The FDA claims a sedentary 40 year old man needs 2400 calories a day, the same as a 17 year old incidentally. [1] Or that everybody just needs 50g of protein a day. [2] Then there's the fat vs sugar food pyramid nonsense that led to more than half a century of health degradation.
It is an average. A guideline. And most countries give an average or range. And the US isn't the highest here: The official recommended averages I found after moving to Norway were higher than in the US and much more reasonable to keep to. (I'm female, my averages are lower).
That doesn't mean that the food pyramid is a good thing or that we've been giving good health advice. It also doesn't mean that our health advice is all that good now. We know more than we did before, but nutrition science seems tricky to do and even trickier to communicate well with the general public in ways that most people can follow. And that's before the disinformation from business interests and dealing with outright scams and lies.
Here's the thing: It may be that 2400 calories would take the average 40 year old male and only have him continue the socially acceptable weight gain of a few lbs a year. Or maybe the average (already overweight) male would maintain his weight at 2400 calories.
But in any sane world, that's like the 90th percentile of calories required when consumed with a carb-heavy american diet and I'd argue almost no sedentary person requires that much. Just plugging in the basal metabolic rate numbers gets something well below that.
Norwegian Institute of Health has a calorie calculator[1] based on scientific studies.
For a 40 yo male, 180 cm (5' 10") high and weighing 80 kg (176 punds), it spits out 1800 kcal at complete rest.
That then gets multiplied by a factor of 1.4-1.5 if you're a sedatary office worker, resulting in around 2400-2500 kcal.
This number is for maintaing weight. I used the calculator to find my 500 kcal deficit to lose weight, and based on my actual losses it seems quite accurate.
I ran similar numbers and experiments over and over. In the end I found composition and "starting weight" matters quite a lot. https://jodavaho.io/tags/diet.html
You can easily go +/- 5-10 lbs at my height, just by choosing carbs over protein or fat, and it's not "Fat loss" or body composition, it's water weight associated with converting carbs to something your body can use.
Then a fast day drops you another 5-10 lbs for opposite reasons + burning glycogen stores. And that >10% swing in body "weight" is just noise on the calorie estimates if you plug it directly into such a calculator.
(as an example, if I choose 2000 calories of carb-heavy foods, I will weigh more, increasing my calorie "budget" to maintain weight b/c I eat more carbs, producing a higher weight, further increasing my calorie "budget", etc etc).
I can find 2200 for my 2 meter height, or 2500, or 1800, depending on input weight, and since input weight varies by day, and by caloric intake (due to food weight, water weight, and weight gain), it's not reliable to say the "average" person is healthy with 2400 calories. Because perhaps that person should be eating different foods or have 10 lbs less bodyfat to begin with!
I find you have to reverse-engineer it given what you know to be a healthy weight including muscle and fat composition.
The 3800 number was from the media misunderstanding/misrepresenting the data. The 3800 is calorie availability, not consumption. With calorie availability you take absolutely all food produced/imported and then divide by the population size. There's no reduction for waste, spoilage, inedibility, etc. [1]
Americans aren't eating anywhere near 3800 calories on average. 2400 calories is already a massive amount of food. That's 15 100g servings of chicken breast (cooked weight) for some baseline of what it means in terms of healthy food. Obviously lots of people are eating lots of junk that makes it easy to bring up the consumption, but it's still nowhere near 3800 on average.
Using unseasoned cooked chicken breast as your proxy for healthy food is...less absurd than using grapefruit would be, but not as much as you might think.
At least add like a quarter teaspoon of olive oil, an eighth of a cup of whole grain rice, and a side of like some sweet potatoes with its own seasoning or something.
Straight chicken breasts is like the meme level of what celebrities have to eat to maintain their figure, not what a reasonable human diet looks like. Chicken thighs with the skin on are reasonably healthy.
I'm about to say something that is easy to dismiss as bullshit, so feel free to, but you're right, people were healthier in terms of weight in the 60s, and right around that is when we changed dietary guidance to be carb-focused, low fat, etc. Since then, obesity has skyrocketed. The book Obesity Code covers this.
As sibling comments have pointed out, 3800 is availability, not consumption, so it's not an indicator of how much people do eat, just how much they could eat.
You can see it if you watch any US documentary filmed before the late 70s that shows ordinary people in the street. They're much fitter, and exercise for weight loss wasn't really a thing yet; people didn't jog. That's not far enough back that everyone was a farmer or laborer; there were plenty of fairly sedentary office workers. They also weren't starving; it was a prosperous time. They were generally eating meat-and-potatoes diets with plenty of animals fats (I have a 1960s barbeque cookbook that tells you to put a pat of butter on pretty much everything). And obesity wasn't a problem.
And since we started letting the government tell us how to eat healthy, not only has obesity skyrocketed, but so have diseases connected with it.
My parents were vegetarians in the 80s, also no weight issues. I don't believe it's carbs or seed oils or any of the modern scapegoats. Since they were eating plenty of that. They even had cake.
I think it doesn't matter what you eat as long as it isn't super processed. The one thing that's changed a lot in the 90s is more and more convenience food.
"processed" is also a modern scapegoat, unfortunately.
But all three are correct, I think: Food has gotten more laden with sugar, seed oils, and carbs because it's processed to be that way after we tried to go Low Fat for so long.
A conscientious vegetarian is probably eating damn near an ideal diet by avoiding all that.
But they were eating plenty of seed oils, and sugar in cake, and loads of bread.
So mostly carbs, but with a lot of fiber. It just goes counter to the current trend in major ways. I looked through the old cookbooks. The biggest difference is no processed foods. And maybe less microplastics.
It's hard to really appreciate how many calories are added to things like bread, just by virtue of changing the recipe to be more "USA tasty" (e.g., sugary). My EU friends always commented on how sweet everything is in USA, even store-bought bread. If we didn't do that, when we started reducing fat, everything would taste like hardtack. But 200 extra sneaky calories a day + insulin spikes from the refined carbs, and here we are - all fat.
The government shapes diets both through guidance (food pyramid, “plates”, etc) and regulation. For example, a major criticism revolves around farm bill payouts that incentivize corn production, leading to cheap fructose that finds its way into everything.
