Seemingly minuscule changes to the types of protein and carbohydrates we consume could profoundly affect long-term weight maintenance, according to a new study at the Friedman School of Nutrition Science & Policy at Tufts University.

Evidence spans over 16 years of follow-up among 120,000 men and women in the US in the study, published in the American Journal of Clinical Nutrition.

Diets with a high glycemic load (GL), which is found in refined grains, starches and sugars, lead to long-term weight gain, according to the researchers.

Although prior studies have linked GL with chronic diseases such as type 2 diabetes, this is the first to establish a relationship between GL and long-term weight gain.

Every four years, the research team observed changes in types of proteins consumed in relation to participants' weight changes.

Increased consumption of red meat and processed meat was most strongly associated with weight gain.

Eating more yoghurt, seafood, skinless chicken and nuts was most strongly associated with weight loss.

Consuming more dairy products such as full-fat cheese, whole milk and low-fat milk did not seem to influence participants' weight one way or another.

"The fat content of dairy products did not seem to be important for weight gain," says first author Dr. Jessica Smith of Friedman. "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."

Increased servings of foods that cause weight gain such as red meat while upping GL by adding more low-quality carbs was more likely to cause weight gain than upping red meat consumption and eating more vegetables, too.

For those who increased consumption of fish, nuts and other such weight-loss promoting foods, reducing GL by eating less low quality carbs enhanced the weight loss effect.

Yet increasing one's intake of low quality carbs appeared to reduce the weight loss effect of foods such as fish and nuts, even if they upped their consumption.

Foods such as eggs and cheese were not linked with weight change except when participants upped their intake and consumed increased portions of low quality carbs.

On the flipside, decreasing the GL of one's diet was associated with weight loss when participants ate more eggs and cheese.

The researchers say that to reap the full benefits of protein-rich foods such as fish, nuts and yoghurt, it's important to avoid refined grains, starches and sugars.

This not only translates into new benefits for foods such as eggs and cheese -- the dietary effects of which haven't always been clear -- but also reduces the weight gain associated with meats.