Macronutrients

Macronutrients are nutrients required in large amounts for energy and bodily functions. They include protein, carbohydrates, and fat.

Protein

• Functions:
  • Growth and development
  • Tissue repair
  • Enzyme and hormone production
  • Transport of molecules
• Protein composition:
  • Made of amino acids, which are classified as:
    • Essential amino acids (must be obtained from food)
    • Nonessential amino acids (synthesized by the body)
    • Conditionally essential amino acids (required during stress or illness)

Protein quality and bioavailability

• Protein quality depends on amino acid content and digestibility.
• Animal-based proteins (meat, dairy, eggs) contain all essential amino acids.
• Plant-based proteins may lack certain essential amino acids but can be combined to provide a complete protein source.
• Protein digestibility-corrected amino acid score (PDCAAS) is used to evaluate protein quality.

Protein requirements

• General recommendations:
  • 0.8 g per kg of body weight for sedentary adults
  • 1.2–2.0 g per kg of body weight for athletes
• Higher protein intakes may be beneficial for:
  • Strength athletes
  • Endurance athletes in heavy training
  • Individuals in a caloric deficit to maintain lean muscle mass

Concerns about protein intake

• Higher protein intakes are often debated:
  • Some research suggests higher intake benefits muscle repair and growth.
  • Excess protein is metabolized and may increase calcium excretion.
  • Athletes should balance protein intake with carbohydrates and fats for optimal performance.

Protein intake and metabolism

• Optimal protein intake for stimulating muscle protein synthesis ranges from 20 to 48 grams per meal.
• Leucine content plays a key role in muscle protein synthesis.
• Protein needs increase with age due to reduced amino acid sensitivity.
• Excess protein consumption:
  • Surplus protein is broken down, with nitrogen excreted as urea.
  • Remaining components are converted to carbohydrates (via gluconeogenesis) or stored as fat.
  • Studies indicate that high protein intake (up to 2.8 g/kg body weight) does not impair renal function in healthy individuals.

Protein content in foods

• Examples:
  • Chicken breast (3 oz): 25g protein
  • Eggs (1 large): 7g protein
  • Greek yogurt, nonfat (6 oz): 17g protein
  • Black beans (½ cup): 7.5g protein
  • Peanut butter (2 tbsp): 8g protein
  • Tuna (3 oz): 21.5g protein
  • Salmon (3 oz): 17g protein
  • Sirloin steak (3 oz): 26g protein
  • Almonds (¼ cup): 8g protein
  • Pork tenderloin (3 oz): 22.5g protein

Carbohydrates

• Primary function: Serves as the body’s main energy source.
• Not an essential nutrient, but critical for athletic performance.
• Types of carbohydrates:
  • Monosaccharides: Simple sugars (glucose, fructose, galactose).
  • Disaccharides: Composed of two sugar units (sucrose, lactose, maltose).
  • Polysaccharides: Complex carbohydrates, including starch, fiber, and glycogen.

Glycogen storage and energy

• Glycogen:
  • Stored form of glucose in muscle and liver.
  • Muscle glycogen is used for exercise energy.
  • Liver glycogen helps maintain blood sugar levels.
  • The process of glycogen formation is called glycogenesis.

Glycemic index and glycemic load

• Glycemic index (GI) ranks carbohydrates by how quickly they raise blood sugar.
• Glycemic load (GL) accounts for both GI and portion size, making it more accurate for evaluating blood sugar impact.

GI categories

• Low GI (≤55): Apple juice, lentils, yogurt.
• Medium GI (56-69): Brown rice, popcorn, oatmeal.
• High GI (≥70): White bread, potatoes, rice cakes.

• High-GI foods are digested quickly, providing rapid energy.
• Low-GI foods help sustain energy levels and improve insulin sensitivity.

Carbohydrate metabolism and function

• Primary role: Provides energy for athletic performance.
• Types of carbohydrates:
  • Monosaccharides: Single sugar molecules (glucose, fructose, galactose).
  • Disaccharides: Two sugar molecules (sucrose, lactose, maltose).
  • Polysaccharides: Complex carbohydrates (starch, fiber, glycogen).

Carbohydrate requirements for athletes

• Carbohydrates enhance endurance and performance by delaying fatigue.
• High glycogen levels spare protein from being used as fuel, reducing muscle breakdown.
• Carbohydrate recommendations vary by training type:
  • Aerobic endurance athletes (training ≥90 min/day at 70–80% VO₂ max):
    • Require 8–10 g of carbohydrates per kg of body weight per day.
  • Strength, sprint, and skill athletes:
    • Require 5–6 g of carbohydrates per kg of body weight per day.
• Carbohydrate intake post-exercise:
  • Within 30 minutes post-training, 1.5 g/kg of high-GI carbohydrates should be consumed to enhance glycogen resynthesis.
  • Regular carbohydrate intake every 2 hours post-exercise further supports recovery.
• Athletes on low-carbohydrate diets:
  • Adapt by relying more on fat for energy.
  • Performance effects vary based on individual adaptation

Fiber

• Low-fiber diets are associated with:
  • Constipation
  • Heart disease
  • Colon cancer
  • Type 2 diabetes
• Dietary Reference Intakes (DRI) for fiber:
  • Women: 21–29 g/day (varies by age, pregnancy, and lactation)
  • Men: 30–38 g/day (varies by age)
• Good sources of fiber:
  • Fruits and vegetables
  • Nuts and seeds
  • Whole-grain products (e.g., whole-grain bread, oatmeal, popcorn)

Fiber and digestion

• Soluble fiber: Lowers cholesterol and improves blood sugar control.
• Insoluble fiber: Increases stool bulk and supports digestive health.
• High-fiber foods: Whole grains, legumes, fruits, and vegetables.

Fats

• Types of fats:
  • Saturated fats (found in animal products, coconut oil, and palm oil) contain no double bonds.
  • Unsaturated fats (found in nuts, seeds, and oils) are further classified as:
    • Monounsaturated fats (olive oil, peanut oil, avocados)
    • Polyunsaturated fats (soybean oil, safflower oil, fatty fish)
      • Includes essential fatty acids:
        • Omega-3 fatty acids (EPA & DHA): Found in fatty fish like salmon, mackerel, and trout.
        • Omega-6 fatty acids: Found in vegetable oils and nuts.
• Fat intake recommendations:
  • Fat provides ~9 kcal/g, more than carbohydrates and protein.
  • Less than 10% of daily calories should come from saturated fats.
  • Avoid trans fats found in partially hydrogenated oils.

Fat and cholesterol

• Cholesterol functions:
  • Essential for cell membranes and hormone production.
  • High cholesterol levels are linked to atherosclerosis (plaque buildup in arteries).
• Types of cholesterol:
  • LDL (low-density lipoprotein): “Bad” cholesterol; high levels increase heart disease risk.
  • HDL (high-density lipoprotein): “Good” cholesterol; helps remove LDL.
• Classification of LDL, total, and HDL cholesterol
  • LDL cholesterol levels:
    • <100 mg/dL = Optimal
    • 130–159 mg/dL = Borderline high
    • ≥190 mg/dL = Very high
  • Total cholesterol:
    • <200 mg/dL = Desirable
    • ≥240 mg/dL = High
  • HDL cholesterol:
    • <40 mg/dL = Low (increased heart disease risk)
    • ≥60 mg/dL = High (protective against heart disease)

Guidelines for protein, carbohydrates, and fat

• Protein:
  • Choose lean meats, poultry, seafood, eggs, nuts, beans, and soy.
  • Strength athletes: 1.4–1.7 g/kg/day
  • Endurance athletes: 1.0–1.6 g/kg/day
  • Reduced-calorie diet: 1.8–2.7 g/kg/day
• Carbohydrates:
  • Reduce intake of added sugars.
  • Consume whole grains instead of refined grains.
  • Eat a variety of vegetables (dark green, red, orange, legumes).
• Fats & alcohol:
  • <10% of calories should come from saturated fats.
  • Avoid partially hydrogenated oils and trans fats.
  • Limit alcohol intake (1 drink/day for women, 2 drinks/day for men).
  • Avoid alcohol post-exercise, as it impairs muscle recovery.