Background: Several studies evaluate whether the consumption of probiotics can modify body weight. The Lactobacillus fermentum UCO-979C strain is a strain of gastric origin and this constitutes the first study in humans. The objective was to evaluate the effect of the consumption of the L. fermentum UCO-979C strain on weight, percentage of fat mass, lean mass, waist circumference and eating habits of a group of young adults from the University of Concepción, Chile. Methods: One hundred and four university students were divided into two groups. The intervened group (n = 56) consumed a gelatin containing the probiotic strain, while the control group (n = 46) consumed a placebo gelatin. Eating habits and body composition were evaluated at the beginning and at the end of the intervention. Results: No significant differences were observed after 12 weeks of intervention in weight, percentage of fat mass, lean mass, and waist circumference, but significant differences were observed in eating habits. The intra-group analysis showed a very significant increase in lean mass and a higher consumption of dairy products and fruits in the group that received the probiotic. Conclusions: The consumption of the probiotic did not modify neither the weight nor the body composition, but it did modify the eating habits, increasing the consumption of breakfast, fruits and dairy products.