Food and Nutrition Science — Medical Nutrition Therapy and Sports Nutrition

Medical Nutrition Therapy for Diabetes and Hypertension

Diabetes mellitus — medical nutrition therapy:

Type 1 diabetes:

Absolute insulin deficiency, an autoimmune condition
Nutrition goal: stabilize blood sugar + match insulin dose to carbohydrate intake
Carb counting: 15g = 1 unit
An individualized insulin-to-carbohydrate ratio (ICR)

Type 2 diabetes:

Insulin resistance plus reduced insulin secretion
Nutrition goal: manage blood sugar, lipids, blood pressure, and weight

Principles of a diabetic diet:

Appropriate total energy intake, weight loss if overweight
Carbohydrates: 45–60% of total calories choose foods with a low glycemic index (GI) minimize added sugar
Dietary fiber: 25g/day or more (eases blood-sugar response)
Protein: 15–20%
Fat: under 7% saturated fat, minimize trans fat
Sodium: under 2,300mg
Regular meal timing, no late-night eating

Glycemic Index (GI):

How quickly blood sugar rises relative to pure glucose (100)
Low GI (55 or below): lentils, apples, barley, mixed-grain rice
High GI (70 or above): white rice, white bread, watermelon, potatoes
Glycemic Load (GL) = GI × carbohydrate(g) / 100 — a more practical measure

Medical nutrition therapy for hypertension:

The DASH diet (Dietary Approaches to Stop Hypertension):

Limits sodium + emphasizes foods rich in potassium, calcium, and magnesium
Fruit and vegetables 4–5 servings · low-fat dairy 2–3 servings · whole grains, nuts
Reduces systolic blood pressure by 8–14 mmHg
South Korea’s average sodium intake: 3,500–4,000mg (against a 2,300mg target)

Practical steps to cut sodium:

Limit processed food and eating out
Cook soups and stews with less broth and less salt
Use spices, lemon, or vinegar in place of salt
Check the sodium content per serving on instant noodles or convenience-store food

Medical Nutrition Therapy for Obesity and Kidney Disease

Nutrition therapy for obesity:

Assessing obesity:

BMI (Body Mass Index) = weight(kg) / height(m)² underweight: below 18.5 normal: 18.5–22.9 (Asian criteria) overweight: 23–24.9 / obese: 25 and above
Abdominal obesity: waist circumference of 90cm (men) or 85cm (women) or more
Body-fat percentage: 25% or more (men), 30% or more (women)

Energy balance:

1kg of body weight ≈ about 7,700 kcal of energy
Target of 0.5–1kg loss per week = a daily deficit of 500–750kcal
Very low-calorie diets (VLCD): under 800kcal, requires medical supervision

Weight-loss diet strategies:

Limit saturated fat, sugar, and refined carbohydrates
Maintain satiety with fiber and protein
Intermittent fasting (16:8, 5:2): shows some supporting evidence
The Mediterranean diet: the strongest long-term evidence for weight and cardiovascular benefits

Medical nutrition therapy for kidney disease:

Chronic kidney disease (CKD), by stage:

Staged 1–5 based on GFR (glomerular filtration rate)
Protein: early stages (1–3): 0.6–0.8g/kg/day (moderate restriction) dialysis patients: 1.2–1.4g/kg/day (increased)
Potassium: restricted as GFR declines (3,000mg → 2,000mg) hyperkalemia: risk of cardiac arrhythmia potassium-rich foods to limit: bananas, tomatoes, spinach, potatoes
Phosphorus: dialysis patients: restrict phosphorus (800–1,000mg) watch for phosphate additives in processed foods
Sodium: 2,000mg or below
Fluid: restricted in cases of edema or reduced urine output

Hemodialysis:

Potassium and phosphorus drop sharply after dialysis → protein loss must be replaced
Managing weight gain between dialysis sessions (fluid control)

After kidney transplant:

Immunosuppressants raise the risk of diabetes and hyperlipidemia
Infection risk: avoid raw food (limit high-risk foods)

Nutritional Support for Cancer Patients

Cancer and nutrition:

Cancer cachexia: weight loss, muscle wasting, loss of appetite a systemic inflammatory response, elevated basal metabolism
Malnutrition → more treatment side effects · lower survival rates
Goals of nutritional support: maintain weight, improve treatment tolerance, quality of life

Nutrition during cancer treatment:

Nausea and vomiting: small, frequent meals · cold food · ginger
Oral mucositis: soft food, avoiding acidic food
Taste changes: enhance flavor, use favorite foods
Diarrhea: a low-residue diet, the BRAT diet (banana, rice, applesauce, toast)
Swallowing difficulty: texture-modified food, nutritional drinks

Cancer-prevention diet:

WHO and WCRF recommendations: limit processed meat · red meat no more than 3 times a week minimize alcohol fruit and vegetables at least 5 times a day adequate whole grains and fiber
Maintain a healthy weight: obesity raises the risk of 13 types of cancer
Antioxidants (polyphenols, carotenoids): obtain from food (supplement effects differ)

Ways to support cancer patients’ nutrition:

Oral nutritional supplements (ONS): high-protein, high-calorie drinks
Enteral nutrition: delivered through a feeding tube preferred when gastrointestinal function remains
Total parenteral nutrition (TPN): used when the gut can’t be used

Evidence on nutritional supplements:

High-dose antioxidant supplements: anticancer benefit unproven, some may cause harm
Omega-3: some evidence for easing cachexia
Glutamine: may support mucositis and immune function

Sports Nutrition

Energy systems:

ATP-PC system (phosphagen system): immediate, high-intensity effort under 10 seconds (100m sprint, weightlifting) phosphocreatine rapidly regenerates ATP
Glycolytic system (anaerobic): moderate-to-high intensity for 10 seconds to 2 minutes (400m, 800m) glucose → pyruvate → lactate (without oxygen)
Aerobic (oxidative) system: endurance exercise over 2 minutes (marathon, cycling) oxidizes glucose and fatty acids → produces large amounts of ATP

Energy requirements:

Exercise energy expenditure = METs × body weight(kg) × time
By activity type: marathon > swimming > cycling > weightlifting
Energy availability (EA) = energy intake − exercise energy expenditure EA below 30kcal/kg fat-free mass → exercise-induced amenorrhea, osteoporosis, Relative Energy Deficiency in Sport (RED-S)

Carbohydrate strategy:

Before exercise: a high-carbohydrate meal 1–4 hours prior (rice, pasta)
During exercise (90+ minutes): 30–90g/hour of carbohydrate sports drinks, gels, bananas
Carb loading: for marathon and triathlon athletes 3–4 days before competition: a high-carbohydrate diet plus reduced training volume maximizes liver and muscle glycogen stores
After exercise: carbohydrate plus protein within 30 minutes speeds glycogen replenishment

Protein:

Recommended intake: 0.8g/kg for the general public, 1.2–2.0g/kg for athletes
Resistance training: 1.6–2.2g/kg (to maximize muscle growth)
Timing: 20–40g within 30 minutes of exercise
Muscle protein synthesis: a leucine threshold (1.8–2.5g) matters
Animal protein (a complete set of essential amino acids) vs. plant protein (incomplete — needs combining)

Creatine supplements:

The most evidence-backed sports supplement
Increases phosphocreatine stores → improves high-intensity explosive power
Loading: 5g × 4 times/day × 5 days / maintenance: 3–5g/day
Effective for strength, sprinting, and team sports

Hydration strategy:

2% dehydration → reduced aerobic performance and cognitive function
Before exercise: 400–600ml / during exercise: 150–250ml every 15–20 minutes
Electrolytes (sodium): essential during prolonged exercise (prevents hyponatremia)
Sports drink vs. water: a sports drink is preferable for exercise lasting over 60 minutes

Lifecycle Nutrition

Nutrition during pregnancy:

Additional energy: 340kcal in the second trimester, 452kcal in the third
Folate: 400–600mcg (prevents neural-tube defects) · starting before pregnancy
Iron: 27mg/day (hemoglobin production, fetal iron storage)
DHA/omega-3: fetal brain and retina development
Vitamin D and calcium: fetal skeletal formation
Foods to avoid: alcohol: fetal alcohol spectrum disorder (no known safe amount) high-mercury fish: limit tuna, shark, swordfish listeria risk: raw oysters, smoked fish, soft cheese, unpasteurized juice

Nutrition during lactation:

Additional energy: 500kcal
Iodine: 290mcg (thyroid hormone, brain development)
Water: adequate daily intake (supports milk production)
Caffeine: under 200mg (about 2 cups)
Alcohol: avoid where possible

Infant nutrition:

Breastfeeding: exclusive breastfeeding for 6 months is recommended (WHO)
Starting solid food: 4–6 months (iron-fortified foods first)
Allergy prevention: early, varied exposure to allergens
Cow’s-milk protein allergy: soy-based formula as an alternative
No honey for infants: risk of Clostridium botulinum spores

Nutrition in old age:

Lower energy needs, but nutrient requirements remain — creating a subtle imbalance
Protein: 1.0–1.2g/kg (prevents sarcopenia)
Calcium plus vitamin D: prevents osteoporosis
Vitamin B12: reduced absorption (declining intrinsic factor) · supplementation often needed
Dehydration risk: diminished thirst sensation, ensure adequate water intake
Causes of reduced appetite: medication, functional decline, loneliness, poverty

Frequently Asked Questions

Q. Is a low-carb, high-fat diet that eliminates carbohydrates entirely safe? A. Low-carbohydrate, high-fat (LCHF/ketogenic) diets have evidence of short-term benefits for weight loss and improved blood sugar, and may help with blood-sugar control specifically in type 2 diabetes. But several considerations apply. First, long-term safety data (5+ years) remain limited. Second, excess saturated fat intake can raise LDL cholesterol. Third, patients with kidney disease may find that high protein intake burdens the kidneys. Fourth, athletes may see high-intensity performance decline under carbohydrate restriction. Most nutrition guidance emphasizes that the most balanced approach isn’t eliminating carbohydrates entirely, but reducing refined carbohydrates and added sugar while getting adequate intake from whole grains and vegetables.

Q. Are post-workout protein supplements (protein shakes) really necessary? A. Protein supplements are a convenient option but aren’t strictly necessary. For a typical adult pursuing resistance training, 1.6–1.8g/kg of protein can be adequately obtained from food (chicken breast, eggs, tofu, fish, milk). Supplements are useful when it’s hard to hit protein targets through meals alone — due to time constraints or reduced appetite — when a rapid protein supply is needed right after exercise, or when food intake is limited during a calorie-restricted weight-loss phase. Whey protein is high in essential amino acids, particularly leucine, which strongly stimulates muscle protein synthesis. The idea that it burdens the kidneys, however, is an unsupported concern for people with normal kidney function.