Nutrition and health: physiology, therapeutic and preventive diets, public health nutrition
Domain 3 connects nutrient intake to physiological outcomes and to concrete diet plans for groups and patients. Expected of you: naming a physiological reference range, adapting a diet to a diagnosis, and evaluating a public-health measure without overstating the evidence.
Physiological anchors
Fasting blood glucose is roughly 70–110 mg/dL (3.9–6.1 mmol/L); insulin from pancreatic β-cells lowers it, glucagon from α-cells raises it; HbA1c reflects the previous 8–12 weeks. Office blood pressure of 140/90 mmHg or above is classified as hypertension. BMI = kg/m², with WHO cut-offs of 18.5 (underweight), 25 (overweight) and 30 (obesity); waist circumference of ≥94 cm in men and ≥80 cm in women signals additional risk independent of BMI.
Special diets you should be able to justify
- Diabetes mellitus: carbohydrate counting in bread units (BE = 12 g carbohydrate) or carbohydrate units (KE = 10 g), glycaemic index, high fibre, favourable fat pattern.
- Coeliac disease: lifelong strict gluten-free diet avoiding wheat, rye, barley and spelt; oats only from certified gluten-free production. It is autoimmune, not an allergy.
- Lactose intolerance: lactase deficiency; tolerance is dose-dependent, hard cheese is usually tolerated.
- Phenylketonuria: phenylalanine restriction; aspartame is a phenylalanine source and must be avoided.
- Chronic kidney disease: limited protein, phosphate and potassium.
- Vegetarian and vegan diets: critical nutrients are vitamin B12 (supplementation essential in vegan diets), iron (non-haem, absorption improved by vitamin C), omega-3 (ALA conversion to EPA/DHA is poor), calcium and iodine.
- Pregnancy: 400 µg folic acid before conception and in early pregnancy, adequate iodine, no alcohol, avoidance of listeria and toxoplasma risks.
Public health
DGE ten rules, WHO salt target below 5 g/day, and the German reduction and innovation strategy for sugar, fats and salt in processed foods (for example soft drinks and bread) are the reference points for evaluation tasks.
Worked example
A patient is 1.72 m tall and weighs 92 kg. BMI = 92/1.72² = 31.1, i.e. obesity grade I. A realistic initial target is 5–10 % weight loss, so 4.6–9.2 kg. With a daily deficit of 500 kcal, roughly 0.5 kg per week is expected; at about 7 000 kcal per kg of body fat this takes around 10–18 weeks, which makes the plan plausible and checkable.
Traps
- Reading a cohort correlation as proof of causation.
- Using BMI alone for muscular athletes or older adults.
- Presenting a gluten-free diet as generally healthier.
- Mixing BE (12 g) and KE (10 g) carbohydrate.