Adults gain an average of almost a pound a year as they age, and much of that weight gain is caused by changes in diet such as extra servings of foods such as potato chips, french fries, sugar-sweetened drinks, white bread and low-fibre breakfast cereals, says the largest, most comprehensive study of diet and weight gain in adults.
Other contributors: decreased intake of fruits, vegetables, whole grains and other minimally processed foods; less physical activity; more time spent watching TV; and poor sleep habits.
The study provides the strongest evidence yet that weight gain is caused primarily by dietary and lifestyle choices, says senior author Frank Hu, a professor of nutrition and epidemiology at the Harvard School of Public Health.
Small changes in habits add extra pounds, says lead author Dariush Mozaffarian, an associate professor of medicine and epidemiology at Brigham and Women’s Hospital.
Researchers analyzed data on the weight and eating and living habits of nearly 121,000 men and women from the Nurses’ Health Study and the Health Professionals Follow-up study. Participants were tracked every four years for 20 years.
They gained an average of 3.35 pounds over four-year periods and almost 17 pounds over the two decades, says the study, which was reported in today’s New England Journal of Medicine.
n People who made the most unhealthful dietary changes gained nearly 4 pounds more in four years than those who had the healthiest dietary habits.
n People who ate an extra serving of chips a day gained an average of 1.7 pounds more in four years than those who didn’t eat that extra serving.
n People who drank one more sugar-sweetened beverage a day added an extra pound more in four years than those who didn’t.
n Other factors that led to weight gain: decreased physical activity, increased alcohol intake, less than six hours of sleep a night or more than eight, and increased TV viewing.
Though counting calories and watching fat intake have been emphasized recently, the new study suggests it may be better to focus on improving overall diet, Mozaffarian says: “You miss the boat if you just try to watch fat or sugar intake alone.”
Some foods, such as nuts that are high in fat, helped prevent weight gain in the study. Other foods that are generally low in fat, such as white bread and low-fibre cereal, contributed to weight gain.
Other lifestyle factors count, too: People who increased their physical activity gained less weight, he says.
Hu says the research debunks the myth that there are no good or bad foods. “There are clearly healthy foods and less healthy foods and least healthy foods.”