A balanced diet provides adequate nutrients from all food groups in proper proportions, with MyPlate guidance recommending half the plate from fruits and vegetables, plus whole grains and lean proteins. Among well-studied patterns, the Mediterranean diet emphasizes fruits, vegetables, whole grains, fish, olive oil, and nuts while limiting red meat and sweets, and is consistently linked to lower cardiovascular disease and greater longevity. The DASH diet similarly reduces sodium and boosts potassium-rich produce, whole grains, and low-fat dairy, lowering systolic blood pressure by 8-14 mmHg in hypertensives and offering an effect comparable to a single antihypertensive medication, especially when sodium falls below 1500 mg/day. The MIND diet combines Mediterranean and DASH principles with specific brain-healthy foods like leafy greens, berries, nuts, and fish, with cohort studies suggesting a 53% reduction in Alzheimer's risk with strict adherence, though randomized trial evidence remains limited.
Plant-based diets span a spectrum: vegans exclude all animal products and must plan for B12, calcium, iron, omega-3, and zinc; vegetarians (lacto-ovo) include dairy and eggs; pescatarians add fish and seafood. Each lowers cardiovascular risk when well-planned. By contrast, the paleo diet excludes grains, legumes, and dairy, often leading to calcium and vitamin D shortfalls, while the carnivore diet goes further to exclude all plants, risking fiber, vitamin C, vitamin K1, magnesium, and phytochemical deficits over time. The ketogenic diet (under 50 g carbohydrate/day) shifts the body into ketosis within 3-7 days, with the brain eventually deriving roughly 70% of energy from ketones; full keto-adaptation takes 2-6 weeks and is aided by electrolyte repletion. Other named approaches include the four-phase Dukan diet, intermittent fasting and time-restricted eating (which confine intake to 8-10 hour windows or cycle fasting and feeding periods), and the alkaline diet, which falsely claims that food pH alters blood pH, a tightly regulated value around 7.4 regardless of intake. Free sugars, defined as sugars added by manufacturers or present in honey, syrups, juices, and concentrates, are targeted by policy (such as the UK sugar tax) and the WHO because they drive energy overconsumption without satiety.
Therapeutic nutrition tailors patterns to disease. For diabetes, low-GI carbs, fiber, lean proteins, and healthy fats stabilize blood sugar while refined sugars and large portions are limited, with type 1 management centering on carb counting and insulin timing and type 2 emphasizing weight loss and reduced refined carbohydrates. Hypertension responds to sodium restriction (<2300 mg/day, ideally 1500 mg), potassium increases (3500-4700 mg from produce), and weight loss. Heart-healthy approaches, including DASH and Mediterranean patterns, lower LDL and triglycerides while replacing saturated fat with monounsaturated and polyunsaturated sources. NAFLD management relies on 7-10% weight loss, Mediterranean or low-carb patterns, abstention from alcohol, and regular exercise, with coffee consumption (two or more cups/day) associated with reduced fibrosis progression. Gout benefits from reducing purine-rich foods and fructose while increasing low-fat dairy and water; vitamin C supplementation (500 mg/day) modestly lowers urate. PCOS responds to low-GI eating, adequate protein, omega-3 fats, and 5-10% weight loss to restore ovulation, with myo-inositol (4 g/day) showing promise for insulin sensitivity. Hypothyroidism requires adequate but not excessive iodine, plus selenium and zinc, while avoiding soy, calcium, and iron within four hours of levothyroxine. Celiac disease demands strict, lifelong gluten avoidance (wheat, barley, rye, and cross-contaminated oats) with screening for iron, calcium, B12, and folate. SIBO and IBS often respond to low-FODMAP diets that limit fermentable oligosaccharides, disaccharides, monosaccharides, and polyols—lactose, excess fructose, fructans, GOS, and polyols—to reduce bloating and pain. GERD benefits from avoiding trigger foods, eating smaller meals, and elevating the head of bed. CKD requires sodium, potassium, and phosphorus restriction in later stages, with protein moderated to 0.6-0.8 g/kg/day and adequate calories to prevent catabolism.
Malnutrition arises from undernutrition, overnutrition, or imbalances and may lead to stunting, obesity, or specific deficiency syndromes; the short-term BRAT diet (bananas, rice, applesauce, toast) is no longer recommended beyond 24-48 hours for acute diarrhea, with oral rehydration now preferred. Refeeding syndrome is a critical risk when severely malnourished patients (anorexia, chronic alcoholism, post-bariatric) are refed too quickly; insulin surges drive phosphate, potassium, and magnesium into cells, causing hypophosphatemia, cardiac failure, and rhabdomyolysis, so refeeding must start at 5-10 kcal/kg/day with thiamine and electrolyte monitoring. Hypertriglyceridemia is best managed by reducing added sugars and refined carbs, increasing omega-3s (or 2-4 g/day EPA/DHA under medical guidance), limiting alcohol, and replacing saturated fat with unsaturated sources; severe elevations above 500 mg/dL require low-fat diets to prevent pancreatitis. Reverse dieting, used by physique competitors and chronic dieters, gradually raises caloric intake by 50-100 kcal/week after prolonged restriction to restore metabolism without rapid fat regain, though benefits over intuitive eating remain contested.