The age-old adage “the brain controls everything,” is especially true now more than ever, as scientists are deciphering complex hormones that act as signals between the brain and other organ systems.
The gut brain axis is one such complex inter-connection of the brain, which allows a two-way communication between the intestines and the brain. This translates into the intestines being able to tell their boss, the brain about various things like satiety, sugar, mood, even behavior. The hormones released by the brain in turn influence other organ systems in the body. At the same time, the brain can help start and shut down functions of the gut in a manner to control weight, diabetes, bowel movement etc.
But how exactly does the gut-brain axis control weight gain and weight loss?
The answer lies in the hormones Leptin and Ghrelin. Leptin is a hormone released by the fat cells, stomach, muscles and various other cells in the body. It is commonly known as the ‘satiety hormone’, and is almost the opposite of Ghrelin, the ‘hunger hormone’. Leptin is released in the body in response to an adequate meal and fat storage, and plays a crucial role in the regulation of body weight and energy balance. It circulates in the blood and binds to the receptors in the brain which produces a feeling of satiety or fullness.
When the hormone Leptin was discovered in 1994, it was postulated hormone levels would be low in obese patients, leading to a lack of satiety, over-eating and hence the state of obesity. However, subsequent research uncovered significantly elevated levels of Leptin even in obese patients. These patients had a voracious appetite and a tendency to store fat, despite elevated Leptin levels. This proved that such patients developed a state of Leptin resistance, wherein the receptors in the brain were somehow not allowed to sense Leptin, and hence couldn’t carry out its function.
Leptin therapy with drugs such as Myalept® is helpful in only a fraction of all obese patients with low or absent levels of circulating Leptin. Such patients are usually obese since childhood, due to a mutation in the genes encoding the hormone. For all other obese patients, this therapy is not an acceptable treatment option.
Leptin ideally limits adipose tissue accumulation, hence regulates body weight. At the same time, it also signals the brain to increase the energy expenditure to regulate the levels of adipose tissue in the body. Hence, Leptin is aptly labelled as the ‘protector of fat metabolism’.
At Digestive Health Institute, we screen Leptin levels in all our obese children and adolescents, who are before being worked up for Bariatric/Metabolic Surgery. This helps us identify obesity due to either Leptin deficiency Monozygous Obesity (usually seen in infants and children) or Leptin resistance (usually seen in adolescents and adults). This serves as a guide for treatment options and helps select the candidates for different forms of intervention whether medical management or Bariatric/Metabolic Surgery.