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Listener Elena Prizekin from Palmer, Alaska asks:

I’m listening to a report on food waste. They discuss both retail and household food waste. When various shows give the percentage of waste from households, I have to ask – how is this metric researched? Does anyone/any entity look in the trash to see how much food is wasted?

To figure out how much food we waste, researchers sift through something much more hygienic, but in some ways just as messy: data.

Economists Edward Jaenicke and Yang Yu set out to answer the question and published research in 2020 that found the average American household wastes almost 32% of the food they buy.

That’s about $240 billion in wasted food every year.

Jaenicke and Yu, then both at Penn State, examined the difference between the amount of food purchased (or acquired) by households in a week and the basal metabolic rates of household members – the amount of calories or energy necessary to maintain body weight.

To illustrate what this means, let’s simplify their searches. Suppose a person has a basal metabolic rate of 2,000 calories per day, which is the amount needed to keep their body at rest. If they buy an average of 2,936 calories of food, that’s 936 calories of uneaten food per day, or about one-third (32%) of the amount they bought.

Both used an economic method called the stochastic production frontier model, which allows researchers to calculate inefficiencies. In that context, it’s the amount of “food that hasn’t been fully utilized in this process,” Jaenicke said in an interview with Marketplace.

To determine how much food households purchase in the first place, Jaenicke and Yu used data from the Department of Agriculture’s National Household Food Acquisition and Purchase Survey, or FoodAPS, which represents 4,826 households. This data includes information on “food purchased or otherwise acquired for consumption at home and away,” including food received through assistance programs such as SNAP.

Jaenicke said he chose this dataset because it records food purchased or acquired in various places, including supermarkets, restaurants and cafeterias.

However, Jaenicke noted that it’s not the perfect dataset and there are some caveats. For example, some households might have dipped into already existing food stock during the week or purchased more food to store for the future. This means that the food purchase period does not necessarily correspond to the consumption period.

Next, they had to find a data set to represent the amount of food eaten. It was a delicate task.

“In addition to the food waste that is not directly measured in any of these datasets, the food eaten or consumed is almost never measured,” Jaenicke said.

That’s why they chose to calculate BMRs for the people they studied, he explained.

The two aren’t the only researchers to calculate how much food we waste. The USDA’s Economic Research Service also released estimates using survey data, finding that in 2010, 31% of food at the retail and consumer level was uneaten. , which is similar to the findings of Yu and Jaenicke. Instead, they calculated this amount using the ERS loss-adjusted food availability data series.

Jaenicke said when the ERS calculates food waste, it uses two databases that look at the differences between food purchases, or acquisitions, and consumption. For example, they can see the average number of apples households buy and can subtract the number of apples the average household eats to get the amount of waste associated with apples.

“That’s great, but it doesn’t make any difference between households,” Jaenicke said.

Jaenicke and Yu found that even the most efficient households wasted about 9% of their food, while the least efficient ones wasted almost 90%. Most households fell in the middle, wasting between 20% and 50%.

Jaenicke said higher incomes, smaller households and healthier diets are linked to higher levels of food waste.

“If you’re a wealthy household, you have the luxury of overbuying. If you are a low-income household, you can manage your food inventory by switching to less perishable and potentially less healthy foods.

Jaenicke pointed out that food waste seems “irrational” – after all, why would people throw away the food they bought? But these results show that food waste is not arbitrary and that there are very real reasons why food is not consumed, depending on income level or household size.

Jaenicke said he is still considering how the issue should be resolved. Maybe supermarkets could offer smaller portions. And because of the environmental consequences associated with food waste ending up in landfills, Jaenicke said, policies could be formulated to encourage people to compost.

It turns out that our trash can reveal a lot about us.