High levels of bacterial flagella in a sample such as a gastrointestinal sample and/or low levels of anti-flagella antibodies serve as an indication for metabolic syndrome (such as insulin resistance, hypertension, elevated cholesterol, increased risk for blood clotting, and obesity) with highest levels of adiposity. An intervention that reduces the level and/or activity of flagella in the gastrointestinal tract can mitigate the severity of metabolic syndrome or in protecting against the development of metabolic syndrome.