Body Composition and Measurement

Body Composition

• Body composition is measured as Body = Fat + Fat-Free Mass
• Newborns have 14% body fat, increasing to 13% for 10-year-old males and 19% for 10-year-old females
• Adult males have 15% body fat, while adult females have 28% body fat
• Obese males have 28% body fat

Measurement of Body Composition

• Methods of measurement include:
  • Body density
  • Body water
  • Total body potassium (K)
  • Methyl histidine or creatinine excretion
  • Skinfold measurements (biceps, triceps, supra iliac, sub scapular)
  • Mid-arm circumference
  • Bioelectrical impedance (uses electrical signal to measure body fat percentage)
  • The Bod Pod (air displacement plethysmography)

Energy Derived from Food

• Energy is derived from food in the following amounts:
  • Carbohydrate: 4 kcal/g, 16.8 kj/g
  • Fat: 9.2 kcal/g, 38.6 kj/g
  • Protein: 5.4 kcal/g, 22.7 kj/g
  • Alcohol: 7 kcal/g, 29.4 kj/g

Energy Requirements

• Energy requirements depend on:
  • Basal metabolic rate (kj/hour/kg body weight)
  • Diet-induced thermogenesis
  • Physical activity (e.g., sitting = 1.7BMR, football = 7BMR)
  • Environmental temperature
  • Growth, pregnancy, lactation (e.g., 0.8 MJ or 200 kcal/day in trimester 3, 2 MJ or 500 kcal/day in lactation)
  • Age (decrease in BMR and activity)

Energy Balance

• Energy balance is achieved when energy intake equals energy expenditure, resulting in no change in body mass
• Energy balance is regulated by the hypothalamus, which receives signals from the body (e.g., leptin, insulin)

Regulation of Energy Intake

• Long-term signals:
  • Leptin and insulin (signal the state of fat stores and carbohydrate stores, respectively)
  • Act in the hypothalamus to regulate hunger and satiety pathways
• Short-term signals:
  • From the GI tract, hepatic portal vein, and liver
  • Bring about the feeling of satiety through the vagus and circulation

Causes of Obesity

• Socio-economic, cultural (e.g., obesity in lower socio-economic class in the UK and Western world)
• Endocrinological (e.g., adrenal hyperactivity, hypothyroidism)
• Physical activity (e.g., children spend 65% less energy than 25 years ago)
• Microbiota (e.g., evidence that GI tract of lean subjects has more diverse microbiota than obese)
• Genetic factors (e.g., FTO gene, 2 oxoglutarate dependent dioxygenase)

Conditions Associated with Obesity

• Cardiovascular disease
• Diabetes mellitus type 2
• Hypertension
• Respiratory problems
• Gall bladder stones
• Osteoarthritis in weight-bearing joints
• Reduced fertility in men
• Polycystic ovary syndrome
• Breast, endometrial, colon, and prostate cancers

Therapy: Diets

• All diets work if energy intake is restricted, but adherence is key
• Fad diets are often metabolically undesirable and may not lead to long-term weight loss
• High-protein diets may be easier to follow due to satiety value of protein
• Keto diet (primarily used for epilepsy, may have concerns about high saturated fat content)
• Intermittent fasting (claims to improve thinking, heart health, and type 2 diabetes, but most studies are on animals and human studies show no benefit compared to continuous calorie restriction)

This quiz assesses knowledge on body composition, including measurement methods and percentage of body fat in different populations. Test your understanding of bioelectrical impedance, skinfold measurements, and more.