Fat Distribution & Physiology Nketi Forbang, MD, MPH Good afternoon. Today, I will be discussing fat distribution and physiology.

Fat Distribution Body fat distribution is has individual variations, but can be categorized into 4 types. Lower body: fat storage around the buttocks, hips and thighs. Abdominal subcutaneous: subcutaneous fat storage around the stomach and chest. Overall coverage: fat accumulation in the arms, breast, thighs, buttocks, lower back and breast. Visceral: intra-abdominal fat deposition among organs such as the intestines, stomach, liver and pancreas. Fat distributed within the visceral cavity is highly associated with obesity-related health consequences.

Fat Distribution Total Body Fat ~ 80% subcutaneous (under the skin, but outside body cavity ~10% visceral or intra-abdominal (inside the abdominal cavity) ~5% other Ectopic Skeletal muscle Heart Liver Pancreas Marrow Ect… About 80% of fat is subcutaneous or underneath the skin but out side the body cavities, about 10% is visceral or intra-abdominal, meaning the its in the abdominal cavity were the organs are housed, and another 5% is ectopic, found in the tissues of skeletal muscle and organs.

Fat Distribution Sex differences Women Men 50% more fat cells Store more fat peripherally Men Store more fat centrally Important sex differences exist regarding fat distribution. In fact, there are important ethnic differences that also exist which I wont get into. In general women have 50% more fat cells than men, and tend to store more fat peripherally, while men tend to store fat more centrally. As an FYI, the Gold standard measure for fat distribution, is the CT or MRI, as seen in the image on the right.

Fat Distribution Anthropometrics and heart disease risk Body mass index (BMI): Kg/Ht2 Waist-to-hip-ratio (WHR) However, CT and MRI are very expensive, and most of what we know about the hazards of different fat depots, stem from Epidemiologic studies using anthropometric measurements of body mass index and waist to hip ratio. These studies have largely shown that for a given BMI which measures total adiposity, higher WHR which measures central adiposity, is more highly associated with poor obesity related health consequences such as metabolic syndrome, diabetes, and ischemic heart disease.

Fat Physiology There are important physiological differences between visceral and subcutaneous adipose tissue depots. First is Drain location: the visceral depot (left) releases products into the portal vein, while the subcutaneous depot (right) releases products into the systemic circulation. In obesity, portal vein effluent to the liver contains higher concentrations of free fatty acids and interleukin-6 compared with the systemic circulation. The second is Adipose depot characteristics: When compared with subcutaneous fat, visceral fat is characterized by reduced adiponectin and leptin, increased inflammatory adipo/cytokines, enhanced lipolysis, a reduced response to insulin and reduced differentiation and angiogenesis.

The End References Foster MT, Pagliassotti MJ. Metabolic alterations following visceral fat removal and expansion: Beyond anatomic location. Adipocyte. 2012 Oct1;1(4):192-199. PubMed PMID: 23700533; PubMed Central PMCID: PMC3609102. https://www.slideshare.net/peterbuck/fat-distribution-health-risks-and- adaptations-to-exercise https://www.precisionnutrition.com/sex-diff-in-fat-loss