Who doesn’t love a rainbow? In the West, the rainbow is a symbol of hope. In Hindu culture, the colours of the rainbow represent the body’s 7 energy centres, or chakras. The chakra association with colour is interesting, as it suggests that access to all colours is important for our energetic health.
You may also have heard the advice to “eat the rainbow”. Today I’d like to explore what this statement means, and what benefits eating the rainbow can have for your health.
I never cease to find it amazing that we have evolved with nature in such a way that we can use the colour of plants as a way to gauge their health benefits. Think about it for a moment – nutrition can seem so confusing at times with trends that come and go, and contradictory advice from different experts. However, here is a message from nature that we can see in colour, which can guide our food choices. What could be simpler?
Despite arguments such as low carbohydrate vs low fat, vegan vs Paleo, most nutritionists and health professionals agree that for the vast majority of people, the basis of a nourishing diet should be a wide variety of plant foods, primarily vegetables. The key here is not just the amount of plant foods we eat (clue: aim for 8-10 a day rather than 5 a day), but in the variety. Why is variety important?
The gut microbiome
As I’m sure you know by now, the human gut is teeming with microbes such as bacteria, fungi and viruses. Most of these benefit our health – we have evolved together and in turn for us feeding them, they help train our immune system, combat inflammation in the body and even provide us with some nutrients. (Read more about the gut microbiome here.)
Good health is associated with a diverse microbiome; that is, one in which many species are represented and no single species has overgrown. Like us, our gut microbes need food, and they metabolise certain compounds in our food that make it into the colon. Different microbes prefer different foods – it’s an ecosystem in which there are different niches for different microbes – and they rely on us to provide it for them.
The American Gut Project is the largest published study on the human microbiome. The study(1) collected over 15,000 faecal samples from people in 45 countries and analysed the microbiomes. The study authors found that the subjects who ate a more diverse plant-based diet had a more diverse gut microbiome. This shouldn’t come as a surprise, given that we need a range of foods in order that a range of microbes can survive and thrive. In particular, the study found that those people who ate more than 30 different plant foods each week had much more diverse microbiomes than those who consumed 10 or less different plant foods. They also seemed to have a lower incidence of antibiotic resistance.
Do you eat more than 30 different plant foods each week? Other authors have recommended aiming for 50(2). Why not try keeping track for a week to see how close you are? Each different plant food (including vegetables, fruit, grains, nuts, seeds, herbs and spices) counts as one. If you eat the same food but in a different form (eg wheat in both bread and pasta) you can only count it once.
Polyphenols
Brightly coloured plant foods contain compounds called polyphenols. They are produced by plants as part of their defence mechanisms. We often get caught up in thinking about protein, carbohydrates and fats, vitamins and minerals in our diets, but how often do we think about polyphenols?
Polyphenols are found in vegetables, fruits, herbs, spices, tea and dark chocolate. They have long been known as antioxidants, quenching the damage that free radicals can cause to our tissues. However, there are some situations in which it is actually helpful for the body to experience small amounts of oxidative stress, and in these situations, polyphenols can act as pro-oxidants (the opposite of antioxidants). This is an example of the wisdom of nature and of eating whole foods – our body can use them in the way it needs at the time we eat them.
The benefits of polyphenols go far beyond their role as antioxidants. Polyphenols support the production of brain-derived neurotrophic factor (BDNF), which directs nutrients and energy to the brain. Low BDNF has been associated with depression, schizophrenia and Parkinson’s disease. Polyphenols also support the mitochondria, the “energy powerhouses” of our cells, and thus can be important foods to consider in avoiding or preventing fatigue and low energy.
Many polyphenolic compounds have anticancer properties, such as EGCG in green tea, quercetin in red onions and curcumin in turmeric. Different polyphenols have diverse actions such as being anti-inflammatory, antifungal, antiviral and anti-allergic. This is another reason to eat as wide a variety as possible.
Going back to the gut microbiome, polyphenols also act as food for the microbes in the gut and tend to enhance the growth of beneficial flora at the expense of potentially pathogenic microbes.
Benefits of colours
The information that follows is just a small selection of the benefits of certain colours of food.
Red foods such as tomatoes contain lycopene, a fat-soluble nutrient that supports healthy cholesterol levels and has anticancer benefits, particularly researched in prostate cancer.
Orange and yellow foods contain beta-carotene which the body converts to vitamin A. This is important for eye health (hence the claim that “carrots help you see in the dark”). A diet high in beta-carotene has been found to be protective against breast and ovarian cancer and against breast cancer recurrence.
Green vegetables contain vitamin K which supports blood clotting, magnesium to relax muscles and blood 
vessels, folate to support the health of red blood cells, potassium to control blood pressure, and they often taste bitter, which stimulates digestion.
Blue and purple foods, such as berries, aubergine and purple sweet potatoes, contain anthocyanins. These polyphenols are cardio-protective, anticancer and have anti-diabetic actions.
Don’t forget white/brown foods (the vegetable kind, not beige processed foods)! Garlic is an antiviral superfood, mushrooms are superstars when it comes to immune support, and cinnamon has blood sugar balancing properties.
So, can you eat the rainbow?
If you’ve realised that you’re not eating the rainbow at present, it’s never too late to start! I challenge you to keep a track of the plant foods you eat over the course of the week. Firstly, check out how many different plant foods you eat in a week, aiming for at least 30 and ideally 50. Next, check that you are eating all the colours of the rainbow. If you are eating them all in a week, great! Can you eat them all twice a week? How about daily?
Let me know what health benefits you feel by doing this. As you’ve read above, eating the rainbow can benefit just about every body system, so don’t be surprised if you start to feel great!
References
- McDonald, D., Hyde, E., Debelius, J.W. et al. (2018). “American Gut: an Open Platform for Citizen Science Microbiome Research”, mSystems, 3(3), e00031-18. Available at https://msystems.asm.org/content/msys/3/3/e00031-18.full.pdf (Accessed 21 October 2020).
- Toribio-Mateas, M. (2018). “Harnessing the Power of Microbiome Assessment Tools as Part of Neuroprotective Nutrition and Lifestyle Medicine Interventions”, Microorganisms, 6(2), 35. Available at https://www.mdpi.com/2076-2607/6/2/35/htm (Accessed 21 October 2020).