Taking probiotics - live microorganisms such as bacteria or yeast that are believed to improve health - may help women, and not men, shed those extra kilos.
Certain probiotics could help women lose weight and keep it off, said researchers at Universite Laval in Quebec, Canada.
To test their hypothesis, researchers recruited 125 overweight men and women.
The participants underwent a 12-week weight-loss diet, followed by a 12-week period aimed at maintaining body weight.
Throughout the entire study, half the participants swallowed two pills daily containing probiotics from the Lactobacillus rhamnosus family, while the other half received a placebo.
After the 12-week diet period, researchers observed an average weight loss of 4.4 kg in women in the probiotic group and 2.6 kg in the placebo group.
However, no differences in weight loss were observed among males in the two groups.
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"We don't know why the probiotics didn't have any effect on men. It may be a question of dosage, or the study period may have been too short," said Angelo Tremblay, a professor who is also the Canada Research Chair in environment and energy balance.
Studies have demonstrated that the intestinal flora of obese individuals differs from that of thin people.
That difference may be due to the fact that a diet high in fat and low in fibre promotes certain bacteria at the expense of others.
Tremblay and his team tried to determine if the consumption of probiotics could help reset the balance of the intestinal microbiota in favour of bacteria that promote a healthy weight, said the study published in the British Journal of Nutrition.
In short, women consuming probiotics lost twice as much weight over the 24-week period of the study.
Researchers also noted a drop in the appetite-regulating hormone leptin in this group, as well as a lower overall concentration of the intestinal bacteria related to obesity.