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Explore health recommendationsDo you really need to eat 30 plants a week?
It's a popular piece of health advice, but it can be daunting. We investigate whether the science backs it up, and what really matters for your gut health
Hannah has three years of experience overseeing investigations around health, pet care and home improvements.
If you're partial to reading up on healthy living advice you've probably come across the '30 plants diet', which advocates for eating 30 different plant-based foods every week.
Proponents of the diet claim that eating a diverse range of plants (e.g. fruit, veg, legumes, pulses, herbs, spices, nuts and seeds) supports your gut microbiome, which in turn supports your wider health.
But is the science solid on this one, or, like the advice to walk 10,000 steps a day, is it a somewhat arbitrary number that you shouldn't beat yourself up for falling short of?
As someone who has tried and failed to consistently meet that number, I was interested to find out. So I spoke to a range of microbiome experts to get to the bottom of it.
Our gut health experts:
Raphaela Joos is a PhD candidate at the APC Microbiome Ireland (part of University College Cork) a world-leading research centre focused on understanding the microbiome. Her recent paper, 'Examining the healthy human microbiome concept' was published in Nature Reviews Microbiology.
Jens Walter is Professor of Ecology, Food, and the Microbiome at University College Cork and the APC Microbiome Ireland. His research seeks to understand the ecological and evolutionary forces shaping the gut microbiome, to inform the development of strategies for microbiome modulation and human health.
Why '30 plants a week' isn't as set in stone as you think
Having reviewed the research this advice is based on, and talked to a range of microbiome experts, I found that the evidence for 30 plants being a magic bullet for your health isn't as strong you might assume.
So why 30? This number is based on results from a research project - the American Gut Project (now the Microsetta Initiative). This ongoing project uses information from a database of thousands of volunteers, who provide diet and lifestyle questionnaires as well as samples of their poo, to help map the human microbiome.
In 2018, researchers compared stool samples from people on the database who ate more than 30 plants per week with people who ate less than 10, to see if they could find any differences in their microbiomes.
They found that people who ate more plants had more bacteria in their gut associated with the production of short-chain fatty acids (SCFAs). These compounds are associated with a range of beneficial health effects, including supporting the gut lining and reducing inflammation (and recent research shows it benefits your skin too).
People who ate over 30 plants also had higher levels of a certain type of long-chain fatty acid (LCFA; another beneficial compound) in their poo, again indicating that their gut is better able to synthesise important chemicals.
30 isn't necessarily the magic number
This study shows that eating a wide range of plants per week supports microbiome diversity and the production of important compounds in the gut. However, more research is needed to conclude that 30 plants specifically is an important number to aim for.
Why? The study compared people who ate more than 30 plants per week to people who ate less than 10. As the researchers themselves put it: these two groups were selected for being 'at the extremes of plant type consumption' - i.e the opposite ends of the dietary spectrum.
We don't know whether people who ate more than 30 plants per week also had more diverse microbiomes than people who ate, for example, 20 or 25 - or even 15, or how big the difference was between these groups.
The study also didn't control for other dietary habits. For example, people who eat less than 10 plants might have other dietary habits that decrease the diversity of their microbiome, like eating lots of ultra-processed food. This means the difference might not be driven exclusively by plant consumption.
Concerns have also been raised about the limited nature of the sample, which was dominated by health-conscious, wealthy people living in the West. It's not clear if the findings would generalise to other populations.
Taken together, although it’s an exciting place to start, the study doesn’t definitively prove that 30 plants is an essential number that yields meaningful health benefits.
Plus, recent research reveals other factors are also important when it comes to microbiome diversity and overall health.
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Diverse plant foods aren't the only thing that influences microbiome diversity
I spoke with Raphaela Joos, PhD candidate at the APC Microbiome Ireland (part of University College Cork). She explained:
'As there is so much diversity in the microbiome, and in the composition of plant fibres and nutrients, it is clear that eating a diverse range of plants is important.
'However, it is not the only dietary factor that influences the composition of the microbiome.'
For example, it is well-established that the total amount of fibre you eat, regardless of type, is a key factor in supporting the gut microbiome.
On the other hand, heavy alcohol consumption is associated with decreased levels of beneficial bacteria, as are ingredients used in UPFs, such as some artificial sweeteners and emulsifiers.
'There is also good evidence that lifestyle factors can influence microbiome diversity,' said Raphaela. Some of the most influential factors appear to be exercise, sleep, and stress.
Diversity is not the only feature of a healthy microbiome
A diverse microbiome is not always correlated with health - in fact, people with certain health conditions can show similar levels of diversity to healthy people, and healthy people can show lower diversity than some sick people.
This suggests that factors beyond diversity have an important influence on the health of your microbiome, and its relationship with your health overall.
Jens Walter, Professor of Ecology, Food, and the Microbiome at University College Cork, explains:
'The microbiome is important because of the functions it performs, like synthesising vitamins and supporting the immune system.
When we talk about a healthy microbiome, rather than focus solely on diversity, we need to consider what the microbiome can do - and what we do to it.'
For example, research has shown that putting healthy people on a very high fibre diet tends to have minimal effects on microbiome composition, but it does have beneficial effects on microbiome function (e.g. through increased synthesis of SCFAs).
'In healthy people, there is not a simple relationship between diversity, function and overall wellbeing,' says Professor Walter.
This is not to say that diversity isn't important - for example, in sick people, very low diversity can result in the overgrowth of bad bacteria. But if you're healthy, eating a highly diverse diet might not yield significantly greater health benefits than just eating a moderately diverse diet that is equally high in fibre.
Dr. Alexandre Almeida, Group Leader of the Microbiome Function and Diversity team at the University of Cambridge, explains why defining what makes a healthy microbiome is tricky:
'We've found that people with certain illnesses (like Crohn’s disease and ulcerative colitis) have less diverse microbiomes than healthy people. But this doesn't prove that reduced diversity makes you sick, or that a diverse microbiome keeps you healthy.
We saw lower diversity in people with inflammatory bowel disease (IBD). But we know that inflammation in the gut kills bacteria in the microbiome, so it isn’t clear whether the inflammation or lower diversity came first.
What's more, healthy people can have vastly different microbiomes.'
Ultimately, there's still a lot we don't know.
It's not all about your microbiome
Finally, it's worth noting that a healthy microbiome is not the only feature of a healthy gut.
A 2024 review argued that there are three key elements of a healthy gut: your microbiome, the structure of your gut, and your liver.
Each influences the function of the others, and all work together to maintain proper digestion and good health.
For example, even if you have a healthy microbiome, damage to the structure of the gut can cause waste products from digestion to 'leak' into the bloodstream. This can lead to systemic inflammation.
Damage to the gut can also lead to increased oxygen flow to the microbiome, which kills beneficial species of gut bacteria.
The verdict on 30 plants
Studies show that eating a broad range of different plants does support diversity in your microbiome, and a diverse microbiome supports your health.
But don't get too worked up on hitting precisely 30 every week. Having a number to aim for can be helpful for some, but you can also choose just to mix it up where you can.
Personally, I found aiming for 30 plants weekly just wasn’t consistently achievable for me. Adding more nuts and seeds to my diet ended up being quite expensive, and I also ended up with a lot of fruit and vegetables going off in my fridge.
I did pick up some habits that I’ve stuck with - adding chia seeds to my porridge was much cheaper than I thought (and adds plenty of fibre), having a handful of nuts with lunch made it more filling, and switching up the fruit I ate was enjoyable and very easy.
So really it's about finding what works for you, and starting small. This is likely to be easier to stick to and it's best to make dietary changes gradually anyway.
How to support your gut health
The advice on this is pretty consistent: enjoy whole foods, fermented foods (like sauerkraut, kimchi, and kefir), and plenty of plants and fibre. Try also to minimise your consumption of processed meats, alcohol, and highly processed foods.
Managing lifestyle factors, such as getting enough exercise and sleep and managing stress, will also support your microbiome - and your health in general.
Raphaela warns that it's important to make dietary changes gradually:
'Adding fibre to your diet can cause some discomfort as your body adjusts. Start slowly, and use trial and error to find the foods that work best for you.'
What about fibre supplements?
Fibre supplements can offer a range of health benefits, especially when the right supplements are used for specific targets, and can support regularity.
However, to improve overall health and prevent chronic diseases, Professor Walter stressed the importance of ensuring you are getting as much as your daily fibre as possible from plants over pills or powders.
'I was involved in several intervention trials and a recent review of studies into fibre supplements,' he explains, 'and we didn't see the same consistent benefits when compared with fibre from whole plant foods.
It's not that supplements do nothing, but it depends on the exact fibre used and what you want it to do.
We don't see the huge range of effects we consistently see with increased intake of fibre from plants. It seems that there's something unique about the structure of that fibre that makes it so beneficial.'
Also important: if you have any pre-existing digestive health issues, or are taking medicines such as PPIs (acid inhibitors), you should take extra care, as excess fibre can exacerbate some issues.
