HPC-UK Bitesize: Sedentary Spread

The development of obesity is not as straightforward as many people suggest, there are at least six main overarching factors which contribute to the obesogenic environment – with each of these factors having a network of sub-factors. One of the major factors in the development of obesity is physical inactivity. The general association between physical inactivity and obesity is that an inactive person has a lower daily energy output, which is ‘generally’ true (it gets complicated, so for the purpose of this piece we’ll accept the standard version). However, physical inactivity promotes obesity in (many) more ways than one, and a new study has strengthened a hypothesis we have held for a little while now – that typically sedentary behaviour actively amplifies adipocyte hypertrophy (growth of a fat cell).

Researchers at the University of Tel Aviv using state of the art microscopy investigated the cellular mechanics within fat cells and how cellular expansion drives adipocyte hypertrophy.(1)
The researchers found that adipocytes (fat cells) that were exposed to chronic, sustained pressure – for example the increased tension on the fat cells in your upper leg as a result of sitting on a chair for extended periods – begin to accelerate growth of the interior lipid droplets. The study demonstrated an expansion of fat deposits in the fat cell by up to 50% as a result of this mechanical pressure. Like all systems in the body, however, you have to consider the principle of synergy – once one aspect is altered, like the butterfly effect, that aspect then alters other aspects, which alters…you get the picture.

The study demonstrated that once the fat cell had accumulated lipid droplets, the structure of the cell became stiffer as it expanded. This stiffness altered the environment of surrounding fat cells by physically deforming them, which in turn caused them to change their own shape and composition, leading to differentiation and expansion of those fat cells too.

We also know that an adipocyte that has undergone hypertrophy (enlargement) will at a specific threshold initiate a process called hyperplasia which increases the number of fat cells.(2) If these new fat cells are exposed to the same increased mechanical loading environment they too will begin to accumulate lipid droplets and undergo expansion, and the cycle continues forward.

You can hopefully see from this that even without dietary alteration (no excess food needed), the simple fact of being sedentary can trigger an increase both in the size and number of fat cells in your body. It also lends credence to a protocol I use with clients who are concerned with fat loss, although it was/ is a supposition based upon known physiological realities, there wasn’t any clear cut evidence to directly support it – this is a step in that direction.

References:

1- Naama Shoham, Pinhas Girshovitz, Rona Katzengold, Natan T. Shaked, Dafna Benayahu and Amit Gefen. Adipocyte Stiffness Increases with Accumulation of Lipid Droplets. Biophysical Journal, March 2014

2- Jo J, Gavrilova O, Pack S, Jou W, Mullen S, Sumner AE, Cushman SW, Periwal V. Hypertrophy and/or Hyperplasia: Dynamics of Adipose Tissue Growth. PLoS Comput Biol. 2009 Mar;5(3):e1000324. doi: 10.1371/journal.pcbi.1000324. Epub 2009 Mar 27. PubMed PMID: 19325873; PubMed Central PMCID: PMC2653640.