how should a person eat

Tell Me About the Planetary Health Diet

Photo: Jana Leon, SSPL/Getty Images

How Should a Person Eat is a monthly nutrition column investigating individual food philosophies.

In January, the influential medical journal The Lancet released a report calling for a dramatic and worldwide overhaul of our collective eating habits. The report is 46 pages long (and lists 37 authors), but its core idea is simple: We should eat less red meat (50 percent less, worldwide) and more nuts, vegetables, fruits, and legumes (100 percent more, worldwide). The authors are calling their proposed plan “The Planetary Health Diet,” and they argue that adopting it would improve both human health and the health of the environment. By reducing red meat production and consumption, they argue, we would reduce premature deaths (the report cites studies that link saturated fat intake with disease) and protect the environment by reducing livestock-related greenhouse-gas emissions.

The report’s lead author is Harvard professor Walter Willett. Willett is also the author of the 2001 book Eat, Drink, and Be Healthy: The Harvard Medical School Guide to Healthy Eating. Our conversation has been condensed for clarity.

Can you give me a short summary of what the Planetary Health Diet is and why a meat-light diet would be beneficial?
First of all, it’s not one highly specific diet, because there are many ways of putting this together. Some people have called it a flexitarian diet, but it’s basically an omnivore diet, although you could be a vegan within it if you wanted to — or a lacto-ovo-vegetarian, or a pesca-vegetarian.

The diet is mainly plant-based, but it can include modest amounts of red meat, and modest amounts of fish, poultry, eggs, and dairy products. But those are not viewed as absolutely essential.

[An outline of the diet can be found here.]

I’ve read that meat has certain nutritional benefits that are unique to animal-source products. Is eating one serving of red meat per week, as the Planetary Health Diet loosely suggests, sufficient for an individual to reap meat’s nutritional benefits?
Yes. You definitely don’t need to have meat. There’s no requirement for meat in a diet. You can get the nutrients from other sources.

There is one nutrient that uniquely comes from animal-source products, though, and that’s vitamin B12. The amount of vitamin B12 in the Planetary Health Diet is at the adequate amount, plus or minus just a little bit. The diet comes out to include about two servings of animal-source foods per day, if you want — from red meat, poultry, eggs, fish, and dairy products — which should be enough for the vast majority of people.

Who needs more vitamin B12? Would anyone not be getting enough in this scenario?
The biggest problem with inadequate B12 is actually in people over 50, who fairly often don’t secrete enough acid in their stomach to absorb enough vitamin B12, even if they’re consuming it.

But also, if someone’s going to be a vegan, they definitely need to get extra vitamin B12 by a supplement or multivitamin, or by fortified food.

Independent of this report, there’s been a lot of discussion over the years about the desirability of fortifying food in the United States with B12. We’re already doing a lot of fortification, like with folic acid, and it would cost virtually nothing to add B12 to that list. I think that’s probably a good idea.

What kinds of food would be fortified with B12 in that scenario?
Grains. If a product says it has “enriched flour,” typically there will be a string of vitamins that are in there. In 1998 we added folic acid to that list, and that’s pretty much eliminated folic acid deficiency in the United States, which was pretty widespread. For another example, most salt is fortified with iodine, because in many parts of the U.S., iodine intake has been insufficient.

If there is a concern about getting adequate B12, eating more red meat — which is costly to produce, takes a heavy toll on the environment, and brings a lot of saturated fat and cholesterol to the diet — is not the best way to do it.

I’ve seen some pushback to the Planetary Health Diet from the paleo/keto/low-carb sectors, arguing that a diet that decreases animal products would encourage people to eat more processed food and refined grains, and that obesity and diabetes would continue to go up as a result. I’m curious what your response would be to the paleo, keto, and otherwise vaguely anti-grain sectors of the nutrition world.
Yeah. Well — the paleo diet is interesting, and there’s a half-truth to it, which is why some people do benefit when they go on these very low-carbohydrate diets. Excessive amounts of refined starch and sugar are the biggest nutritional problem in the United States, now that we’ve gotten trans fat out of the food supply.

High amounts of refined starch and sugar do cause adverse metabolic problems, which are related to weight gain and Type 2 diabetes. So by reducing starch and sugar, many people will experience metabolic benefits. But the benefits that come from reducing those doesn’t mean that increasing red meat consumption is good for you. And, in fact, the long-term studies show that it’s not good for you.

There are definitely ways of reducing refined starch and sugar that do not involve red meat. In fact, you can be a vegan on a paleo diet, if you want to, by eating lots of nuts and soy products, for example, and lots of vegetables. And if you’re not a vegan, having some fish is of course a good idea.

The diet we’ve suggested actually has no refined starch. We’ve suggested that the grains be whole grains. The amounts we suggest are moderate — it’s not a high-carbohydrate diet, it’s in the middle of the range.

How sustainable is the paleo diet, environmentally? Could the whole world eat paleo if they wanted?
I asked in a meeting of Boyd Eaton, an early proponent of the paleo diet, and who’s a nice guy, “How many people could the globe support eating this meat-based paleo diet?” And he said about 200 million people. David Katz did a calculation and came up with 800 million people. But there’s already 7.2 billion people on the world, so somebody’s got to be looking for another planet if more than a very small minority of the world’s population is going to be eating a meat-based paleo-type diet. That would devastate the world, and either a lot of people have to go, or we’re in deep, deep trouble. So it’s just a nonstarter in terms of wide adoption of that diet.

That’s really interesting so it’s essentially a selfish diet.
[Pause.] A shellfish diet. Well.

A selfish! A selfish diet. The paleo since it’s not an option for the whole world.
Oh, I thought you said shellfish! But yes, you could call it a selfish diet.

So, while your proposed Planetary Health Diet is good for the environment, the idea is that it’s also good for humans on an individual basis, too, right?
Yes. There would be huge health benefits to adopting this. We calculated that somewhere in the ballpark of about 11 million premature deaths could be avoided if the world adopted eating this way, due to reduced red meat and sugar intake, which correspond with reduced rates of disease.

If you don’t mind me asking, what’s your own diet like?
Yeah. It would fall within the ranges of what we suggest. I’m an omnivore, but I rarely eat red meat. So I’d be eating less red meat than we suggest, but a little more fish — I’d be making up for some of that red meat with more fish, a little more poultry, and I commonly eat eggs, so I’m doing some of those swappings among the animal-source proteins. And I think that like most Americans I eat fewer beans than we suggest, but I eat more nuts than are on there. So I’m not exactly on the suggested numbers, but by doing some of that mixing and matching, I’m pretty close.

Have you ever been a vegetarian, or been tempted?
I’ve never been a vegetarian, no. But again I do like variety, I do like to have some really good cheese now and then. Once we get down to this level of quite modest amounts of animal-source foods, we don’t really have data saying there’s further gains by being more strictly vegetarian or vegan.

I appreciate that for some people, those choices are philosophical or religious.

How do you plan on reaching people with this stuff? Because it seems like in America at least, it’ll be a real challenge to get people to want to eat less meat.
Yes. That’s important. I grew up in the Midwest, from five generations of farmers, so I had five glasses of milk a day, and red meat three times a day. But as I [got older and] watched the data come in, it was clear that that wasn’t the healthiest way to be eating.

Over time, the Mediterranean Diet, which we did a lot of research on in the 1990s, was a real eye-opener for me. Because people were really healthy when they consumed that. We pulled that diet apart, looked at the pieces, and we put the healthy pieces back together. We know enough about those pieces now to know that you can get that same health package with foods from Southeast Asia, Mexico, and many other parts of the world. You can put this together with an incredible variety of foods.

For me, learning about the Mediterranean Diet made eating much more interesting. I ate foods that I never ate before, that I never experienced growing up. And there’s so much more interesting variety than mashed potatoes, roast beef, and gravy, which is what I grew up with.

To your question, though, I think it’s really important that we emphasize meals, plates, and eating experiences that people enjoy. Different people are motivated by different factors: For some people health is a super-high priority, and they’ll eat healthy foods even if they taste horrible! Other people are motivated by taste, and for them flavor is everything. Other people are very environmentally conscious, and that will motivate them. I think we have to have a sales pitch, basically, that appeals to different people. Because different people are coming from very different places. Some people are struggling economically, and putting food on the table — anything on the table, to get enough to eat every day — is a challenge. And the good thing is that this way of eating can be very economical. Partly because a lot of animal proteins are quite expensive, and plant-based protein sources in general are less expensive. So one can eat economically on this diet.

It seems like there are pros and cons to that, though.
Yes. In some ways the diet’s affordability has also been a hindrance — a barrier — to adoption, because having a lot of meat on the table has historically been identified as prosperity. And aspirational. A more plant-based diet is what you used to have to eat, a reminder of poverty.

We’ve gotten around that with the Mediterranean Diet, and we worked a lot on that, because that was originally viewed as both unhealthy and a poverty diet, in the early 1990s. And now it IS aspirational. So working with journalists, writers, and chefs, to show how these foods can be put together in ways that are attractive, tasty, and enjoyable has been really important. And having food writers and journalists help communicate that has also been important. There’s not a simple answer to your question! Because I think we have to work on multiple fronts, and we need to help a lot of different people to make this transition.

Sometimes when I change my diet, I feel good about it, but it makes my relationships with other people more awkward, since diet changes can feel like an indictment, or a personal rejection. And then that discomfort makes the whole thing feel counterproductive. But, I guess moving slowly is the way to do this.

What sort of time frame do you think would be realistic for adoption of something like the Planetary Health Diet? 
A few decades. We’ve seen big changes in what people eat over time, but it doesn’t happen overnight. Like tobacco reduction, too — that really has involved a cultural change. It was the norm for smart people, intelligent people, to smoke, in the 1950s and ’60s. When I was in medical school, doctors and everybody in the hospital smoked — and that culture’s completely changed. I think it’s realistic that food, which is even more complicated, will take that type of time frame.

As you say, families can sometimes sabotage good efforts, in part because it makes them feel guilty.

It doesn’t have to be a one-step process — it can be a step-by-step process, by shifting. In the United States since 1970, for instance, red meat consumption is actually down by about 40 percent per capita. So that’s a pretty big shift.

And I should add, we can also use economic levers, and we need to be doing more of that. Because red meat is cheap. And the current prices don’t incorporate all the costs that go into it — the environmental costs, and a lot of the government subsidies that go into consuming it.

In Switzerland, for example, I think red meat’s like $20 or $25 a pound. And people treat it differently there. I like to make the analogy with lobster, which I really like. But I don’t have it every day, in fact I only have it a few times a year. But I enjoy it. And I think that for people who do like red meat, we should be thinking about it more that way — as an occasional treat.

You mentioned the 40 percent drop in red meat consumption. I’ve seen people on Twitter sharing a graph that suggests the drop in animal-product consumption corresponds to the rise in obesity and diabetes. And I was wondering if you think they’re related. And, separate question, what the most relevant causes of obesity are.
Right. In terms of the rise in obesity, basically, we’ve looked at this a lot, and actually red meat consumption is related to higher risk of Type 2 diabetes. There has [also] been a huge increase in soda consumption over that period in time. In terms of diet, that is the No. 1 driver [of obesity]. Many low-income groups consume something like three servings of soda a day. And there was also an overall increase in sugar consumption during that time.

There is an element of truth to that idea, though, in that there used to be a big push against consuming all types of fat, and that people should eat more carbohydrates to replace it. And that was based on no good evidence. In fact, it’s actually our research that really showed that that was a mistake, and that there was no evidence to support that big push. We showed that eating a high-carbohydrate diet — especially if those carbohydrates are refined carbohydrates and sugar — will promote obesity and Type 2 diabetes.

But eating more red meat is, again, not the solution to that. It’s a false equation that they’ve created. A lot of refined starch and sugar is bad for you, which is absolutely true. It’s the idea that eating a lot of red meat is therefore good for you that’s completely illogical and false.

I see.
Our recommendations do cut back on refined starch and sugar, and instead we emphasize whole grains, which bring a lot of micronutrients in and reduce glycemic effect. We’re definitely cutting way back on sugar.

I should note that instead of replacing refined starch and sugar with red meat, we suggest replacing it with foods like nuts, soy, and beans, plenty of fruits and vegetables, and healthy fats. Healthy fats are basically plant ones. There are some people [who] claim that vegetable fats [specifically, refined vegetable oils like corn oil, sunflower oil, and canola oil] are dangerous, and that’s — there’s massive amounts of data that say that’s not true. Vegetable fats reduce cardiovascular disease and diabetes risk, and that’s been extraordinarily well-documented.

Do you have any personal pet peeves that people believe about nutrition? Since the internet makes a lot of ideas more easily spreadable, I wonder if there are any that you think are particularly harmful or that you wish people would disabuse themselves of.
Hah. Well, quite a bit.

When people were told that all fat is bad, and that we should eat more carbohydrates — that was absolutely wrong. I think we’ve turned that ship around, though, and fats in the United States diet now are pretty healthy, actually. So, if you’d asked me that question ten years ago, I would’ve said that the “all fats are bad” idea is the single most misguided one. And that was coming from a lot of senior nutrition people. We were on the limb, I would say. Mainstream nutrition was wrong.

But I think now probably this idea that refined vegetable oils, like canola oil and corn oil, are dangerous — and that omega-6 fatty acids are dangerous — IS really dangerous.

Some people have assumed, without any data really, and for hypothetical reasons, that because omega-3s are good that omega-6s must be bad, but that’s entirely wrong. They’re both good, and it’s important that we have enough of both. We see that higher consumption of these vegetable oils is related very clearly to better cholesterol levels and lower risk of cardiovascular disease.

I know that many plant oils are high in omega-6s but low in omega-3s, or have no omega-3s.
If you have only sunflower oil, or only safflower oil, for instance, which contain no omega-3s — and if you have no other sources of omega-3s in your diet — then you would be unbalanced. But if you add some omega-3s, either from enough fish, or from canola oil or soybean oil [which have significant amounts of omega-3s], then you’ll have a very good mix. And that would reduce heart disease risk.

Do you have a favorite meal, or a favorite food that you like to eat?
Um. I like variety, so that’s a hard question. I think that if I had to say something, nuts and berries are my go-tos.

Me too!
Especially because I travel a lot, and I don’t always have easy access to food that I would like to eat. And nuts come in such a variety, and you can eat them in lots of different ways — putting them on salads, having them as a snack, adding them to lots of different things. The evidence of the healthfulness of nuts is extreme, whether you’re looking at dozens of controlled-feeding studies, or at long-term studies of what eating nuts does to your lipids and other parameters. Nuts are an especially good replacement for meat and carbohydrates, too. They’re a good thing to be part of any diet.

Do you eat a lot of beans?
Personally, I eat more nuts and fewer beans. From a health standpoint, nuts have been better studied. And the evidence is much more abundant. But even putting a modest amount of beans into diets, almost everybody can tolerate that. And it adds some more variety and health along the way.

And the planet could withstand producing many, many more nuts, in case everybody switched to a nut-eating diet?
We could produce a lot more, it looks like, yes. We did run the analyses for the amounts that we recommend, and the planet — it can do very well. I think it would mean quite a big increase in nut production — which includes peanuts, by the way. And there are some good aspects of peanut production, in particular, because you don’t need to add nitrogen fertilizer to the soil, because they’re a legume.

When you get down to exact places and conditions for growing nuts, those numbers need to be looked at carefully. And you need careful agricultural research to say, “What’s the best kind of nut or bean to grow in this area?” One of the things we hope for this report is that it will give us more guidance about where we need to do more research. But the basic answer is yes. The planet can handle that kind of nuts.

Well, that’s good. And then I just have one more small question. I personally still eat two eggs a day, although I know the Planetary Health Diet suggests one or two a week is more optimal. Is there a quick and convincing reason for why I should cut back?
Eggs, when we look at the spectrum of healthfulness, they’re sort of in the middle. In most of the studies, we don’t see any relation between eggs and heart disease, but it does look like if instead of eggs for breakfast, you have my breakfast, which is usually steel cut oats, some nuts, some fruit that’s available — in the winter sometimes dried fruit — and a bit of yogurt, that will look even a little bit better than eggs. In terms of health outcomes. As for environmental reasons, eggs are in the middle to lower part of the spectrum for greenhouse-gas emissions and other environmental footprints: lower than red meat and dairy, but not as low as grains, soy, beans, and nuts. If this is your main animal-sourced food, you would be in our target range. And if that’s the only thing you’re doing differently, you’re doing pretty well.

Tell Me About the Planetary Health Diet