Therapeutic diets: principles, modifying the normal diet and diet calculations
A therapeutic diet is the normal diet modified in texture, energy, nutrients, fluid or meal pattern to treat a disease. Start every plan from ideal body weight.
Objectives and principles
- Objectives: keep up or restore good nutritional status; correct deficiencies; rest the diseased organ; adjust to the body's ability to digest and use food; bring weight towards normal; prevent complications.
- Base every therapeutic diet on the normal balanced diet and change only what the disease needs.
- Keep it close to the patient's usual food habits, religion, likes and budget, so she will follow it at home.
- Meet the RDA for all nutrients that are not being restricted.
- Use simple, practical recipes and household measures (cups, katoris, chapatis).
- Review often: change the diet as the patient improves or worsens.
Ways to modify the normal diet
| What is changed | How | Used in |
|---|---|---|
| Consistency (texture) | Clear liquid → full liquid → soft → normal | After surgery, fever, chewing or swallowing problems |
| Energy | High-calorie or low-calorie | High: TB, fever, underweight. Low: obesity |
| Protein | High-protein or low-protein | High: burns, TB, hepatitis. Low: kidney failure before dialysis |
| Fat | Low-fat | Gallstones, pancreatitis, fat malabsorption |
| Carbohydrate | Controlled amount, low glycaemic index | Diabetes |
| Fibre or residue | High-fibre or low-residue | High: constipation. Low: diarrhoea, flare of ulcerative colitis |
| Sodium | Salt restricted | Hypertension, oedema, ascites, kidney disease |
| Fluid | Increased or restricted | More: fever, diarrhoea, kidney stones. Less: oliguric kidney failure, heart failure |
| Specific food omitted | Gluten-free, lactose-free | Celiac disease, lactose intolerance |
| Meal pattern and flavour | Small frequent meals; bland, non-irritating food | Peptic ulcer, diabetes on insulin, typhoid, cancer |
Energy requirement in kcal per kg ideal body weight (adults)
| Activity | Overweight | Normal weight | Underweight |
|---|---|---|---|
| Sedentary | 20-25 | 30 | 35 |
| Moderate | 30 | 35 | 40 |
| Heavy | 35 | 40 | 45-50 |
Worked example 1: ideal body weight and BMI
Mrs. Lakshmi is 45 years old, 160 cm tall and weighs 72 kg. Find her BMI and her ideal body weight (IBW) by Broca's index and by the BMI method.
- Height in metres = 1.60 m, so height² = 1.60 × 1.60 = 2.56 m².
- BMI = weight ÷ height² = 72 ÷ 2.56 = 28.1 kg/m² (rounded to one decimal). This is obese by the Asian Indian cut-off (25 or more).
- Broca's index: IBW = height (cm) − 100 = 160 − 100 = 60 kg.
- BMI method: IBW = target BMI × height². Using a target BMI of 22: 22 × 2.56 = 56.3 kg, about 56 kg.
- Excess weight = 72 − 60 = 12 kg (Broca's) or 72 − 56 = 16 kg (BMI method).
BMI 28.1 kg/m² (obese). IBW is 60 kg by Broca's index and about 56 kg by the BMI method. Some books reduce Broca's value by 10-15%; use the method your teacher uses and name it.
Worked example 2: energy and macronutrients in grams
Mrs. Lakshmi (IBW 60 kg by Broca's index) is sedentary and overweight. Plan her energy, protein (1 g/kg IBW), fat (30% of energy) and carbohydrate (the rest) in grams.
- Energy: sedentary and overweight = 20-25 kcal/kg IBW. Take 25: 25 × 60 = 1,500 kcal.
- Protein: 1 g × 60 kg = 60 g. Energy from protein = 60 × 4 = 240 kcal, which is 240 ÷ 1,500 = 16%.
- Fat: 30% of 1,500 = 450 kcal. Grams = 450 ÷ 9 = 50 g.
- Carbohydrate: 1,500 − 240 − 450 = 810 kcal. Grams = 810 ÷ 4 = 202.5, rounded to 203 g (54% of energy).
- Check: (203 × 4) + (60 × 4) + (50 × 9) = 812 + 240 + 450 = 1,502 kcal, about 1,500. Grams are rounded to the nearest whole number.
About 1,500 kcal a day: protein 60 g (16%), fat 50 g (30%), carbohydrate 203 g (54%).
Before writing any diet chart, weigh and measure the patient, work out IBW and energy, then split energy into grams of protein, fat and carbohydrate. The kitchen can only cook what is written in grams and household measures.
2 marks: “What is a therapeutic diet?” A normal balanced diet modified in texture, energy, nutrients, fluid or meal pattern to treat or manage a disease.
5 marks: “Calculate the ideal body weight of a woman 155 cm tall by Broca's index.” IBW = height (cm) − 100 = 155 − 100 = 55 kg. State the formula, show the working and write the unit.
10 marks: “Explain the principles of therapeutic diets and the ways in which a normal diet is modified.” Define, give objectives and principles, then explain modification of consistency, energy, protein, fat, carbohydrate, fibre, sodium, fluid, specific foods and meal pattern with one disease each.
Modify by C-E-N-F-F-S-M: Consistency, Energy, Nutrients, Fibre, Fluid, Specific foods, Meal pattern.