Normal physiological adaptations (i.e. pregnancy), genetic mutations or polymorphisms (gene-induced obesity, GIO), or a diet with excessive fat or calories (diet-induced obesity, DIO) can promote weight gain and increase adiposity through microbe-independent and microbe-dependent mechanisms. Disrupting the founding microbial community through C-section and/or early-life antibiotic exposure also can lead to increased weight gain and adiposity (microbe-induced obesity, MIO). All effects are microbe-dependent since the initiating factors do not contribute to obesity independent of microbes (e.g. antibiotics have no caloric value). For each pathway that leads to obesity, the altered microbiota can contribute to adiposity through increased energy harvest or by altering metabolic signals, inflammation, or immunity.