Energy Metabolism and Macronutrients

Energy Metabolism

• Metabolism is the collection of physical and chemical processes that break down and build molecules in the body.
• Anabolism builds body compounds and requires energy.
• Catabolism breaks down compounds releasing energy.

Energy-Producing Pathways

• Glycolysis breaks down glucose into pyruvate.
• The Citric Acid Cycle (TCA/Krebs Cycle) generates ATP, NADH, and FADH₂.
• The Electron Transport Chain is the primary site for ATP production.
• Beta Oxidation breaks down fatty acids into acetyl-CoA.
• Gluconeogenesis creates glucose from non-carbohydrate sources.

Macronutrient Metabolism

• Carbohydrates are stored as glycogen or converted to fat.
• Proteins are broken down into amino acids, and excess is converted into glucose or fat.
• Fats are stored as triglycerides and broken down via lipolysis.

Feasting vs. Fasting

• During feasting, excess energy is stored as fat.
• During fasting, glycogen and fat stores are used for energy.
• During prolonged fasting, the body switches to ketone bodies for energy.

Ethanol Metabolism

Alcohol Absorption & Digestion

• Absorption occurs via simple diffusion in the stomach (20%) and small intestine (80%).
• Factors affecting absorption include food intake, body weight, and gender.

Metabolic Pathways for Alcohol

• Alcohol Dehydrogenase (ADH) converts alcohol to acetaldehyde, which is toxic.
• Acetaldehyde damages DNA and proteins and increases inflammation.
• Acetate formation converts acetaldehyde into a less harmful substance.

Effects of Alcohol on the Body

• Short-term effects include dehydration, impaired judgment, and reduced motor function.
• Long-term effects include liver damage (fatty liver, fibrosis, cirrhosis) and increased cancer risk.

Health Risks & Benefits

• Moderate drinking may increase HDL cholesterol and reduce heart disease risk.
• Excess drinking is linked to obesity, hypertension, stroke, and liver damage.

Energy Balance & Body Composition

Energy Balance

• Positive energy balance (intake exceeds expenditure) results in weight gain.
• Negative energy balance (expenditure exceeds intake) results in weight loss.

Components of Energy Expenditure

• Basal Metabolic Rate (BMR) is the energy needed for vital functions.
• Physical activity is the most variable component of energy expenditure.
• The Thermic Effect of Food (TEF) is the energy needed to digest and process food.

Factors Affecting BMR

• BMR increases with muscle mass, male gender, and growth stages.
• BMR decreases with age, fasting, and low muscle mass.

Measuring Energy Needs

• The Estimated Energy Requirement (EER) formula differs for men and women:
• Men: 10 x weight (kg) + 6.25 x height (cm) - 5 x age (years) + 5
• Women: 10 x weight (kg) + 6.25 x height (cm) - 5 x age (years) - 161

Body Composition & Weight

• BMI Categories: Underweight: BMI 30

Fat Distribution & Health Risks

• Visceral fat (abdominal) is associated with a higher risk of heart disease and diabetes.
• Subcutaneous fat (hips/thighs) poses less health risk.

Weight Management & Obesity

Understanding BMI and Body Weight

• Body Mass Index (BMI) = Weight (kg) / Height² (m)
• BMI is not a direct measure of body composition.
• It doesn't account for muscle mass or fat distribution.

Health Risks Associated with BMI

• Overweight doesn't always mean unhealthy; some individuals with a high BMI have no metabolic issues.
• Obese individuals have a higher risk for:
  • Cardiovascular disease (CVD)
  • Type 2 Diabetes
  • Hypertension
  • Certain cancers
  • Sleep apnea

Overweight & Obesity Prevalence

• 70% of U.S. adults are overweight or obese.
• Global trends show increasing rates due to urbanization, processed food, and sedentary lifestyles.

Fat Cell Development & Storage

• Fat cells expand in size and number with weight gain.
• Lipoprotein Lipase (LPL) facilitates fat storage.
  • It is higher in women (hips/thighs) and higher in men (abdomen).

Hormones Influencing Body Weight

• Leptin signals satiety but is decreased in obese individuals due to leptin resistance.
• Ghrelin stimulates hunger and increases with inadequate sleep.
• Insulin also plays a role in energy storage.

Causes of Overweight & Obesity

• Genetics: 25% of body fat is linked to genes, but environment plays a larger role.
• Environment:
  • Overeating: Larger portion sizes and high-calorie processed foods.
  • Physical inactivity: Sedentary lifestyles increase weight gain.
• Social & Psychological Factors:
  • These include stress eating, emotional eating, and cultural norms.

Weight-Loss Strategies

• Gradual weight loss (0.5–2 lbs per week) is most sustainable.
• Caloric Deficit: ~3500 kcal = 1 lb of fat; a 500 kcal/day deficit leads to ~1 lb lost per week.

Eating Patterns for Weight Loss

• Energy balance is achieved by reducing intake by 500–750 kcal/day.
• Intake of nutrient-dense, high-fiber foods (vegetables, whole grains) is recommended.
• Protein intake promotes satiety and muscle preservation.
• Limiting empty calories (sugar, alcohol) is advised.

Physical Activity

• Aim for at least 150–300 min of moderate aerobic activity per week.
• More activity helps prevent weight regain.

Extreme Treatments for Obesity

• Weight-Loss Surgeries (for BMI >40 or 35 with comorbidities) include:
  • Gastric bypass, gastric banding, which reduces stomach capacity and alters digestion.
• Dangerous Interventions to avoid:
  • Fad diets (Keto, Atkins, extreme low-calorie).
  • Herbal supplements, diet pills (often ineffective & unsafe).

Underweight & Eating Disorders

• BMI