Why I'm over the '30 different plants a week' for gut health
“Eat 30 different plants a week for your gut microbiome” is regularly trotted out as the gut health advice of the hour, so much so that chef Hugh Fearnley Whittingstall is even writing a cookbook around it. Health articles and online comments note religiously documenting each and every plant consumed across the week down to the very last smidge of flaxseed in a multi-grain loaf. Yet what is the evidence behind it? And is 30 really the magic number for your microbiome?
The advice to eat more than 30 different plants a week for your microbiome comes from a study by the American Gut Project, a citizen science project where over 10,000 Americans (and Brits too) shipped in their poo for the sake of scientific research for microbiome testing. They also filled out a number of different surveys, which included:
‘In an average week, how many different plant species did you eat?.’
The participants had to roughly guesstimate how many plants they usually ate across a typical week. They were asked one survey question, this was not rigorously collected dietary data.
Now, I can barely remember what I ate yesterday, let alone the average number of plants I usually eat across a week.
To help though, they were given a prompt:
“If you consume a can of soup that contains carrots, potatoes, and onion, you can count this as 3 different plants; If you consume multi-grain bread, each different grain counts as a plant.”
So the amount of the plant didn't matter, rather the mere presence of a plant counted as ‘one’.
The researchers grouped participants into three neatly even groups; lowest (0-10 plants), medium (11-30 plants), and highest plant groups (more than 30 plants) to compare the microbiome diversity of the lowest group vs. the highest group.
They found that those who ate more than 30 plants a week had a higher microbiome diversity, seen as a marker of good health, than those who ate 10 plants or less a week.
So the number 30 wasn’t exactly anything unique or special, it was just that it was better than eating 10 plants or less a week (which is very little at all).
Any fruit, vegetable, grain, legume, bean, nut, seed, herb or spice
In the study, quantity didn’t matter. Meaning even a smidge would count as ‘one’ plant towards your total across the week
I have nothing against advocating for plant diversity - aka eating a variety of different plant foods. In fact, I’m all for it. It’s absolutely one of the key tenets of nutrition advice for general good health, though it’s nothing new. It’s the same advice as ‘eat the rainbow’ that we’re familiar with alongside ‘eat your 5 fruit and veg a day’. Having a variety of different plant foods is undoubtedly one of the best actions you can take for your health.
My issue with the ‘30 different plants a week’ is that it’s rather like a half-baked cake. It hints at great advice, providing an actionable target, but doesn’t quite see it through to the end and you’re left confused and a little deflated.
30 is an arbitrary number, though it’s an achievable and actionable target
From this study, the number 30 is really a fairly arbitrary number, and likely any reasonably higher number than 10 plants would come out looking rather shiny and grand in comparison. I do think that having an achievable and actionable target to aim towards is great - though this advice, for now, falls short because it’s confusing in how you’re meant to count a plant, and whether 20 or 40 might be a more impactful target.
Counting is confusing - what makes a plant point?
The study didn’t set any quantity parameters for how much of a plant needed to be eaten to ‘count’ as a plant point. One KFC chicken with its 11 herbs and spices would take you over the 10 different plant criteria in one sitting. The gut health effects of a KFC bucket do not equate to 11 servings of plant foods (typically 80g each), yet this system would count as the same.
Even if we look at a less extreme example, like a simple honest lasagne, it still seems a little confusing. A lasagne made with onion, tomato, carrot, celery, and oregano together with pasta (wheat) - equals 6 plant points. That’s one meal already meeting a 1/5 of your week’s recommended plant budget.
Multiple gut health experts have created their own ‘plant count’ systems by giving spices and herbs 1/2 or 1/4 points. I think these systems can help to clear up a little of the confusion.
Counting to 30 adds extra stress that no one needs
One of the key reasons I’m not a convert is that it’s a recommendation that requires either a photographic memory or diligently jotting down every item and its contents from fork to mouth, checking every ingredients list, and of sad leftover veggies at the back of the fridge - because you already ate spinach on Monday.
Noting every single different plant down the last smidge of a chia seed doesn’t do anyone any favours, it simply creates food stress. It also can be expensive trying to buy a thousand varieties at each shop and creates a lot of food waste when you can’t get through it all.
If we had overwhelmingly strong scientific evidence for this recommendation it might be worth it, but in this case, we just don’t.
This is one association study
Association studies are useful. They show if one thing is linked to another. But what they don’t do, is say if one thing is caused by another. An example I’ve shared before is how ice cream is linked to sunburn.
We all know though, that ice cream doesn’t cause sunburn, but they both happen to be caused by hot sunny weather. This is one study showing that people who eat more than 30 plants a week have a more diverse microbiome.
The data wasn’t rigorously collected dietary data. It wasn’t adjusted for confounders. It was based on a guesstimate from one survey question.
We need more studies, that are rigorously designed, to confirm if this truly is the magic number, and if this result isn’t explained by people who eat more different plants a week more likely to eat more fruit and veg full stop.
The study showed that getting enough plants first is just as important as plant diversity
With less than 1% of the population meeting the UK dietary guidelines we have a long way to go to get more fruit and veg in our bellies. In fact, for our microbiome, the same research study found that ‘vegetable frequency’ in greeny-orange below has a similar effect size to ‘type of plants’ in green (NB the scale is stretched).
Eating a variety of different plants is great for our health, and makes complete rational sense that it supports our microbiome as well. Our gut bacteria like to feed on different types of fibre and polyphenols, so providing them with a range of different plant foods means that there’s a variety at their table too.
Instead of counting each plant, I prefer to think diverse - you could try this:
Buy the pre-mixed versions: pre-mixed salads, mixed frozen berries, mixed bean cans
Avoid food waste by stocking up your store cupboard and freezer with extra plants: jarred artichokes, capers, sun-dried tomatoes, olives, frozen veggies
Cook extra and freeze: Whenever you make a meal, double it and have the veggies as an extra side at your next meal or another day
Weekly shop, try something new, change it up: At the supermarket be curious about new and different foods that you don’t normally try
Nuts and seeds snack jar: Nuts and seeds are a great snack and fantastic for your heart health too
Think about the ‘eat the rainbow’ advice, and try and get different colours from reds to purples, greens and oranges in your day
All actions that don’t take up any more of your headspace than they need to :)
Have you found the advice 30 different plants a week helpful? or have you felt the same way as I do? I’d love to hear your take.
That’s it for now! If you have a thought percolating about this, I’d love to hear it - drop me a comment below.
Chat soon, Emily xx
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