Based on three long-term studies conducted on 120,877 adult men and women who were followed for periods of 12 to 20 years, scientists at Harvard have isolated a list of foods and other lifestyle factors most and least associated with weight gained every four years.
The new study, entitled, Changes in Diet and Lifestyle and Long-Term Weight Gain in Women and Men, by Dariush Mozaffarian, MD, DrPH, of Brigham and Women’s Hospital and Harvard Schools of Medicine and Public Health, and colleagues, was published in the June 23, 2011 issue of the New England Journal of Medicine.
The new findings were based on data from three large, long-term government-funded trials looking at diet, lifestyle and health in adults. These included the Nurses’ Health Study, which has followed 121,701 women since 1976; the Nurses’ Health Study II, which has tracked 116,686 women since 1989; and the Health Professionals Follow-up Study, which includes 51,529 men and began in 1986. The new analysis is thus based on 12 to 20 years of data on 120,877 men and women. The participants were tracked as to changes in eating and lifestyle habits, and weight, every four years.
The researchers found that, on a combined basis, the study participants (who were all of normal weight at the beginning of the studies) gained an average of 3.35 pound, or 2.4% of their body weight, each four-year period over the length of the studies. Over the 20 years of follow up, that amounted to an average weight gain of nearly 17 pounds.
Worst Foods: Most Weight Gain
On the basis of increased daily servings reported by the participants each four years, the following foods were most strongly associated with weight gain each four years. In the aggregate, each of these foods correlated with the average number of pounds of weight gain shown below per added serving per day, each four year period:
- potato chips (1.69 lb),
- potatoes (1.28 lb on average; with french fries individually associated with more than 3 lb of weight gain),
- sugar-sweetened beverages (1.00 lb),
- unprocessed red meats (0.95 lb), and
- processed meats (0.93 lb)
Best Foods for Weight Loss
The foods most associated with weight loss per added serving per day over each four year period, included:
- yogurt (−0.82 lb),
- nuts (−0.57 lb),
- fruits (−0.49 lb),
- whole grains (−0.37 lb), and
- vegetables (−0.22 lb).
Thus, the foods associated with weight loss fit with the emphasis on fruit, vegetables, and grains in the New Dietary Guidelines for Americans Issued by the U.S. Department of Agriculture and Department of Health & Human Services.
All the above average weight gains or weight losses found in the new Harvard study are per serving added per day to the diet over four years. All of these findings were significant at P≤0.005.
Weight Gain Creeps Up on You
On average, eating more or less of any single food was found to associate with only 0.8 pounds of weight gain per one year. “But accumulated over time, even modest increases in weight have implications for long-term adiposity-related metabolic dysfunction, diabetes, cardiovascular disease, and cancer,” the study authors wrote.
Other Lifestyle Factors
Other lifestyle factors were also found to be independently associated with weight change, including:
- physical activity (−1.76 lb across quintiles),
- alcohol use (+0.41 lb per drink per day),
- smoking (new quitters, +5.17 lb; former smokers, +0.14 lb),
- sleep (more weight gain with less than 6 or more than 8 hours of sleep), and
- television watching (+0.31 lb per hour per day).
The study found that while any single food may have a modest effect on weight, together the changes in diet and exercise accounted for large differences in weight gain over time.
Its Not Just How Much You Eat; It’s What You Eat
As noted by the study authors, conventional wisdom holds that avoiding weight gain simply means eating fewer calories and exercising more. However, the new study suggests that it is not just the quantity of calories that one eats, but the types of foods comprising those calories that correlates with long-term weight gain.
“For diet, conventional wisdom often recommends ‘everything in moderation,’ with a focus only on total calories consumed,” Dr. Dariush Mozaffarian, lead author of the study, told Time Magazine. “Our results demonstrate that the quality of the diet — the types of food and beverages that one consumes — is strongly linked to weight gain,” he said.
Why are potatoes particularly fattening? It’s not clear, but Dr. Mozaffarian suggests it may be because they’re generally eaten in large quantities, and because, as previous studies have shown, they are the type of food that causes large spikes in blood sugar and insulin, similar to other starches and refined carbohydrates like white bread, white rice, low-fiber breakfast cereal, candy and desserts. The big spikes in blood sugar associated with these foods tend to make people hungrier and overeat at their next meal, Dr. Mozaffarian reportedly explained to Time Magazine.
Other scientists suggest that the weight gains associated with potato chips and potatoes and the weight losses associated with foods such as yogurt may have less to do with the foods per se, and more to do with the fact that people who eat potato chips may eat more calories and more junk food overall, and conversely, people who eat foods like fruit and yogurt probably are more health-consciously. Marion Nestle, professor of nutrition at New York University and author of Food Politics, commented to Time, “I think it’s likely that potato chips and French fries are markers for junk food diets, and yogurt is a marker for healthy diets.”
Lessons from the Study
Whatever the causes, it is clear from the study that incremental weight gains over a period of 12 to 20 years were strongly associated with even modest changes in intake of certain foods and other lifestyle changes over this period. A lesson, according to the researchers, is that small changes in diet and lifestyle, over time, can make a significant difference in body weight and accordingly in health.
As summed up to Time by Professor Nestle, “The study has a clear and consistent message: if you want to gain weight, eat junk foods and drink sodas. If you want to maintain a healthy weight, eat healthy foods. This means following basic dietary recommendations and choosing relatively unprocessed foods — vegetables, meat, dairy, grains, fruits. And don’t drink too much alcohol.”
“It’s not that calories don’t count; indeed they do,” she said. “But it’s a lot easier to control calories by eating healthfully and avoiding junk foods and sodas than it is to delude yourself into thinking you can count them accurately,” she concluded.
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