A review of previous studies suggests that people who eat yogurt have lower body weight, less body fat and smaller waists - but it's not clear if the yogurt is the reason.

"Studies that look specifically at weight loss are very limited," said coauthor Irene Lenoir-Wijnkoop of Utrecht University in The Netherlands.

"Scientifically speaking, based on this it cannot be concluded that yogurt causes weight loss, even if the tendency in this analysis is promising," she told Reuters Health by email.

The researchers reviewed 22 studies. Thirteen of the studies observed people at one point in time and compared their yogurt intakes, finding that those who ate more yogurt had lower body weight or healthier body composition.

More rigorous studies, in which subjects were randomly assigned to eat yogurt or not and their weights were monitored, had mixed results. One found significant weight loss in the yogurt group but did not rule out the possibility that differences in calcium intake were responsible, as reported in the International Journal of Obesity.

"Yogurt has several micronutrients which may have potential beneficial effects, for instance calcium is involved in the metabolism of fat," said Dr. Nita Forouhi of the University of Cambridge School of Clinical Medicine in the U.K. "As yogurt is a fermented product, there are likely effects on obesity also through its effect on the gut microbiome, which is a field that is gathering more research attention now."

"There is a lack of well conducted randomized controlled trials that test different types and amounts of yogurt versus no or low yogurt consumption and that are of sufficient duration and quality," said Forouhi, who was not part of the new study.

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In principle, a well-conducted randomized controlled trial would determine whether eating yogurt leads to weight loss, Lenoir-Wijnkoop said.

"However, to maximize the likelihood of detecting a causal effect, it would be critical to have an adequate number of participants, a follow up over a sufficiently long timespan (ideally 12 months) and a proper design to address effects of yogurt alone," she said.

If yogurt does lead to weight loss, it could be because people who eat it regularly use it to replace less healthful foods, she said.

"Furthermore yogurt is a nutrient dense food and as part of balanced and healthy diet it can have a positive effect on feelings of fullness," she said. "Research is currently on-going in many places in order to unravel the underlying mechanisms of action."

Among children, frequent yogurt consumers tend to also consume more fruit, whole grains, and milk, Lenoir-Wijnkoop said.

"Yogurt consumers tend to eat less fast food, French fries and fried foods, processed and red meats, pizza, snacks, regular soft drinks or alcohol," she said.

Adults who eat yogurt also tend to be more active and are less likely to smoke, she said.

"Future studies should aim to address specifically the effects on weight management of different types of yogurt such as full-fat yogurt, Greek-type yogurt, low-fat, low-fat with or without added sugar, with or without added fruit and so on, to better guide choice by consumers," Forouhi said.