Updating guides…
Covers macronutrients and micronutrients, their functions and sources, the Eatwell Guide, and how energy needs change across life stages.
Macronutrients are needed in large amounts and provide the body with energy. Carbohydrates — found in bread, pasta, rice and potatoes – are the body's main energy source. Starch is a complex carbohydrate that releases energy steadily, while sugars provide quick energy. Fat is the most concentrated energy source at around 9kcal per gram (compared to 4kcal per gram for carbohydrate and protein), and also insulates the body and protects organs. Protein, found in meat, fish, eggs, beans and dairy, is mainly used for growth and repair of body cells, though it can be used for energy if other sources are lacking. Proteins are made of amino acids; some are described as high biological value (HBV) because they contain all the essential amino acids the body cannot make itself, while low biological value (LBV) proteins are missing one or more.
Micronutrients are needed in much smaller amounts but are still essential. Vitamin A supports vision and skin health and is found in liver, eggs and orange vegetables. Vitamin C, found in citrus fruits and peppers, supports the immune system and helps the body absorb iron, but it is easily destroyed by heat and dissolves in cooking water. Vitamin D helps the body absorb calcium and is made in the skin from sunlight, as well as being found in oily fish and eggs. B vitamins release energy from food. Key minerals include calcium (bones and teeth), iron (making haemoglobin to carry oxygen in the blood) and sodium (fluid balance, though excess sodium is linked to high blood pressure). Dietary fibre (also called non-starch polysaccharide or NSP) is not fully digested but is essential for gut health, and water makes up around 60% of the body and is vital for almost every bodily process.
The Eatwell Guide is the UK government's model for a healthy, balanced diet. It shows that just over a third of the plate should be fruit and vegetables, and just over a third should be starchy carbohydrates (ideally wholegrain). Smaller sections are given to protein foods (meat, fish, eggs, beans and pulses), dairy and alternatives, and a small amount of unsaturated oils and spreads. Foods high in fat, salt and sugar should be eaten less often and in small amounts. The guide also recommends drinking 6 to 8 glasses of fluid a day.
Energy and nutrient needs change throughout life. Babies and young children need proportionally more energy and calcium and vitamin D for rapid growth and bone development. Teenagers have increased needs during growth spurts, and teenage girls need more iron to replace losses during menstruation. Adults generally need a stable, balanced diet to maintain a healthy weight, while energy needs often reduce slightly in older age as activity levels and muscle mass decrease, although protein, calcium and vitamin D remain important for maintaining bone and muscle strength. Pregnant women need extra folic acid, particularly in early pregnancy, to reduce the risk of neural tube defects, plus additional iron and vitamin D.