Advice to ‘eat the rainbow’ has been circulating in the nutrition sphere for some time. And no, it is not a call to action to get more Skittles in your life. Instead, it is all about choosing a variety of fruits and vegetables primarily based on their colour. Red, blue, orange, purple, yellow and green are the important colours here. And those colours occur because of the presence of a family of different polyphenol pigments naturally found in foods. It is those coloured pigments that could explain many of the health benefits from eating these foods on your longevity, body weight, blood lipids and risk of chronic diseases such as type 2 diabetes and heart disease. In this podcast episode, I’ll explore the science behind ‘eating the rainbow’.
Here’s some shocking news: fruits and vegetables are good for you. I know, crazy, right? But just why are they so good for you? The list is long and includes the multitude of nutrients they contain and also all that fibre, a lot of it prebiotic fibre which is A-grade fuel for your gut microbiome. And then there is a class of chemicals called polyphenols.
Talking about polyphenols is akin to opening up Pandora’s box. That’s because there are thousands, of different types. And you find them in fruits, vegetables, wholegrains, legumes, herbs and spices, tea and even coffee. And the key theme is that they’re all plant foods which is why they are also referred to as phytonutrients.
Polyphenols are much more than their stereotyped antioxidant ability. They have a multitude of benefits and actions in the body such as:
- regulating cell growth and death
- slowing down cancer cell proliferation
- altering glucose responses and insulin sensitivity
- increasing activity of enzymes involved in removing harmful substances from the body
- and decreasing inflammation.
With so many different classes and types of polyphenols, the best way to get plenty of these in your diet is to eat a wide variety of fruits and vegetables. Easy to say, hard to do when you consider how few of these foods most people eat compared to what dietary guidelines advocate for.
One bit of helpful advice you may have heard is to ‘eat the rainbow’. It is a simple way of using the colour of these foods as a guide to polyphenol and other phytonutrients variety. Because the colours you see in nature are normally a direct result of the presence of polyphenol and other phytonutrient pigments in the food. Carrots are orange because of all that beta-carotene. Berries are red, purple or blue because of a group of flavonoids called anthocyanins. Tomatoes and watermelon get their red colour from lycopene and other pigments in the vitamin A family. That yellow colour in corn, peaches and pumpkin? It is from lutein and zeaxanthin which also belong to the vitamin A family. I could go on, but you get the picture.
And when you look at research that groups fruits and vegetables by their colour, you can find associations between colour and cardiovascular disease, cognitive decline and even colorectal cancer. But until now, no one has set out to combine all this research together in one place. So, that was the topic of a just-published review that set out to answer the question of if we should ‘eat the rainbow’.
The review included a total of 86 studies that looked at over 400 different outcomes and used data from over 37 million people. And I’ll link to this review in the show notes. https://www.mdpi.com/1420-3049/27/13/4061/htm
And it is well worth accessing the paper which is open access as Figure 2 is an amazing infographic showing the spectrum of the colours, the fruits and vegetables in each colour group, the beneficial phytonutrients they contain, the health benefits seen and the level of evidence to support the health benefits. That infographic went off the charts when I shared it on my social channels. So, the infographic alone will tease out all the key themes from the paper. For this podcast, I’ll just touch on a couple of things of interest.
So, let’s dig into key findings from the paper. Almost half of the health outcomes they looked at were improved by eating foods high in colourful pigments. Red, orange, yellow, pale yellow, white, purple, blue and green are the pigments to go for.
And the health outcomes that were linked to favourable benefits from three-or-more coloured pigments were the big ones: body weight, blood lipids, inflammation, cardiovascular disease, type 2 diabetes, many forms of cancer and longevity.
And the evidence was pointing to colour being an independent factor linked to good health on top of the many known generic benefits of fruits and vegetables such as the essential nutrients and fibre they contain.
Now I need to state that the level of evidence for many of the health links was not always high because most of the studies were observational. Most health links had a low level of evidence, but the direction of benefit was consistent across having more coloured pigments in your diet and having better health.
And there are lots of plausible reasons to explain why those pigments are good for us. To start with, polyphenols can interact with the gut microbiota which translates into improvements in the gut barrier function, production of short-chain fatty acids such as butyrate, and down-regulation of genes associated with inflammation. Anti-inflammatory and anti-oxidant are two traits shared by all the bioactive pigments.
So, let’s wrap all this up. You didn’t need to listen to this podcast to know that fruit and vegetables are good for you. But now we have better evidence that variety is the spice of life – especially when it comes to having different colours of these in your diet. Eat the rainbow and the pot of gold at the end of it will be your better health. A pretty lame analogy I know, but true.
So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on if it supports it, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.
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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.