Hunger / Satiety / Metabolic

Blood glucose level refers to the concentration of glucose in the blood. Regulation of blood glucose levels is central to metabolic health, and elevations outside of the healthy range occur in the context of metabolic disorders, like diabetes. Fasting blood glucose levels, when coupled with fasting insulin levels, can be used to measure insulin resistance. Note that serum and plasma levels of glucose are slightly higher than whole blood levels.

Ghrelin is a hormone produced primarily in the stomach. It is termed the ‘hunger hormone’ because it stimulates appetite, increases food intake, and promotes fat storage. It also stimulates the release of growth hormone. When administered to humans, ghrelin increases food intake by up to 30%; it circulates in the bloodstream and acts at the hypothalamus, an area of the brain crucial in regulating eating behavior. Ghrelin has also been shown to act on regions of the brain involved in reward processing, such as the amygdala and mesolimbic dopamine pathway.

Glucagon-like peptide 1 [GLP-1] belongs to a family of hormones called ‘incretins’ because they enhance the secretion of insulin in response to food intake. Increased levels of GLP-1 are generally detectable after 10 minutes of starting to eat and levels remain elevated in the blood for several hours after food has been consumed. GLP-1 is a satiety hormone as it plays a role in reducing appetite in response to food intake. It has been hypothesized that too little GLP-1 released after a meal may promote obesity because it could prompt individuals to continue eating even after their energy needs have been met.

Hemoglobin A1c (HbA1c) is often measured to estimate what a person’s average blood sugar levels have been over a period of months. It is frequently used to assess how well blood sugar is being controlled in patients with diabetes and can be an index of appropriate glucose regulation.

Insulin is an anabolic hormone produced by the pancreas. It promotes glucose uptake and metabolism in liver, fat, and muscle cells. Thus, increases in insulin levels lead to decreases in circulating blood glucose. Absent and dysregulated insulin signaling are at the core of Type I and Type II diabetes, respectively.

Leptin is a hormone produced primarily by adipocytes (or fat cells) in the body that plays a role in bodily energy homeostasis. While leptin shows some ability to acutely reduce hunger following a meal, it primarily acts to alter food intake and control energy expenditure over the long term. Leptin has its most profound effect when weight is lost and levels of the hormone fall, which increases hunger and appetite. Diminished tissue sensitivity to leptin (i.e., leptin resistance) is involved in the etiology of obesity and other metabolic disorders.