It is, these days, an overwhelmingly familiar sight: adorning every packet of food or drink, the little table of nutritional information. Snacks today are duty-bound to relate their concentrations of certain vitamins; to warn us of how much sugar and fat they contain; most of all, looming large above all other attributes, they must inform us of the dreaded calorie count.<\/p>\n
But that\u2019s not all. A, say, Mars bar won\u2019t only be labeled as containing 260 calories \u2013 less if you\u2019re outside the US, for reasons that aren\u2019t what you\u2019re probably expecting<\/a> \u2013 but it will invariably also express that amount as a proportion of your supposed daily allowance. For energy, that\u2019s \u201c2,000 calories a day\u201d, according to the little note<\/a> found at the bottom of the label (and yes, we know they\u2019re technically kilocalories, but the Food and Drug Administration [FDA] doesn\u2019t care and neither do we; you know as well as we do what we mean).<\/p>\n Even for those of us who aren\u2019t habitual dieters, the 2,000-a-day figure is practically baked into our brains these days \u2013 but have you ever wondered where it came from?<\/p>\n 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 \u2013 it takes x calories to watch TV, y calories to walk the dog around the block, z\u00a0calories to host this week\u2019s book club; add it all up, and you get, more or less, around 2,000. That\u2019s not how it was done.<\/p>\n Maybe you had a simpler imagined origin story: perhaps those government eggheads took some kind of standardized \u201chealthy\u201d diet plan, and worked out how many calories<\/a> would be contained within. That\u2019s not how it was done either.<\/p>\n No: the truth is, sadly, much stupider.<\/p>\n The problem with calories<\/p>\n \u201cTwo-thousand calories a day was not based on nutritional or medical best practices,\u201d argued author and podcaster Aubrey Gordon in a 2022 episode<\/a> of the food science podcast Maintenance Phase. \u201cIt 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.\u201d<\/p>\n Why is that bad? Well, put simply, people are really bad at accurately reporting what they ate in a day. Sometimes that\u2019s on purpose \u2013 if you\u2019re reporting your diet<\/a> to some official healthy diet folks from the USDA, then hey, maybe you don\u2019t want to admit to that extra eight cookies you scarfed down at midnight \u2013 but sometimes it\u2019s 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\u2019s share?<\/p>\n It all adds up \u2013 sometimes to quite ridiculous results. \u201cIn the early 1980s [USDA] scientists observed glaring inconsistencies in the results of the agency’s national surveys of dietary intake,\u201d noted food scientists Marion Nestle and Malden Nesheim in their 2012 book Why Calories Count: From Science to Politics<\/a>. \u201cThey 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.\u201d\u00a0<\/p>\n \u201cEven more suspicious, during the thirteen-year period from 1965 to 1978 the average heights and weights of survey participants had increased,\u201d Nestle and Nesheim added, \u201cmeaning that they should have been eating more calories, not fewer.\u201d<\/p>\n Upon further study \u2013 that is, recruiting about 30 volunteers to painstakingly record their diets and calorie intake for four weeks spaced throughout the year \u2013 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 \u2013 some 200 or 300 higher than the averages reported in more general surveys.\u00a0<\/p>\n And here\u2019s the kicker: even those figures were too low.<\/p>\n \u201cThe investigators knew that the calories had to be underreported. They had the proof,\u201d Nestle and Nesheim wrote. As a reliability check, they had collected duplicate meals from the volunteers, they explained \u2013 and upon analysis, \u201cthey found actual calories to exceed reported calories by an average of 13 percent.\u201d<\/p>\n Evidently, self-reported data is problematic. But here\u2019s the thing: even if it wasn\u2019t, 2,000 calories is still the wrong number.<\/p>\n Where did 2,000 come from?<\/p>\n There\u2019s something you may have noticed about those numbers in the USDA study: they\u2019re\u2026 kinda high, right?<\/p>\n Oh, sure, the figure for women is lower than 2,000 \u2013 though we should point out that correcting for a theoretical 13 percent undercount brings that figure up to about 2,126 calories per day \u2013 but the men\u2019s figure is stonkingly high compared to the guideline amount. Assuming these guys weren\u2019t all piling on the pounds like a British billionaire, why were the numbers so large?<\/p>\n 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 \u201cWhat We Eat in America<\/a>\u201d 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.\u00a0<\/p>\n 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, \u201cmost of the people who responded [\u2026] judged the proposed benchmark to be too high,\u201d Nestle and Nesheim wrote. \u201cNutrition educators worried that it would encourage overconsumption, be irrelevant to women who consume fewer calories, and permit overstatement of acceptable levels of \u2018eat less\u2019 nutrients such as saturated fat and sodium.\u201d<\/p>\n<\/p>\n \u201cInstead, they proposed 2,000 calories,\u201d 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<\/a> women \u2013 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).<\/p>\n \u201cWhether a rounding down of nearly 20 percent is reasonable or not, the FDA ultimately viewed these arguments as persuasive,\u201d Nestle and Nesheim wrote. The 2,000 calories per day benchmark was born \u2013 even though for almost all adults, it was wildly low.<\/p>\n How many calories do I actually need?<\/p>\n So, what\u2019s the real number of daily calories an adult should be consuming? Well, like basically everything biological, there\u2019s really no hard-and-fast rule \u2013 and in fact, there was never meant to be.<\/p>\n \u201cThe FDA [\u2026] didn’t actually intend this \u20182,000 calories per day\u2019 to be a nutritional guideline,\u201d Gordon pointed out. \u201cThey said that they designed it to be a popular education tool.\u201d<\/p>\n It turns out that, rather than knowledge around calories informing those nutritional labels<\/a> on food, the exact opposite happened. \u201cEssentially, 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,\u201d Gordon explained. \u201cBut 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.\u201d<\/p>\n