Findings from the study, that followed more than 120,000 men and women for 16 years, suggest that people consuming diets with a high glycaemic load (GL) – like those eating refined grains, starches, and sugars – are associated with more weight gain than those with a lower glycaemic load - and that small but consistent changes to the levels of protein and types of carbohydrate we eat could play a big role in altering such risks.
Writing in the American Journal of Clinical Nutrition, the researchers behind the study noted that while previous research has linked the GL of a diet to the risk of chronic diseases like type 2 diabetes, it had not been established how GL is related to weight-gain over many years.
"There is mounting scientific evidence that diets including less low-quality carbohydrates, such as white breads, potatoes, and sweets, and higher in protein-rich foods may be more efficient for weight loss," said lead author Dr Jessica Smith from the Friedman School and a research fellow at the Harvard T.H. Chan School of Public Health. "We wanted to know how that might apply to preventing weight gain in the first place."
"Our study adds to growing new research that counting calories is not the most effective strategy for long-term weight management and prevention," said senior author Dr Dariush Mozaffarian. "Some foods help prevent weight gain, others make it worse.”
“Most interestingly, the combination of foods seems to make a big difference,” he added – noting that the new findings “suggest we should not only emphasize specific protein-rich foods like fish, nuts, and yogurt to prevent weight gain, but also focus on avoiding refined grains, starches, and sugars in order to maximize the benefits of these healthful protein-rich foods, create new benefits for other foods like eggs and cheese, and reduce the weight gain associated with meats."
Small changes for big benefits?
Based on more than 16 years of follow-up data from 120,784 men and women from three long-term studies of U.S. health professionals, the authors first found that diets with a high GL were associated with more weight gain over time.
Next, the team determined whether changes in the GL of a diet impacted the relationship between major protein-rich foods and long-term weight gain by analysing the relationship between changes in protein foods and weight gain during every four-years of follow-up.
They found that increasing intakes of red meat and processed meat were most strongly associated with weight gain, while increased intake of yogurt, seafood, skinless chicken, and nuts were most strongly associated with weight loss – or more specifically the more people ate, the less weight they gained.
Smith and colleagues also noted that increasing other dairy products, including full-fat cheese, whole milk, and low-fat milk, did not significantly relate to either weight gain or weight loss.
"The fat content of dairy products did not seem to be important for weight gain," she said. "In fact, when people consumed more low-fat dairy products, they actually increased their consumption of carbs, which may promote weight gain.”
“This suggests that people compensate, over years, for the lower calories in low-fat dairy by increasing their carb intake."
The authors also noted several synergistic relationships between changes in protein-rich foods and changes in GL of the diet. For example, they noted that increases in the consumption of protein-rich foods linked to weight gain (like red meat) were generally coupled with an increasing dietary GL which comes from eating more low quality carbohydrates like white bread.
This synergy strengthened the foods' association with weight gain. However, when people consumed a lower GL diet alongside these foods (for example, red meat with vegetables) the risks of weight gain were softened.
For fish, nuts, and other foods associated with weight loss, decreasing GL enhanced their weight loss effect, while increasing GL decreased the weight loss effect, said the team.
Source: American Journal of Clinical Nutrition
Published online ahead of print, doi: 10.3945/ajcn.114.100867
“Changes in intake of protein foods, carbohydrate amount and quality, and long-term weight change: results from 3 prospective cohorts”
Authors: Jessica D Smith, et al