Energy Balance and Body Weight Regulation

3 components of energy balance

energy intake, expenditure, and stored

energy stored = energy consumed - energy expended

Positive energy balance

energy imbalance where more energy is consumed than required → weight gain

needed in infancy, childhood, adolescence, and pregnancy

Negative energy balance

imbalance where less energy is consumed than required → weight loss

Adipose tissue

used to think it was a static reservoir of stored energy

now we know it’s an active endocrine organ, produces hormones - adipokines

Adipokines

Some are involved in pathogenesis of type 2 diabetes and atherosclerosis

Some regulate immune and inflammatory processes

Adipocytes

number and size determine a person’s body fat mass

typically increases until early adulthood, then remains relatively constant

mostly determined by genetics

Hypertrophic growth

diameter of adipocytes can increase by 50x in positive energy balance

Hyperplastic growth

when adipocytes are full, new adipocytes are formed

Fat loss

size of adipocytes will shrink, but number of adipocytes will remain constant

Adipocytes genetics and weight gain/loss tendency

Smaller, greater number of adipocytes → easier to gain weight

Larger, fewer adipocytes → easier to lose weight

Visceral adipose tissue

adipose tissue surrounding internal organs

worse metabolically

Subcutaneous adipose tissue

adipose tissue found throughout the body - usually thighs, butt, belly

White adipose tissue

mostly involved in energy storage

Brown adipose tissue

contain more mitochondria, more metabolically active, used to generate heat

adults lose this over time

leaner individuals are more likely to have brown adipose tissue

Satiety

physiological response to having eaten enough

signals: gastric distension, elevated blood glucose after a meal promotes, elevated levels of amino acids - tryptophan and serotonin, and lesser - lipids

Region of brain that regulates hunger and satiety

hypothalamus

receives info from GI tract

releases neurotransmitters that influence hunger and satiety

Gastric distension

stomach stretching

powerful satiety signal

stomach returns to its previous size when chyme passes into the small intestine

high volume foods (high in water or fiber) can increase gastric stretching, helping people feel full longer

Bariatric surgery

weight loss surgery

Vertical sleeve gastrectomy - most common type, removes 80% of the stomach

very invasive