There is a medical concept known as metabolically healthy obesity that applies to as much as 1/3 of all obese adults. The term applies to individuals who are significantly overweight but lack the usual health problems associated with obesity like high cholesterol, high blood pressure, and diabetes.
Recent studies have found that the amount of fat in an individual’s liver indicates whether or not there is a metabolic problem. In healthy obese people additional fat is stored by creating new fat cells. The size of their fat cells remains relatively constant.
In unhealthy individuals additional fat is stored by packing it into existing fat cells to the point that the cells can no longer function properly and the cells begin to die. Fatty tissue becomes inflamed and the body can no longer retrieve energy from their fat stores. When fat cells can no longer function, the body begins storing fat in organs like the liver. A fatty liver becomes insulin resistant and leads to type II diabetes.
Fat biopsies from healthy obese people showed much smaller fat cells than their unhealthy counterparts. Their livers had only 10-20% as much fat. Healthy individuals showed no inflammation, indicating they still had functioning fat cells able to store and retrieve fat.
Much of the recent research findings on obesity have come from studies being carried out on sets of identical twins where one twin was obese and the other was not. Using twins helps to differentiate between hereditary versus environmental and lifestyle factors. Several sets of twins were followed for as long as 10 years and on average there was a 40lb weight difference between the fat and the lean twin. Two distinct groups of obese twins emerged.
Roughly half of the heavier twins exhibited unhealthy symptoms compared to their sibling. Insulin resistance, high blood pressure, and high cholesterol were all a problem. Surprisingly these unhealthy twins had 8% fewer fat cells than their genetic match.
The other half of the heavier twins fell into the healthy obese category and enjoyed equally good health to their thinner brothers and sisters. Healthy obese individuals had 11% more fat cells than their thinner twin. It is not certain however, whether healthy obesity is a metabolic state or simply a stage on the way to unhealthy obesity.
Metabolically healthy obesity is much more common in younger individuals. An Australian study conducted on thousands of people over a span of up to 10 years showed that about 1/3 of those people who were classified as healthy obese at the beginning of the study had gone down the road to unhealthy obesity. There were some indications however that certain individuals were able to carry more weight with no unhealthy side effects.
Studying healthy obese people may contribute more understanding to the mechanisms that cause obesity and how obesity is linked to health problems like diabetes.