Insulin is a key hormone regulating lipolysis, but it primarily acts as an inhibitor. Lipolysis, the breakdown of stored fats (triglycerides) into fatty acids, can only occur significantly when insulin levels are low, such as during fasting or exercise. This is because insulin's primary role is to store energy, not mobilize it.
However, several other hormones stimulate lipolysis, including:
- Glucagon: This hormone counters insulin's effects, promoting the release of stored energy.
- Epinephrine (adrenaline) and Norepinephrine (noradrenaline): These "fight-or-flight" hormones accelerate lipolysis to provide energy for physical exertion.
- Growth Hormone: Growth hormone plays a role in increasing lipolytic rates, particularly during prolonged fasting.
- Leptin: This hormone, produced by fat cells, can influence lipolysis, although its role is complex and not solely stimulatory.
- Atrial Natriuretic Peptide (ANP) and Brain Natriuretic Peptide (BNP): These hormones, involved in fluid balance, also affect lipolysis.
- Oxytocin: Recent research indicates a role for oxytocin in stimulating lipolysis.
The interplay between these hormones is crucial for maintaining energy balance. During periods of energy surplus, insulin predominates, inhibiting lipolysis. Conversely, during fasting or exercise, the activity of counter-regulatory hormones like glucagon, epinephrine, and norepinephrine increases, leading to increased lipolysis and release of fatty acids for energy production. Furthermore, hormones like FABP4 are involved in regulating lipolysis-driven insulin secretion, highlighting a complex interplay of hormonal influences.
Studies like those published in the Journal of Clinical Investigation Insight (https://insight.jci.org/articles/view/164642) and Nature Reviews Endocrinology (https://www.nature.com/articles/s41574-023-00947-9) highlight the complexity of this regulatory network.
