Researchers combined data from 31 trials conducted across the globe and found that on average, there was very little difference in changes in weight or waist measurements between people who were put on a normal or nut-supplemented diet.
Dr. David Bleich, head of Endocrinology, Diabetes and Metabolism at the University of Medicine and Dentistry of New Jersey in Newark added that, "Most of the nut-enriched studies don’t show that patients gain a significant amount of weight, in contrast to what one might think."
Gemma Flores-Mateo from the Institut Universitari d’Investigacio en Atencio Primaria Jordi Gol in Tarragona, Spain and colleagues said previous research has tied nut-containing diets to a lower risk of death, diabetes and high blood pressure.
Bleich, who wasn’t involved in the new report, said his own work has shown measures of insulin resistance were lower when people added nuts to their diets.
Bleich added that, "One would generally think if you’re increasing the ‘fat content’ of the diet, you might in fact make insulin resistance worse." "It speaks to this issue of the quality of the fats that we consume." Nuts may also suppress hunger because of their unsaturated fats, fiber and protein, the researchers noted.
In the trials they looked at, participants were randomly assigned to a normal diet or one that included extra nuts — or, more often, nuts substituted for other food items — and followed for anywhere from two weeks to five years.
At the end of follow-up, people on nut diets had dropped about 1.4 extra pounds and lost close to half an inch off their waists, compared to those in the nut-free groups. However, the differences could have been due to chance.
Although the magnitude of these effects was modest, the results allay the fear that nut consumption may promote obesity. "Our findings support the inclusion of nuts in healthy diets for cardiovascular prevention."
However it’s not simply a matter of "throwing additional nuts into your already poor-quality diet," Bleich said. Heart protection comes from looking at a fuller picture of the diet — and adding fruits, vegetables and olive oil, for example, in addition to nuts.
Dr. Adam Gilden Tsai, an obesity researcher from the University of Colorado in Denver, said he wouldn’t recommend people eat nuts on top of their normal diet, but that substituting them for other foods may lead to some benefits, such as on cholesterol levels.
"It’s fine to eat nuts if you can still limit your calories," Tsai told Reuters Health. But he cautioned that it can be hard for people to eat just one serving.
"Normally what I would say to a patient is, ‘A small handful of nuts can be a very good and filling snack, but you have to be very careful because it’s high in calories.’ "
American Journal of Clinical Nutrition, online April 17, 2013.