Ok, again, go and read the study.

They measured the calories dumped in the fecal waste excreted following a fixed calorie intake.

Lean people dumped more calories out per calorie in, their gut didn’t absorb as much of the intake as an obese person did. For the same given intake of calories.

This isn’t about maintaining mass, this is about physically absorbing more of the energy in a given parcel of food.

You’re so fixated on how you think the human body works you aren’t even reading what is in the study.

To couch it in your own words - it’s physics: why is it when a lean person eats a given calorie input do they excrete more calories out in there faeces than an obese person for the same input. How does a lean person get the same calorie absorption when more of the energy went into the toilet?

You didn’t read the study I posted, or what I said.

Obese people absorb more calories from a given amount of food than a lean person given the same amount. We know this because fewer calories are excreted in their waste. So we know that obese people extract more calories from the same input calories than lean people do.

I didn’t claim I knew it, I referred to a study proving it.

But you are too fixated on your worldview to actually read and understand what the evidence shows over what you think you know. You’re falling for your own personal biases all while claiming that’s what I’m doing.

I’m not denying science, there’s a lot to learn, but we already know that lean individuals absorb fewer calories from their intake than obese ones.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3127503/

This means an obese persons calories in ~ calories out equation is different and prejudicial to maintaining obesity.

And that’s just one scratch on the surface of an ultimately meaningless reduction of a vastly complex system, once you start to gain weight, it gets harder and harder to lose it.

But some people stop eating at the right amount of calories for their demands. Why is that possible for some and not others.

Also there is evidence for people increasing their activity levels when they eat more calories, not going out and exercising, but their average activity level increases.

The reality is we don’t know. There are some fundamentals, but they aren’t well understood: if you had no gut biome, you would have to eat 3 times the calories you do now to maintain your current weight. The biome has a huge impact on the way and amount of calories Welch individual can extract from food, and as of now, we don’t have a realistic method to measure it, and no understanding of what a biome change makes to the calorie absorption rate of any individual.

That’s why literally any absolute statement or claim is not useful, or accurate. In either direction.

The interesting part of this is targets to study - what happens if we wipe out some of these species from the biome, does the persons hunger drive change, do they lose weight?

These biome changes likely do occur based on diet change, but does another diet change revers these changes back down the line toward normal biome?

The biome changes appear to be a symptom, but are they also a contributor to future obesity - by changing the gut function or by changing behaviour?

Most of the states of chemistry in your body are pretty tightly regulated, mostly because you die fairly quickly if they get too far off of very narrow margins. Eg electrolytes, water, temperature, acidity. It appears that our food systems aren’t so tightly controlled for most people. That at a population level this is significant and growing is indicative of influence beyond people choosing it.

Edit to add: this isn’t necessarily an unexpected thing - humans succeeded through developing a very wide dietary compatibility, meaning this variability that is good enough to reach reproduction age would appear to be the selected evolution. The problem is now we want longer healthier lives way beyond what evolution would bother with, this study seems to show that the gut biome varies predictably with obesity, says nothing of causation, but does identify potential study targets eg, does this variance then make hunger change, reinforcing obesity maintaining behaviour etc.