Nutrition and Physical Activity: Nutrients, Energy Balance, and Guidelines
Core concepts
Know the six nutrient classes: carbohydrates, proteins, fats, vitamins, minerals, and water. Carbohydrates and fats are primary energy sources; protein supports growth, repair, and enzyme/hormone production. Macronutrients supply energy (carbohydrate 4 kcal/g, protein 4 kcal/g, fat 9 kcal/g); micronutrients (vitamins and minerals) do not supply energy directly. Water is essential for transport, temperature regulation, and metabolism.
Distinguish fat-soluble vitamins (A, D, E, K - stored in body fat, risk of toxicity with excess) from water-soluble vitamins (B complex and C - excess generally excreted, so intake must be regular). Know that fiber aids digestion and that empty-calorie foods provide energy with few nutrients.
Understand energy balance: weight is stable when intake equals expenditure; surplus leads to storage, deficit leads to loss. Physical activity recommendations emphasize aerobic activity for cardiovascular fitness, strength training for muscle and bone, and flexibility for range of motion. Know the difference between moderate and vigorous intensity (the talk test: able to talk but not sing = moderate).
Understand food labels: serving size, calories per serving, and percent daily values. Recognize that nutrient-dense foods deliver more nutrients per calorie than energy-dense, nutrient-poor foods.
Traps
Questions confuse fat-soluble and water-soluble vitamin risks, or ask which nutrient is the body's preferred quick energy source (carbohydrate, especially glucose). Another trap misreads calories per serving versus per package. Watch for claims that a micronutrient supplies energy.
Worked example / rule of thumb
Rule of thumb: 4-4-9. Multiply grams of carbohydrate by 4, protein by 4, and fat by 9, then add. Example: a snack with 20 g carbohydrate, 5 g protein, and 10 g fat = (20×4) + (5×4) + (10×9) = 80 + 20 + 90 = 190 kcal. If the label says two servings per package, double it to 380 kcal for the whole package.
Exam strategy
Always check the serving size before comparing labels or computing calories.