Diet and Disease Prevention

What You Eat Is Your Most Powerful Medicine

In 2023, researchers analysing data from nearly 200,000 adults found that ultra-processed food now accounts for more than half of all calories consumed in the average British diet. That figure matters because ultra-processed food isn't just nutritionally empty. It actively disrupts the biological systems that protect against disease — raising inflammation, destabilising blood sugar, damaging gut microbiome diversity, and accelerating cellular ageing. The gap between what most people eat and what their biology requires is one of the largest and most consequential mismatches in modern health.

What makes this particularly striking is that we now understand the mechanisms in real detail. This isn't "eat your vegetables" advice dressed up in scientific language. We know which specific compounds in which specific foods activate which pathways — anti-inflammatory, antioxidant, insulin-sensitising — and we know how quickly those effects show up in measurable biomarkers. Diet is not a vague background factor in disease risk. For chronic disease, it is often the primary one.

Diet & Disease Prevention

What the Evidence Actually Says — Disease by Disease

Generic dietary advice is everywhere. What's harder to find is the specific evidence linking particular foods and patterns to particular diseases. This is what the research actually shows — by condition.

Heart disease & stroke

Leading cause of death in the UK

PROTECT WITH

Extra-virgin olive oil (PREDIMED: 30% fewer events) · oily fish 2–3×/week · legumes daily · whole grains · nuts · leafy greens · berries

AVOID

Trans fats · processed meat · sugary drinks · excessive sodium · refined carbohydrates

The Mediterranean dietary pattern reduces cardiovascular mortality by roughly 25–30% in large randomised trials — a larger effect than many medications.

Type 2 diabetes

Affects 4.5 million people in the UK — largely preventable

PROTECT WITH

Legumes · whole grains · leafy greens · vinegar with meals (blunts glucose spike) · time-restricted eating · weight loss of 5–10% body weight

AVOID

Sugary drinks (strongest single dietary risk factor) · refined carbohydrates · ultra-processed food · late-night eating

The DiRECT trial showed ~50% remission rate with structured dietary weight loss — not medication. Pre-diabetes is fully reversible with diet and exercise in most cases.

Cancer

Diet is estimated to account for 10–20% of cancer risk

PROTECT WITH

High-fibre diet (30g+ daily reduces colorectal cancer risk significantly) · cruciferous vegetables (broccoli, kale, Brussels sprouts — sulforaphane) · berries · green tea · maintaining healthy weight

AVOID

Processed meat (WHO Group 1 carcinogen — 18% higher colorectal cancer risk per 50g daily) · alcohol (causes 7 types of cancer) · excess body fat · ultra-processed food

Alcohol causes cancer at any level of consumption — there is no safe threshold for cancer risk. This is often underappreciated.

Dementia & cognitive decline

Up to 40% of cases are attributable to modifiable factors

PROTECT WITH

MIND diet (leafy greens daily + berries 2×/week + oily fish + olive oil + nuts + legumes) · adequate B12 and folate · extra-virgin olive oil · dark chocolate (70%+)

AVOID

Alcohol (directly neurotoxic, shrinks brain volume) · ultra-processed food · elevated homocysteine (correct with B vitamins if high) · high saturated fat from processed sources

The MIND diet reduced Alzheimer's risk by 53% at high adherence and 35% at moderate adherence — more than any other dietary pattern studied for brain health.

Osteoporosis & fracture risk

Affects 3.5 million people in the UK — bone loss starts in your 40s

PROTECT WITH

Calcium from food (dairy, sardines with bones, fortified plant milks, leafy greens) · vitamin D (test and supplement if deficient) · adequate protein · magnesium · resistance training

AVOID

Very high sodium (increases calcium excretion) · excessive alcohol · smoking · crash dieting / very low calorie intake · sedentary lifestyle

Calcium supplements without vitamin D have limited evidence and may slightly raise cardiovascular risk — food sources are preferable wherever possible.

Bowel cancer

2nd most common cause of cancer death in the UK — highly diet-responsive

PROTECT WITH

High fibre (30g+ daily — wholegrains, legumes, vegetables) · garlic and onions (allicin) · calcium from food · resistant starch · regular bowel screening from age 50

AVOID

Processed meat (strongest single dietary risk factor for bowel cancer) · red meat more than 3×/week · alcohol · low-fibre diet · excess body weight

💡 The same foods appear across every disease category. Extra-virgin olive oil, oily fish, legumes, leafy greens, berries, and whole grains protect against cardiovascular disease, diabetes, dementia, and cancer simultaneously — which is why overall dietary pattern matters more than any single food or nutrient.

How food drives inflammation — and why that matters after 50

The central mechanism linking diet to chronic disease is inflammaging — a term researchers use for the low-grade, chronic inflammation that accumulates with age and sits at the root of cardiovascular disease, type 2 diabetes, dementia, and several cancers. Poor diet is one of its main drivers. Refined carbohydrates and added sugars cause repeated blood glucose spikes, which trigger inflammatory signalling. Trans fats — still present in many processed foods despite partial bans — directly impair endothelial function, the protective lining of blood vessels. Processed meats generate compounds during digestion that promote colorectal inflammation. The cumulative effect of eating this way for years is not subtle.

The PREDIMED trial — one of the most important dietary studies ever conducted — put this in sharp relief. It randomised over 7,000 adults at cardiovascular risk to either a Mediterranean diet or a low-fat control diet and tracked them for five years. The Mediterranean diet group had a 30% reduction in major cardiovascular events. The trial was stopped early because the benefit was so clear it was considered unethical to continue withholding the intervention from the control group. That is not a marginal finding. It is the kind of effect size you see from pharmaceutical interventions — achieved entirely through food.

What the evidence actually says about specific foods

Fibre is probably the single most underconsumed nutrient in the Western diet, and the consequences are measurable. Most adults eat around 18g per day; the recommended minimum is 30g. Fibre feeds the gut microbiome, which in turn produces short-chain fatty acids that reduce systemic inflammation, regulate immune function, and protect the gut lining. Studies consistently find that higher fibre intake is associated with lower rates of colorectal cancer, cardiovascular disease, and type 2 diabetes — not through one mechanism but through several operating simultaneously.

Omega-3 fatty acids, found in oily fish, walnuts, and flaxseeds, reduce the production of pro-inflammatory eicosanoids and lower circulating triglycerides. The evidence for their effect on cardiovascular risk is strong enough that some cardiologists use prescription-strength omega-3 preparations. For most people, two to three portions of oily fish per week achieves a meaningful effect at no cost beyond the food itself.

Cruciferous vegetables — broccoli, kale, Brussels sprouts, cauliflower — contain sulforaphane, a compound that activates the Nrf2 pathway, one of the body's main antioxidant defence systems. Sulforaphane has shown anti-cancer properties in cell and animal studies; human data is more limited but consistent in direction. The mechanism is real and biologically plausible. Eating these vegetables regularly is not a marginal lifestyle choice — it is activating a specific protective system.

The blood sugar problem most people don't know they have

Insulin resistance develops slowly, quietly, and usually without symptoms until it's well established. It is driven primarily by repeated large glucose loads — the kind produced by refined carbohydrates, sugary drinks, and ultra-processed foods — combined with insufficient physical activity. Once established, insulin resistance raises the risk of type 2 diabetes, accelerates cardiovascular ageing, impairs cognitive function, and promotes fat accumulation in the liver and around abdominal organs. The Nurses' Health Study, which followed over 120,000 women for decades, found that dietary patterns characterised by high glycaemic load were among the strongest modifiable predictors of type 2 diabetes risk.

The practical implication is not that carbohydrates are bad. Complex carbohydrates — oats, legumes, whole grains, root vegetables — release glucose slowly and come packaged with fibre, vitamins, and minerals. The problem is the refined versions: white bread, white rice, breakfast cereals, biscuits, and sweetened drinks, which deliver glucose rapidly with almost nothing else. Swapping refined for complex carbohydrates is one of the highest-leverage dietary changes most people can make, and it doesn't require calorie counting or dramatic restriction.

'The evidence on diet and disease isn't about eating perfectly. It's about understanding which changes move the needle most — and making those first.'

Foods to Avoid or Limit

It used to be thought that processed food was simply unhealthy because of what it contained — too much sugar, salt, and fat. The emerging picture is more troubling. Ultra-processed food appears to cause harm beyond its nutritional composition. Large prospective studies have found that high UPF consumption is associated with increased risk of cardiovascular disease, depression, type 2 diabetes, and all-cause mortality — even after controlling for sugar, salt, fat, and calorie content. The leading hypotheses involve food additives, emulsifiers that disrupt the gut lining, and hyper-palatability engineering that overrides normal satiety signals. The science is still developing, but the direction is consistent and the effect sizes are not small.

Personalisation — what it means in practice

One important caveat to all of this: individual responses to diet vary more than average statistics suggest. Continuous glucose monitors have shown that two people eating identical meals can have very different blood sugar responses, depending on gut microbiome composition, sleep quality, stress levels, and genetics. This doesn't mean the evidence on population-level dietary patterns is wrong — it means the best approach combines those evidence-based patterns with attention to individual response. Tracking how you feel, how you sleep, and how your energy holds up after different meals gives you information that no population study can provide.

The broad principles hold for almost everyone: more whole food, more plants, more fibre, more oily fish, less ultra-processed food, less added sugar. Getting those foundations right accounts for the vast majority of diet's influence on disease risk. The personalisation layer sits on top — useful, but not where most people should be focusing their energy first.