A small gift from your Prehistoric ancestors
The relationship between sun exposure and fat loss most likely dates back before we humans could walk upright. Way back, before the invention of video games and office cubicles, humans had to spend the majority of their time outside in the weather finding food. We hunted, we gathered, and we developed a natural adaptation to the seasons. As the days shortened, our bodies instinctually knew that winter was coming and our metabolism slowed to conserve calories. Then as warmer weather approached again, and food became more plentiful, we came out of our semi-hibernation to begin the cycle again (1).
This is where it gets fascinating. Apparently, when we are exposed to increasing amounts of UV rays, our bodies activate a protection mechanism to lessen the damage caused by the sun. Protection is created by increasing the amount of protective pigment, called eumelanin, in the skin. This increase in eumelanin is known as tanning. This is nothing big, the body responds to UV over exposure by tanning, but it doesn’t stop there (2).
Increased sun exposure causes more than just a healthy glow. An entire chain reaction is formed that activates the most powerful substances in the human body, hormones. One of these hormones, melanocortin, also decreases appetite and performs actions on fat cells, causing them to be broken down and used as fuel by the body and you to lose weight. So one of the same hormones produced by the skin when we tan, also suppresses the appetite center of our brains and makes it easier to burn fat for fuel, causing weight loss (2,3).
An Easy Explanation
It makes a lot of sense, our hunter gatherer bodies would sense winter by a shorter period of daylight. Fat serves us both as a source of energy during food shortage and as a thermal insulator protecting us against the cold. As the weather warmed and our skin was irritated by added sunlight, a little chain reaction was started; after all, we needed to shed our layers of fat to be more mobile and facilitate heat loss during summer. If we had not, we would have been at a disadvantage by being slow and prone to heat exhaustion during the hunt. Part of this sequence as well, melanocortin is also able to increase your body’s metabolism by causing increased output of thyroid hormone (3).
Here Comes Big Pharma
Melanocortin can effect fat storage and release, the metabolic rate, and the appetite. Its production is influenced by the amount of fat stored in the body and is also involved in maintaining your weight as well as getting a good tan. The power of this substance is why several major pharmaceutical companies have recently patented a number of new drugs that try to produce the same effects. The new drugs will treat obesity, get you a tan, and treat impotence as well, just in case(4).
For those who prefer the natural way, getting just enough sun to cause a slight tan can help you lose weight by: decreasing your appetite, helping increase your metabolism and making it easier to burn fat for energy. Indoor tanning could have its uses after all (4).
1. Healy E, Flannagan N, et al. Melanocortin-1 receptor gene and sun sensitivity in individuals without red hair. Lancet 2000 Mar 25;355(9209):1072-3.
2. MacNeil DJ, Howard AD, et al. The role of melanocortins in body weight regulation: opportunities for the treatment of obesity. Eur J Pharmacol 2002 Apr 12;440(2-3):141-57.
3. Voisey J, van Daal A. Agouti: from mouse to man, from skin to fat. Pigment Cell Res 2002 Feb;15(1):10-8.
4. Zemel MB. Agouti/melanocortin interactions with leptin pathways in obesity. Nutr Rev 1998 Sep; 56(9):271-4.
