Topic 1: Principles of Human Nutrition

The digestive system mechanically and chemically breaks food into small molecules that are absorbed in the small intestine. Specific enzymes act on carbohydrates, proteins and fats.

Basal metabolic rate is the energy the body uses at complete rest. Together with physical activity and the energy used to digest food, it sets total energy expenditure and the kilojoules a person needs each day.

Digestive enzymes are biological catalysts that break large food molecules into small absorbable units. Each enzyme is specific to one substrate and works best at the temperature and pH of its part of the gut.

The gut microbiome is the community of trillions of microbes living in the large intestine. Fed by dietary fibre, it ferments food, makes some vitamins, trains the immune system and is linked to many aspects of health.

Carbohydrates, proteins and lipids are the three macronutrients. They provide energy and raw materials, with each gram of fat releasing roughly twice the kilojoules of carbohydrate or protein.

Malabsorption is the failure to absorb nutrients properly, often from missing enzymes or a damaged gut lining. Lactose intolerance and coeliac disease are common examples with distinct causes and dietary management.

Vitamins and minerals are needed in small amounts but are vital for body processes, while water is the medium for almost every reaction. Deficiencies cause specific, often serious, disorders.

Nutritional needs change across life: pregnancy and infancy demand extra nutrients for growth, adolescence raises energy and iron needs, and older age shifts requirements as activity and absorption change.