In this episode of the Leading Voices in Food podcast, host Norbert Wilson is joined by food and nutrition policy economists Will Masters and Parke Wilde from Tufts University's Friedman School of Nutrition, Science and Policy. The discussion centers around the concept of the least cost diet, a tool used to determine the minimum cost required to maintain a nutritionally adequate diet. The conversation delves into the global computational methods and policies related to least cost diets, the challenges of making these diets culturally relevant, and the implications for food policy in both the US and internationally. You will also hear about the lived experiences of people affected by these diets and the need for more comprehensive research to better reflect reality.

Interview Summary

I know you both have been working in this space around least cost diets for a while. So, let's really start off by just asking a question about what brought you into this work as researchers. Why study least cost diets? Will, let's start with you.

I'm a very curious person and this was a puzzle. So, you know, people want health. They want healthy food. Of course, we spend a lot on healthcare and health services, but do seek health in our food. As a child growing up, you know, companies were marketing food as a source of health. And people who had more money would spend more for premium items that were seen as healthy. And in the 2010s for the first time, we had these quantified definitions of what a healthy diet was as we went from 'nutrients' to 'food groups,' from the original dietary guidelines pyramid to the MyPlate. And then internationally, the very first quantified definitions of healthful diets that would work anywhere in the world. And I was like, oh, wow. Is it actually expensive to eat a healthy diet? And how much does it cost? How does it differ by place location? How does it differ over time, seasons, and years? And I just thought it was a fascinating question.

Great, thank you for that. Parke?

There's a lot of policy importance on this, but part of the fun also of this particular topic is more than almost any that we work on, it's connected to things that we have to think about in our daily lives. So, as you're preparing and purchasing food for your family and you want it to be a healthy. And you want it to still be, you know, tasty enough to satisfy the kids. And it can't take too long because it has to fit into a busy life. So, this one does feel like it's got a personal connection.

Thank you both for that. One of the things I heard is there was an availability of data. There was an opportunity that seems like it didn't exist before. Can you speak a little bit about that? Especially Will because you mentioned that point.

Will: Yes. So, we have had food composition data identifying for typical items. A can of beans, or even a pizza. You know, what is the expected, on average quantity of each nutrient. But only recently have we had those on a very large scale for global items. Hundreds and hundreds of thousands of distinct items. And we had nutrient requirements, but only nutrient by nutrient, and the definition of a food group where you would want not only the nutrients, but also the phytochemicals, the attributes of food from its food matrix that make a vegetable different from just in a vitamin pill. And those came about in, as I mentioned, in the 2010s. And then there's the computational tools and the price observations that get captured. They've been written down on pads of paper, literally, and brought to a headquarters to compute inflation since the 1930s. But access to those in digitized form, only really in the 2000s and only really in the 2010s were we able to have program routines that would download millions and millions of price observations, match them to food composition data, match that food composition information to a healthy diet criterion, and then compute these least cost diets. Now we've computed millions and millions of these thanks to modern computing and all of that data.

Great, Will. And you've already started on this, so let's continue on this point. You were talking about some of the computational methods and data that were available globally. Can you give us a good sense of what does a lease cost diet look like from this global perspective because we're going to talk to Parke about whether it is in the US. But let's talk about it in the broad sense globally.

In my case the funding opportunity to pay for the graduate students and collaborators internationally came from the Gates Foundation and the UK International Development Agency, initially for a pilot study in Ghana and Tanzania. And then we were able to get more money to scale that up to Africa and South Asia, and then globally through a project called Food Prices for Nutrition. And what we found, first of all, is that to get agreement on what a healthy diet means, we needed to go to something like the least common denominator. The most basic, basic definition from the commonalities among national governments' dietary guidelines. So, in the US, that's MyPlate, or in the UK it's the Eat Well Guide. And each country's dietary guidelines look a little different, but they have these commonalities. So, we distilled that down to six food groups. There's fruits and vegetables, separately. And then there's animal source foods altogether. And in some countries they would separate out milk, like the United States does. And then all starchy staples together. And in some countries, you would separate out whole grains like the US does. And then all edible oils. And those six food groups, in the quantities needed to provide all the nutrients you would need, plus these attributes of food groups beyond just what's in a vitamin pill, turns out to cost about $4 a day. And if you adjust for inflation and differences in the cost of living, the price of housing and so forth around the world, it's very similar. And if you think about seasonal variation in a very remote area, it might rise by 50% in a really bad situation. And if you think about a very remote location where it's difficult to get food to, it might go up to $5.50, but it stays in that range between roughly speaking $2.50 and $5.00.

Meanwhile, incomes are varying from around $1.00 a day, and people who cannot possibly afford those more expensive food groups, to $200 a day in which these least expensive items are trivially small in cost compared to the issues that Parke mentioned. We can also talk about what we actually find as the items, and those vary a lot from place to place for some food groups and are very similar to each other in other food groups. So, for example, the least expensive item in an animal source food category is very often dairy in a rich country. But in a really dry, poor country it's dried fish because refrigeration and transport are very expensive. And then to see where there's commonalities in the vegetable category, boy. Onions, tomatoes, carrots are so inexpensive around the world. We've just gotten those supply chains to make the basic ingredients for a vegetable stew really low cost. But then there's all these other different vegetables that are usually more expensive. So, it's very interesting to look at which are the items that would deliver the healthfulness you need and how much they cost. It's surprisingly little from a rich country perspective, and yet still out of reach for so many in low-income countries.

Will, thank you for that. And I want to turn now to looking in the US case because I think there's some important commonalities. Parke, can you describe the least cost diet, how it's used here in the US, and its implications for policy?

Absolutely. And full disclosure to your audience, this is work on which we've benefited from Norbert's input and wisdom in a way that's been very valuable as a co-author and as an advisor for the quantitative part of what we were doing. For an article in the journal Food Policy, we use the same type of mathematical model that USDA uses when it sets the Thrifty Food Plan, the TFP. A hypothetical diet that's used as the benchmark for the maximum benefit in the Supplemental Nutrition Assistance Program, which is the nation's most important anti-hunger program. And what USDA does with this model diet is it tries to find a hypothetical bundle of foods and beverages that's not too different from what people ordinarily consume. The idea is it should be a familiar diet, it should be one that's reasonably tasty, that people clearly already accept enough. But it can't be exactly that diet. It has to be different enough at least to meet a cost target and to meet a whole long list of nutrition criteria. Including getting enough of the particular nutrients, things like enough calcium or enough protein, and also, matching food group goals reasonably well. Things like having enough fruits, enough vegetables, enough dairy. When, USDA does that, it finds that it's fairly difficult. It's fairly difficult to meet all those goals at once, at a cost and a cost goal all at the same time. And so, it ends up choosing this hypothetical diet that's almost maybe more different than would feel most comfortable from people's typical average consumption.

Thank you, Parke. I'm interested to understand the policy implications of this least cost diet. You suggested something about the Thrifty Food Plan and the maximum benefit levels. Can you tell us a little bit more about the policies that are relevant?

Yes, so the Thrifty Food Plan update that USDA does every five years has a much bigger policy importance now than it did ...

E286: How 'least cost diet' models fuel food security policy