Tell me how much Lactobacillus you have in your saliva, and I’ll tell you how likely you are to gain weight!

Low levels of Lactobacillus in the oral microbiota may predict weight gain over time.


According to recent studies, the composition of the intestinal microbiota, particularly the amount of bacteria from the genus Lactobacillus, may play a role in weight management. Danish researchers set out to check this in 322 volunteers, who consented to assorted analyses six years apart: height and weight to measure BMI*, dietary intake control, and analysis of their microbiota. The researchers took samples of saliva, which reflects the oral microbiota, then divided the participants into four groups according to the number of Lactobacilli present in their mouth. Slightly overweight at the beginning of the study, they gained an average of 900g in 6 years (all groups combined).

In individuals with low to moderate consumption of complex carbohydrates (bread, dried pulses, pasta, etc.) who also had little Lactobacilli in their oral flora, the researchers noted a correlation with weight gain. However, if the Lactobacilli were numerous, an individual would lose weight if they ate few complex carbohydrates, or maintain their weight if their consumption was average. On the other hand, an individual’s weight increased regardless of the volume of Lactobacilli if their level of complex carbohydrate consumption was high. In other words, the study concludes that there is an interaction between the microbiota and diet that underlies obesity. The proportion of Lactobacillus in the saliva (the researchers will soon study the individual strains) may be a marker for the likelihood of weight gain.


*BMI, or body mass index, is the ratio of weight in kilograms to height in meters squared (m2). It determines whether a person is healthy (underweight, normal weight, overweight, obese)



Rosing et al. Oral Lactobacillus Counts Predict Weight Gain Susceptibility: A 6-Year Follow-Up Study. Obes Facts 2017;10:473–482