Hormonal Influences on Body Composition

Multiple hormonal systems regulate body composition through effects on nutrient storage, tissue synthesis, and energy metabolism. Understanding these hormonal signals provides context for how the body maintains and adjusts tissue composition.

Insulin Signaling

Insulin is the primary hormone signaling nutrient abundance. Elevated insulin promotes glucose uptake by muscle and adipose tissue, increases fat synthesis, and suppresses fat oxidation. Insulin also stimulates amino acid uptake and protein synthesis. Insulin sensitivity (tissue responsiveness to insulin signaling) influences how effectively nutrients are stored after feeding.

Glucagon and Catabolic Hormones

Glucagon and other catabolic hormones (cortisol, epinephrine) are released during fasting or energy deficit states. These hormones promote mobilization of stored glucose and fat, suppress protein synthesis, and increase fat oxidation. Their actions oppose insulin, directing the body toward energy mobilization rather than storage.

Thyroid Hormones

Thyroid hormones regulate metabolic rate and energy expenditure. Elevated thyroid hormone increases the rate at which tissues use energy. Thyroid function influences how efficiently the body processes nutrients and utilizes stored energy. Metabolic rate varies with thyroid hormone levels.

Growth Hormone and IGF-1

Growth hormone and insulin-like growth factor-1 influence protein synthesis and tissue growth. These hormones promote muscle protein synthesis and fat mobilization during fasting states. Their actions support tissue remodeling and adaptation to changing conditions.

Sex Hormones

Testosterone and estrogen influence body composition through effects on protein synthesis, fat storage patterns, and bone density. Sex hormone levels vary across the lifespan and contribute to sex differences observed in body composition. Hormonal status influences tissue responsiveness to metabolic signals.

Leptin and Energy Signaling

Leptin is produced by adipose tissue and signals energy stores to the brain. Leptin influences feeding behavior, energy expenditure, and metabolic rate. The relationship between leptin signaling and tissue energy status represents a regulatory feedback system influencing whole-body composition.