It's a common belief that eating in moderation, whatever you eat, is the key to successfully managing your weight. But that belief is being challenged by a new study of the diet and lifestyle habits of more than 120,000 adult Americans over the past 20 years. Researchers found that even small changes in diet had a significant impact on long-term weight gain.
U.S. adults gain on average a half-kilogram, or about one pound, each year, and the kinds of food they at are important factors in that weight gain.
“It's very hard for the average person to notice that, but over 20 years it's 20 pounds [10 kg.] and so that’s really an enormous public health problem,” said Dr. Dariush Mozaffarian, lead researcher on the study by the Harvard School of Public Health. He says the foods most closely associated with weight gain are those highest in starch, and the worst offenders are potatoes - baked, boiled, mashed, or fried. Eaten daily in whatever form, they can add more than half a kilogram [0.68 kg, or 1.5 lbs.] to an adult's weight every four years.
To control that weight over the long term, the researchers say it is more important to focus on eating right than on eating less, suggesting that the type of food matters more than a simple calorie-count.
“Foods which were strongly associated with weight gain were meats, refined grains, and then sweets. Interestingly, refined grains like a bagel or white bread were similarly associated with weight gain as sweets,” Mozaffarian said.
Sugar-sweetened beverages and even one hundred percent fruit juices were also associated with weight gain.
Laura Jeffers, a registered dietitian at Cleveland Clinic, did not take part in the study but believes it confirms what dieticians and nurtritionists have known for years about sweetened drinks:
“I basically always talk to patients about can we reduce the calories you’re getting from beverages? That’s one of the easiest things to do and this research shows that sugary beverages contribute to weight gain,” she said.
But the study findings also run counter to conventional wisdom. Several high-calorie foods were found to lead to less weight gain when their consumption was increased. In particular nuts, whole grains, yogurt, fruits, and vegetables, were all associated with less weight gain over time.
The study also found that lifestyle factors such as daily physical activity, exercise, and sleep patterns are also important variables in any weight management program.
“The dangers are that if you don’t pay attention to these small aspects of lifestyle you may gain weight...and slowly, over time, and not notice it. And that is what we have seen in the obesity epidemic. On the other hand, if you pay attention and focus on the appropriate aspects of lifestyle you won’t gain that weight over time," Mozaffarian said.
The study showed that together with certain foods, long periods of television-watching and chronically getting too little sleep also contributed to long-term weight gain.
On the positive side, researchers were surprised to find that people who ate an extra daily serving of yogurt - regardless of its fat content - tended to lose nearly a half kilogram, or one pound, every four years.