Fast-forward to modern bleeding-edge research from Dr. Peter Light who's been investigating the effects of light on fat cells, or what researches call adipocytes (1).

When the researchers subjected fat cells in a dish to blue light, it caused an increased glycerol release and reduced lipid droplet size. Yep, that means the fat cells got smaller.

This is from an increased rate of fat being broken down (lipolysis) or reduction in the free fatty acids and glycerol backbone being reassembled, known as fatty acid re-esterification. In addition, smaller fat cells are healthier since large fat cells are associated with increased insulin resistance and inflammation (2, 3).

"When the sun's blue light wavelengths – the light we can see with our eyes – penetrates our skin and reaches the fat cells just beneath, lipid droplets reduce in size and are released out of the cell. In other words, our cells don't store as much fat," wrote Dr. Light (4).

It's not a double-blind randomized controlled trial in lifting bros, but it is super fascinating. Maybe the old-school Muscle Beach lifters were onto something.

1. Ondrusova K et al. Subcutaneous white adipocytes express a light sensitive signaling pathway mediated via a melanopsin/TRPC channel axis. Sci Rep. 2017;7(1):16332. PubMed.
2. Henninger AMJ et al. Adipocyte hypertrophy, inflammation and fibrosis characterize subcutaneous adipose tissue of healthy, non-obese subjects predisposed to type 2 diabetes. PLoS One. 2014 Aug 22;9(8):e105262. PubMed.
3. Kim JI et al. Lipid-overloaded enlarged adipocytes provoke insulin resistance independent of inflammation. Mol Cell Biol. 2015 May;35(10):1686-99. PubMed.
4. Young, L. Reduced sunlight may contribute to winter weight gain. University of Alberta Faculty of Medicine & Dentistry. January 10, 2018.