Macronutrients, Energy Balance, and Nutrition-Related Diseases

Macronutrients: Carbohydrates

• Carbohydrates (CHO) are composed of carbon, hydrogen, and oxygen ($C - H - O$).

• Main function: provide energy ($4 ext{ kcal/g}$ for sugar/starch).

• Dietary fiber: exception, provides $2 ext{ kcal/g}$, not considered truly essential. Recommended minimum is $100-130 ext{ g/day}$.

• Important components of cell membranes and nucleic acids (e.g., RNA).

• Classifications:

  • Simple: Monosaccharides (glucose, fructose, galactose), Disaccharides (lactose, sucrose, maltose).

  • Complex: Oligosaccharides (raffinose, stachyose), Polysaccharides (starch, glycogen, dietary fiber).

• Fate in Body: Glucose (and fructose, with limitations) used directly for energy. Galactose converted to glucose.

• Stored as glycogen in muscle and liver. Excess converted to body fat.

• Brain, blood, and kidney cells require constant glucose supply.

• Insulin: A storage hormone, transports glucose into cells, turns off fat oxidation, helps store amino acids.

• Recommendations:

  • Adults: $45-65\%$ of total energy intake, approx. $200-350 ext{ g/day}$, or $3-5 ext{ g/kg/day}$.

  • Athletes: $5-12 ext{ g/kg/day}$.

• Dietary Fiber:

  • Found naturally in plant foods; functional fiber extracted/produced commercially.

  • Recommendations: $25 ext{ g/day}$ for women, $38 ext{ g/day}$ for men (often under-consumed). $14 ext{ g/1000 ext{ Cal}}$ intake.

  • Health benefits: lowers LDL and total cholesterol, regulates blood sugar, alleviates constipation, may prevent colon cancer, promotes satiety.

Macronutrients: Fats (Lipids)

• Long carbon-hydrogen chain molecules ($14-22 ext{ C}$).

• Contribute to food texture, taste, and aroma. Structural component of cell membranes.

• Precursors to Vitamin D, estrogen, testosterone. Aids fetal/infant vision and CNS development.

• Energy dense: $9 ext{ kcal/g}$. Contributes to satiety.

• Types: Phospholipids, Cholesterol, Triglycerides ($95\%$ of dietary fats).

• Cholesterol: Body makes $2/3$; not an essential nutrient. Critical for cell membranes, brain/nerves, sex hormones, Vitamin D, bile production.

• Fatty Acids:

  • Saturated: Carbons saturated with hydrogens, single bonds, solid at room temperature (animal products, palm/coconut oils). May not increase heart disease risk as previously believed.

  • Unsaturated: Not fully saturated, contain double bonds (monounsaturated or polyunsaturated), liquid at room temperature (plant oils, nuts/seeds, olive oil). Includes Omega 3, 6, 9.

• Hydrogenated Fats: Unsaturated fats made solid by adding hydrogens, can create trans fatty acids (trans fats).

• Recommendations: Choose quality fats, don't fear whole food fats, consume a variety focusing on Omega 3s. Avoid burning/frying fats; store unsaturated fats away from heat, oxygen, sun.

Macronutrients: Protein

• Essential structural component and involved in virtually all biological cell processes.

• Key Functions: Structural (muscles, organs, hemoglobin), Regulatory (hormones), Functional (transporters, enzymes, cell recognition, contractile), Tissue repair and maintenance.

• Amino Acids: Building blocks of proteins.

  • $20$ different amino acids: $9$ essential (indispensable), $11$ non-essential (dispensable).

  • $6$ conditionally indispensable (e.g., arginine, glutamine) during stress.

• Energy: Less preferred source than carbs or fats. Requires stripping nitrogen (excreted as urea, needs extra water).

• Recommendations (DRI): $10-35\%$ of total calories.

  • Sedentary: $0.8 ext{ g/kg/day}$ (e.g., $56 ext{ g/day}$ for $70 ext{ kg}$).

  • Athletes: $1.2-2.0 ext{ g/kg/day}$ (e.g., $84-140 ext{ g/day}$ for $70 ext{ kg}$). Ideally spaced over multiple meals.

• Quality:

  • Complete (High Quality): Contain all essential amino acids (animal sources: fish, meat, eggs, dairy).

  • Incomplete: Deficient in one or more essential amino acids (plant sources). Require combination (complementary proteins) daily for complete synthesis.

Energy Balance

• First Law of Thermodynamics: "Energy can neither be created nor destroyed. It can only change forms." Implies Calories In = Calories Out.

• ATP (Adenosine Triphosphate): Cellular molecule for quick energy access.

• Calories: Unit of measure for energy from food. $1 ext{ calorie} = 1 ext{ kilocalorie (kcal)} = 4.2 ext{ kilojoules (KJ)}$.

• Energy Balance Types:

  • Balanced: Energy intake = need (stable body weight).

  • Positive: Energy intake > need (weight gain; important for growth, pregnancy, recovery).

  • Negative: Energy intake < need (weight loss).

• Atwater Factors (Energy in Foods):

  • CHO: $4 ext{ kcal/g}$

  • Fat: $9 ext{ kcal/g}$

  • Protein: $4 ext{ kcal/g}$

  • Alcohol: $7 ext{ kcal/g}$

• Energy Density: Calories per gram of food (e.g., $10 ext{ potato<br>chips} = 107 ext{ calories} / 20 ext{ grams} = 5.4$). Focus on nutrient density over just energy density.

• Calorie Regulation:

  • Hunger: Unpleasant physical/psychological sensations for food intake.

  • Satiety: Feeling of fullness.

  • Appetite: Desire to eat, pleasant sensation.

• Methods of Energy Expenditure:

  • Basal (Resting) Metabolism (BMR/RMR): $60-70\%$ of total energy. Energy for life-sustaining functions at rest. Influenced minimally in healthy individuals (e.g., $1 ext{ lbs}$ muscle uses $6-10 ext{ kcal/day}$ vs. $1 ext{ lbs}$ fat using $2-4 ext{ kcal/day}$).

    • Quick estimate: Body weight (lbs) $imes<br>11$ (men), $imes<br>10$ (women).

  • Physical Activity: $10-35\%$ of total energy. Energy for muscular work.

    • Equations: $30\%$ of BM (inactive), $50\%$ of BM (average), $70\%$ of BM (active).

  • Dietary Thermogenesis (Thermic Effect of Food): $5-10\%$ of total energy. Energy expended for digestion, absorption, transport, storage of nutrients.

  • Total Energy Needs: BMR + Physical Activity + Dietary Thermogenesis.

Nutrition and Disease

• Physical Inactivity: Leads to visceral fat accumulation, chronic systemic inflammation, insulin resistance, atherosclerosis, and increased risk of Type 2 diabetes, cardiovascular diseases, cancers, dementia, depression.

• Atherosclerosis: Plaque buildup in arteries (LDL cholesterol a factor; HDL regulates LDL storage and promotes excretion).

• Vitamins:

  • Water-soluble: Cannot be stored (except B12), need constant replenishment. Deficiency/excess within weeks/months causes ill effects.

  • Fat-soluble: Can be stored in liver and fat tissue.

  • Deficiencies linked to altered behavior (reduced attention, poor appetite, irritability, depression).

  • Vitamin C: Can reduce cold symptoms and duration.

  • Vitamin D: Facilitates calcium absorption ($80\%$ increase) for strong bones/osteoporosis prevention. Functions as a prohormone combatting chronic inflammation, linked to diabetes, CVD, MS, cancers, rheumatoid arthritis. Regulates insulin secretion/blood glucose.

    • Sources: Few natural foods. Mostly made by skin from sun exposure (D3). Darker skin, indirect sun, SPF reduce production. Best dose: $10-15$ minutes, $2-3$ times/week direct sunlight (can yield $15,000-20,000 ext{ IU}$ naturally). Production stops when stores are full; cannot overdose naturally.

• Minerals:

  • Calcium: Crucial for bone density. Peak density around $30-40$ years. Osteoporosis major concern (women > men), high fracture risk. Sources: dairy, fish, greens, almonds, sun. Influenced by physical inactivity, genetics, menopause, unhealthy practices.

  • Iron: Most widespread nutritional deficiency (oxygen deficient). Symptoms: weakness, fatigue, poor appetite, irritability, increased infection susceptibility. Untreated -> anemia. Vitamin C improves absorption.

    • Sources: Animal sources (liver, beef, fish) more readily absorbed. Plant/egg sources less absorbed (bound by phytates, etc.). Cooking in cast iron increases levels.

  • Sodium: Maintains water balance via sodium-potassium pump. High intake linked to high blood pressure (risk for kidney failure, heart attack, stroke). Not everyone is salt sensitive. UL: $2,300 ext{ mg}$ for adults. Major source: processed foods ($70\%$).

  • Potassium: Increased intake (especially from fruits/vegetables) shown to lower blood pressure. Recommend >5 (ideally $7-8$) servings of fruits and vegetables daily.