Eat the Rainbow: Phytonutrients, Inflammation and Your Health

What Are Phytonutrients?

Phytonutrients (also called phytochemicals) are natural compounds produced by plants. There are thousands of them, and they're responsible for much of the colour, flavour and aroma of fruit, vegetables, herbs, spices, legumes, wholegrains, tea and coffee. Unlike vitamins and minerals, phytonutrients aren't classed as 'essential'; you won't develop a deficiency disease without any single one, but a growing body of research links diets rich in them to better long-term health.

Some of the most studied families include: carotenoids (the orange and red pigments in carrots, sweet potato and tomatoes), anthocyanins (the blue-purple pigments in berries, red cabbage and eggplant), flavonoids and other polyphenols (abundant in tea, cocoa, olive oil, citrus and onions), and glucosinolates (found in cruciferous vegetables like broccoli, kale and Brussels sprouts).

The 'eat the rainbow' idea works because different colours signal different phytonutrient families. By eating a variety of colours across the week, you naturally take in a broad range of these compounds, along with the fibre, vitamins and minerals that whole plant foods provide. It's a simple, memorable rule that maps onto genuine nutritional diversity.

Importantly, the benefits appear to come from whole foods eaten as part of an overall pattern, not from isolated phytonutrient supplements, which have generally failed to reproduce the benefits seen from food in clinical trials.

What 'Inflammation' Actually Means

'Inflammation' is one of the most used and least understood words in wellness. It's worth being precise, because the term covers two very different things.

Acute inflammation is the body's normal, healthy response to injury or infection (the redness, heat and swelling around a cut, or the immune response that fights off a virus). This kind of inflammation is essential and protective, and you wouldn't want to suppress it.

Chronic low-grade inflammation is different. This is a persistent, low-level activation of the immune system that can simmer in the background for years without obvious symptoms. It's associated with ageing and with the development of several chronic diseases, including cardiovascular disease, type 2 diabetes and some cancers. Factors that contribute to it include excess body fat (especially around the abdomen), smoking, physical inactivity, poor sleep, and dietary patterns high in ultra-processed foods and low in plants.

This is where diet comes in. While no single food 'cures inflammation', dietary patterns rich in colourful plants, fibre, healthy fats and oily fish are associated with lower levels of inflammatory markers, whereas patterns high in ultra-processed foods, refined sugar and excess kilojoules tend to be associated with higher levels. The phrase 'anti-inflammatory diet' is really just shorthand for this kind of whole-food, plant-rich pattern; there's nothing exotic or extreme required.

How Colourful Plants Support Your Health

The evidence that fruit and vegetable intake supports health is among the most consistent in all of nutrition. Large reviews suggest that eating more fruit and vegetables is associated with lower risks of heart disease, stroke and premature death, with benefits continuing to rise up to around five or more serves a day (Aune et al., 2017).

Several mechanisms likely contribute. Phytonutrients with antioxidant properties help the body manage oxidative stress, an imbalance linked to ageing and disease. Polyphenols appear to support healthy blood vessels and may help regulate blood pressure. Compounds in cruciferous vegetables support the body's natural detoxification enzymes. And because colourful plants are also rich in fibre, they feed the gut microbiome, which in turn produces anti-inflammatory short-chain fatty acids.

It's important to be honest about what the evidence does and doesn't show. Much of it comes from observational studies, which can show association but not prove cause. And single 'superfoods' rarely live up to their marketing. The reliable signal across decades of research is at the level of dietary pattern: people who eat more whole plant foods, in more variety, tend to live longer and healthier lives. That's a strong reason to fill half your plate with vegetables and eat a range of colours, without needing to chase the latest exotic berry or expensive supplement.

The Australian Reality: We're Not Eating Enough

Despite the strong evidence, most Australians fall well short on plant foods. The Australian Bureau of Statistics reports that only around 1 in 15 adults (6.5%) eat the recommended five serves of vegetables a day, and only around half meet the recommendation of two serves of fruit (ABS, 2022). Variety is often limited too, with a handful of common vegetables making up much of total intake.

At the same time, ultra-processed foods make up a large share of energy in the typical Australian diet. These foods tend to be low in phytonutrients and fibre and high in refined sugar, salt and unhealthy fats, the opposite of an anti-inflammatory pattern.

This gap matters because diet-related chronic diseases are among Australia's biggest health burdens. Cardiovascular disease remains a leading cause of death, type 2 diabetes affects more than a million people, and poor diet is one of the leading modifiable risk factors for ill health nationally (AIHW, 2024). Increasing the amount and variety of colourful plant foods is one of the most accessible, evidence-based steps most people can take, and unlike many interventions, it carries no downside.

See the bigger picture of your health

An anti-inflammatory, plant-rich diet supports your long-term health in ways that build over time. Blood markers like hs-CRP and your metabolic panel can help you and your GP track the direction you're heading.

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Can Blood Tests Measure Inflammation?

There's no single blood test for 'how healthy your diet is', but a few markers relate to inflammation and can be measured.

The most widely used is high-sensitivity C-reactive protein (hs-CRP). CRP is a protein made by the liver that rises with inflammation, and the high-sensitivity version can detect the low-grade levels relevant to chronic disease risk. Persistently elevated hs-CRP is associated with higher cardiovascular risk. However, CRP is non-specific; it rises with any infection, injury, recent illness or even a temporary cold, so a single reading can be misleading, and it should always be interpreted in context by your GP.

Other markers sometimes discussed in relation to inflammation include certain ratios derived from a full blood count, such as the neutrophil-to-HDL or monocyte-to-HDL ratios, and homocysteine. These are areas of ongoing research and are best understood as part of a bigger picture rather than as standalone diet scores.

The realistic takeaway is that blood tests can flag chronic inflammation as a risk signal worth acting on, but they don't grade your last meal or prove a particular food is helping. They're most useful tracked over time, alongside other markers of metabolic and cardiovascular health, and interpreted by your GP in the context of your weight, lifestyle, family history and any symptoms. An anti-inflammatory eating pattern is worth adopting for its broad, well-established benefits, whether or not you ever measure a marker like hs-CRP.

Putting 'Eat the Rainbow' Into Practice

Turning this into everyday habits is refreshingly straightforward, and it aligns closely with the Australian Dietary Guidelines.

Aim for colour and variety. Try to include several different colours of vegetables and fruit each day, and rotate your choices through the week. Red tomatoes and capsicum, orange carrots and sweet potato, yellow corn, green leafy vegetables and broccoli, blue and purple berries, cabbage and eggplant, plus white and brown garlic, onions and mushrooms; each colour brings different phytonutrients.

Fill half your plate with vegetables. This single habit naturally increases your intake of phytonutrients and fibre while moderating less healthy components of the meal.

Use herbs, spices, tea and extra-virgin olive oil. These are concentrated sources of polyphenols and an easy way to add both flavour and phytonutrients.

Include legumes and wholegrains. Beyond vegetables and fruit, these add fibre and their own phytonutrients, and support the gut microbiome.

Favour whole foods over supplements. The evidence supports food, not isolated antioxidant pills, which have generally failed to deliver the same benefits and in some cases caused harm at high doses.

If you have a chronic condition, are pregnant, or are considering major dietary changes, your GP or an accredited practising dietitian can help tailor an approach to your needs, and use appropriate blood tests to keep an eye on your overall health over time.