Year 2 Nutrition Unit I: Energy Balance & Obesity

Energy Available in Foods

• Nutrients that provide energy include carbohydrates, proteins, and fats.
• Stored chemical energy is released through cellular respiration.

Determining Energy Content of Food

• Calorimetry measures energy through the combustion of food, producing heat that raises water temperature.
• Specific heat of water: 4.2 J or 1 calorie (cal) raises 1 g of water by 1ºC.
• 1 dietary calorie (Cal) = 1000 calories (1 kcal).
• Energy obtained from food combustion parallels energy utilized by the body during metabolism.

Respiratory Quotient (RQ)

• RQ = Volume of CO2 produced / Volume of O2 consumed indicates which macronutrient is oxidized.
• Carbohydrates: RQ = 1 (complete oxidation).
• Fats: RQ = 0.7 (more O2 required for oxidation).
• Proteins: RQ = 0.8.
• Mixed diet RQ approximates to 0.8; RQ decreases in conditions like Diabetes Mellitus.

Basal Metabolic Rate (BMR)

• BMR represents minimum energy needed for physiological functions at rest (12-14 hrs post-meal).
• Average BMR: 2000 kcal/day; expressed as Cal/m²/hr.
• Factors affecting BMR include height, weight, surface area, sex, age, muscular exertion, and environmental temperature.

Hypothalamic Networks in Feeding Regulation

• Neuropeptidergic networks in the arcuate nucleus regulate appetite.
• Orexigenic (hunger-inducing) neuropeptides: Agouti-related protein (AgRP) and Neuropeptide Y (NPY).
• Anorexigenic (appetite-suppressing) neuropeptides: Pro-opiomelanocortin (POMC) and Cocaine-and-amphetamine-regulated transcript (CART).
• Hypothalamic second-order neurons produce orexigenic peptides (orexin) or anorexigenic factors (oxytocin, TRH, CRH).

Influential Neurotransmitters & Hormones

• Anorexigenic: α-MSH, Leptin, Serotonin, Insulin, CCK, CRH.
• Orexigenic: NPY, AgRP, MCH, Orexins, Endorphins, Cortisol, Ghrelin.
• NPY is the most potent orexigenic peptide, activated by decreased leptin levels.

Role of Leptin in Energy Regulation

• Leptin is a peptide hormone from white adipose tissue signaling energy storage levels.
• Low leptin indicates reduced fat stores, promoting hunger and energy conservation; high leptin signals increased energy expenditure and decreased hunger.
• Genes involved: ob gene (leptin production) and db gene (leptin receptor signaling).

Leptin and Obesity

• Obesity leads to leptin desensitization; weight gain is linked to leptin resistance.
• Leptin resistance causes include disrupted receptor signaling, altered leptin production, and impaired transportation across the blood-brain barrier.
• Mouse models: ob/ob mice (leptin gene mutation) and db/db mice (leptin receptor mutation).

Treatment of Obesity

• Pharmacological:
  • Amphetamines to inhibit feeding.
  • Bupropion (Dopamine and NE reuptake inhibitor) stimulates POMC neurons for satiety.
  • GLP-1 agonists.
  • SGLT2 inhibitors prevent renal glucose reabsorption.
  • Orlistat reduces lipid absorption (lipase inhibitor).
• Surgical options:
  • Gastric bypass, vertical sleeve gastrectomy, and gastric banding.

Inanition, Anorexia, and Cachexia

• Inanition represents the extreme opposite of obesity, indicating a state of starvation or severe weight loss.

This quiz covers the regulation of energy balance, food intake, and body weight with a focus on obesity. It explores concepts such as energy yielding nutrients and the method of calorimetry for determining energy content in foods. Test your understanding of these vital nutrition principles.