Gut health

Should You Eat 30 Plants a Week? What the Gut Research Shows

You may have seen the number everywhere. Thirty plants a week. It sounds like a challenge, and it is a catchy one. Where does it come from, and does it hold up?

Here is what the research actually says, and a practical way to use it.

Where the number 30 comes from

The idea traces back to the American Gut Project, a citizen-science study that collected stool samples and diet information from more than 10,000 volunteers, mostly in the United States, the United Kingdom and Australia.

Participants answered a simple question: in an average week, how many different plants do you eat? The researchers then compared the people at the two extremes, those who ate more than 30 types of plants a week and those who ate 10 or fewer.

What they found:

• People who ate more types of plants had more diverse gut bacteria.
• The more than 30 group had more bacteria thought to ferment plant fiber into short-chain fatty acids, including Faecalibacterium prausnitzii and a group called Oscillospira.
• Plant variety mattered more than diet labels. Categories such as "vegan" or "omnivore" did not line up with the bacteria nearly as well as the number of different plants did.

That last point is the surprising one. It suggests that what matters may be less about the name of your diet and more about how varied your plate is.

A second clue from a Stanford trial

A different kind of study adds another piece. Researchers at Stanford ran a 17-week randomized trial with healthy adults, 18 in each group, comparing two diets: one high in fiber from plants and one high in fermented foods.

The two diets did different things:

• The high-fiber diet increased the gut's fiber-digesting enzymes, even though the overall diversity of gut bacteria stayed stable.
• The high-fermented-food diet steadily increased the diversity of gut bacteria and lowered markers of inflammation.

This was a small study in healthy adults, so treat it as a promising lead and not a conclusion. But it points to a useful idea: fiber from many plants and fermented foods, such as yogurt, kefir, sauerkraut and kimchi, may each support your gut in a different way.

How to count to 30 without stress

Here is a simple way to count. It is a practical rule of thumb, not a method from the study.

• Count each different plant once per week. Eating oats five times still counts as one.
• Fruits, vegetables, whole grains, beans and lentils, nuts, seeds, herbs and spices all count.
• Do not count in grams or servings. A teaspoon of cumin counts the same as a cup of lentils.

That last rule is why 30 is more reachable than it sounds. Herbs, spices, nuts and seeds are small additions that add a lot of variety.

A sample week

This is one way a week could reach 30 with ordinary groceries. It is an illustration, not a prescription.

Easy ways to add variety

1. Swap your grain. If you always eat white rice, try brown rice, barley or quinoa on different days.
2. Buy mixes. A bag of mixed frozen vegetables, a mixed nut and seed blend or a three-bean mix brings several plants in one purchase.
3. Use herbs and spices freely. Parsley, cilantro, ginger, garlic, cinnamon and cumin each count.
4. Add one new plant a week. A vegetable or grain you have not tried before is enough.
5. Add a fermented food. Plain yogurt, kefir, sauerkraut or kimchi are easy places to start.

This also helps your fiber. Different plants are different sources of fiber, and a varied plate makes it easier to reach your daily goal. If you want your number, see our guide on how much fiber you need per day.

Go slowly, especially with fiber

If you are used to a low fiber diet, adding many new plants at once can cause gas, bloating and cramps. MedlinePlus advises adding fiber gradually over a few weeks and drinking plenty of fluids. Adding one new plant a day or two is a gentle way to start.

If you have a digestive condition, or you have been told to follow a special diet, check with your doctor first.

30 plants a week questions people ask

Sources

1. McDonald D, Hyde E, Debelius JW, et al. American Gut: an open platform for citizen science microbiome research. mSystems. 2018;3(3):e00031-18.
2. Wastyk HC, Fragiadakis GK, Perelman D, et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021;184(16):4137-4153.
3. MedlinePlus, National Library of Medicine. Fiber.

This guide is for general education. It is not medical advice and is not intended to diagnose, treat, cure or prevent any disease. Talk to your doctor or a registered dietitian before changing your diet, especially if you take medication or manage a health condition.