HUNGER, EATING, AND HEALTH

Digestion

The process through which food is broken down into nutrients that can be absorbed and used by the body.

glucose

amino acids

lipids

3 Major Nutrients

Glucose

— major immediate energy source

Amino acids

— building blocks of proteins

Lipids

— major form of stored energy

Cephalic Phase

Begins with the sight, smell, or expectation of food

Absorptive phase

Nutrients from a meal are used, and excess energy is stored

Fasting Phase

Stored energy is mobilized to meet current needs

Cephalic phase

absorptive phase

fasting phase

Three Phases of Energy Metabolism

Insulin

— promotes glucose utilization and energy storage

Glucagon

— promotes mobilization of stored energy

Set-Point Assumption

- The traditional view is that hunger occurs when the body's energy resources fall below an optimal level and eating restores them toward a set point.

Glucostatic Theory

Hunger and satiety are regulated partly by a blood-glucose set point.

Lipostatic Theory

Hunger and eating are regulated partly by a body-fat set point.

Positive-Incentive Theory

People are normally motivated to eat not simply because they have an energy deficit, but because food has positive-incentive value—the anticipated pleasure associated with eating.

Factors affecting this theory:

• Flavor and palatability

• Previous experience with food

• Time since the last meal

• Food currently in the gastrointestinal tract

• Presence of other people eating

• Blood glucose levels

Hunger

is influenced by the interaction of multiple factors rather than by a single internal energy signal.

Satiety

— the motivational state that causes eating to stop even when food remains.

Nutritive density

— calories per unit volume of food

Sham eating

— food is chewed and swallowed but prevented from reaching the

stomach

Appetizer effect

— eating can sometimes increase rather than decrease subsequent eating

Sensory-specific satiety

— satiety develops toward a particular food while interest in other foods remains.

Lateral hypothalamus (LH)

→ hunger/feeding center

Ventromedial hypothalamus (VMH)

→ satiety center

Gastrointestinal Signals

Satiety Peptides

Hunger Peptides

Serotonin

4 Signals of Hunger and Satiety

Gastrointestinal Signals

The g_______ tract provides information to the brain regarding food consumption.

Satiety Peptides

Peptides that reduce appetite and food intake.

Examples:

Cholecystokinin (CCK)

Bombesin

Glucagon

Alpha-melanocyte-stimulating hormone

Somatostatin

Hunger Peptides

- Peptides associated with increased appetite.

Examples:

Neuropeptide Y

Galanin

Orexin-A

Ghrelin

Serotonin

The monoaminergic neurotransmitter serotonin also plays a role in satiety.

Eating

is regulated by multiple interacting physiological signals, not glucose or fat alone.

Set-Point Model

Body weight is assumed to be regulated around a biologically determined optimal level.

Settling-Point Model

Body weight is viewed as the result of the interaction among:

Food intake

Energy expenditure

Environmental conditions

Behavioral factors

Physiological factors

Human Obesity

Obesity results from complex interactions among:

Eating behavior

Energy expenditure

Environment

Learning

Genetics

Physiological mechanisms

Leptin

A hormone involved in the regulation of body fat and energy balance.

Anorexia Nervosa

A disorder of underconsumption characterized by severe restriction of food intake and potentially life-threatening weight loss.

Bulimia Nervosa

Characterized by episodes of binge eating followed by efforts to eliminate consumed calories

through behaviors such as:

Vomiting

Laxatives

Enemas

Diuretics

Excessive exercise

Body weight

is influenced by interacting biological, behavioral, and environmental factors.