F is for Food Waste (Shallow Thoughts)

Akkana's Musings on Open Source Computing and Technology, Science, and Nature.

Mon, 06 Apr 2020

F is for Food Waste

I keep seeing people claim that 40% of consumer food in the US is thrown away uneaten, or hear statistics like 20 pounds of wasted food per person per month.

I simply don't believe it.

There's no question that some food is wasted. It's hard to avoid having that big watermelon go bad before you have a chance to finish it all, especially when you're a one- or two-person household and the market won't sell you a quarter pound of cherries or half a pound of ground beef. And then there's all the stuff you don't want to eat: the bones, the fat, the banana peels and apple cores, the artichoke leaves and corn cobs.

But even if you count all that ... 40 percent? 2/3 of a pound per day per person? And that's supposed to be an average -- so if Dave and I are throwing out a few ounces, somebody else would have to be throwing out multiple pounds a day. It just doesn't seem possible. Who would do that?

When you see people quoting a surprising number -- especially when you see the same big number quoted by lots of people -- you should always ask yourself the source of the number.

Our county's zero-waste team says the number comes from the EPA, but doesn't give details. But a web search found a few articles that referenced a 2009 study: The Progressive Increase of Food Waste in America and Its Environmental Impact (Kevin D. Hall, Juen Guo, Michael Dore, Carson C. Chow) . Fortunately it's on PLOS One so you can read the actual study.

They use a fairly complicated formula (explained in the article) to take the increase of average body weight among US adults over the past 30 years and map that to number of calories (kcal) consumed by the entire US population. Then they take the total number of calories available in the US national agricultural production, as tracked by the US Food and Agriculture Organization (FAO), and compare the two numbers. They calculate a waste of 1400 kcal per person per day in 2003, representing 40% of the total food stream, compared with 900 kcal in 1974 (30%).

It all seems kind of hand-wavey and makes a lot of assumptions. To their credit, the authors acknowledge that there's potential for errors on both sides: in the FAO's estimate of food calories, and in their calculation of calories burned. They make an effort to be clear about their calories-burned calculations (that's most of the paper). But it's not so easy to find out anything about the methodology used for the FAO estimates of calories in the food stream. I tried, but the FAO website is a mess and I gave up after a while. The paper also doesn't address the bone/fat/corncob issue, so I have to assume that's all counted as waste.

In any case, this paper has nothing to do with consumer food waste, the difference between what people buy at the supermarket and what they end up throwing out. It's a measure of how much food produced by agriculture ends up not being consumed: a very different number.

There's another study referenced by a few sources: the 2014 USDA study The Estimated Amount, Value, and Calories of Postharvest Food Losses at the Retail and Consumer Levels in the United States (Buzby, Wells, Hyman). They come up with much lower numbers: 31% food loss for the retail and consumer levels combined, 21% for consumer loss. "Food loss", as they define it, is all postharvest food that isn't consumed for any reason, including loss to spoilage, pests and moisture loss, as opposed to "food waste" which they define as edible food going unconsumed.

But the USDA study isn't a useful source, because they don't have any methodology: they're just quoting numbers that come from somewhere else, with lots of hand-waving references like "details are available on the ERS website" -- but all the links given in the paper to specific ERS pages are broken, and they don't cite any specific studies that someone might be able to look up.

In my hunt for relevant food-waste numbers, by far the best study I found was from Canada in 2018: The quantity of food waste in the garbage stream of southern Ontario, Canada households (van der Werf, Seabrook, Gilliland). They analyzed the trash from 2,800 single-family households located in different parts of southern Ontario. It's a great study, full of interesting details, and really addresses the important issue: how much food are people throwing out? They found that on average, households threw out 43.0 kg/person/year, which works out to about a quarter pound a day per person. That includes items they classified as "unavoidable" waste, like banana peels, bones and coffee grounds. Alas, I couldn't find any similar studies for the US.

So: the guesses for the US are all over the place, and mostly don't seem to be backed up with any real science. Nobody has really studied how much food people in the US throw away. But that doesn't stop people from citing unrelated numbers!

I know, I know ... it's fun to get all ragey about how all those unenlightened people just don't "get" environmental issues and need to shape up. I don't even disagree. I'm sure lots of food really is wasted, and we should all try to waste less.

But -- making stuff up doesn't help the cause. Don't perpetuate bogus statistics, quoting numbers where you haven't checked the source. Just because lots of other web pages repeat the same statistic doesn't make it true.

Information spreads like a virus. We're all trying to be so careful and not spread coronavirus. Spreading fake statistics might be less lethal, but it takes a lot longer to find a cure.

Just remember: 27.6% of all statistics are made up.

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[ 20:08 Apr 06, 2020    More science | permalink to this entry | comments ]