondary analysis of data from several prospective studies

Results: The investigators analyzed data from three large prospective studies. These investigations included the Nurses' Health Study (NHS), the Nurses' Health Study II (NHSII), and the Health Professionals Follow-up Study (HFPS). In the two Nurses Health studies, nearly 240,000 female nurses were followed over time while the HFPS included more than 50,000 male health professionals from all US states who were followed for an extended period of time. In each of these longitudinal studies, a variety of lifestyle factors were examined, typically on a biennial basis, after an initial baseline assessment, through the use of validated questionnaires. The lifestyle habits of interest that were examined in the present investigation included physical activity, watching television, alcohol use, duration of sleep, diet, and cigarette smoking; a variety of dietary factors were assessed including consumption of fresh fruits and vegetables, whole grains, refined grains, dairy products, processed and unprocessed meats, fried foods, snacks, and nuts. Height and weight were assessed at the time of baseline enrollment in each of these studies and changes in weight were assessed at every four years.

The average ages, at the time of baseline enrollment, in the two Nurses Health Studies were 38 and 52 years, respectively, whereas the average age of participants included in the HPFS was 51 years. The average BMIs in these studies ranged from 23 to nearly 25, the average duration of daily sleep was approximately seven hours, and the average number of hours spent watching television ranged from four hours to nearly 11 hours in these three studies of health care professionals.

The average weight gain for all the four year periods combined ranged from 1.6 pounds for men in the HPFS, to 2.3 pounds for women in the NHS, and 5.2 pounds for women enrolled in the NHS-II. The average weight gain across the 3 cohorts was 3.4 pounds during each four year period, which corresponds to a weight gain of nearly 17 pounds over a follow-up of 20 years.

After multivariable adjustment, essentially every dietary factor examined was independently related to weight change, with these associations observed for both men and women in each of the 3 study cohorts. The dietary factors with the largest positive associations with non-desirable weight changes were increases in the consumption of potato chips, potatoes, sugar-sweetened beverages, and either processed or unprocessed meats. On the other hand, several factors were inversely associated with weight gain including the increased consumption of vegetables, whole grains, fruits, nuts, and yogurt.

In terms of other lifestyle factors, participants with greater increases in physical activity over time gained fewer pounds during each four year period, duration of sleep had a U-shaped association with weight gain, and increases in weight gain were associated with increased time spent watching television.