Whole Foods: What They Are and Why They Are Good for You

What counts as a whole food?

The term "whole food" does not have a single regulatory definition, but in nutritional science it broadly refers to food that is unprocessed or minimally processed, consumed in a form close to how it exists in nature, without significant addition of substances or removal of nutrients.

In the NOVA classification system (the framework used by most contemporary food processing research), whole foods sit in NOVA Group 1. The defining language is plain enough:

Foods in this group have not been altered, or have been altered in ways that do not substantially change their nutritional properties. Processes include: removal of inedible or unwanted parts, drying, crushing, grinding, fractioning, filtering, roasting, boiling, pasteurisation, refrigeration, freezing, placing in containers, vacuum packaging, fermentation.

Alongside NOVA Group 1, NOVA Group 2. Processed culinary ingredients such as plain oils, butter, vinegar, salt, and flour. These are not typically eaten alone but are used to prepare and cook whole foods. They are not ultra-processed.

What whole foods include

• Fruit. Fresh, frozen, or dried (without added sugar). Browse the fruit encyclopedia.
• Vegetables. Fresh, frozen, or plain tinned (without added sauces or additives). Browse the vegetables encyclopedia.
• Whole grains. Plain oats, brown rice, whole wheat, rye, barley, quinoa, plain wholegrain bread (short ingredient list: grain, water, yeast, salt). See grains.
• Pulses and legumes. Lentils, chickpeas, kidney beans, black beans, edamame. Dried or tinned in water. See pulses.
• Nuts and seeds. Plain, unsalted or lightly salted. See nuts and seeds.
• Eggs. Whole eggs, in any form of cooking. See eggs.
• Plain meat and poultry. Unprocessed cuts, without added sauces, flavourings, or fillers. See meat and poultry.
• Plain fish and seafood. Fresh, frozen, or tinned in brine or olive oil. See fish and seafood.
• Plain dairy. Whole milk, plain yogurt, natural cheese (short ingredient list), butter. See dairy.
• Herbs and spices. Dried or fresh, without additives. See herbs and spices.

What whole foods do not include

Mass-produced sliced bread, flavoured yogurts, breakfast cereals with added ingredients, processed meats such as supermarket sausages and chicken nuggets, ready meals, crisps, biscuits, chocolate bars, fizzy drinks, or diet drinks. These are NOVA Group 4. See the ultra-processed foods guide for a full breakdown.

Why whole foods are better. The nutritional basics

Before looking at the large-scale evidence, it is worth understanding what whole foods provide that ultra-processed foods typically do not.

Fibre

The UK reference intake for adults is 30g of dietary fibre per day. The average UK adult consumes around 18g, less than two-thirds of the target. Fibre is found almost exclusively in plant-based whole foods: vegetables, fruit, whole grains, pulses, nuts, and seeds. It is largely absent from ultra-processed foods, and the small amounts present in some UPFs are often in isolated or fragmented forms that may not behave like intact food fibre in the gut.

Fibre feeds beneficial gut bacteria, which produce short-chain fatty acids. Compounds that reduce inflammation, strengthen the gut lining, and are increasingly understood to influence immune function and brain chemistry. Fibre also slows digestion, reducing blood sugar spikes after meals, and contributes to satiety, making it harder to overeat.

Micronutrients

Whole foods carry their vitamins and minerals in the context of the whole food matrix. The plant cell walls, fats, and other compounds that influence how nutrients are absorbed and used. Processing typically destroys or removes micronutrients; some UPFs add synthetic vitamins back in during fortification, but the evidence that fortified nutrients behave identically to naturally occurring ones is mixed.

Key micronutrients well-supplied by a whole food diet include:

• Potassium (fruits, vegetables, pulses). Important for blood pressure regulation.
• Magnesium (nuts, seeds, whole grains, leafy greens). Involved in over 300 enzymatic reactions.
• Folate (leafy vegetables, pulses, eggs). Essential for cell division and DNA repair.
• Iron (red meat, pulses, leafy greens). Central to oxygen transport.
• Zinc (meat, shellfish, pulses, nuts). Immune function and wound healing.
• Iodine (fish, dairy, eggs). Thyroid function.
• Vitamin C (fruit, vegetables). Antioxidant, collagen synthesis, iron absorption.
• Vitamin D (oily fish, eggs). Bone health, immune function. Usually requires supplementation in the UK.
• Omega-3 fatty acids (oily fish, walnuts, flaxseeds). Anti-inflammatory, brain health.

Phytonutrients and antioxidants

Whole plant foods contain thousands of naturally occurring plant compounds. Polyphenols, flavonoids, carotenoids, glucosinolates, and others. These are not classified as vitamins or minerals but appear to have significant health effects. They are largely absent from ultra-processed foods, or present only in negligible amounts after processing. They are poorly replicated by supplements. The only practical way to get them is to eat whole plant foods.

The food matrix effect

Nutrients in whole foods do not act in isolation. The physical structure of the food (the cell walls, the fat content, the fibre) affects how quickly nutrients are absorbed, how satisfying the food is, and what signals it sends to the gut. An apple and a glass of apple juice contain similar amounts of sugar, but the apple's fibre slows digestion and triggers satiety in ways the juice does not. This "food matrix effect" is one reason nutrition scientists increasingly argue that studying individual nutrients in isolation misses the bigger picture.

What the evidence shows. Health outcomes

This section summarises the evidence for whole food diets and specific health outcomes. Most of the large-scale human evidence comes from cohort studies and systematic reviews comparing dietary patterns. The consistent thread is that diets rich in whole foods and low in ultra-processed foods are associated with better outcomes across virtually every health measure studied.

Cardiovascular disease

The evidence linking whole food dietary patterns to lower cardiovascular risk is among the most mature and consistent in nutrition science, with decades of prospective cohort data, multiple meta-analyses, and several well-designed randomised trials.

A systematic review of prospective studies (Neuenschwander et al., BMJ, 2019) found that dietary patterns emphasising fruit, vegetables, whole grains, nuts, legumes, vegetable oils, and fish (with less processed meat and refined sugar) were consistently associated with decreased risk of cardiovascular events, cancer, and type 2 diabetes.

• Whole grains: A BMJ meta-analysis (Aune et al., 2016) of 45 prospective studies found that eating three servings of whole grains per day was associated with a 22% lower risk of cardiovascular disease. The association was dose-dependent up to around three servings daily.
• Oily fish: Two portions of oily fish per week (as recommended by the NHS) is associated with reduced cardiovascular mortality, largely through the anti-inflammatory effects of EPA and DHA omega-3 fatty acids.
• Fruit and vegetables: Large epidemiological studies consistently show that higher fruit and vegetable intake is associated with lower cardiovascular risk, with the strongest effects seen in the range of five to eight portions per day.
• Nuts: Regular nut consumption (around 30g per day of unsalted, unprocessed nuts) has been associated in multiple large cohorts with lower risk of coronary heart disease.

Type 2 diabetes

High-fibre, whole food diets are associated with substantially lower rates of type 2 diabetes, and with better glycaemic control in people who already have the condition.

The mechanisms are clear: whole foods (particularly whole grains, legumes, and vegetables) have a lower glycaemic index than their refined equivalents. Their fibre content slows the absorption of glucose, reducing the demand on the pancreas to produce insulin after meals. Over time, consistently lower post-meal glucose spikes reduce the risk of insulin resistance developing.

A burden-of-proof meta-analysis (Zhou et al., 2024) confirmed strong evidence that higher whole grain intake is associated with meaningfully reduced risk of type 2 diabetes. Pulses (lentils, beans, chickpeas) have similarly strong evidence. They are among the lowest glycaemic-index foods available, delivering protein and fibre with minimal blood sugar impact.

Cancer

The link between diet and cancer is complex, and whole food research is generally less definitive for cancer than for cardiovascular disease, partly because cancer is many different diseases. However, the overall direction is clear.

• The World Cancer Research Fund (WCRF) and Cancer Research UK both recommend a diet high in whole grains, vegetables, fruit, and pulses, and low in processed and red meats, based on the accumulated evidence.
• A BMJ meta-analysis (Aune et al., 2016) found that three servings of whole grains per day was associated with a 15% lower risk of total cancer mortality.
• Higher fruit and vegetable intake is associated with lower risk of several cancers, including colorectal, lung, and oesophageal cancer.
• Processed meats (a NOVA Group 4 product) are classified as a Group 1 carcinogen by the WHO's IARC, with sufficient evidence for a link to colorectal cancer. Plain, unprocessed red meat sits at Group 2A (probable carcinogen), and NHS guidance recommends limiting it to no more than 70g per day.

Gut health and the microbiome

This is one of the most rapidly developing areas of nutrition research, and whole foods are central to it.

The human gut microbiome (the community of trillions of bacteria, fungi, and viruses living in the gastrointestinal tract) is now understood to play a major role in immune function, metabolism, inflammation, and brain chemistry. A healthy microbiome is diverse. A diet rich in a wide variety of whole plant foods feeds that diversity; a diet dominated by ultra-processed foods tends to reduce it.

Fibre as prebiotic fuel. The main mechanism is simple: gut bacteria ferment dietary fibre. When fibre reaches the large intestine (where it arrives largely intact because humans cannot digest it), bacteria break it down into short-chain fatty acids, particularly butyrate, propionate, and acetate. These compounds fuel the cells lining the colon (maintaining the gut barrier), signal to the immune system and dampen systemic inflammation, influence insulin sensitivity and energy metabolism, and cross the gut-brain axis where they appear to influence mood and cognition.

Fermented whole foods. Plain yogurt, kefir, sauerkraut, kimchi, miso, kombucha, tempeh. These contain live bacteria (probiotics) and may further support microbiome diversity. A Stanford University randomised controlled trial (Wastyk et al., Cell, 2021) found that a diet high in fermented foods significantly increased microbiome diversity and reduced markers of immune activation compared to a high-fibre diet over ten weeks. Both dietary approaches have merit; combining them is consistent with a whole food dietary pattern.

The gut-brain axis. Evidence is accumulating that gut microbiome composition influences brain chemistry, partly through the production of neurotransmitter precursors (around 90% of the body's serotonin is produced in the gut) and partly through the production of short-chain fatty acids that cross the gut-brain axis. Research published in 2024 and 2025 has continued to build the case that dietary patterns rich in fibre, polyphenols, and fermented foods (hallmarks of a whole food diet) are associated with lower rates of depression and anxiety. The mechanisms are plausible; the causal evidence in humans is still developing.

Mental health

The field of nutritional psychiatry is relatively new but growing rapidly, and whole food dietary patterns consistently come out ahead of poor-quality diets in studies of depression, anxiety, and cognitive function.

A 2024 review of the literature (Matas Ochoa et al., European Psychiatry) found that several studies link healthy dietary patterns to lower risk of mental illness or improvement in depressive symptoms. Poor dietary habits, particularly ultra-processed food-heavy diets, were associated with increased risk of developing anxiety, depression, and cognitive decline. A diet rich in fibre, polyphenols, and micronutrients appears to improve gut microbial composition and reduce the neuroinflammation associated with depression.

The SMILES trial (2017), still one of the few randomised controlled trials in nutritional psychiatry, found that a Mediterranean whole food dietary intervention led to significantly greater reduction in depression scores than social support alone, in people with moderate-to-severe depression.

Specific nutrients found almost exclusively in whole foods are consistently associated with better mental health:

• Omega-3 fatty acids (oily fish, walnuts, flaxseeds). Anti-inflammatory; DHA is structurally essential for the brain.
• Folate (leafy greens, pulses). Involved in serotonin synthesis.
• Magnesium (nuts, seeds, whole grains). Low levels associated with depression.
• Polyphenols (colourful fruits and vegetables, tea, olive oil). Cross the blood-brain barrier and reduce neuroinflammation.
• Tryptophan (eggs, poultry, legumes, dairy). The amino acid precursor to serotonin.

Healthy weight

Whole foods tend to promote a healthy weight through several mechanisms that are largely absent in ultra-processed foods:

1. Satiety per calorie. Whole foods, particularly those high in protein, fibre, and water, are more satiating per calorie than ultra-processed foods. You feel fuller on fewer calories.
2. Eating pace. Whole foods typically require more chewing, which slows eating and gives satiety signals time to reach the brain before overconsumption occurs.
3. Hormonal signalling. Intact whole foods trigger appetite-regulating hormones (leptin, GLP-1, PYY) more effectively than processed alternatives, in part because of the food matrix effect and the interaction with gut bacteria.
4. Lower energy density. Vegetables, fruits, and legumes provide large volumes of food per calorie, making it physically easier to feel full without exceeding calorie needs.

A 2024 randomised controlled trial (Ribeiro et al., Aging Cell) involving 113 adults aged 65 to 75 found that transitioning to a whole food diet led to significant improvements in body composition, cardiometabolic parameters, and gut microbiome markers, with benefits appearing within weeks, regardless of whether the diet was higher in plant or animal protein.

Longevity and ageing

The most compelling population-level evidence for whole food diets comes from longevity studies.

UK Biobank: Mediterranean lifestyle (2024). A study of 110,799 UK Biobank participants (Maroto-Rodriguez et al., Mayo Clinic Proceedings, 2024) found that those in the highest quartile of Mediterranean lifestyle adherence (a whole food-centred dietary pattern combined with physical activity and social habits) had a 29% lower risk of all-cause mortality and a 28% lower risk of cancer mortality over a 9.4-year follow-up compared to those in the lowest quartile.

UK Biobank: dietary patterns and life expectancy (2026). A 2026 study of 103,649 UK Biobank participants (published in Science Advances) assessed five healthy dietary patterns. All five were associated with lower all-cause mortality and longer life expectancy. Compared to those in the bottom fifth for dietary quality, those in the top fifth gained between 1.5 and 3.0 additional years of life expectancy at age 45 depending on sex and dietary index.

Mediterranean diet and inflammation. A UK Biobank study of 23,784 premature deaths over a median follow-up of 12.65 years found that the harmful effect of systemic inflammation on premature death was significantly blunted in people who adhered more closely to a Mediterranean dietary pattern (a predominantly whole food diet).

Blue Zones. The populations with the highest concentrations of centenarians in the world (in Sardinia, Okinawa, the Greek island of Ikaria, Loma Linda in California, and Nicoya in Costa Rica) all share a dietary pattern based on local whole foods. Largely plant-based, with legumes, whole grains, and vegetables as staples, and moderate amounts of fish, eggs, and dairy.

The science behind why whole foods work

The consistent finding across thousands of studies that whole food diets produce better health outcomes is not a coincidence. Researchers have identified several mechanisms.

1. Anti-inflammatory profile. Chronic low-grade inflammation is a shared underlying driver of cardiovascular disease, type 2 diabetes, cancer, depression, and accelerated ageing. Whole plant foods are rich in anti-inflammatory compounds (particularly polyphenols, carotenoids, and other phytonutrients) while being low in the pro-inflammatory substances (refined sugars, oxidised fats, certain additives) that characterise ultra-processed foods. The Mediterranean diet specifically has been shown to reduce circulating inflammatory markers in multiple intervention studies.
2. Nutrient synergy. Nutrients in whole foods interact with each other in ways that cannot be replicated by supplements or fortified products. Vitamin C in fruit enhances iron absorption from plant foods. Fat in nuts and avocados enables absorption of fat-soluble vitamins A, D, E, and K from vegetables eaten alongside them. Fibre and resistant starch in whole grains interact with gut bacteria to produce butyrate. This synergy is disrupted when foods are fractionated and reassembled during ultra-processing.
3. Caloric density and satiety. Whole foods (especially those high in fibre, protein, and water) deliver more satiety per calorie than ultra-processed foods. This is partly structural (chewing requirements, stomach volume) and partly hormonal (whole foods trigger satiety hormones more effectively). The practical result is that it is much harder to passively overeat a diet of whole foods.
4. Microbiome support. The diversity of plant whole foods in a diet is the single most powerful lever for gut microbiome diversity. Every different plant food provides different types of fibre, feeding different bacterial species. Eating a wide variety of whole plant foods is the most evidence-based approach to supporting microbiome health.
5. Stable blood glucose. Whole foods (particularly those with intact cell walls and natural fibre) produce slower, lower, more stable rises in blood glucose than their refined or processed counterparts. This reduces the demand on the pancreas, protects against insulin resistance, and reduces the inflammatory cascade triggered by large blood sugar spikes.
6. Reduced toxic load. Ultra-processed foods may introduce compounds not present in whole foods. Processing contaminants, packaging chemicals, and certain additive combinations. A diet based on whole foods avoids these by default.

How much whole food is enough?

UK government guidance, as reflected in the NHS Eatwell Guide, already implies a predominantly whole food dietary pattern, though it does not use the term explicitly.

The five-a-day target. At least five 80g portions of fruit and vegetables daily. This remains the most widely communicated UK dietary goal. It is a minimum, not an ideal; large epidemiological studies suggest benefits continue to increase up to seven to ten portions per day, with the strongest effects from vegetables and whole fruit (not juice).

30 plant foods per week. A figure popularised by the British Gut Project and the work of Professor Tim Spector at King's College London. Eating thirty or more different plant foods per week (across vegetables, fruit, whole grains, legumes, herbs, spices, nuts, and seeds) has been associated with significantly greater gut microbiome diversity. This is not as daunting as it sounds: counting different varieties (red onion and white onion are different, broccoli and cauliflower are different) and including herbs, spices, and seeds makes thirty achievable in a week of normal cooking.

30g of fibre per day. The SACN recommended intake for UK adults. Most UK adults consume around 18g. The gap is largely explained by insufficient whole grain, vegetable, pulse, and fruit consumption.

Two portions of fish per week. NHS guidance, with one portion being oily fish (salmon, mackerel, sardines, trout, herring). This delivers the EPA and DHA omega-3 fatty acids best supported by evidence for cardiovascular and brain health.

Practical ways to eat more whole foods

Shifting towards a more whole food diet does not require expensive specialist foods, cooking expertise, or dramatic changes. The most effective approach is to displace ultra-processed foods with whole food alternatives, one or two changes at a time.

Start with breakfast

Most UK breakfast cereals are ultra-processed. Plain porridge oats (rolled or steel-cut) are not. They are NOVA Group 1. Adding whole fruit, plain nuts, seeds, or a spoon of plain yogurt keeps it whole and nutritious. This one swap removes a daily UPF and adds fibre, micronutrients, and a more sustained energy release.

Make pulses a staple

Tinned lentils, chickpeas, and beans (in water, without added sauces) are cheap, quick, NOVA Group 1, and among the most nutrient-dense foods available per pound spent. Adding a tin to soups, stews, curries, or salads displaces refined carbohydrates or processed meat, adding fibre, protein, and a low glycaemic index carbohydrate in one step.

Buy plain, add your own flavour

Plain chicken, plain fish, plain oats, plain yogurt, plain nuts. These are whole foods. The flavoured, coated, or sauce-included versions of the same products are usually NOVA Group 4. Buying the plain version and seasoning at home with herbs, spices, lemon, garlic, and olive oil gives you full control of the ingredients.

Use frozen vegetables and fruit freely

Frozen vegetables and fruit are NOVA Group 1, often more nutritious than their fresh equivalents (because they are frozen at peak ripeness and do not degrade in transit or on the shelf), and substantially cheaper. Frozen peas, sweetcorn, spinach, edamame, and berries are practical whole food staples.

Cook in batches

The main reason ultra-processed food wins on convenience is time. Batch cooking (making a large pot of soup, a tray of roasted vegetables, a pan of lentils) removes that advantage. Most whole food meals freeze well. Spending two hours cooking on a Sunday removes the convenience case for ready meals on busy weekdays.

Rethink snacks

Most packaged snacks are ultra-processed. A handful of unsalted nuts, a piece of fruit, a boiled egg, or plain cheese and oatcakes (check the ingredient list) are not. These alternatives are typically more filling per calorie and substantially more nutritious.

Add something green to every meal

Not a rule, just a useful habit. Spinach in scrambled eggs, rocket in a sandwich, frozen peas in pasta, a side salad with any main. Each addition increases your daily plant diversity and fibre intake without requiring a meal overhaul.

Use the food scanner

Not sure whether something is whole food or ultra-processed? Scan the barcode with Food Insight to see the NOVA group, the full ingredient list, and the nutrition breakdown.

Whole food categories at a glance

Each of the categories below has an encyclopedia entry on this site with per-100g nutrition data sourced from USDA SR Legacy, plus storage advice, allergen notes, and serving suggestions for individual foods within the category.

Key statistics at a glance