A new study in obese mice suggests that increasing the growth of fat located under the skin (subcutaneous) actually led to an improvement in glucose tolerance and insulin sensitivity, both precursors to diabetes. The expansion of subcutaneous fat was also associated with a reduction in the fat stored in places that aren’t meant to store fat, such as the liver.
The study, published online at the journal Obesity, induced the growth of subcutaneous fat through hyperplasia (increasing the number of fat cells) rather than hypertrophy (growth of existing fat cells) by injecting “acellular adipogenic cocktails” around the subcutaneous fat depots in obese mice. Ten weeks post-injection, the mice showed evidence of subcutaneous fat expansion and the corresponding metabolic improvements described above.
So, just to recap: obese mice became healthier by getting fatter.
Should we be surprised? Not if you’ve been following our blog over the years.
Let’s do a quick review.
First, it is important to understand that fat, or adipose tissue, which is mostly composed of many individual fat cells (adipocytes) is not inherently unhealthy. To the contrary, adipose tissue is absolutely necessary to allow the body to store excess calories during times when we ingest more calories than we expend through activity and resting metabolism. By doing so, adipose tissue acts as a buffer of excess calories, and thus protects other tissues of the body from accumulating fat (i.e. heart, liver, muscle). This notion is best represented by the fact that individuals who completely lack fat tissue (a disorder known as congential lipodystrophy) are very unhealthy and are almost guaranteed to develop diabetes and heart disease, despite having an athletic and lean appearance.
In other words, fat tissue is essential for health.
Where many people get into trouble is when they have exhausted their body’s ability to store more calories in adipose tissue – we all have a certain threshold to which our fat depots can expand. When we get to that point, our fat cells become so big that they are no longer able to buffer excess calories and thus cannot protect other tissues from fat accumulation and damage. This is when many of the classical metabolic problems of obesity become apparent – increased blood fats, blood glucose levels, etc.
But wait, isn’t losing fat through diet and exercise good for health?
Yes, when we expend more energy (exercise) or reduce the amount of food we ingest (diet), or both, our body draws on our extra stores of energy in our adipose tissue – this process gradually reduces the size of the individual fat cells. That is, fat loss occurs due to a reduction in size of fat cells, not a reduction in the number of fat cells. Not surprisingly, your pants start fitting better. Also, this process makes fat cells more efficient at sucking up excess calories the next time we again eat more than we expend.
What about liposuction?
Fat loss through diet/exercise is completely different from the scenario of liposuction, where a whole bunch of fat cells are removed from the body – that is, you reduce the number of fat cells, but the remaining ones don’t get any smaller or healthier. In fact, the opposite may be true, with less place to store excess calories than before surgery, so enlargement of those fat cells left behind.
In a 2004 study, obese women who underwent abdominal liposuction, losing approximately 30- 45 % of the subcutaneous fat in the abdominal region (~10kg of fat), did not show improvements in any of the metabolic markers assessed, including insulin sensitivity, blood pressure, blood glucose, insulin, or lipid levels.
Just to recap: simply surgically removing subcutaneous fat tissue does not make one healthier.
How about increasing subcutaneous fat stores in obese people? Do they also become healthier like the fat-gaining obese mice?
In a prior study, 12 overweight or obese and metabolically unhealthy subjects were given a drug (Pioglitazone) for a duration of 12 weeks. Pioglitazone belongs to the thiazolidinediones (TZD) class of drugs that seem to upregulate the production of healthy new fat cells (a process known as adipogenesis) – that is they make you fatter. By doing so, these drugs increase the storage capacity of your fat tissue – something that is limited in unhealthy obese individuals.
And that is precisely what happened in these subjects following 3 months of pioglitizone administration. First, they gained about 2kg of body weight. Their amount of subcutaneous fat in the belly went up by about 10% and that in their butt/thigh by about 24%. Interestingly, their amount of dangerous visceral fat decreased by about 11%.
Also, a fat biopsy from the belly of the subjects showed that the increase in fat mass was due to an increase in the number of small and healthy adipocytes (hyperplasia – just like in the mice study) which are better able to take up more circulating fat.
And what happened to their insulin sensitivity?
It improved by over 28%!
That’s right – they got fatter and yet healthier. Just like the mice.
As we have attempted to highlight over the years, fat is not inherently unhealthy. Losing fat isn’t always beneficial nor is gaining it always detrimental to health. Matters related to excess fat and health risk are much more nuanced than previously thought.
1. Qiqi Lu et al. Induction of adipocyte hyperplasia in subcutaneous fat depot alleviated type 2 diabetes symptoms in obese mice. Obesity. 2014
2. Klein S. et al. (2004). Absence of an Effect of Liposuction on Insulin Action and Risk Factors for Coronary Heart Disease New England Journal of Medicine, 350, 2549-2557
3. McLaughlin, T et al. (2009). Pioglitazone Increases the Proportion of Small Cells in Human Abdominal Subcutaneous Adipose Tissue. Obesity.