10.2 Hunger and Eating

Hunger and eating are complex processes shaped by both biological and psychological factors. The hypothalamus, hormones, and blood glucose levels all work together to regulate appetite and food intake, while your body constantly strives for homeostasis, or a stable internal environment.

Beyond biology, emotions and social influences also shape eating behaviors. Understanding these mechanisms helps explain why we eat, how much we eat, and the challenges some people face with disordered eating.

Biological and Psychological Factors in Hunger and Eating

Mechanisms of hunger regulation

The hypothalamus, a small structure deep in the brain, is the control center for hunger and satiety (the feeling of fullness). Two specific regions do opposite jobs:

• The lateral hypothalamus (LH) acts as the "hunger center." When it's activated, it stimulates appetite and drives you to eat.
• The ventromedial hypothalamus (VMH) acts as the "satiety center." When it's stimulated, it suppresses hunger and tells you to stop eating.

Several hormones communicate hunger signals between your body and brain:

• Ghrelin is secreted by the stomach and stimulates hunger. An easy way to remember: ghrelin makes your stomach growl. Ghrelin levels rise before meals and drop after eating.
• Leptin is released by fat cells (adipose tissue) and suppresses hunger. It signals to the brain that the body has enough energy stored. Think: leptin keeps you lean by reducing appetite.
• Insulin, produced by the pancreas, regulates blood glucose levels. When insulin causes blood sugar to drop too low, you start feeling hungry again.

Blood glucose levels directly affect hunger sensations. When glucose drops, you may feel lightheaded or shaky, and your body signals you to seek food. After eating, glucose rises and hunger fades.

Psychological factors also play a major role in eating behavior:

• Emotional eating is consuming food in response to feelings like stress, sadness, or boredom rather than actual physical hunger.
• Social influences shape what and how much you eat. Cultural norms, family dinners, and celebrations all affect eating patterns. People tend to eat more when dining in groups.
• Learned preferences develop through repeated exposure and conditioning. For example, you might acquire a taste for spicy food after growing up in a household that regularly cooked with hot peppers.

Physiological regulation of hunger and eating

Your body uses homeostasis to maintain a stable internal environment, and weight regulation is part of that process. Set point theory suggests that each person's body has a natural weight range it tries to maintain. If you eat less, your metabolism may slow down to conserve energy; if you overeat, it may speed up.

Metabolism refers to the chemical processes that convert food into usable energy. People differ in their metabolic rates, which partly explains why some people gain weight more easily than others. Neurotransmitters like serotonin also help regulate appetite and food intake, and satiety signals from the stomach and intestines tell the brain when you've had enough.

Body Weight Classifications and Health

Spectrum of body weight classifications

Body Mass Index (BMI) is a widely used measure to classify body weight. It's calculated with this formula:

$BMI = \frac{weight \, (kg)}{[height \, (m)]^2}$

The standard BMI categories are:

• Underweight: BMI below 18.5. Associated with increased risk of malnutrition, osteoporosis, and a weakened immune system.
• Normal weight: BMI 18.5–24.9. Generally linked to better health outcomes and lower risk of chronic diseases.
• Overweight: BMI 25.0–29.9. Carries increased risk of type 2 diabetes, cardiovascular disease, and certain cancers.
• Obesity: BMI of 30.0 or higher. Greatly increases risk of chronic diseases like heart disease and sleep apnea, joint problems, and reduced life expectancy.

BMI has limitations, though. It doesn't distinguish between muscle and fat, so a very muscular person could be classified as "overweight" despite being healthy. Waist circumference is another useful measure because it specifically targets abdominal fat, which is more strongly linked to health risks. For men, a waist over 40 inches (102 cm) signals increased risk; for women, the threshold is 35 inches (88 cm).

Eating Disorders

Characteristics of eating disorders

Eating disorders are serious mental health conditions involving persistent disturbances in eating behavior and related thoughts and emotions. Three major types show up most often in intro psych:

Anorexia nervosa involves severe restriction of food intake driven by an intense fear of gaining weight. People with anorexia often have a distorted body image, perceiving themselves as overweight even when they are dangerously underweight. Health consequences include malnutrition, osteoporosis, cardiovascular problems, organ damage, and loss of menstruation (amenorrhea).

Bulimia nervosa involves repeated cycles of binge eating followed by purging. Purging behaviors can include self-induced vomiting, laxative abuse, or excessive exercise. It's often driven by fear of weight gain and negative body image. Health consequences include electrolyte imbalances, tooth decay from stomach acid, esophageal damage, and dehydration.

Binge eating disorder (BED) is characterized by recurrent episodes of eating large amounts of food in a short period while feeling a loss of control. Unlike bulimia, there's no regular purging afterward. Episodes are often accompanied by shame, guilt, and secretive eating. Health consequences include obesity, cardiovascular disease, type 2 diabetes, and high blood pressure.

Risk factors for eating disorders

Eating disorders don't have a single cause. Risk factors span multiple categories:

1. Biological factors: Genetic predisposition plays a role, as eating disorders tend to run in families. Neurochemical imbalances, particularly involving serotonin, are also linked to disordered eating.
2. Psychological factors: Low self-esteem, perfectionism, body dissatisfaction, anxiety, and depression all increase vulnerability.
3. Sociocultural factors: Media portrayals of the "thin ideal," societal pressure around appearance, and peer pressure can all contribute, especially during adolescence.