Colour on the plate: what fruit and vegetables actually do

"Eat more fruit and vegetables" is advice so worn out that it has stopped meaning anything. It is worth explaining what the colours are actually doing, because the reasoning is more interesting than the slogan.

Colour is a chemical signal

The colour of a plant is produced by the compounds it makes to protect itself — from sunlight, from insects, from oxidation. Those compounds are the reason a red pepper is red, and they are largely what we are after when we eat it.

Because different pigments do different jobs, variety of colour is a decent proxy for variety of compound. That is the whole basis of the "eat the rainbow" advice, and it is a better rule of thumb than counting portions of the same green salad.

• Red — tomatoes, watermelon, pink grapefruit. Lycopene, the carotenoid most often studied in relation to the prostate. It is fat-soluble and is absorbed better from cooked tomatoes with a little oil than from raw ones. Tomato sauce beats salad here, which surprises people.
• Orange and yellow — carrots, sweet potato, pumpkin, apricots. Beta-carotene, which the body converts to vitamin A as it needs it.
• Green, dark — spinach, kale, broccoli. Folate, lutein, and in the brassicas the sulphur compounds that give them their smell.
• Blue and purple — blueberries, blackberries, red cabbage, beetroot. Anthocyanins, among the more potent antioxidants in ordinary food.
• White — garlic, onions, leeks. Not colourless in the chemical sense at all.

What this does and does not mean

The evidence that populations eating more fruit and vegetables have less chronic disease is strong and consistent. The evidence that any single compound, extracted and taken as a pill, reproduces that benefit is considerably weaker — and in a few cases trials of isolated antioxidants at high doses have gone the wrong way.

The reasonable conclusion is not that antioxidants are useless. It is that food appears to deliver them in combinations and quantities that isolated supplements do not reproduce, and that this is an argument for the plate rather than the pill.

It is also worth saying clearly: nothing on this list treats an enlarged prostate. Diet belongs in the conversation about long-term risk and general health, not in the conversation about fixing symptoms you already have.

Making it ordinary

The practical version is duller than the science and more useful.

• Aim for three different colours a day rather than a number of portions. It is easier to remember and harder to fake.
• Cook the tomatoes. Heat and a little olive oil make the lycopene far more available.
• Frozen counts. It is picked ripe and frozen quickly, and often has more left in it than something that spent a week in transit.
• Do not drink it. Juice loses the fibre and concentrates the sugar. Eat the fruit.

This article is general health information. It is not medical advice and does not replace an assessment by your doctor.