Diet, Nutrition and Health — Diet-Related Disease

The Link Between Diet and Health

What you eat does not only affect your weight — it shapes your long-term risk of several serious conditions. The written paper expects you to explain these relationships as cause-and-effect chains, not just lists. For every condition below, you need to know: which dietary factors increase the risk, what happens in the body as a result, and what dietary changes reduce the risk. Starting with a clear chain — “high saturated fat intake raises LDL cholesterol, which builds up in artery walls, narrowing them, which raises the risk of heart attack” — is far more valuable than a list of “foods to avoid”.

Obesity

Obesity results from sustained positive energy balance — eating more calories than the body uses — so the excess energy is stored as body fat. Dietary risk factors include: a diet high in energy-dense foods (those rich in fat and/or free sugars); large portion sizes; frequent consumption of processed snack foods, fast food and sugary drinks; and low intake of fibre (which promotes satiety). Obesity raises the risk of type 2 diabetes, coronary heart disease, certain cancers, osteoarthritis and mental health difficulties. Dietary modifications to prevent or reduce obesity: reduce energy-dense foods; increase fibre (promotes fullness); increase fruit and vegetables; choose leaner cooking methods (grill or steam rather than deep-fry); reduce alcohol (which is energy-dense but nutrient-poor); control portion sizes.

Cardiovascular Health — CHD and High Blood Pressure

Coronary heart disease (CHD) develops when the coronary arteries supplying the heart become narrowed or blocked. The key dietary chain is: a high intake of saturated fats raises the level of LDL (“bad”) cholesterol in the blood. Over time, LDL cholesterol deposits form plaques on the artery walls (a process called atherosclerosis), narrowing the arteries. A narrowed coronary artery reduces blood flow to the heart, which can cause angina (chest pain) or, if a clot blocks the artery completely, a heart attack.

Hypertension (high blood pressure) is independently linked to a high sodium (salt) intake. Excess salt causes the body to retain water, increasing blood volume and pressure against artery walls. High blood pressure damages artery walls, speeding up atherosclerosis and raising the risk of stroke and heart failure. The maximum recommended adult intake is 6 g of salt (2.4 g sodium) per day; most UK adults exceed this because processed foods, bread and ready meals are the main contributors.

Bone Health — Rickets and Osteoporosis

Bones need calcium and vitamin D to develop and stay strong. Without adequate calcium, the body draws calcium from bones to maintain blood levels, gradually weakening them. Without vitamin D, calcium cannot be absorbed from the gut, so even a calcium-rich diet does not fully protect bones if vitamin D is deficient.

• Rickets (in children) — caused by deficiency of vitamin D and/or calcium. The leg bones soften and bow outwards because they cannot mineralise properly. Dietary sources of vitamin D include oily fish, eggs and fortified foods; sunlight exposure also triggers skin synthesis. Risk groups: children in the UK who have limited sun exposure, especially in winter.
• Osteoporosis (in adults) — gradual loss of bone density, making bones fragile and prone to fracture. Risk factors include a long-term low-calcium diet, vitamin D deficiency, low oestrogen (after the menopause in women), smoking and physical inactivity. Peak bone mass is reached in the early twenties, so calcium and vitamin D intake during childhood and adolescence directly affects long-term osteoporosis risk.

Dental Health

Tooth decay (dental caries) occurs when bacteria in the mouth ferment sugars to produce acids, which dissolve tooth enamel. Frequent consumption of free sugars — particularly between meals, when saliva flow is lower — increases the time teeth are exposed to acid attack. Sugary drinks, sweets, biscuits, cakes and fruit juices are the main culprits. Fluoride strengthens tooth enamel and increases its resistance to acid, which is why fluoridated water and fluoride toothpaste are public health measures. Calcium and phosphorus in dairy products help remineralise enamel. Reducing the frequency and amount of free sugar consumed is the most effective dietary strategy to protect dental health.

Iron-Deficiency Anaemia

Iron-deficiency anaemia develops when the body does not have enough iron to make adequate haemoglobin. Haemoglobin is the protein in red blood cells that carries oxygen to every tissue; when levels are low, the body cannot supply enough oxygen, causing tiredness, pale skin, breathlessness and poor concentration. Risk groups: teenage girls and adult women (menstrual losses); pregnant women (iron demand rises to support the fetus and placenta); young children (rapid growth increases demand); and people following vegetarian or vegan diets (plant sources of iron are less well absorbed). Dietary strategies: eat iron-rich foods (red meat, liver, oily fish, fortified cereals, lentils, dark green vegetables); eat these alongside vitamin C (orange juice, pepper, tomato) to enhance non-haem iron absorption; avoid drinking tea with meals (tannins in tea inhibit iron absorption).

Type 2 Diabetes

Type 2 diabetes occurs when the body becomes resistant to insulin or cannot produce enough insulin to keep blood glucose at a normal level. After eating, blood glucose rises; insulin is released by the pancreas to move glucose into cells for energy. In type 2 diabetes, cells become less responsive to insulin (insulin resistance), and blood glucose remains elevated. Over time, high blood glucose damages blood vessels and nerves, increasing the risk of heart disease, kidney failure, blindness and amputations.

The main dietary risk factors for type 2 diabetes are: obesity (excess body fat, especially around the abdomen, is strongly associated with insulin resistance); a high intake of refined carbohydrates and free sugars (which cause rapid spikes in blood glucose, repeatedly demanding high insulin output); and low dietary fibre intake (fibre slows glucose absorption, reducing blood glucose spikes). Dietary management after diagnosis: reduce free sugars and refined carbohydrates; choose low-glycaemic-index foods (wholegrain bread, oats, lentils, pulses); increase dietary fibre; control portion sizes; lose weight if overweight to improve insulin sensitivity.