Comment by y4mi
3 years ago
And yet the article you're commenting on says that you don't burn more calories by exercising... If it is true, it definitely changes the narrative.
3 years ago
And yet the article you're commenting on says that you don't burn more calories by exercising... If it is true, it definitely changes the narrative.
I'm a bit confused by this point in the article, because it also states:
> There seems to be a hard limit on how many calories our bodies can burn per day, set by how fast we can digest food and turn it into energy. He calculates that the ceiling for an 85-kilogram man would be about 4650 calories per day.
Given that "regular" people clearly do not burn 4650 calories per day, and it is possible to burn 4650 calories per day, there must be a point at which exercise _does_ increase energy expenditure. I'm guessing it just doesn't happen for regular doses of exercise (including, evidently, walking 14km per day).
Perhaps the body down regulates calorie-consuming processes to a point where it's just the bare minimum, and calorie expenditure increases from there. Or perhaps we should take the opposite view and say that our bodies up regulate unwanted processes (like inflammation) to use the energy of an engine designed to keep running at a certain level?
Either way I find this incredibly interesting. And either way I'm probably also going to keep stuffing my face on a day I run 30km :).
Yeah, the article isn't very clear on this. ISTM the claim is not that exercise doesn't increase energy consumption at all, but just that it increases it by much less than the amount of energy expended in the exercise, because the body (partially) compensates elsewhere. Whether the degree of compensation varies based on amount of exercise I'm not sure, and I wish it had explained. I expect it probably would, as presumably there would only be so much 'low hanging fruit' for your body to use when compensating.
I can definitely see how that works. I'm a cyclist and often ride 60-100 miles on a weekend day, plus 3 days pf 20-30 miles during the week. That should be a lot of extra calories. But, after those long rides, I usually need a nap and don't do much else (maybe grocery shopping, but definitely not woodworking or other serious projects).
That said, at the peak of my training (12 hours/week), I can definitely consume more calories without putting on weight. Like, a giant bowl of ice cream most nights. But, if I continue that diet during recovery periods, I'll put on a few pounds. So, it's not that exercise has zero impact, but possibly quite a bit smaller an impact that one might assume.
Yeah, I thought this. There's clearly an amount of exercise that will cause you to lose weight. An interesting question is whether your body prevents you from achieving that.
Cycling was always interesting to me in this context because it seems easier to burn energy on a bike than other forms of exercise.
seems easier to burn energy on a bike than other forms of exercise
I'm not sure this is true. Cycling isn't weight-bearing (you're sitting down) and only engages the large leg muscles. Running and rowing likely provide more calorie burn for a given RPE (rate of perceived exertion) over a fixed time period. Running because it's weight-bearing; rowing because it engages more muscle groups. That said, you can probably cycle for more hours total, if you have nothing else to do.
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When cycling there's this "wall" you hit after a few hours. At least I do. After that it's much harder to keep pace or go uphill.
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> there must be a point at which exercise _does_ increase energy expenditure
Of course there is. The problem is that it's much easier to eat than it is to exercise. You can eat a Big Mac in 5 minutes, and you'd have to run or bike for hours to burn those calories off. A 30 minute jog on a treadmill won't do it.
Most people eat more calories than they need, and would have to exercise much more than they realize to burn them off. So losing weight over a reasonably short period of time almost always requires cutting calories. Few people have enough free time to do it with exercise alone.
The efficiency of our bodies (or the amount of calories in food) is astounding. Makes one think whether there is any acceptable use case for serving snacks and other high-calorie-density food.
out of context, that quote is really funny; what happens once you reach 4650 calories? you start violating the rules of thermodynamics?
(i know your body starts compensating for it and burning less calories, but still)
> what happens once you reach 4650 calories?
Well, we probably need to look at the direct quote again.
> There seems to be a hard limit on how many calories our bodies can burn per day, set by how fast we can digest food and turn it into energy.
Maybe i'm reading this wrong, but if one's body were to burn calories at 100% of this supposed possible rate, then by the time you'd reach 4650, a new day would start.
If digestion would top out at 4650 calories at day, with 24 hours per day, it would come down to 193.75 calories per hour. Or, in other words, it'd be about 3.23 calories per minute.
> what happens once you reach 4560 calories?
There are loads of videos on YouTube of what happens. You may or may not want to watch them. Spoiler alert: you vomit when you eat too much.
The vomit limit is probably higher than 4560 (which BTW has a suspicious number of significant digits), there might be a range between too many calories and vomiting where your body breaks down the food into waste without digesting any more nutrients/calories. Kinda like how if you eat too much vitamin C, you’ll just pee most of it out.
At some point your body will also fail to exert energy; there are also metabolic safeguards ahead of the point where your body can no longer manage the energy to keep basic functions going where the lower-priority functions (immune system, cognitive function, motion muscles) start to degrade.
You don't need to be at the limit of human energy intake to see what happens to people when their energy expenditure greatly exceeds the energy available from food over a sustained time period; there is quite a lot of medical literature on the effects of such... er... malnutrition.
Long term, yes. Short term you might be able to get some from fat stores. But the claim is that ~4650 is the most you can persistently get from food intake per day.
Sort of makes sense, the body is a machine and will get worn down/depleted at some point and not some infinite bag of holding. Surprised its as low at 4650 calories though, figured marathoners + swimmers and such could burn more.
The article says you can't keep unhealthy diet and get fit just by exercising. Which is true in my experience as well - I was eating over 3000 kcal a day before I started counting calories, and if I haven't reduced that - no reasonable amount of exercise would have helped.
What's tricky is that in early 20s I was eating about as much and it was fine.
There's a huge variation between individuals based on size, sex, and activity level. As a large, fairly active man I have to consume around 3100 kcal per day just to maintain body weight. But a small, sedentary woman might gain weight with even half that consumption.
All else being equal, resting metabolic rate doesn't tend to slow down much as we age. The notion that people in their 20s can eat as they want without gaining weight is mostly a myth. It's more likely that you don't accurately remember what you consumed and your activity level in your early 20s.
You’re reading that wrong. Of course you burn more calories through exercise. Michael Phelps couldn’t have eaten 12k cals a day if exercise didn’t burn calories.
Well that's what the article says. The Hazda who walk 8-12 km a day burn the less calories as an average American (or the same after adjusting for body weight).
Also that Phelps thing is highly questionable. He says he "probably" burns 8-10k, not 12k. Not the type of statement you want to rely on to dismiss all this work.
I just have a hard time believing it to be true that no amount of exercise will increase the overall caloric expenditure. For example, I've done a few multi-week bike tours, and we ate an enormous amount of mostly pasta every day, and managed to peel off a few pounds each by the end of it.
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The article says pretty explicitly that, while you do burn more calories while exercising, your body finds other ways to compensate and generally keeps about the same total energy expenditure in a day.
I'm pretty sure this doesn't apply to extreme cases like modern athletes, who explicitly push their bodies in many ways that normal fit people don't, and who have teams of doctors and coaches that can force them to keep up with exercise and diet even when their bodies are telling them to stop.
Is it certain that we absorb all of the calories we consume? I went on a backpacking trip with my friends recently and despite similar activity levels everybody was surprised when they noticed that I eat twice as much as anybody else in the group.
Maybe I should bring it up with a doctor, but I feel fine, I just also spend more on food than most.
No, there's lots of calories in stool, but it depends on the type of food. For example, eating lots of fats and oils tends to "go through". On the other hand, rate of metabolism varies between people too.
Yes, this. These conversations about weight loss are so rife with spherical cows and people come to ridiculous generalizations because of it. Bodies are complicated and varied. "Michael Phelps eats 12kcal a day and yet he's not fat" is just a correlation, it doesn't mean anything. He's an extreme outlier of a person in many ways.
I was eating similarly in my 20s and 30s and in 20s I kept about 80kg but in 30s I got to 130kg :/
BTW there are diseases that reduce calories absorbed, you might want to get checked for colitis ulcerosa and crohn's disease. They have nasty side effects so better to know earlier even if you don't have the worst symptoms.
The body absorbs refined carbs very quickly. The glucose rush will increase insulin levels to very high levels and make you feel hungry again soon leading to the consumption of even more calories.
Anecdotally, this has been my experience as well. I tend to think of my base metabolic rate as the integral over my physical activity over the last N years (it used to be N=5, but even that window is way too small I think now). Point being, you can be inactive for a long time without a meaningful change in body fat/weight, but eventually your body adjusts. Or rather, the first gain in body fat is offset by the loss of muscle weight. Once you're at a slower metabolic rate and less muscle, exercise becomes more difficult and it takes years of consistent activity to raise your metabolic rate again.
I'm not sure how base metabolic rate relates to incidental energy expenditure. My gut feeling is that every body has its own limits on energy expenditure, and max TDEE doesn't need to correlate directly with base metabolic rate. That's why I mentioned the integral above. I tend to think of $TDEE_{max} \simeq MBR_{base} + E_{available}$ but $MBR_{base} \simeq \int_{t=-5}^0 TEE(t)$ -- and in my experience, weight loss correlates more with base metabolic rate than with caloric intake ($E_{available}$).