I've known very active cyclists that couldn't lose weight despite riding hundred mile rides weekly. In my youth, I could eat anything and do nothing and not suffer the consequences. I definitely fit the "run hot" part but I was the plate-cleaner in my family and didn't really stop eating like that until I was in my late 30s and suddenly started gaining weight.

> I've known very active cyclists that couldn't lose weight despite riding hundred mile rides weekly.

Isn’t this against the laws of physics? If you’re burning a ton of energy and not eating excessively, where are their bodies getting mass from to maintain weight?

100 miles weekly isn't THAT much in terms of kcal. 10 miles is about 600 kcal. 100 miles is 6000 kcal, let's say 7000 to round that to 1000 kcal a day.

Eating 1000 kcal more a day is pretty easy to do without noticing. Especially when you eat a lot on the day that you biked (cause "you earned it").

For example 2 liter bottle of coke is 800 kcal and 1 protein bar is about 250 kcal and you're already over the budget (assuming you also eat your "regular" food).

I think most people (especially people who think they're eating healthy) would notice a 2L bottle of coke.

I agree with your point. In fact I think it's even stronger as I don't think 10 miles on a bike is anywhere close to 600kcal unless we are talking very serious hills on a MTB. 10 miles on a flattish road is usually half an hour of moderate effort.

Paradoxically, pushing a larger body through wind resistance should burn even more calories! The people I knew weren't explicitly trying to lose weight, they were cycling for their cardiovascular health and on that front their doctors were happy. But, yeah, distance cyclists tend to eat their fill.

> Isn’t this against the laws of physics?

No because they were also eating a lot, the lower bound on this established by physics.

I've known a lot of roadies who sort-of-correctly believed they could eat as much as they could physically manage, as they were expending enough (3+ hour intense riding daily) that it was a chore to keep up. At least when they were 20-something and racing. Many struggle a bit when the a) get a bit older/metabolically slower and b) life gets in the way and they ride a lot less. All of a sudden a guy who was rail thin gains 30lb that "sticks".

> couldn't lose weight ... they were also eating a lot

So really it's that they weren't losing weight because they were eating too much... exactly like most people in modern western society. And really the moderate amount of cycling was irrelevant.

The operative word was "couldn't". If they didn't eat as much, they could lose weight

I would guess that they are very metabolically efficient bicyclists and that they underestimate how much food they eat.

I think this is pretty common for people who exercise intensely. If you don’t increase your eating, you’re going to 1) feel hungry all the time and 2) negatively impact your performance. I trained for a marathon two years ago after only doing half marathons. I basically couldn’t lose weight unless I trained less.

As someone who exercises a lot, the body ends up being extremely hungry all the time similar as to when I hit puberty as a child. `

Doing tons of endurance cardio gives you massive carb cravings and catabolizes muscle mass, slowing your metabolism. Especially when none of it is max effort. To keep your body fat percentage low and metabolism up you really need to combine endurance cardio with high intensity cardio and strength training. This is why things like Crossfit and HIIT are so popular.

Sorry I just don't agree with this. I run 50 miles a week and mix in some cycling too, and I actively have to make an effort to eat enough to maintain weight. Endurance cardio doesn't trigger hunger or cravings for me unless it's a long (90 mins plus) effort.

Of course it's no surprise that people who eat less weigh less. The surprise, I think, is that people who are underweight are relatively sedentary.

Maybe this is not that much of a surprise either though? I wonder how much of this has to do with muscle. BMI infamously ignores muscle mass. An interesting followup would be whether people with low body fat % are sedentary. My guess is that they aren't.

Side note: maybe there is a disparate importance of "Calories In" vs "Calories Out" for people who are under/over weight. Maybe underweight people should focus on exercise more, and overweight people should focus on eating less?

I am mostly sedentary, and maintain body fat below 10%. It's mainly genetics, and probably 20% diet.

Sub-10% body fat is underwear model territory. At that low level of fat, every muscle is well-defined, no matter how small.

A lot of guys severely underestimate their body fat %. Sub 10% generally isn't possible without heavy dieting unless you're still going through puberty; genetics has nothing to do with it.

I'm aware of what it looks like, and I've been up at 12-15% before. It's absolutely genetic, most of my family runs very skinny. I have generally decent muscle definition, although the fat I have tends to sit in my hips and shoulders. My doctor suggested I might have less interstitial fat than most people, which explains a few other health effects.

I'm not bragging, there are serious downsides, but it's absolutely possible to sit at 10% year-round, just not while maintaining any serious level of elevated muscle mass.

and on top of that, it looks like there's other factors of diet than just choosing what to eat - it sounds like some people are just less hungry for indefinite reasons. genetics, gut biome, etc all probably play a part.

you missed the important point, IMO: being hungry. it's bizarre that we can be mechanically and nutritionally full yet still be hungry. These low BMI individuals were not hungry.

WTF is going on with the hunger response being so messed up in a huge segment of the population?

It’s not messed up. It’s just maladapted to our food environment where there is high calorie, highly rewarding, cheap food available to us at all times. Countries where traditional diets predominate don’t have widespread obesity, and we can see obesity rise in developing nations as they adopt Western diets.

Some people, including the Chinese-resident subjects of this study, have hunger responses that are not susceptible to the temptations of our food system.

> It’s just maladapted to our food environment where there is high calorie, highly rewarding, cheap food available to us at all times.

I visited China and they seemed to have plenty of access to high-calorie, highly-rewarding food. What's special about the temptations of our food system?

It's possible that as China transitions to a post-food-scarcity environment like the West it will see high obesity like in the West:

"The unparalleled rise of obesity in China: a call to action"

International Journal of Obesity volume 45, pages 921–922 (2021)

https://www.nature.com/articles/s41366-021-00774-w

While Chinese people may have a low obesity rate, they aren’t significantly healthier in other respects. High cholesterol, blood pressure, and type 2 diabetes (white rice) are a big problem.

IMO this is one of the biggest and most interesting questions of the last century with the widest and most frightening implications.

If literally a majority of people in wealthy nations are what we define as overweight, and we keep finding new ways that is at least somewhat out of our control or difficult to perfectly control, why do we keep framing it as solely a matter of individual discipline or virtue? I have my own guesses about why of course, but pretty much all of the possibilities are unsettling.

This article is a great analysis of the environmental theory of obesity: https://slimemoldtimemold.com/2021/07/07/a-chemical-hunger-p...

"Being hungry" has different definitions and corresponds to two very different body sensations. If you eat at a regular time every day, you'll get "hungry" around that time, whether your body really needs it or not. But if you skip that meal at some point the cravings disappear… so it wasn't really physiological then, just a mind trick from hormones. The other "hungry" you can feel it like a vacuum in your stomach and is painful.

It's interesting how effectively GLP-1 (ozempic, etc.) eliminate that, though.

This entire "you just need to eat better" discussion seems to fall apart badly in the face of medicines like GLP-1 agonists (e.g., Ozempic/Wegovy.)

It's like arguing that pneumonia can be cured through "healthy living" even after you've established the mechanism and effectiveness of penicillin.

It fits into a mode of thought where fat people are fat because of character flaws, and thin people are thin because of superior moral character. Thus, it justifies the better treatment of thin people over fat people.

I've even heard the "thinness is a sign of godliness" folks get really angry at the suggestion of using GLP-1 agonists, because it's "lazy" and "cheating."

Having seen friends and relatives succumb to cardiovascular disease, it's really heartbreaking. I've watched people starve themselves on brown rice and broccoli for years (with only modest results, followed by total failure) because diet-only interventions are completely unrealistic and don't work long term.

Those friends and relatives weren't really starving themselves brown rice and broccoli. They were eating a bunch of other stuff when you weren't looking.

We have existence proofs that diet-only interventions work for some people. I literally know people who have lost large amounts of weight and kept it off for years that way. Medications have risks and side effects, so should only be prescribed if behavior modification has failed.

We have many unsuccessful treatments that work for a small percentage of patients. That's why we measure treatments by effectiveness rather than identifying existence proofs that it worked for someone.

You're really missing the point. Every patient is unique. That's why competent healthcare providers take a step therapy approach and try cheaper, lower-risk treatments first before moving on to more expensive and riskier medication or bariatric surgery.

You seem to have misread my posts as saying that healthcare providers should immediately move to medication rather than try dietary intervention. I didn't say that, I didn't imply that, I didn't even think it.

What I did say is that we are increasingly learning that overeating is a very complex and life-threatening medical concern that often cannot be solved through dietary intervention. Even people who may die if they don't adhere to a diet frequently have difficulty adhering to one. Saying that there are "existence proofs" that diets sometimes they work is a terrible response.

My view is that we should treat diet as one possible medical treatment, and evaluate it apples-to-apples (in terms of efficacy and side effects) against more recent FDA-approved treatments. And now that we've seen how much impact those treatments can have -- and particularly how critical the GLP-1 mechanism is to the sustainability of weight-loss interventions -- we should work our asses off to find more and better treatments that treat overeating as a health condition rather than a question of mind-over-matter.

You seem extremely attached to your position, to the point where defending your position required you to declare that my relatives "were eating a bunch of other stuff when you weren't looking."

It makes sense evolutionarily: if there's lots of food available now, you should eat it, because there might not be enough in winter.

We live in a society where there's always lots of food available for most people in developed countries (who are mainly the people who are overweight), so it makes sense that you will instinctively eat more than you need to.

Hunger is not only about not getting enough food, it’s about not getting enough of the right type of food for you genetically.

When I was 16, I was playing varsity basketball, baseball, track and was working on a farm doing heavy work all summer.

Per the doctor, I was obese. My wife was obese because breasts. BMI is bullshit imo, it has some general value but creates a lot of distress for people, especially women.

BMI is useful for screening and population studies, but it's (mostly) bullshit for individuals. For most people it's body composition that really matters. Excess adipose tissue, especially visceral fat, has a wide range of negative health effects. Anyone who cares about their health should get a DXA scan at least every few years; it will give a highly accurate reading on body composition including fat distribution.

When I was 16 I waffled between the top edge of healthy and the bottom edge of overweight, according to BMI. When I dropped into the top edge of healthy I had a 6-pack. I wasn't even that muscular, just broad-shouldered.

BMI is pretty good for populations.

If you are standing in front of your doctor and he or she is telling you that you are obese because of your BMI score and not actually measuring you (like with calipers), I’d probably look for a new doctor.

Calipers are not the proper medical standard of care for measuring body composition. They don't produce accurate, repeatable results. The current best practice for most patients is a DXA scan.

How many physicians can do a DXA scan in their office? Calipers give you ballpark numbers and often that's good enough for a physician. It's certainly better than BMI.