Source: Lectures 18 and 19 | Biology, University of Michigan
Difficulty: Intermediate. Familiarity with energy balance concepts from Lecture 17 is helpful.
Obesity rates are rising because of an interplay between food environment, portion sizes, sedentary behaviour, sleep deprivation, genetics, and more. The body regulates hunger through short-term (ghrelin) and long-term (leptin) hormone systems. Even modest weight loss of 5 to 10% of body weight can cut chronic disease risk and all-cause mortality by roughly 50%, making sustainable dietary and lifestyle changes far more important than any fad diet.
Energy balance
The relationship between energy intake (food consumed) and energy output (energy burned). When they are equal, weight is maintained. A positive balance leads to weight gain; a negative balance leads to weight loss.
BMI (body mass index)
Body weight in kilograms divided by height in metres squared. Categories: underweight 15 to 17, normal weight 17 to 25, overweight 25 to 30, obese 30 to 40. In simple terms, a quick screening tool that estimates whether someone's weight is in a healthy range.
Ghrelin
A hormone produced in the stomach that stimulates hunger by activating specific neurons in the brain. Ghrelin secretion decreases once nutrients are absorbed into the blood. Think of ghrelin as the "growling" hormone.
Leptin
A hormone produced by adipose (fat) tissue that suppresses hunger and adjusts food intake and energy expenditure to maintain adequate fat stores. Leptin concentration in the blood is correlated with the amount of adipose tissue (True on exam).
Satiation
The sense of fullness during a meal that leads to termination of eating.
Satiety
The effect of a meal after it ends. Reduced interest in food between meals. In simple terms, satiation stops you mid-meal; satiety keeps you satisfied afterwards.
Visceral fat
Fat stored around the internal organs in the abdomen. An independent health risk for cardiovascular disease, type 2 diabetes, and premature mortality, measured by waist circumference.
Waist circumference
An estimator of abdominal obesity. Thresholds: greater than 35 inches in women, greater than 40 inches in men.
EER (estimated energy requirement)
The average dietary energy intake predicted to maintain energy balance. Calculated using formulas that account for age, physical activity, weight, and height.
Negative energy balance
Energy intake is less than expenditure, leading to weight loss.
Positive energy balance
Energy intake exceeds expenditure, leading to weight gain.
Food environment: cheap, palatable, energy-dense foods widely available
Portion sizes: larger portions lead to eating more
Television: increases sedentary time, promotes snacking and unhealthy food choices
Sedentary lifestyle: decreased energy output promotes positive energy balance
Fewer home-cooked meals: eating out is linked to higher obesity risk
Sleep deprivation: increases food consumption
Communities: lack of sidewalks, parks, or recreation centres creates barriers to activity
Emotions: boredom, anger, stress can trigger overeating
Smoking cessation: people often eat more after quitting
Genes: genetic makeup affects food intake regulation and weight gain susceptibility. Genes are the contributor NOT within our control to change.
Pregnancy: some women struggle to lose pregnancy weight
Prescription drugs: may increase appetite or decrease metabolism
Energy is required for all cell functions; cells use ATP
Measured in kcal (the energy required to raise 1 kg of water by 1 degree Celsius)
Energy in = energy consumed; energy out = energy burned
Negative energy balance: intake < expenditure = weight loss
Energy balance: intake = expenditure = weight maintenance
Positive energy balance: intake > expenditure = weight gain
Exam example: a woman who requires 2,000 kcal to maintain weight should consume 1,500 to 1,800 kcal/day for healthy weight reduction
Short-term system: Mediated by ghrelin (produced in stomach, stimulates hunger) and stomach pressure. Once nutrients are absorbed into blood, ghrelin secretion decreases.
Long-term system: Mediated by leptin (produced by adipose tissue, suppresses hunger). Leptin adjusts food intake and energy expenditure to maintain adequate fat stores. Leptin concentration correlates with amount of adipose tissue (True on exam).
Classic experiment: mouse with normal leptin gene (skinny) vs mouse with leptin gene mutation (obese, cannot produce leptin)
Satiation: sense of fullness during a meal, leads to stopping eating
Satiety: reduced interest in food after a meal
Gastric distention
Hormones in the small intestine
BMI: weight (kg) / height (m)^2
Underweight: 15 to 17
Normal: 17 to 25
Overweight: 25 to 30
Obese: 30 to 40
BMI advantages: easy, fast, cheap, no special equipment needed
BMI limitations: indirect measure of body fat; overestimates fat in muscular individuals; underestimates fat in the elderly
A person with a BMI of 17 has higher mortality risk than someone with a BMI of 21 (True)
Abdominal obesity thresholds: greater than 35 inches (women), greater than 40 inches (men)
Visceral fat is an independent risk factor for cardiovascular disease, type 2 diabetes, and premature mortality
Dual-energy X-ray absorptiometry (DEXA)
Underwater weighing (hydrodensitometry)
Bioelectrical impedance
Skinfold thickness
Enlarged fat cells produce excess hormones and hormone-like messengers
These attract immune cells and cause low-grade chronic inflammation (True on exam)
Inflammation linked to: heart disease, type 2 diabetes, insulin resistance, Alzheimer's disease and stroke, hypertension and atherosclerosis, fatty liver, certain cancers, arthritis, gout, sleep apnoea, gastroesophageal reflux, infertility, erectile dysfunction
5 to 10% of body weight loss can reduce chronic disease risk and all-cause mortality by roughly 50%
Benefits: increases HDL, decreases triglycerides, reduces inflammation, reduces blood pressure, reverses insulin resistance, reduces risk of type 2 diabetes, CVD, and certain cancers
A man (5'9", 210 lbs) who loses 11 lbs and maintains it for 2 years will see big health improvements (True)
Men: EER = (662 - (9.53 x age)) + PA x (15.91 x weight in kg) + (539.6 x height in m)
Women: EER = (354 - (6.91 x age)) + PA x (9.36 x weight in kg) + (726 x height in m)
Convert lbs to kg by dividing by 2.2; convert inches to metres by multiplying by 2.54 then dividing by 100
Recommended for anyone with BMI of 30+ or overweight with two or more risk factors: elevated waist circumference, CVD, family history of CVD, smoking, hypertension, diabetes, physical inactivity, age (men 45+, women 55+ or postmenopausal)
Surgical approaches: for BMI 40+ or BMI 35+ with additional risk factors. Benefit must outweigh risk.
Healthy weight loss is less than 2 pounds per week, achieved by eating according to healthy plate guidelines and increasing activity
Low-carb and Mediterranean diets produce greater weight loss than low-fat diets (study: >300 participants, mean BMI 31, 2-year duration: low fat lost 7.3 lbs, Mediterranean lost 10.1 lbs, low-carb lost 12.1 lbs; blood lipids best in low-carb, blood glucose best in Mediterranean)
High-protein, low-glycaemic-index diets produce greater weight loss than high-GI diets (study: >1,200 participants, mean BMI 34; only the high-protein, low-GI group continued losing weight on maintenance)
Mediterranean diet reduces CVD risk: >7,400 participants, 4.8 years, 30% reduction in heart attacks and strokes with Med diet plus extra olive oil or nuts vs low-fat diet
Skip diet pills and quick fixes
Be active
Eat lots of vegetables, fruits, and high-quality foods
Watch less TV
Eliminate soda
Eat lower glycaemic foods
Get support
Think before you eat
Maintain a healthy eating plan
Eat breakfast
Weigh yourself at least once a week
Watch fewer than 10 hours of TV per week
Exercise about one hour per day on average
Increase daily NEAT
Students often think BMI directly measures body fat. It does not. BMI is an indirect estimate that can overestimate fat in muscular people and underestimate it in the elderly.
Students sometimes confuse satiation and satiety. Satiation is fullness during a meal (stops eating); satiety is reduced hunger after a meal (delays the next meal).
Students may assume that all contributors to obesity are within our control. Genes are not.
Students often think dramatic calorie restriction is the best way to lose weight. Research shows that modest, sustained loss of 5 to 10% of body weight produces the greatest health benefits.
⚠️ Leptin concentration correlates with adipose tissue amount (True).
⚠️ Enlarged fat cells produce hormones that cause low-grade inflammation (True).
⚠️ A BMI of 17 carries higher mortality risk than a BMI of 21 (True).
⚠️ Genes are the obesity contributor NOT within our control.
⚠️ Healthy weight loss = less than 2 lbs/week via healthy plate guidelines + increased activity.
⚠️ A woman needing 2,000 kcal should consume 1,500 to 1,800 kcal/day to lose weight healthily.
⚠️ Losing 5 to 10% of body weight can cut chronic disease risk and all-cause mortality by about 50%.
⚠️ Know the EER formulas for men and women.
⚠️ Mediterranean diet + olive oil or nuts: 30% reduction in heart attacks and strokes vs low-fat diet.
True or False: Leptin is produced in the stomach and stimulates hunger. (False, that is ghrelin. Leptin is produced by adipose tissue and suppresses hunger.)
Fill in the blank: BMI is calculated as weight in kg divided by height in _____ squared. (metres)
True or False: Genes are a contributor to obesity that is within our control to change. (False)
Fill in the blank: Waist circumference thresholds for abdominal obesity are >_____ inches in women and >_____ inches in men. (35, 40)
True or False: A 5 to 10% body weight loss can reduce all-cause mortality by about 50%. (True)
Q: A woman requires 2,000 kcal to maintain her body weight. If she wants to reduce her weight in a healthy manner, how many kcal should she consume per day?
A: 1,500 to 1,800 kcal per day.
Q: Which of the following contributors of obesity are NOT within our control to change: genes, diet, activity levels, sleep deprivation, or eating out?
A: Genes.
Q: What are two hormones involved in energy balance, and what does each do?
A: Ghrelin (produced in the stomach, stimulates hunger) and leptin (produced by adipose tissue, suppresses hunger).
Q: What is the difference between satiation and satiety?
A: Satiation is the sense of fullness during a meal that leads to stopping eating. Satiety is the reduced interest in food after a meal.
Q: What leads to healthy weight loss (less than 2 pounds a week) in a person who needs to lose weight?
A: Eating according to the healthy plate guidelines and increasing physical activity.
Q: In the diet comparison study, which diet produced the greatest weight loss over 2 years, and which had the best blood glucose levels?
A: The low-carb diet produced the greatest weight loss (12.1 lbs). The Mediterranean diet group had the best blood glucose levels.
This material builds directly on Lecture 17's energy expenditure concepts (BMR, NEAT, total energy expenditure). The hunger hormones (ghrelin and leptin) connect to Lecture 20 (Eating Disorders), where disrupted eating patterns alter these hormonal signals. The discussion of inflammation from excess body fat relates to Lecture 16 (Dietary Supplements), since some people take supplements to address inflammation. The dietary research findings (Mediterranean diet, low-GI diets) also tie to Lecture 22 (Food Security and Climate Change) through their emphasis on whole foods and sustainability.
Obesity, weight loss, energy balance, BMI, body mass index, ghrelin, leptin, satiation, satiety, visceral fat, waist circumference, DEXA, hydrodensitometry, bioelectrical impedance, skinfold thickness, negative energy balance, positive energy balance, EER, estimated energy requirement, basal metabolism, NEAT, inflammation, adipose tissue, chronic disease, Mediterranean diet, low-carb diet, glycaemic index, Paleo diet, bariatric surgery, gastric bypass, gastric banding, modest weight loss, weight loss maintenance, healthy plate guidelines