Accumulating research indicates microbiota in lean individuals is different from that of obese people; lean people tend to have a higher proportion of two types of beneficial bacteria, Bacteroidetes and Firmicutes, than obese people.
Emerging evidence also indicates that probiotics--live microorganisms that boost healthy gut bacteria populations--provide many health benefits, including enhanced immune response and mitigation of gastrointestinal conditions like diarrhea and irritable bowel syndrome and may factor in obesity prevention.
SCIENCE ON "SKINNY" BUGS
There are "roughly" 100 trillion bacteria in the average person's gastrointestinal tract comprising more than 500 species. Collectively called gut microbiota, they are influenced throughout your lifetime by your genetics, environment, diet, and immune system. In a 2010 study published in the European Journal of Clinical Nutrition, the probiotic Lactobacillus gasseri SBT2055 was found to lower abdominal fat and body weight in adult subjects with tendencies to become obese.
In another study, of post-operative weight loss surgery patients, researchers found greater weight loss among those who took daily Lactobacillus acidophilus probiotics (Journal of Gastrointestinal Surgery, July 2009.) And studies have found that probiotics showed positive results in suppressing or reducing body weight in rats (Bioscience, Biotechnology, and Biochemistry, 2010, Obesity Research and Clinical Practice, 2008.)