Why eat 30 plant foods a week?
Is 30 plant-based foods a week the new five-a-day? We hear from the lead scientist behind the study that promotes a new healthy way of eating
Where has the idea of eating 30 different plant foods come from?
The suggestion that eating this number of plant foods every week can lead to improved health comes from a large study I worked on back in 2019. The British & American Gut Project looked at the diets of thousands of people, assessing how different dietary patterns were associated with different health outcomes.
One of the most interesting findings was around fibre. The recommended portion of fibre for an adult is 30-35g a day, but what the study was showing us was that the amount of fibre is not as important as the variety. Different plants have different fibres, so eating more plants diversifies the types of fibre you eat.
The study showed us that people who ate the largest variety of plant foods were found to have the healthiest microbiomes (the microbe environment that exists naturally in our guts) and were likely to report the best health outcomes. The study suggested that 30 was the optimum number of different plants for fibre diversity, as there wasn’t much improvement when you increased from 30 to 35 or 40.
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What counts as a ‘plant’ food?
Basically, everything that comes from a plant! Fruit and vegetables all count, of course (even potatoes – particularly if you eat the skin), but so can wholegrains, pulses, seeds, nuts, mushrooms, beans, herbs and spices. The important factor is that you’re consuming plant fibre, so juice and oil wouldn’t count, but something like matcha (which is made from whole powdered leaves) would.
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It’s hard to recommend exact portion sizes, but we do know that diversity is key. And, the beauty of this way of eating is that it’s not about restricting, it’s about adding more in. For instance, for a simple tomato sauce, make it by frying onion, garlic, carrots and celery in extra virgin olive oil, then add the tomatoes, and finish with basil and oregano – you’ve got seven plants there already.
What are the health benefits?
1. Supports a healthier gut biome
The gut microbiome is the population of bacteria living in our large intestines (other biomes exist in the vagina, mouth and on your skin). We think having a diverse gut microbiome with more helpful bugs and less unhelpful ones leads to better health. Gut bugs are especially important for our overall health, as they are strongly connected to our immune system. Gut microbes process information from everything we ingest (whether that’s food, saliva or mucus) to figure out what’s happening to our bodies. This helps the function of our immune system.
2. Supports good immune system function
One study on a group of cancer patients receiving immunotherapy (which relies on our immune system to create the right antibodies to fight cancer cells) found that those eating a Mediterranean diet (which is a diet based on a fibre-rich, diverse range of plants) had an improved microbiome and stronger immune system. They had better health outcomes and cancer survival rates.
3. May decrease your risk of covid
During the pandemic, it was also found that people taking probiotics and who had healthier microbiomes were less likely to catch covid, and less likely to die from covid. Supporting your gut microbes is essential for reducing the risk of infectious diseases through a healthy immune response.
4. Reduced depression symptoms
The connection between the gut and brain is known as the gut-brain axis. As gut microbes produce many different chemicals (including enzymes, hormones and certain vitamins such as B12 and K), these chemicals travel to the brain and impact vagus nerve transmission, impacting our mood and mental well-being. This was shown in one study, in which patients eating a Mediterranean diet were found to have reduced depression symptoms compared to patients receiving just social support intervention.
5. Lower risk of inflammation
We know that ‘good’ bacteria helps keep gut lining intact. There's also ‘bad’ bacteria that thrives on highly processed foods and animal products, so if you’re eating a lot of these, you’re likely to have not only an unhealthy microbiome, but also increased intestinal permeability – what some people call a ‘leaky gut’. If the gut lining becomes too easy to pass, microbes travel to different tissues around the body and cause inflammation. For instance, microbes travelling to the skin and causing inflammation would result in acne.
How easy is it to eat 30 plant foods a week?
Once you’re in the mindset of aiming to add as much variety as possible (and not worrying about quantity), it’s not difficult to achieve this number. Keep a simple list on your fridge or in a notebook, and always aim to add one more plant food to whatever you’re eating.
One of the simplest tricks is to buy prepared mixes, whether that's a bag of mixed nuts to snack on, frozen mixed berries, cans of beans, or seed mixes to sprinkle over salads or cereals. This is the quickest way to add another four or five different plant foods to your day. I keep a spice mix by the hob to add to dishes when I’m cooking. It all counts.
In a nutshell:
Eating a wide variety of plant fibres has been linked to both a healthier digestive system and, in turn, a number of other health benefits.
Further reading
Gut health: what does it really mean?
Top 15 probiotic foods to support gut health
Does diet affect gut health?
What is a plant-based diet?
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