Energy Balance and Weight Regulation - Week 3

Energy Balance

State where energy intake matches expenditure via basal metabolism and physical activity.

Long-Term vs. Daily Balance

Daily intake fluctuates, but long-term energy intake roughly equals expenditure to maintain body weight.

De Novo Lipogenesis

Pathway where excess carbohydrate, protein, and alcohol are converted to fatty acids for storage.

Adipose Tissue Function

Dynamic endocrine organ that stores excess energy and secretes bioactive substances called adipokines.

Effects of Negative Energy Balance

Depletes liver glycogen, triggers muscle breakdown via gluconeogenesis, and oxidizes fat stores into ketones.

Static Model of Energy Balance

Assumes intake and expenditure are independent, predicting linear weight changes based on fixed energy deficits.

Dynamic Model of Energy Balance

Accounts for non-linear weight loss where metabolic and body composition changes alter energy requirements.

Components of Energy Expenditure

Resting metabolism (50-75%), physical activity (15-40%), and thermic effect of food (5-10%).

Energy Assessment Limitations

Assessing energy balance is challenging, with combined error rates reaching up to 4,200 kJ/day.

Hypertrophy

Increase in the size of a tissue or organ due to the enlargement of its component cells.

Hyperplasia

Increase in the size of a tissue or organ caused by an increase in the number of cells.

Liver Glycogen Depletion

Liver glycogen is largely depleted after approximately 24 hours of fasting or negative energy balance.

Adipose Tissue Hyperplasia

The permanent increase in fat cell number during chronic energy surplus, which explains why fat cells do not easily disappear.

Fat Cell Shrinkage During Weight Loss

Dieting causes fat cells to shrink in size by releasing stored lipids, but their total number remains largely unchanged.

Hypertrophy vs. Hyperplasia in Obesity

Initial fat gain occurs via cell enlargement (hypertrophy), followed by the recruitment and formation of new fat cells (hyperplasia) when capacity is reached.