Our bodies possess an intricate internal communication network, relying on various hormones and signals to maintain balance across numerous physiological processes. Among these internal messengers, hormones originating from the gut play a particularly significant role in managing our feelings of hunger and fullness. These digestive signals help the body understand its energy status and respond accordingly.
Understanding Peptide YY
Peptide YY (PYY) is a hormone primarily produced by specialized cells known as L-cells. These L-cells are predominantly found in the lining of the small intestine and colon. PYY is released into the bloodstream, with its levels increasing noticeably after a meal.
PYY exists in two main forms: PYY(1-36) and PYY(3-36). PYY(1-36) is the full-length version, consisting of 36 amino acids. However, the enzyme dipeptidyl peptidase-IV (DPP-IV) rapidly processes PYY(1-36) into PYY(3-36) by removing the first two amino acids. This modification makes PYY(3-36) the more abundant and biologically active form regulating appetite.
Peptide YY’s Impact on Appetite
PYY’s primary function is to reduce appetite and promote satiety. It acts on specific receptors in the brain. PYY(3-36) shows a strong preference for the Y2 receptor (Y2R), found in both the brain and peripheral tissues.
The arcuate nucleus of the hypothalamus, an appetite-regulating brain region, is where PYY acts. When PYY binds to Y2 receptors on neurons in the arcuate nucleus, it inhibits the activity of neurons that typically stimulate appetite, such as those producing neuropeptide Y (NPY) and agouti-related peptide (AgRP). This inhibition sends a signal to the brain that the body has received sufficient nutrients, leading to a decrease in the desire to eat and a prolonged feeling of satisfaction. Studies in humans have shown that increasing PYY(3-36) to post-meal levels can reduce food intake by approximately 33% over a 24-hour period.
What Influences Peptide YY Levels
The release and circulating levels of PYY are influenced by various physiological states and external inputs, particularly meal intake. PYY levels are low during fasting but rise after consuming food. This increase can be observed within 15 minutes of eating, with levels usually peaking around 1 to 2 hours post-meal and remaining elevated for several hours.
The specific composition of a meal also plays a role in PYY secretion. Meals rich in protein and fat stimulate a greater release of PYY compared to those high in carbohydrates. For instance, certain fatty acids, such as saturated fatty acids (SFA) and polyunsaturated fatty acids (PUFA), induce a more substantial PYY response than monounsaturated fatty acids (MUFA). Beyond dietary factors, conditions like bariatric surgery often lead to higher post-meal PYY levels, which is thought to contribute to the observed weight loss.
Peptide YY and Managing Body Weight
Understanding PYY’s role has implications for managing body weight and metabolic health. Individuals with obesity often exhibit a lower PYY response after meals compared to lean individuals. This reduced post-meal PYY secretion may contribute to difficulty achieving satiety, potentially leading to increased food intake and weight control challenges.
Studying PYY has spurred research into its potential as a therapeutic target for obesity. Scientists are developing PYY analogues—synthetic versions of the hormone—to enhance satiety and reduce food intake. For example, a PYY analogue called Y14 has shown promising results in early trials, reducing body weight and food intake in overweight volunteers. Research also continues into naturally enhancing the body’s PYY release for weight management.