Nutrition is fuel, signaling, and substrate for the body's systems. Protein needs scale with activity and age: roughly \(0.8\ \text{g/kg}\) minimum for adults, and \(1.2\)–\(2.0\ \text{g/kg}\) for active or aging adults to protect muscle and bone. Complete proteins (meat, eggs, dairy, soy, quinoa) supply all essential amino acids. Carbohydrates differ in their speed of digestion: simple carbs spike blood sugar quickly, while complex carbs from whole grains and legumes release it steadily, as measured by the glycemic index. Fats are not interchangeable: unsaturated fats (olive oil, nuts) tend to be liquid and support cardiovascular health, saturated fats (butter, lard) are typically solid, and industrial trans fats are linked to heart disease and largely banned. Added sugar is a particular concern—linked to obesity, diabetes, cardiovascular disease, and dental decay—and the WHO recommends keeping it below 10% of daily calories, ideally below 5%.
The gut microbiome—the community of microbes in the digestive tract—influences immunity, mood, and metabolism. Fiber supports digestion, blood sugar control, satiety, and microbial diversity; vegetables, fruits, legumes, whole grains, and fermented foods all feed a diverse microbiota. Prebiotics (onions, garlic, oats) feed beneficial bacteria, while probiotics (yogurt, kefir, kimchi) add live organisms. The Mediterranean diet—rich in vegetables, olive oil, fish, nuts, and whole grains—is consistently associated with reduced cardiovascular disease, dementia, and all-cause mortality. Intermittent fasting and time-restricted eating compress eating into a daily window (often 8–10 hours) and can improve metabolic markers for some people, though results vary.
How you eat matters as much as what you eat. Hydration supports cognition, energy, joint health, and kidney function—roughly 2–3 liters daily for adults, more with exercise or heat, with thirst as a reasonable guide. Vitamin D supports bone health, immune function, and mood; omega-3 fatty acids (EPA and DHA from fatty fish, walnuts, flaxseed, chia) are anti-inflammatory and support brain and heart health. Mindful eating—slowing down, attending to flavor, texture, and satiety cues—takes advantage of the fact that fullness signals take time to register, and intuitive eating replaces rigid rules with attention to internal hunger and fullness. Meal timing affects hunger, energy, sleep, and metabolic health; breakfast matters for many but is not universally required, and quality typically beats timing.