Writing in the Journal of Health, Population and Nutrition, researchers from Baqiyatallah University of Medical Sciences in Iran reported an improvement in depression scores, measured using the Geriatric Depression Scale-15 (GDS-15).
Overweight and obese people can experience changes in their GI microflora that lead to increased permeability of intestinal epithelial cells and insulin resistance. The gut microbiota affects fat storage, energy regulation, nutrient absorption and mental health.
“In addition, gut microbiota may play an essential role in modulating behavior and mood disorders through various mechanisms,” the researchers wrote. “Improving gut dysbiosis reduces inflammation, resulting in changes in brain function, mood and behavior.”
Pre and probiotics may help counteract these effects, the study noted, and in addition, kefir itself has been shown to have anti-inflammatory, anti-cancer and anti-diabetic properties. One key factor in mood disorders is inflammation, which can lead to stress-induced reductions of beneficial microbiota populations of Lactobacillus and Bifidobacterium.
“Bifidobacterium has been shown to reduce pro-inflammatory immune responses and increase tryptophan, a precursor to serotonin synthesis…” the researchers wrote. “Improving gut dysbiosis reduces inflammation, resulting in changes in brain function, mood and behavior.”
Previous research has shown a relationship between being overweight and depression risk in the elderly. According to the researchers on the current study, this is the first investigations of the effects of probiotic-fortified kefir on inflammatory parameters and depression in the elderly.
Study details
The randomized, double-blind, placebo-controlled clinical trial administered Lactobacillus helveticus and Bifidobacterium longum to 67 overweight or obese Iranian men over the age of 65.
After eight weeks of supplementation, the researchers observed a significant difference in depression scores and total antioxidant capacity between the control and supplemented group. Both groups showed a significant increase in appetite scores, with no differences between groups.
Some limitations of the study included the fact that none of the participants were clinically diagnosed with a depression condition, the exclusion of women as participants and the lack of stool sampling and analysis.
“If the results of this study are confirmed by future clinical trials involving depressed individuals, probiotics may serve as an adjunctive treatment for depression, positively influencing the disease process,” the study concluded. “Further research is required to confirm these findings and explore the mechanisms by which probiotics affect the evaluated parameters.”
Source: Journal of Health, Population and Nutrition 2025, 44(30). doi: 10.1186/s41043-025-00773-x. “The effect of probiotic-fortified kefir on depression, appetite, oxidative stress, and inflammatory parameters in Iranian overweight and obese elderly: a randomized, double-blind, placebo-controlled clinical trial”. Authors: M. Noori, et al.