I've been doing intermittent fasting (16:8) since 2016 (9 years).
I have a belly and am what you would call "a little chubby". I don't exercise that much (once a week). I drink one black coffee in the morning.
After all these years of IF, net-net I haven't lost any weight, but I find if I stop IF (i.e. I start eating 3 meals a day), I feel sluggish. So in the absence of doing anything else, at least IF keeps my mind sharp.
p.s. the only times I've lost weight is when I've fasted once a week, cut out 50% of all carbs from diet, and starting lifting weights. I lost water weight at first, then plateaued because I gained muscle, then after that muscles did the work of burning excess calories.
I was that way for at least 3 years. Then I decided I loved food too much and added certain carbs back into my diet. These days I just do IF and nothing else, and my weight is stable.
alexey-salmin · 30m ago
You can try long-distance running. 100km a week allows you to indulge extra 5000-8000k calories.
I also enjoy food and always ate a lot (like 2 meals at lunch), and I was thin all the way up to 30 thanks to fast metabolism I guess. If I didn't start running 5 years ago my choice would be between severe cuts to my diet or obesity.
AstroBen · 15m ago
Getting into cycling actually has me about to stop intermittent fasting. I go out and can burn 1200 calories in a few hours and that's hard to make up with an 8-hour eating window unless I want to start eating a bunch of junk food. Not trying to lose any more weight
taeric · 37m ago
Did you keep up the weight lifting?
knowitnone2 · 9m ago
I did intermittent fasting. I think this conditioned me to being in the hunger state and to ignore hunger. Along with exercise and portion control, I did lose 20 pounds. I could have gone further but I became lacking in certain nutrients and a doctor told me to stop.
Almondsetat · 53m ago
What all these diets are desperately trying to do is psychologically manipulate you into eating less by playing with your sense of fullness. For weight loss, thermodynamics cannot be beaten: eating at different times and in a different order does not matter.
svnt · 34m ago
This is trivially shown to be false.
Imagine a system with a background/quiescent energy consumption of 1000kCal/day.
Imagine that same system can buffer up to 500kCal for up to 24 hours store excess energy in circulation.
Imagine it converts excess energy to stored energy at an efficiency of 50%.
Assume activity correlates with marginal energy consumption but also increases in the presence of excess energy.
A system such as the one described would have very different behaviors during alternate day fasting (0kCal for 24hrs, 5000kCal for 24hrs) than consuming 2500kCal daily.
The human body is more complex than the system I just described, but it is a useful model to consider for this context.
greysphere · 12m ago
Real world efficiency factors are in the 90s and basal rates aren't constant. The model you're proposing is too artificial to draw conclusions about fasting over a short timeframe.
red_trumpet · 14m ago
So, the excess energy in your model is just excreted? Does that also happen in the human body?
wouldbecouldbe · 5m ago
Yes. On the other spectrum, the body becomes more efficient when moving a lot.
ourmandave · 5m ago
Confirmed by the study of populations of 34 countries.
Food — not lack of exercise — fuels obesity, study finds
Unfortunately calories out is a function of calories in.
You eat less calories, your body might start consuming less calories.
Also, there are two different pathways for using glucose in the body: aerobic and anaerobic. The aerobic one produces 15x more ATP (cellular level energy) than the anaerobic one. The anaerobic one wastes more as heat. So if for some reason you're in the second one, even though you ingest the same amount of calories, the amount of energy you have usable is much less.
So yeah, calories in calories out is true, but it's not really helpful.
rkomorn · 16m ago
> So if for some reason you're in the second one, even though you ingest the same amount of calories, the amount of energy you have usable is much less.
This is technically true but not particularly relevant.
It's quite difficult to be in only anaerobic effort, though (and I'd say pretty ill advised since that basically means stuff like all out sprinting without warmup or cooldown).
Higher intensity effort burns more calories than lower intensity (eg [1]). It's just harder to sustain.
You’re assuming the body is a constant machine that metabolizes at a fixed rate but that can’t be true.
tekla · 44m ago
Until the human body becomes capable of creating energy out of nothing, this is irrelevant
alexey-salmin · 36m ago
It's not. Human body can't create energy out of nothing, but it can vary the consumption of energy in a wide range which is very similar in terms of externally observable effects.
It's a common story when people start to eat 20% less, continue the same lifestyle and lose exactly zero weight as the result. Their body didn't create 20% of energy out of nothing but it just started to waste less energy as body heat.
californical · 42m ago
It can use different amounts of energy depending on different stimulus. Things like fidgeting and body temperature can make a pretty decent difference
anon84873628 · 43s ago
Just to add some color for folks, this is referred to as NEAT in the literature: Non-Exercise Activity and Thermogenesis.
When caloric intake is reduced, the body can decrease this type of expenditure without the person even realizing it.
objektif · 37m ago
Very bad take. What if our bodies adjusts the burn rate based on when we eat when we exercise? if that is true you can potentially eat more and lose more weight.
BennyH26 · 1h ago
In our medical practice, we would use intermittent fasting as part of a comprehensive medical plan to increase longevity. There are studies which demonstrate this is beneficial, at least in Macaque monkeys. Weight loss was just a nice side effect.
garrickvanburen · 28m ago
After briefly looking into it, my assumption is intermittent fasting works great for people that are eating throughout the entirety of the day.
abracadaniel · 25m ago
I’ve often wondered about this. If you have a sugary drink, would it be better to drink it in one sitting or sip it throughout the day.
strken · 56m ago
I'm not sure that a reduction in body weight tells us all the relevant information. One of the possible downsides of fasting is loss of lean body mass, generally meaning muscle. This is a problem for older people in particular because it's harder to keep muscle as you age and because muscle protects from falls, frailty, etc.
testing22321 · 49m ago
If a person is obese or morbidly obese, losing weight is the number one to increase overall health, lifespan, quality of life, etc etc.
Losing a bit of lean muscle mass along the way is not important compared to the huge health gains of losing the weight.
AstroBen · 34m ago
I don't think this is specific to fasting?
You need to be getting enough protein + strength training to maintain muscle in a caloric deficit
Someone1234 · 36m ago
Weight loss is linked with some loss of lean body mass, regardless of the method used. Intermittent fasting has been shown to match any other calorie deficit in terms of lean body mass loss, rather than more as you're implying.
Regardless of how you lose weight the advice is and remains:
> Eat a minimum of 0.36 grams of protein per day, per pound of LEAN* body weight. Increasing to 0.5-0.7 grams of protein per day, per pound of LEAN* body weight for older adults or when undergoing weight loss.
*LEAN is a vital detail for overweight people, they commonly miscalculate protein requirements due to this. The easiest way for overweight people to determine their requirement, is just find an "ideal body weight calculator" online, enter height and gender, and then multiply THAT figure by 0.5-0.7.
For example a man who is 6' tall and 400 lbs should eat 62 grams of protein per day MINIMUM, but during weight loss 86-120 grams of protein per day. It is common, unfortunately, to read online people in this situation miscalculate this to 280(!) grams of protein per day which is incorrect and harms their weight-loss goals.
1024core · 1h ago
Every study ends with something along the lines of:
Longer duration trials are needed to further substantiate these findings.
pdxandi · 11m ago
I read that as needing funding. Somebody has to pay for the research. In order to get it funded, you have to show your research has a basis. My interpretation anyway.
lkrubner · 17m ago
I have read that before the Industrial Revolution, most people faced famine for about 10% of their lives. And while, historically, that would have probably been concentrated into a few bad years during their lifetime (months of starvation, during a few bad years), if we were to generalize that and make it a rule, it would work out to 3 days a month.
There is some evidence that there are health benefits that are specific to the fasting mode. This has mostly been studied in the context of chemotherapy, where fasting can protect against some of the side-effects of chemotherapy:
Most of this has only been studied in animals, not humans, but in animals the results were clear:
"Fasting before chemotherapy (CT) was shown to protect healthy cells from treatment toxicity by reducing the expression of some oncogenes, such as RAS and the AKT signaling pathway [2]. This reduction is mediated by the decrease of circulating insulin-like growth factor 1 (IGF-1) and glucose. In addition, starvation and calorie restriction activate other oncogenes in cancer cells, induce autophagy, and decrease cellular growth rates while increasing sensitivity to antimitotic drugs [2]."
If we assume that we have been shaped by millions of years of frequent famine, then our evolution has been shaped by famine. It is possible that our immune system simply makes the assumption that we will soon face famine, and therefore some important tasks, such as extreme autophagy, are normally postponed till the famine arrives. However, in the modern era the famine never arrives, and so we may have to induce it by artificial means.
I have experimented with very long fasts. My longest fast ever was in September of 2015 when I managed to go 12 straight days on nothing but water.
Obviously, any health benefits from that incident might have been psychosomatic, since I was expecting health benefits. But all the same, I did find some of the health benefits to be shocking and completely unexpected. Since at least 1995, and possibly 1990, I had a mole on my skin on my left arm. I wasn't worried about it, so I simply ignored it. I had it on my arm at least 20 years, maybe 25 years. I recall one morning in November of 2015 when I was in my kitchen, making breakfast, and I reached over to pour myself some coffee, and of course my arm was in my field of vision, and after a moment of thinking something was different, it occurred to me that the mole was gone. It had been there at least 20 years, and then it disappeared, at some point during the weeks after I had done the 12 day fast. I don't know when it disappeared, it just slowly faded away at some point between September and November. There was no remaining sign of it on my arm.
Again, that might have been purely psychosomatic, but it was interesting.
bargainbin · 1h ago
The takeaway here is that if you do “alternate day fasting”, that is you eat normally on one day then do not eat all the next, you will lose weight.
I can’t believe that losing 3.5 days of caloric intake would result in weight loss. In other news, water is wet.
m4r71n · 57m ago
Alternate day fasting normally means you eat up to 500 calories on your fasting day, but then eat more than usual on normal days. So on average if you eat 500 one day and 2500 another, that is no different than eating a restricted diet of 1500 every day. The finding here is that the former results in slightly more weight loss than the latter. That restrictions in calorie intake will result in weight loss is a given.
scns · 33m ago
> eating a restricted diet of 1500
Keeping this up is hard, many fail. Alternating normal eating with IF days is easier to do.
fred_is_fred · 1h ago
Or if you just ate 50% less calories 7 days a week perhaps.
treetalker · 48m ago
My understanding is that, yes, the weight loss results end up being similar — but that the story is not so simple (or linear) because "true" fasting activates certain metabolic pathways (e.g., mTOR) that mere calorie reduction does not, and that those pathways have different effects, such as autophagy and others that increase lifespan in different ways.
I have a belly and am what you would call "a little chubby". I don't exercise that much (once a week). I drink one black coffee in the morning.
After all these years of IF, net-net I haven't lost any weight, but I find if I stop IF (i.e. I start eating 3 meals a day), I feel sluggish. So in the absence of doing anything else, at least IF keeps my mind sharp.
p.s. the only times I've lost weight is when I've fasted once a week, cut out 50% of all carbs from diet, and starting lifting weights. I lost water weight at first, then plateaued because I gained muscle, then after that muscles did the work of burning excess calories.
I was that way for at least 3 years. Then I decided I loved food too much and added certain carbs back into my diet. These days I just do IF and nothing else, and my weight is stable.
I also enjoy food and always ate a lot (like 2 meals at lunch), and I was thin all the way up to 30 thanks to fast metabolism I guess. If I didn't start running 5 years ago my choice would be between severe cuts to my diet or obesity.
Imagine a system with a background/quiescent energy consumption of 1000kCal/day.
Imagine that same system can buffer up to 500kCal for up to 24 hours store excess energy in circulation.
Imagine it converts excess energy to stored energy at an efficiency of 50%.
Assume activity correlates with marginal energy consumption but also increases in the presence of excess energy.
A system such as the one described would have very different behaviors during alternate day fasting (0kCal for 24hrs, 5000kCal for 24hrs) than consuming 2500kCal daily.
The human body is more complex than the system I just described, but it is a useful model to consider for this context.
Food — not lack of exercise — fuels obesity, study finds
https://www.npr.org/2025/07/24/nx-s1-5477662/diet-exercise-o...
You eat less calories, your body might start consuming less calories.
Also, there are two different pathways for using glucose in the body: aerobic and anaerobic. The aerobic one produces 15x more ATP (cellular level energy) than the anaerobic one. The anaerobic one wastes more as heat. So if for some reason you're in the second one, even though you ingest the same amount of calories, the amount of energy you have usable is much less.
So yeah, calories in calories out is true, but it's not really helpful.
This is technically true but not particularly relevant.
It's quite difficult to be in only anaerobic effort, though (and I'd say pretty ill advised since that basically means stuff like all out sprinting without warmup or cooldown).
Higher intensity effort burns more calories than lower intensity (eg [1]). It's just harder to sustain.
1- https://www.webmd.com/fitness-exercise/what-to-know-heart-ra... )
It's a common story when people start to eat 20% less, continue the same lifestyle and lose exactly zero weight as the result. Their body didn't create 20% of energy out of nothing but it just started to waste less energy as body heat.
When caloric intake is reduced, the body can decrease this type of expenditure without the person even realizing it.
Losing a bit of lean muscle mass along the way is not important compared to the huge health gains of losing the weight.
You need to be getting enough protein + strength training to maintain muscle in a caloric deficit
Regardless of how you lose weight the advice is and remains:
> Eat a minimum of 0.36 grams of protein per day, per pound of LEAN* body weight. Increasing to 0.5-0.7 grams of protein per day, per pound of LEAN* body weight for older adults or when undergoing weight loss.
*LEAN is a vital detail for overweight people, they commonly miscalculate protein requirements due to this. The easiest way for overweight people to determine their requirement, is just find an "ideal body weight calculator" online, enter height and gender, and then multiply THAT figure by 0.5-0.7.
For example a man who is 6' tall and 400 lbs should eat 62 grams of protein per day MINIMUM, but during weight loss 86-120 grams of protein per day. It is common, unfortunately, to read online people in this situation miscalculate this to 280(!) grams of protein per day which is incorrect and harms their weight-loss goals.
Longer duration trials are needed to further substantiate these findings.
There is some evidence that there are health benefits that are specific to the fasting mode. This has mostly been studied in the context of chemotherapy, where fasting can protect against some of the side-effects of chemotherapy:
https://pmc.ncbi.nlm.nih.gov/articles/PMC5870384/
Most of this has only been studied in animals, not humans, but in animals the results were clear:
"Fasting before chemotherapy (CT) was shown to protect healthy cells from treatment toxicity by reducing the expression of some oncogenes, such as RAS and the AKT signaling pathway [2]. This reduction is mediated by the decrease of circulating insulin-like growth factor 1 (IGF-1) and glucose. In addition, starvation and calorie restriction activate other oncogenes in cancer cells, induce autophagy, and decrease cellular growth rates while increasing sensitivity to antimitotic drugs [2]."
If we assume that we have been shaped by millions of years of frequent famine, then our evolution has been shaped by famine. It is possible that our immune system simply makes the assumption that we will soon face famine, and therefore some important tasks, such as extreme autophagy, are normally postponed till the famine arrives. However, in the modern era the famine never arrives, and so we may have to induce it by artificial means.
I have experimented with very long fasts. My longest fast ever was in September of 2015 when I managed to go 12 straight days on nothing but water.
Obviously, any health benefits from that incident might have been psychosomatic, since I was expecting health benefits. But all the same, I did find some of the health benefits to be shocking and completely unexpected. Since at least 1995, and possibly 1990, I had a mole on my skin on my left arm. I wasn't worried about it, so I simply ignored it. I had it on my arm at least 20 years, maybe 25 years. I recall one morning in November of 2015 when I was in my kitchen, making breakfast, and I reached over to pour myself some coffee, and of course my arm was in my field of vision, and after a moment of thinking something was different, it occurred to me that the mole was gone. It had been there at least 20 years, and then it disappeared, at some point during the weeks after I had done the 12 day fast. I don't know when it disappeared, it just slowly faded away at some point between September and November. There was no remaining sign of it on my arm.
Again, that might have been purely psychosomatic, but it was interesting.
I can’t believe that losing 3.5 days of caloric intake would result in weight loss. In other news, water is wet.
Keeping this up is hard, many fail. Alternating normal eating with IF days is easier to do.