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Americans are overeating by at least 300 kcal/day on average, according to some sources:

Twenty-five years ago, the average American consumed about 1,850 calories each day. Since then, our daily diet has grown by 304 calories (roughly the equivalent of two cans of soda). That's theoretically enough to add an extra 31 pounds to each person every year.

(Since 25 years ago, they were grossly overeating too, I'd guess this number is much higher, but let's use this conservative estimate)

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Why aren't Americans gaining 31lb per year (or much more)?

Instead, the average person only gains about 2lb per year in his or her 20s and 30s. Why?

Here's why @C.Lange's "equilibrium" hypothesis does not hold (too long for a comment)

Consider his example:

Random statistic: Male, 30, 6', 200 lb, Sedentary, 15% BF (i.e. 30 lb fat to start).

200 lb @ BF 15% = 2443 kcal
300 lb @ BF 35% ((30 + 75)/300)*100 = 2737 kcal (+294 kcal)
400 lb @ BF 45% ((30 + 150)/400)*100 = 3031 kcal (+294 kcal)
500 lb @ BF 51% ((30 + 225)/400)*100 = 3325 kcal (+294 kcal)

If this person eats at a 300 kcal/day surplus, his equilibrium weight is 300lb, and the initial weight gain (31lb/year) is mostly unaffected by the hypothetical increases in TDEE down the road.

(If my estimate that Americans are overeating by 1000 kcal/day is right, then this person should balloon from 200 to 500lb)

But we don't see this happening. People eat the standard American diet of pizza and donuts, gain weight, but they do it slowly.

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    What do you base this on? How do you know people on avg gain about that much per year? And how do you know people out about 1000 kcal more than they need every day? This all seems pretty vague.
    – MJB
    Aug 22 '19 at 7:03
  • @MJB counting my own calories obsessively, observing what I eat vs what other people eat, calculating TDEE for different people and myself.
    – MWB
    Aug 22 '19 at 16:36
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    So how many people have you observed? And have you observed them from the moment they wake up to the moment they go to bed? And did you count their calories or just roughly estimate what they were eating? I'm sorry but this doesn't feel like a bullet proof test/hypothesis. It sounds rather anecdotal.
    – MJB
    Aug 23 '19 at 5:48
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    I would guesstimate that your guesstimate overestimates the caloric intake of the average person and/or underestimates their total daily energy expenditure.
    – David Scarlett
    Aug 23 '19 at 6:30
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    @DavidScarlett - That's just a guess, though, right?
    – JohnP ♦
    Aug 27 '19 at 20:52
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I would guesstimate that most people in the developed world consume at least 1000 kcal more per day than they spend.

While I can't confirm that the 1000 kcal fact is true, it is fairly common knowledge that the United States of America has an obesity epidemic. Any quick search can show you hundreds of charts and figures. I won't argue that we're overeating. Personally, I'm from Canada and while it isn't quite as prevalent here, people still overeat.

If calories-in-calories-out is correct, this overeating should lead to 2lb (1kg) of fat gained per week. However, the average person only gains about this much per year in his or her 20s and 30s. Why not much more?

If you think about it, this is all about equilibrium. I currently weigh a modest 200 lbs. If I put on 100 lbs by overeating, I wouldn't necessarily gain 100 lbs of fat. My muscles would build up in order to move my body around (assuming I wish to stay mobile). As such, my TDEE would increase. At some point, my mass, the muscles I've gained to move my mass, and the number of calories I enjoy intaking will all balance, and I would stop gaining weight.

If someone were to consistently gain 2 lbs per week, they would need to eat 1000 kcal more than their TDEE. With 100 lbs of weight gain, my TDEE could change as much as 600 calories meaning than I now have to eat 1600 calories more than before. At 200 lbs I need to eat 2200 calories more, 300 lbs I need 3000 calories more, etc.

EDIT 1:

This scholarly article that shows that obese individuals have higher muscle activation even though overall muscular strength is reduced. Articles like this prove that we can't assume 100 lbs of weight gain is 100% fat.

For TDEE comparison let's assume for every 100 lbs of weight gain, 25% is muscle mass.

Random statistic: Male, 30, 6', 200 lb, Sedentary, 15% BF (i.e. 30 lb fat to start).

200 lb @ BF 15% = 2443 kcal
300 lb @ BF 35% ((30 + 75)/300)*100 = 2737 kcal (+294 kcal)
400 lb @ BF 45% ((30 + 150)/400)*100 = 3031 kcal (+294 kcal)
500 lb @ BF 51% ((30 + 225)/400)*100 = 3325 kcal (+294 kcal)

EDIT 2:

That's theoretically enough to add an extra 31 pounds to each person every year.

I think this is where you might be getting confused because this is a misleading statistic. The source states that we're overeating by 304 calories a day. Which then finds that:

(304 calories/day * 365 days/year) / (~3500 calories/lb fat) = 31.7 lb fat/year

This is theoretical. In reality, if everyone in America put on 31.7 lbs of fat this year, we would no longer be overeating by 304 calories per day for our new weight. Now we'd only be overeating by 200 calories per day, so, we'd gain 20.8 pounds in the second year.

So, to be clear, 31 lbs/year is misleading. It would be 31 lbs in the first year.

Additionally, the source states that the average diet used to be 1850 kcal a day twenty-five years ago. With 304 kcal added to that, we're now at a daily consumption of 2154 calories on average. The gentleman in my example would be losing weight at this level of eating. It's not that everyone is putting on fat every day, it's that America as a whole is just heavier already. That's why you see the weight being gained slowly because most people, on average, are already eating in the 2100 calories range (which includes that 304 increase) instead of the 1850 range.

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  • If you were a weight-lifter, and gained 100lb via "lean-bulking", I'd say yes. But your average person, eating too many donuts will mostly gain fat with unclear/negligible effect on TDEE (more weight, but also more insulation and probably more sedentary)
    – MWB
    Aug 22 '19 at 16:34
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    @MaxB TDEE increases even with fat gain. The more living mass there is, the more energy it takes to keep it alive. Muscle cells use more energy than fat cells, but that doesn't mean fat cells have a negligible effect on energy production.
    – DeeV
    Aug 22 '19 at 17:17
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    @MaxB, I agree with what DeeV wrote. Fat is still living cells that still requires energy to keep alive. Also consider this, if you were to put on a 200 lb weight vest on right now and wear it 24/7, are you telling me you wouldn't build muscle? Even if it was just walking around the grocery store. I can't even think of how much energy I'd use if I had to do that. I don't know what the % split between fat and muscle gain would be but I don't think it's negligible.
    – C. Lange ♦
    Aug 22 '19 at 17:47
  • @DeeV Not according to the TDEE models I'm using. Make sure you input the bf%. Most estimates don't even consider bf%, which is probably what you are using.
    – MWB
    Aug 22 '19 at 20:09
  • @C.Lange I see people with "200lb vests" in Walmart all the time. They are the primary reason why Walmart has scooters.
    – MWB
    Aug 22 '19 at 20:19

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