Lecture 8

• Obese individuals possess higher absolute metabolic rates compared to non-obese individuals due to larger organs, more muscle mass, increased food intake leading to more digestion, and higher energy costs of movement.
• Relative metabolic rate is lower because extra fat is not very energy-intensive.
• Obesity is defined as an increase in body adipose tissue mass, where the body's energy stores are excessively large, typically with a BMI > 30.
• Obesity is problematic as it complicates or leads to cardiometabolic diseases, increases the risk of premature morbidity and mortality, and can cause metabolic syndrome.
• Metabolic syndrome (Syndrome X) involves insulin resistance and leptin resistance, leading to hormonal signaling dysfunctions that disrupt the ability to regulate weight.
• Approximately 25% of the US population has metabolic syndrome, with incidence increasing with age and inactivity.
• Obesity is primarily caused by consuming too much energy and moving too little, leading to a chronic energy imbalance especially in genetically susceptible individuals.
• Metabolic disorders or diseases account for only 1% of obesity cases.
• The fat mass and obesity-associated gene (FTO) influences food intake and satiety.
• Homozygous individuals for the FTO gene (16% of the population) face a 1.7-fold increased risk of obesity.
• Children of obese parents do not exhibit major defects in energy expenditure, suggesting genetics interplay with environmental factors.
• Overconsumption of energy relative to requirements is a major cause of obesity but why expenditure can't keep up is influenced by the obesogenic environment.
• The obesogenic environment makes unhealthy choices the easy choices, with engineered declines in physical activity and easy availability of energy-dense foods.
• Creeping obesity is a slow, gradual gain of body fat over time.
• Individuals with a BMI of 30 may have an excess of 382 kcal/day, whereas those with a BMI of 40 may have an excess of 1000 kcal/day.
• Epigenetics relates to the balance of energy expenditure and storage genes.
• Thermogenesis is the body's generation of heat, and total energy requirements include BMR, TEF, and TAT.

Total Energy Thermogenesis Components

• Basal metabolic rate (BMR) is the minimum metabolism rate to sustain life.
• Thermic effect of food (TEF) is the energy cost of digestion, about 10% of food energy.
• Total activity thermogenesis (TAT) includes both exercise activity thermogenesis (EAT) and non-exercise activity thermogenesis (NEAT).

Predictive Equations for Metabolic Rate

• Simple equations, based on mass, does not differentiate between fat mass and muscle mass.
• Formulas based solely on body mass do not account for metabolic activity differences between fat-free and fat mass.
• Fat-free mass is more metabolically active than fat mass.
• Formulas factoring in body composition include Katch-McArdle (BMR) and Cunningham (RMR).
• The Harris-Benedict formula factors in activity level by multiplying BMR by 1.25 for moderately active individuals and 1.5 for very active ones.
• Resting metabolic rate is dynamic, with inter- and intra-personal differences, potentially due to adaptive thermogenesis.

Adaptive Thermogenesis

• Adaptive thermogenesis involves changes in total energy thermogenesis in response to changes in diet, functioning as a negative feedback system during caloric deficits and a positive feedback system during caloric surplus.
• Is hormonally regulated by adipokines secreted from adipose tissue like leptin.
• Increased BMR, TET, and TEF prevent or slow weight gain when dietary input is high.
• Decreased BMR, TET, and TEF prevent or slow weight loss when dietary caloric input is low.
• According to Levine (1999), subjects fed an extra 1000 kcal a day for 8 weeks gained ~5kg, with increases in fat mass, muscle mass, RMR, TEF, and NEAT.
• Abdominal fat is very endocrinic and secretes hormones that enter the circulation and interact with brain centers, regulating adaptive thermogenesis through appetite, activity, metabolic set point, and TEF.

Adipokines and Leptin

• Adipokines are adipose-derived hormones, such as leptin, that circulate and interact with brain centers to regulate adaptive thermogenesis.
• Leptin levels are equivalent to adiposity, increased leptin secretion decreases appetite and increases activity.
• Leptin deficiency is rare, causing 1% of obesity cases, while leptin resistance is more common, occurring in response to chronically high leptin levels.
• Physical activity prevents leptin resistance by maintaining leptin signaling.

Exercise and Diet for Weight Loss

• A deficit of >500 kcal a day is needed for acute weight loss
• Decreasing fat intake to decrease cardiometabolic risk factors.
• Decreasing simple carbs.
• Increasing complex carbs.
• Exercise is needed to sustain weight loss.
• The source doesn't matter when concerning calories and weight gain.
• Weight loss was not significantly different between groups with low fat and low CHO diets.
• High intensity activity expends more kcal per time unit.

Recommendations for Lifespan

• 3-4 hours/week is valuable when concerning weight management.
• Exercise combined with strict diet does not always increase weight loss.
• 500 kcal a day from exercise prevents long term weight gain.
• Value of exercise for decreased disease, such as cancer risk and cardiometabolic risk.
• Resistance work (reps) can prevent creeping obesity.
• Steps or cardio will give more METS.
• Resistance training will raise RMR more than steps.
• Kcal expended DURING exercise is better.