Energy Balance and Food Intake vs. Energy Output

Energy Balance

• Chemical Bonds & Energy:
  • Potential energy in chemical bonds of consumed molecules.
  • Energy released through oxidation = Total energy output.
• Energy Output:
  • 60% of energy lost as heat (not usable).
  • 40% usable energy for work or stored as fat/glycogen.

Weight Balance

• Stable Weight: Intake = Output
• Weight Gain: Intake > Output
• Weight Loss: Output > Intake

Heat and Body Temperature

• Heat generated maintains body temperature.
• Facilitates faster diffusion and chemical reactions.

Obesity & BMI

• Calculation of BMI:
  • Weight in pounds x 705 / (height in inches)^2
• Categories:
  • 25-30: Overweight

  • 30: Obese

• Health Risks:
  • Atherosclerosis, type 2 diabetes, hypertension, heart disease, osteoarthritis.

Regulation of Food Intake

• Brain Regions:
  • Arcuate nucleus (ARC), lateral hypothalamic area, ventromedial nucleus of hypothalamus.
  • Neurons release peptide hormones affecting feeding behavior.
• Peptide Hormones:
  • Enhance Appetite: Neuropeptide Y, agouti-related peptide.
  • Suppress Appetite: Pro-opiomelanocortin (POMC), CART peptides.

Factors Influencing Hunger and Food Intake

• Neural Signals:
  • From GI tract, including protein content, vagal signals from GI distension.
• Nutrient Signals:
  • Increased blood levels of glucose, amino acids, fatty acids suppress eating.
• Hormonal Signals:
  • Suppress Hunger: Insulin, CCK.
  • Stimulate Hunger: Glucagon, epinephrine, ghrelin.

Long-term Regulators of Food Intake

• Leptin:
  • Secreted by adipose tissue in response to increased fat mass.
  • Suppresses neuropeptide Y, promotes appetite suppressors like CART.
  • Rising levels can lead to weight loss; resistance in obese patients.
• Purpose: Prevent excessive weight loss during nutritional deficiency.

Additional Factors

• Temperature: Cold activates hunger.
• Stress: Increases appetite through cortisol release.
• Psychological & Physiological Factors:
  • Viral infections, sleep deprivation.
  • Gut bacteria composition affects systemic health and weight.

Innovative Approaches

• Fecal Transplants:
  • Transplanting gut bacteria from fit individuals to those who are less healthy.