Not all fat cells are created equal

Fat cells behave differently in different parts of the body, a new study has found. Writing in PNAS, Mayo Clinic researcher Michael Jensen and his colleagues put a group of 28 healthy, non-overweight men and women on an 8 week excess-eating regimen to see how their fat cells reacted to the ensuing 4kg average weight-gain experienced by each participant.

Understanding the relative behaviours of fat-storing cells around the body is critical because it's clear that certain distributions of body fat are associated with more significant health impacts than others; for instance, a high waist to hip ratio, also known as being "apple" shaped, carries a higher heart disease risk than being pear shaped (with a lower waist to hip measurement). Also, a long-standing medical dogma is that, outside of childhood, weight gain is reflected by an increase in the size of individual fat cells, but not an increase in their numbers. 

However, CT scans and adipose tissue biopsies collected from the participants in the present study showed that the fat cells (adipocytes) in different parts of the body actually respond to increasing body mass in different ways. Samples from the upper body (including around the waist), the team found, do follow this rule and become larger with increasing fat mass. But adipocytes in the lower body (around the hips and thighs) actually increase in number; in fact the team found that, on average, their study subjects added a further 2.5 billion fat cells in this body region over the 8 week study. This, they suggest, might be a protective mechanism to prevent unhealth abdominal fat accumulation by sequestering the fat around the thighs.

This indicates that fat cells are not all equal and how fat is handled in the body differs regionally; understanding how these changes occur and their biochemical consequences will in turn provide vital clues in tackling the worldwide obesity epidemic and its partner in crime, diabetes.