Module 5, Emotion & Motivation: 10.2 Hunger and Eating

Learning Objectives

  • By the end of this section, you will be able to:

    • Describe how hunger and eating are regulated.

    • Differentiate between levels of overweight and obesity and the associated health consequences.

    • Explain the health consequences resulting from anorexia and bulimia nervosa.

Introduction to Hunger and Eating Regulation

  • Eating is essential for survival, leading to the natural drive of hunger which ensures that we seek sustenance.

  • This chapter focuses primarily on physiological mechanisms regulating hunger and eating, while acknowledging the impact of social, cultural, and economic influences on these behaviors.

  • The section will cover:

    • Regulation of hunger, eating, and body weight.

    • Adverse consequences of disordered eating.

Physiological Mechanisms of Hunger

  • Several physiological mechanisms underpin the experience of hunger:

    • Empty Stomach: When the stomach is empty, it contracts, leading to hunger pangs.

    • Chemical Messengers: Chemical messages travel to the brain signaling to initiate feeding behavior.

    • Blood Glucose Levels: When blood glucose levels drop, the pancreas and liver generate chemical signals to induce hunger (Konturek et al., 2003; Novin et al., 1985).

    • Upon eating, individuals feel satiation due to several physiological signals which regulate the cessation of eating.

  • Satiation Mechanisms:

    • As blood glucose levels rise after eating, the pancreas and liver send signals to terminate hunger (Drazen & Woods, 2003; Druce et al., 2004; Greary, 1990).

    • Food passing through the gastrointestinal tract provides satiety signals to the brain (Woods, 2004).

    • Fat cells release leptin, a hormone crucial for signaling satiety.

  • The integration of hunger and satiety signals predominantly occurs in specific areas of the hypothalamus and hindbrain (Ahima & Antwi, 2008; Woods & D’Alessio, 2008).

  • Ultimately, brain activity dictates whether an individual engages in feeding behavior.

Metabolism and Body Weight Regulation

  • Body weight is influenced by various factors:

    • Interactions between genes and the environment.

    • Caloric intake vs. calories burned through daily activity.

  • Caloric Balance:

    • Excess caloric intake compared to expenditure leads to energy storage in fat.

    • Insufficient caloric intake relative to expenditure results in energy derived from stored fat.

  • Energy Expenditure Influences: Includes physical activity levels and metabolic rates.

    • Metabolic rate: The amount of energy expended over a period, which varies widely among individuals.

    • Those with higher metabolic rates burn calories efficiently compared to those with lower rates.

  • Weight Fluctuations: Most individuals experience normal fluctuations within a narrow range, absent extreme dietary or exercise changes.

  • Set-Point Theory of Body Weight Regulation:

    • Asserts individuals have an ideal body weight set point resistant to change, influenced by genetics; compensatory mechanisms oppose weight changes (Speakman et al., 2011).

    • Limitations of the Set-Point Theory:

    • Lacks empirical support for metabolic rate changes among individuals who lost significant weight (Weinsier et al., 2000).

    • Fails to address social and environmental impact on body weight regulation (Martin-Gronert & Ozanne, 2013).

    • Often serves as a simplistic explanation for body weight regulation.

Overweight and Obesity Definitions

  • Definitions:

    • An individual is overweight if their body mass index (BMI) is between 25 and 29.9 (CDC).

    • An individual is considered obese if their BMI is 30 or higher.

    • Severe Obesity: Defined as a BMI over 40, associated with risk for death.

  • BMI Limitations:

    • Although utilized by organizations like the WHO and CDC, its effectiveness as an individual assessment tool is questioned.

    • BMI does not differentiate between fat and muscle, leading to misclassification (e.g., athletes).

    • Fails to account for racial and ethnic differences in body composition.

    • In 2023, the American Medical Association recommended downplaying BMI as a health measure.

Health Risks Associated with Overweight and Obesity

  • Being overweight or obese is a risk factor for various medical complications, including:

    • Cardiovascular disease

    • Stroke

    • Type 2 diabetes

    • Liver disease

    • Sleep apnea

    • Certain cancers (colon, breast)

    • Infertility

    • Arthritis

  • Prevalence of Obesity:

    • Approximately 40% of U.S. adults are classified as obese.

    • Nearly 75% of adults and 1 in 6 children qualify as overweight (CDC, 2018).

  • Factors Contributing to Obesity:

    • Caloric Imbalance: Exceeding caloric consumption over expenditure.

    • Socioeconomic Status: Impacts access to healthy food options and opportunities for physical activity.

    • Environmental Influences: For example, neighborhoods with high crime rates may discourage active transportation.

    • Food Accessibility and Affordability: Individuals may resort to high-calorie, low-nutritional foods due to economic constraints.

Bariatric Surgery as a Weight Loss Method

  • Bariatric surgery, aimed at reducing weight, modifies the gastrointestinal system to:

    • Reduce food intake capacity.

    • Limit nutrient absorption.

  • Efficacy of Bariatric Surgery:

    • A meta-analysis indicates that bariatric surgery is more effective than non-surgical treatments for obesity in the short term.

    • Long-term efficacy studies are currently lacking (Gloy et al., 2013).

Prader-Willi Syndrome (PWS)

  • Definition: A genetic disorder leading to intense hunger and reduced metabolic rates.

    • Affected children often require constant supervision to prevent excessive eating.

    • PWS is the leading genetic cause of severe obesity in children and is associated with cognitive deficits and emotional problems.

  • Diagnostic Criteria:

    • Behavioral signs in early development (e.g., poor muscle tone, sucking difficulties).

    • Symptoms of excessive eating generally manifest later in childhood.

  • There is no cure; however, controlling weight can increase life expectancy, as historically affected individuals had lower survival rates due to obesity-related complications.

  • Advancements in psychoactive medications and growth hormones can improve quality of life for individuals with PWS.

Eating Disorders Overview

  • A significant portion of individuals (two out of three U.S. adults) experience issues related to being overweight; a smaller segment suffers from eating disorders characterized by being underweight.

  • Individuals with eating disorders such as bulimia nervosa and anorexia nervosa often fear weight gain and face multiple adverse health outcomes.

Bulimia Nervosa

  • Individuals engage in binge eating followed by compensatory behavior (e.g., inducing vomiting, using laxatives, excessive exercise).

  • Health consequences include:

    • Kidney failure

    • Heart failure

    • Tooth decay

    • Psychological issues such as anxiety, depression, and increased risk of substance abuse.

  • Prevalence: Estimated lifetime prevalence of around 1% in women and less than 0.5% in men (Smink et al., 2012).

Binge Eating Disorder

  • Recognized by the American Psychiatric Association (APA), characterized by eating binges followed by psychological distress but not compensatory behaviors.

  • Differentiates from general overeating. Prevalence studies indicate a focus on psychological aspects rather than pure behavior.

Anorexia Nervosa

  • Characterized by maintaining a significantly below-average body weight through starvation and/or excessive exercise.

  • Commonly affects individuals’ body image, leading to disordered thoughts regarding weight perception.

  • Health outcomes include:

    • Bone loss

    • Heart failure

    • Kidney failure

    • Amenorrhea

    • Increased susceptibility to psychological disorders (anxiety, mood disorders, substance abuse).

  • Prevalence Estimates: Generally range from just under 1% to over 4% for women, lower for men (Smink et al., 2012).

  • Culturally binds the disorder predominantly in White females from Western societies, with females aged 15-19 being most at risk.

  • Culturally derived ideals of thinness in media portrayals contribute to the prevalence of eating disorders.

  • Genetic factors also play a role in predisposition to these disorders (Collier & Treasure, 2004).