Food and Nutrition Sciences
Food and Nutrition Sciences underpins the exam's calculation and physiology items: energy expenditure, macronutrient metabolism, digestion and absorption, and food composition. Expect to convert intake into kilocalories, interpret indirect calorimetry, and explain how nutrient handling changes in disease.
Core rules
- Atwater factors: carbohydrate 4, protein 4, fat 9, alcohol 7 kcal/g; fiber is usually counted at about 2 kcal/g.
- Total energy expenditure = resting energy expenditure (roughly 60-70%) + thermic effect of food (~10%) + physical activity (20-30%).
- Respiratory quotient: 1.0 for pure carbohydrate, ~0.8 for protein, 0.7 for fat, ~0.85 on a mixed diet. An RQ above 1.0 suggests lipogenesis or overfeeding.
- Protein needs are estimated from nitrogen balance: nitrogen intake minus (urinary urea nitrogen + 4 g) captures obligatory losses; protein grams = nitrogen × 6.25.
- Nine amino acids are indispensable; linoleic and alpha-linolenic acid are essential fatty acids.
Worked example
A 24-hour recall provides 250 g carbohydrate, 80 g protein, 70 g fat, and 20 g alcohol. Energy = (250×4) + (80×4) + (70×9) + (20×7) = 1,000 + 320 + 630 + 140 = 2,090 kcal. Fat contributes 630/2,090 = 30.1% of energy, within the acceptable range; alcohol supplies 6.7%. If the same patient had an RQ of 1.05, the interpretation would be net fat synthesis, not fat oxidation.
Traps
Using 4 kcal/g for alcohol, or 9 kcal/g for carbohydrate; treating resting metabolic rate as identical to basal metabolic rate (RMR is measured under less strict conditions); labeling a high RQ as fat oxidation; and reporting nitrogen balance without the 4 g insensible and fecal constant.