Journal club: smell drives obesity

A fascinating study has just come out in Cell Metabolism. Two groups looked at the role of the sense of smell in altering metabolism.

In one set of experiments, mice were depleted of their sense of smell and then put on a high-fat diet. Unlike their smelling-competent peers, the smelling-defective mice did not put on as much weight. In fact, if mice were first made obese, removing the sense of smell resulted in weight loss. This was not due to altered food consumption, which was equal in both mouse strains. 

In a second set of experiments, a strain of mice were generated which were "super-sniffers", with an enhanced ability to smell. When these mice were put on a high fat diet, they gained weight at a faster level then their wildtype siblings, the reverse effect of knocking out the sense of smell. Again, this was not due to any change in the amount of food eaten - the conclusion is that smelling fatty foods acts in an independent circuit to eating fatty foods, and reprogrammes the adipocytes into a high storage setting.

These studies should be the end of the silly "physics model" of obesity, which postulates that humans are essentially perfect machines where weight is driven only by calories in (diet) and calories out (exercise). This model has been proven over and over again to be incorrect in essentially every aspect. Adipose tissue is not an inert storage for extra calories, it is an active tissue that can be programmed and reprogrammed to increase or decrease. This adipocyte program is altered by genetics, epigenetics, microbiomics, immunology and the environment, as well as the diet and exercise postulated in the physics model. Unfortunately I doubt very much that this study, or future studies, will throw off the allure of the "physics model" to replace it with a biological model - victim blaming is too well entrenched in both the public and medical spheres.

Read the paper here: Riera et al, "The sense of smell impacts metabolic health and obesity", Cell Metabolism 2017. 26(1) p198.