Basic and Applied Sciences and Nutrition Concepts
Energy and Macronutrients
Carbohydrate and protein supply 4 kcal/g, fat 9 kcal/g, and alcohol 7 kcal/g. Acceptable macronutrient distribution ranges are roughly 45–65% carbohydrate, 20–35% fat, and 10–35% protein. Protein needs rise with training: about 0.8 g/kg/day for sedentary adults, 1.2–2.0 g/kg/day for active adults, and higher for athletes. Keep saturated fat below 10% of energy, minimize trans fat, and target fiber around 25–38 g/day.
Digestion and Metabolism
Carbohydrate digestion begins with salivary amylase; protein with gastric acid and pepsin; fat is emulsified by bile and digested by pancreatic lipase. Most absorption occurs in the small intestine through villi and brush-border enzymes. ATP is produced via the phosphagen system, glycolysis, and oxidative phosphorylation. Glycemic index and load describe blood-glucose response; total diet and portion matter more than a single score.
Hydration and Supplements
Total water intake is about 3.7 L/day for men and 2.7 L/day for women from food and fluid; exercise, heat, and sweat increase needs. Recommend third-party-tested products such as NSF Certified for Sport or Informed Sport. Food first; supplements fill gaps, not replace meals.
Worked Example
An 80 kg client resistance trains four days weekly. Protein target: 1.6–2.2 g/kg = 128–176 g/day. At 2,400 kcal that is reasonable; at 1,600 kcal it competes with carbohydrate for training fuel, so prioritize.
Traps
Mixing kcal/g values; assuming more protein is always better; ignoring total energy; treating “natural” as safe; forgetting caffeine and alcohol in hydration.