Weight Loss Is Influenced by Hormones

The short answer is that your body can easily confuse weight loss with starvation. We think of fat cells as just being bags of fat, but they are not. They produce a hormone called leptin. Your brain monitors leptin. If you have a lot of fat, you produce a lot of leptin and your brain gets used to it. This is called “leptin resistance”.  Dieting causes the leptin level to fall; if this happens too quickly, your brain thinks you are starving [3].

The Hunger Hormone

A second hormone, ghrelin, is known as the hunger hormone. When we lose weight, the stomach releases greater amounts of ghrelin. This hormone makes us feel hungry. Everyone has this hormone, but if you’ve been overweight and then lose weight, the hormone level increases.

Your Hormones Protect You From Weight Loss

Your body will do several things when it perceives that it is starving:

  • Your metabolism slows down: Weight loss affects the thyroid, which is the thermostat of the body. You produce less “T3”, which is the active thyroid hormone. This means that for any given activity, you will burn fewer calories1,2.
  • You become hungry: Your brain thinks you are starving because of the drop in leptin levels. Ghrelin levels increase after a diet4. People who are overweight commonly have leptin resistance. Loss of fat causes a drop in leptin.
  • You crave high-calorie and (possibly) processed food: Processed food, which is high in sodium and high fructose corn syrup, may increase ghrelin levels5,7,8, thus increasing hunger. In other words, processed foods interfere with feeling satisfied after a meal. So, it plays out like this, your leptin levels drop, you get really hungry and eat a McMeal. The McMeal is high in calories but does not fully satisfy your hunger.

This has nothing to do with willpower 

If you have dieted in the past, you may have noticed a pattern. The first week usually goes well, with significant weight loss. The second week is harder, and there is less weight loss because your metabolism is slowing down. After some time, even basic discipline becomes difficult. Sometimes you are able to complete the diet, but the maintenance portion is too difficult. Sometimes the weight is lost but is regained over time. Most people fail at dieting because of the hormonal mechanisms mentioned above, not because they lack will power. For the most part, limiting food intake to lose weight is not successful. You can have rapid weight loss, or you can have permanent weight loss, but not both. People lose a lot of weight by taking GLP-1 drugs, but the majority will regain the weight when discontinuing the drug. This is because of leptin.

Click for part 2: Making Leptin Work for You

References:

  1. 2014 Jan;24(1):19-26 Moderate weight loss is sufficient to affect thyroid hormone homeostasis and inhibit its peripheral conversion
  2. Int J Obes. 1990 Mar;14(3):249-58. Effects of a very low calorie diet on weight, thyroid hormones and mood
  3. Arch Pharm Res. 2013 Feb;36(2):201-7. Molecular mechanisms of central leptin resistance in obesity
  4. N Engl J Med 2002 May 23;346(21):1623-30 Plasma ghrelin levels after diet-induced weight loss or gastric bypass surgery
  5. 2016 May 26;8(6):323. Elevation of Fasting Ghrelin in Healthy Human Subjects Consuming a High-Salt Diet: A Novel Mechanism of Obesity?
  6. Obesity (Silver Spring). 2015 Feb;23(2):313-21 Effects of α-lipoic acid and eicosapentaenoic acid in overweight and obese women during weight loss
  7. Nutr Diabetes. 2013 Dec 23;3(12):e99 Ghrelin receptor regulates HFCS-induced adipose inflammation and insulin resistance
  8. J Clin Endocrinol Metab. 2004 Jun;89(6):2963-72 Dietary fructose reduces circulating insulin and leptin, attenuates postprandial suppression of ghrelin, and increases triglycerides in women