Nutrition Basics: A Complete Guide to Healthy Eating for Beginners

Macronutrient Biochemistry and Energy Pathways

Nutrition fundamentals begin with understanding how your body processes macronutrients. Each macronutrient follows distinct metabolic pathways—glycolysis for carbohydrates, beta-oxidation for fats, and amino acid catabolism for proteins.

Carbohydrates: The Primary Fuel Source

Caloric density: 4 calories per gram. Carbohydrates are rapidly converted to glucose, which enters glycolysis (10-step pathway) producing ATP (cellular energy). Excess carbohydrates are stored as glycogen in liver (~120g) and muscle (~400g).

• Simple carbs (glucose, fructose, sucrose): Rapid absorption; quickly raise blood glucose; best immediately post-workout
• Complex carbs (starches, fiber): Slower absorption; sustained energy; 30-50g daily fiber optimal for gut health
• Endurance athletes need: 6-10g carbohydrate per kg body weight daily for glycogen repletion

Proteins: Building Blocks and Signaling

Caloric density: 4 calories per gram. Proteins are digested into 20 amino acids, 9 of which are essential (cannot be synthesized). Amino acids are incorporated into muscle tissue, hormones, enzymes, and immunoglobulins.

• PDCAAS (Protein Digestibility-Corrected Amino Acid Score): Measures protein quality. Egg score 1.0 (perfect); whey 1.0; beef 0.92; soy 0.91; pea 0.72; complete amino acid profile required
• Daily requirement: 0.8g per kg body weight (RDA); 1.0-1.2g/kg for muscle building; 1.2-2.0g/kg for athletes in strength training
• Thermic effect: Protein requires 20-30% of calories consumed for digestion (TEF), higher than carbs (5-10%) or fat (0-3%)

Fats: Hormone Production and Vitamin Absorption

Caloric density: 9 calories per gram (highest). Fats are hydrolyzed into glycerol and fatty acids, then undergo beta-oxidation producing acetyl-CoA for ATP synthesis. Essential fatty acids (omega-3 and omega-6) cannot be synthesized.

• Minimum intake: 20% of total calories to support hormone production (testosterone, estrogen, cortisol synthesis require cholesterol)
• Omega-3 to Omega-6 ratio: Optimal ~1:4; typical Western diet ~1:20 (pro-inflammatory)
• Fat-soluble vitamins: A, D, E, K absorption requires dietary fat; deficiency symptoms include vision problems, bone disease

Macronutrient Ratios and Individual Variation

Micronutrient Bioavailability and Absorption Factors

Understanding Bioavailability

Bioavailability is the percentage of ingested nutrient that is absorbed and available for physiological use. Two identical nutrient amounts from different sources yield different absorption rates due to food matrix, compound form, and individual factors.

Phytic Acid and Mineral Absorption

Phytic acid (inositol hexaphosphate) present in legumes, grains, and nuts binds minerals, reducing absorption 20-60% depending on mineral and food type. Processing reduces phytic acid:

• Soaking legumes 12 hours: Reduces phytic acid 30-50%
• Sprouting: Reduces phytic acid 50-90% and increases bioavailability of iron, zinc, magnesium
• Fermentation: Reduces phytic acid 20-70% and increases amino acid availability
• Cooking: Minimal effect (5-15% reduction); doesn't significantly improve bioavailability

Vitamin and Mineral Bioavailability Examples

Practical Nutrition Application by Goal

For Muscle Gain (Hypertrophy)

• Caloric surplus: 300-500 calories above maintenance
• Protein: 0.8-1.0g per pound body weight; minimum 2.5-3.0g leucine per meal (triggers mTOR)
• Carbohydrates: 4-5g per kg body weight; timing pre and post-workout optimizes glycogen repletion and growth hormone
• Expected rate: 0.5-1 lb lean mass gain per week with progressive resistance training

For Fat Loss (Cutting)

• Caloric deficit: 300-500 calories below maintenance (aggressive deficits dysregulate hormones)
• Protein: 1.0-1.2g per pound body weight; higher protein during deficit prevents muscle loss and improves satiety
• Fiber: 30-40g daily; increases satiety signals and improves body composition outcomes
• Expected rate: 1-2 lb fat loss per week; faster rate indicates muscle loss

For Endurance Performance

• Carbohydrates: 6-10g per kg body weight daily; 60-90g per hour during events >2 hours
• Protein: 1.2-2.0g per kg body weight; supports muscle repair post-endurance activity
• Fat: 1-1.5g per kg; supports hormone balance and reduces inflammation
• Hydration: 500-1,000 mL per hour depending on sweat rate and environmental conditions

Budget-Friendly Nutrient-Dense Food Options

Budget meal example: 1 cup oats ($0.05) + 2 eggs ($0.40) + banana ($0.20) = ~$0.65 for 20g protein and 400 calories

Research Citations

• Appetite Journal: Satiation and protein thermic effect (2019)
• American Journal of Clinical Nutrition: Bioavailability of plant-based nutrients (2020)
• Journal of Clinical Investigation: Macronutrient metabolism pathways (2021)
• Nutrients: Meta-analysis of protein quality scoring systems (2020)