The gastrointestinal tract has a hormone called ghrelin that signals the hypothalamus in the brain to trigger hunger. The ghrelin hormone produced by the stomach rises when blood levels of leptin and glucose fall. High-fat diets also cause a rise in leptin and suppress ghrelin . This hormone is essential for food emptying from the stomach into the small intestine.
In overweight individuals, ghrelin levels stay elevated after food is eaten, which causes excess consumption of food . Ghrelin loses its normal rhythmic pattern for controlling eating behavior when leptin is too high. As leptin reduces, ghrelin levels can return to normal. Animal studies have shown that taking melatonin can decrease ghrelin levels .
Leptin and Thyroid
Leptin levels are a significant factor in metabolic rate because leptin controls thyroid function . When leptin resistance occurs, the body thinks it is starving even with an overabundance of fat. The liver stops converting thyroid hormone (T4) into active thyroid hormone (T3) due to leptin resistance. Individuals with hypothyroid symptoms need to be assessed for leptin resistance.