30th July 2023

Background

Nutrition refers to the biological process by which an organism utilises food to sustain life. Nutrients are the various components of a diet. Macronutrients form the majority of the diet and hence are the main supply of energy to the body, being grouped into fats, carbohydrates, and protein. Micronutrients are not required in as great amounts, but are still essential, and include vitamins and minerals. Greater detail on micronutrients and their importance in human physiology and disease can be found in the Nutrition and Physiology topic.

‘Good nutrition’ refers to dietary intake which enables a person to appropriately meet their energy demands. ‘Malnutrition’ is whenever the nutritional process falls short of this, including inadequate intake by amount or imbalance, impaired absorption, or due excessive demands. Malnutrition can be of all nutrients, individual nutrients, and also include excessive diet, i.e. obesity.

A technical definition of malnutrition can be given as:

• BMI of less than 18.5
• Unintentional weight loss greater than 10% within the last 3–6 months
• BMI of less than 20 and unintentional weight loss greater than 5% within the last 3–6 months

Malnutrition has the potential to affect every organ system. Common manifestations include reduced muscle and fat mass, which in turn contributes to a state of frailty. It can also lead to reduced cardiac output and respiratory function, and a variety of biochemical abnormalities owing to inadequate intake of particular nutrients. Impaired immune function and delayed wound healing are also frequently seen in malnourished people.

The focus of this topic is on malnutrition. Further information can also be found in the Nutrition and Physiology topic.