Energy expenditure and obesity across the economic spectrum, McGrosky et al. 2025

[Hoopoe]

The microbiome also has to play a role. All the food we eat passes through the gut and it's microbial ecosystem. It's hard to believe that it doesn't affect what happens to the calories we ingest.

I quickly gained several kg after taking antibiotics and I know antibiotics are a well established method for increasing the weight of livestock.

 

[Jesse]

But overall I think the more likely scenario is just that "weight = (apparent) calories ingested - (apparent) calories expended" is an insufficient model for a large portion of the population.

Then how come a gastric bypass surgery is extremely effective in almost all with morbid obesity patients?

 

[Utsikt]

I have no trouble accepting that due to various mechanisms, different bodies will get a different amount of energy out of the same food input, and that different processes in the body might modulate how much energy is expended throughout the day with the same activity level.

What I have trouble understanding is how normal, otherwise healthy people could have what would have to be a substantially lower requirement for food input than others in order to not lose weight over long term at e.g. 1500-1800 calories in nutritious and non-ultraprocessed food a day for an average height and moderately active man.

 

[EndME]

I have no trouble accepting that due to various mechanisms, different bodies will get a different amount of energy out of the same food input, and that different processes in the body might modulate how much energy is expended throughout the day with the same activity level.

Agree some obvious things that even the layman as myself can think of are things such as muscle mass or thyroid conditions affecting such things as basal metabolic rate.

What I have trouble understanding is how normal, otherwise healthy people could have what would have to be a substantially lower requirement for food input than others in order to not lose weight over long term at e.g. 1500-1800 calories in nutritious and non-ultraprocessed food a day for an average height and moderately active man.

Yes, I agree and the examples mentioned by Jonathan are compelling. But on the other hand I don't understand why some people can eat so much more calories than other people without gaining any weight and I have known several examples of such people including myself in younger years, having gone by the nickname "fastest metabolism in the west" in my university cafeteria. But maybe that also has to do with how we perceive things and how such things can sometimes be hard to estimate (one person might have a chubby face whilst the other has fat in areas where one wouldn't perceive them as being overweight etc).

I do think it's pretty clear that people in the US are more overweight than people in South Korea without some magical factor playing any role in that whatsoever, but I can appreciate that some degree there might be a difference in a population level observation (people are eating more calories than necessary due to complex factors) and trying to make inferences in some more specific individuals.

 

[jnmaciuch]

I'll clarify my main point a little bit:

If you could theoretically measure all the various factors that account for "energy" expenditure from caloric intake, you would get a balanced equation--you have to. We have ways to estimate these factors that seem reasonably accurate in most cases. The issues mainly come from extrapolating truisms about sustainable weight loss from those relationships.

The pattern I've witnessed over and over again is that people who restrict food intake will initially lose X amount of pounds, after which point they stop losing weight or paradoxically start gaining weight. This is associated with changes in endocrine signaling, as well as thousands of cellular adjustments that are collectively considered part of "basal metabolic rate." This is also the point at which people begin to exhibit really strong cravings, and most people abandon their diets. Once they go back to a higher food intake, you also observe a rapid regain of weight, even if the increased food intake was only a bit higher than the dietary restriction. We only know the tip of the iceberg about all the compensatory processes that encourage weight gain after a period of loss.

I have witnessed some individuals with an iron willpower continue to try to restrict their intake even more at this point to continue losing weight. At which point they became so thoroughly exhausted and began exhibiting other serious health issues due to the level of food restriction needed to ensure weight loss at this stage. The friend I mentioned stopped their dieting attempts because their doctor eventually realized that they were rapidly losing muscle tone faster than they were losing fat. And then they gained it all back despite going back to a level of food intake that was still substantially lower than before they attempted dieting.

And again, this will not account for everyone. Some people will be able to reach and maintain a target weight just by cutting out some sweets. The point is that these behavioral modifications will not work for all, simply because continuing to restrict calories for those individuals will trigger such a massive restructuring of metabolism that continuing to lose weight after this point requires starving oneself to the point of other health problems.

So yes, removing processed foods might have an effect on population-wide trends. But there would also continue to be many people who are obese and stay obese even if they perfectly avoided all junk food and avoided "overeating". I think acknowledgement of both realities is important here.

 

[Midnattsol]

I have no trouble accepting that due to various mechanisms, different bodies will get a different amount of energy out of the same food input, and that different processes in the body might modulate how much energy is expended throughout the day with the same activity level.

What I have trouble understanding is how normal, otherwise healthy people could have what would have to be a substantially lower requirement for food input than others in order to not lose weight over long term at e.g. 1500-1800 calories in nutritious and non-ultraprocessed food a day for an average height and moderately active man.

1800 would be within the normal recommended range for an active woman in Norway, just for reference. Our new dietary guidelines are a bit higher, based on a maintenance of a person with a BMI of 23, I think it was 8 megajoule for women and 11 for men.

And as you suggested earlier, people are terrible at guesstimating their intake. And the formulas used to calculate energy requirements/usage aren’t necessarily very good either (one that is very much in use is known to overestimate requirements by a significant amount as the population used to create it was ~70% young males). When training as a dietitian we used numerous methods to calculate energy needs, and mine varied by ~200 kcal, someone taller and/or heavier than me would likely see more of a difference). For that matter, you don’t just have to guestimate intake, but also what the food contains. Food composition datatables are not always correct. A common fallacy is equating «healthy» with «low calorie», this can get really problematic for a low calorie diet when applied to nuts and seeds which are generally healthy but high calorie foods.

As mentioned by others some do all the right things and still don’t lose weight. It’s complex. What do you do when your patient is bedridden, but gaining weight at an intake of ~1000kcal? And you know this is their intake as they are unable to eat anything besides what is given to them. It gets extremely difficult to meet requirements for non-energy nutrients (these are sadly often overlooked and everything ends up being about calories..) I have no problem believing some bodies are more adept at absorbing energy from foods, and our metabolism can be different, and for some there are likely more than one cause behind easy weight gain. But going on a very low calorie diet to lose weight is not necessarily healthy either. One can supplement certain nutrients, but not all beneficial compounds in food can be supplemented.

I don’t like the «have tried everything» arguments though, «everything» is a very loose term. One patient I met had «tried everything» but was adamant they had never heard of calorie tracking/looking at what they were ingesting and calculating intake. Another had «tried everything» but done so in two weeks which is never going to work. And similar to how some people are secret eaters, many who claim to «eat everything» skip meals or have other behaviors so that their actual intake when analysed is well within their energy budget.

 

[jnmaciuch]

Yes, I agree and the examples mentioned by Jonathan are compelling. But on the other hand I don't understand why some people can eat so much more calories than other people without gaining any weight and I have known several examples of such people including myself in younger years, having gone by the nickname "fastest metabolism in the west" in my university cafeteria. But maybe that also has to do with how we perceive things and how such things can sometimes be hard to estimate (one person might have a chubby face whilst the other has fat in areas where one wouldn't perceive them as being overweight etc).

I think it definitely comes down to metabolism, going on vyvanse shifted things substantially for me, way more than can be explained by slight changes in food intake in that time. And then after a few months things shifted back despite staying on vyvanse and not changing my food habits at all, and I stopped shedding pounds. I was also tracking things extremely carefully because this was the time period where I was tracking everything trying to understand illness trends. Any changes I might have overlooked were not enough to account for those differences

 

[Utsikt]

I have witnessed some individuals with an iron willpower continue to try to restrict their intake even more at this point to continue losing weight. At which point they became so thoroughly exhausted and began exhibiting other serious health issues due to the level of food restriction needed to ensure weight loss at this stage. The friend I mentioned stopped their dieting attempts because their doctor eventually realized that they were rapidly losing muscle tone faster than they were losing fat.

I am by no means an expert, but that feels like overdoing it. I’m curious about what would have happened long term if they maintained a smaller deficit without that first extreme diet?

And I think there might be an important distinction here: we’ve been talking about weight, but it seems like that person lost weight, but not from the «right» part of their body?

There’s also the issue of «healthy» weight loss that might add some nuance. If you put someone under famine conditions they will lose weight, but it will also damage their overall health.

So the relevant question might be: does there exist a condition under which all otherwise relatively healthy overweight humans can lose excess fatty tissue and maintain the new body composition long term without compromising their overall health?

 

[jnmaciuch]

I’m curious about what would have happened long term if they maintained a smaller deficit without that first extreme diet?

They had tried that repeatedly throughout their life as well. The extreme diet only came because their surgeon didn’t believe that they had really dieted “correctly” the first 8 times.

So the relevant question might be: does there exist a condition under which all otherwise relatively healthy overweight humans can lose excess fatty tissue and maintain the new body composition long term without compromising their overall health?

Yup, that’s exactly the question I was after. And that’s what my friends eventually showed me—no. Not for all people, anyways.

 

[Midnattsol]

So the relevant question might be: does there exist a condition under which all otherwise relatively healthy overweight humans can lose excess fatty tissue and maintain the new body composition long term without compromising their overall health?

It likely does, but if one looks at long term follow up after weight loss, fhe numbers are depressing in a 5-10 year timeframe. Including when people have surgery to change their digsestive system (gastric sleeves etc)

But behavior is important here, it is more difficult to maintain weight in a social circle where you have to eat foods that make you gain weight to fit in. Some have to choose between their family, friends and/or job to lose weight/maintain weightgain. The social consequences of not partaking in a meal can be severe.