Do you really need thirty plants a week?

You have probably seen the number: thirty different plant foods a week. It is worth knowing where it came from before deciding what to do with it, because the study is thinner than the headlines and the target is better than the study.

The source is the American Gut Project, a citizen-science effort in which more than ten thousand people mailed in stool samples and filled out questionnaires about what they ate. When the researchers sorted people by how many different plants they reported eating in a week, those above thirty had more diverse gut bacteria than those at ten or fewer. That is the whole finding. It is observational, the diets were self-reported, the people who send stool samples to a science project are not a random slice of the population, and a more diverse microbiome is a marker, not an outcome. Nobody has shown that hitting thirty makes you live longer. When fiber has been added in controlled trials, certain bacteria increased but overall diversity, the thing the thirty-plant number is about, mostly did not change.

So why do I like the target anyway? Because of what it does to a shopping cart. Most people, when they first count, land somewhere between eight and fifteen, because a normal week is the same six vegetables on rotation. A diet built on six plants is narrower than it looks: different plants carry different kinds of fiber and different compounds, and the evidence that fiber itself matters is not thin at all. Across 185 cohort studies and 58 trials, the highest fiber intakes went with fifteen to thirty percent less death from all causes and from heart disease, with the largest gains around 25 to 29 grams a day. Most Americans eat about sixteen.

The other reason is that thirty is a game rather than a restriction. It asks you to add rather than subtract, which is a rare and pleasant thing in a diet, and it naturally pushes you toward the herbs, spices and acid that make this food worth eating in the first place.

How to count: every different bean, nut, seed, grain, leaf and fruit is one. Herbs count. Spices count. The seeds on a salad count. A bowl of lentils with cumin, coriander, a squeeze of lemon and a handful of parsley is five before you have added a vegetable. Frozen counts, and canned counts. Different colors of the same thing, a red and a yellow pepper, most people counting generously call two, and I would not argue.

The practical version, which is what the LP3 plate actually asks for: half the plate, or a little more, is vegetables and legumes. Something from the legume family most days. Aim at variety rather than volume. You do not need to count fiber, and you do not need to hit thirty; if you build the plate that way, the fiber number takes care of itself and the plant count drifts upward on its own.

Where the plants sit under the protein, and why the two halves of the plate are there together, is chapter two of The LP3 Diet.