Principles of nutrition, physiology, and health

Nutrition connects food intake with the substances that cells need for energy, growth, maintenance and regulation. Carbohydrates are commonly digested to simple sugars, proteins to amino acids, and fats to fatty acids and other products. Digestion makes many food molecules small enough for absorption across the small intestine. Absorbed nutrients enter transport systems and reach tissues. Cellular respiration releases usable energy from nutrients; eating and respiration are connected processes but are not the same process.

A flow chart can show food → digestion → absorption → transport → cellular use. A blockage or impairment at any stage can affect nutritional status even when intake appears adequate.

Carbohydrate and fat supply energy, while protein supports structures, enzymes and tissue repair and can also supply energy. Water supports transport and temperature regulation. Vitamins and minerals have diverse regulatory and structural roles and do not directly provide food energy. Iron is needed for haemoglobin, which carries oxygen in blood. Calcium supports bone structure and other functions. Dietary fibre supports bowel function.

Food contains mixtures of nutrients, so labelling an entire food as only protein or only carbohydrate is usually misleading. Nutrient requirements vary with growth, activity and individual circumstances.

Undernutrition can involve insufficient energy or particular nutrients. Overnutrition can involve excessive energy or particular nutrient intakes over time. A person may have excessive energy intake and inadequate micronutrient intake simultaneously. Long-term dietary patterns can contribute to disease risk, but one meal does not determine health. Dietary disorders require careful language and appropriate professional care; students should analyse evidence rather than diagnose classmates.

Macronutrients and overnutrition, micronutrients and undernutrition, and dietary disorders are possible study contexts, not a compulsory diagnostic checklist.