How Did The FDA Settle On The “2,000 Calories Per Day” Guideline?

But that’s not all. A, say, Mars bar won’t only be labeled as containing 260 calories – less if you’re outside the US, for reasons that aren’t what you’re probably expecting – but it will invariably also express that amount as a proportion of your supposed daily allowance. For energy, that’s “2,000 calories a day”, according to the little note found at the bottom of the label (and yes, we know they’re technically kilocalories, but the Food and Drug Administration [FDA] doesn’t care and neither do we; you know as well as we do what we mean).

Even for those of us who aren’t habitual dieters, the 2,000-a-day figure is practically baked into our brains these days – but have you ever wondered where it came from?

Perhaps you thought some boffins in the US Department of Agriculture (USDA) or FDA had calculated it based on the average daily energy expenditure of an American adult – it takes x calories to watch TV, y calories to walk the dog around the block, z calories to host this week’s book club; add it all up, and you get, more or less, around 2,000. That’s not how it was done.

Maybe you had a simpler imagined origin story: perhaps those government eggheads took some kind of standardized “healthy” diet plan, and worked out how many calories would be contained within. That’s not how it was done either.

No: the truth is, sadly, much stupider.

The problem with calories

“Two-thousand calories a day was not based on nutritional or medical best practices,” argued author and podcaster Aubrey Gordon in a 2022 episode of the food science podcast Maintenance Phase. “It was not based on recommendations from scientists; it was not based on research into any optimal diet, or weight management, or any of that stuff. It was based on Americans’ self-reported calorie intakes through USDA surveys.”

Why is that bad? Well, put simply, people are really bad at accurately reporting what they ate in a day. Sometimes that’s on purpose – if you’re reporting your diet to some official healthy diet folks from the USDA, then hey, maybe you don’t want to admit to that extra eight cookies you scarfed down at midnight – but sometimes it’s just forgetfulness or optimism. Was it one cup of ice cream you had last Tuesday, or two? Did you really split that pizza with your pals evenly, or did you have the lion’s share?

It all adds up – sometimes to quite ridiculous results. “In the early 1980s [USDA] scientists observed glaring inconsistencies in the results of the agency’s national surveys of dietary intake,” noted food scientists Marion Nestle and Malden Nesheim in their 2012 book Why Calories Count: From Science to Politics. “They noticed that the number of calories reported as consumed by men and women in 1977-78 was lower than the number reported in 1965. Not only that, but respondents to the 1977-78 survey reported intakes 300 to 400 calories below the amounts needed to maintain their weights.” 

“Even more suspicious, during the thirteen-year period from 1965 to 1978 the average heights and weights of survey participants had increased,” Nestle and Nesheim added, “meaning that they should have been eating more calories, not fewer.”

Upon further study – that is, recruiting about 30 volunteers to painstakingly record their diets and calorie intake for four weeks spaced throughout the year – the USDA researchers confirmed what we all already know. When forced to be honest, the men in the study reported an average of 2,760 calories per day and the women 1,850 – some 200 or 300 higher than the averages reported in more general surveys. 

And here’s the kicker: even those figures were too low.

“The investigators knew that the calories had to be underreported. They had the proof,” Nestle and Nesheim wrote. As a reliability check, they had collected duplicate meals from the volunteers, they explained – and upon analysis, “they found actual calories to exceed reported calories by an average of 13 percent.”

Evidently, self-reported data is problematic. But here’s the thing: even if it wasn’t, 2,000 calories is still the wrong number.

Where did 2,000 come from?

There’s something you may have noticed about those numbers in the USDA study: they’re… kinda high, right?

Oh, sure, the figure for women is lower than 2,000 – though we should point out that correcting for a theoretical 13 percent undercount brings that figure up to about 2,126 calories per day – but the men’s figure is stonkingly high compared to the guideline amount. Assuming these guys weren’t all piling on the pounds like a British billionaire, why were the numbers so large?

Well, it turns out that even in self-reported data, the average calorie intake of an adult is higher than 2,000 per day. The “What We Eat in America” study from 2008 found an average of 2,500 calories per day for men and 1,800 for women; the average of all USDA self-reported dietary intake surveys prior to 1990 works out to 2,350 calories per day. 

And in fact, it was this latter figure that the FDA originally wanted to use as the daily standard. But almost immediately, they ran into objections: during the mandatory public comment period on the new policy, “most of the people who responded […] judged the proposed benchmark to be too high,” Nestle and Nesheim wrote. “Nutrition educators worried that it would encourage overconsumption, be irrelevant to women who consume fewer calories, and permit overstatement of acceptable levels of ‘eat less’ nutrients such as saturated fat and sodium.”

“Instead, they proposed 2,000 calories,” they explained, with the arguments being that this figure was easier to remember and use than 2,350; consistent with widely used food plans; and closer to the calorie requirements for postmenopausal women – the population group most prone to weight gain, with the lowest caloric needs for adults (for reference, Nestle and Nesheim also note that 2,000 calories is around the number expended daily by 9-year-old children).

“Whether a rounding down of nearly 20 percent is reasonable or not, the FDA ultimately viewed these arguments as persuasive,” Nestle and Nesheim wrote. The 2,000 calories per day benchmark was born – even though for almost all adults, it was wildly low.

How many calories do I actually need?

So, what’s the real number of daily calories an adult should be consuming? Well, like basically everything biological, there’s really no hard-and-fast rule – and in fact, there was never meant to be.

“The FDA […] didn’t actually intend this ‘2,000 calories per day’ to be a nutritional guideline,” Gordon pointed out. “They said that they designed it to be a popular education tool.”

It turns out that, rather than knowledge around calories informing those nutritional labels on food, the exact opposite happened. “Essentially, they wanted consumers to be able to compare the nutritional value of different foods to one another, and compare apples to apples a little bit,” Gordon explained. “But in order to do that, they had to standardize serving sizes, they had to standardize calorie counts, they had to come up with a standardized system, so that everybody was getting the same information.”

The 2,000 figure is, overall, a flawed figure, based on flawed data, being used in a way for which it was never originally intended. So how many calories is a more reasonable figure?

“Studies using doubly labeled water – as close to a gold standard as exists – find that the average non-overweight adult man needs about 3,050 calories a day to maintain a stable body weight, and the average woman about 2,400,” Nestle and Nesheim wrote. “The FDA’s 2,000-calorie standard for food labels is 50 percent lower than the average for men and 20 percent lower than that for women.”

If you think you’re under or over that count, however – and you’re not gaining or losing weight without wanting to – don’t worry too hard. “Nutritionists do not define precise standards for appropriate levels of calorie intake,” Nestle and Nesheim wrote. 

“We can’t,” they admitted. “People vary too much in dietary intake and physical activity levels to set meaningful levels.”