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.
The results are a bit different on my side. I've been doing intermittent fasting (23:1) since 2019 (~6 years). During this period, I did IF (46:2) for a year (one meal every two days).
I have never been overweight in my life but I lost ~10 kg in the first year and my weight has remained stable since then. I haven't measured it, but my body fat percentage is probably around 15%.
By the way I do moderate exercise every days. Walking at very slow speed for 3-4 hours or swimming for an hour. My muscle mass is always increasing, albeit slowly.
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.
I fundamentally think pushing people who want to lose weight into cardio is a mistake. It’s definitely good for you but unless you know how to eat you are going to find yourself over eating very quickly
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
In my experience IF is better thought of as a way to break bad eating habits, not as a direct way to lose weight. Merely eating the same amount of food but in a certain time frame (which is what a lot of people end up doing) doesn’t accomplish much in terms of weight loss.
But I have found it successful in breaking bad habits, which results in weight loss indirectly.
For example, I had a bad habit of eating a large breakfast 1-2 hours within waking up. I was never really that hungry, but it was just something I did out of habit. Doing an IF routine made me realize that I’m not actually that hungry in the morning and can get by until 10-11am on just a coffee with milk.
I'd go further and say adopting any sort of diet regimen is useful for identifying and correcting bad eating habits. Even if the diet ends up being a temporary discipline.
Having any high duty-cycle behavior go from un-tracked to tracked and from (largely) unconscious habitual practice to conscious practice can be a real eye opener.
I'd agree and generalize that intermittent fasting is a great way to remind yourself that that feeling in your stomach when you get hungry doesn't mean you need to eat now. In fact, there's no real rush whatsoever. The first time I did a 24 hour fast, it was brutal and I treated myself to a feast at the end which I rapidly gobbled down.
After doing intermittent fasting for a few years, I have accidentally fasted for 24+ hours multiple times. And after you do it for a while, it makes it clear that this whole modern thing of 3 meals a day, let alone with snacking, is really just weird.
I didn’t elaborate enough in my comment. Basically I mean that I stopped eating breakfast with IF and then gradually realized a coffee with milk was enough to serve as a replacement.
The point being that rigidly sticking to IF rules is less useful than just using it as a way to reset your eating habits. (At least in my experience.)
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.
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.
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.
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.
> 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.
This is an entirely useless thing to say. Your body can make choices, based on what and when and how you eat, that you can't control with your psychology.
Your body can raise or lower its temperature. It can put energy towards cell repair or cell reproduction. It can store energy as fat, or signal to burn fat, or build muscle or catabolize muscle.
It’s not just different times though. When doing intermittent fasting you easily ingest less calories overall, skipping a meal doesn’t mean you’ll eat twice as much for the next meal.
I don’t understand what’s "desperate" about IF, it’s just an easy way (for some people) to lower their calories intake. It has other benefits and some caveats but it’s one way to get healthier.
Calories in / Calories out might be broadly accurate, but reality is a lot more complicated than that. People are really bad at tracking how many calories they take in. Its impossible to measure how many calories you're actually exerting with exercise. Its even more impossible to measure how many calories you pee, poop, perspire, breathe, and radiate out. Microvariations across your current body state, body temperature, and even the time of day can influence how efficient your gut is at absorbing incoming energy.
Some people operate with a goal of a caloric deficit of even something as small as e.g. 200kcal. But because all these things are impossible to measure accurately, a difference of just 10% beyond a daily BMR of 2000kcal isn't just a possibility; its the norm. You run for an hour; what if that burns an extra 50kcal that your Apple Watch did not account for? You eat a slice of bread which advertises it contains 80kcal; but it actually contains 100kcal [1]? You sleep poorly, which causes some mild systemic inflammation the next day, which raises your body temperature?
The really cool part is you don’t have to accurately track how many calories go in and out. The proof is in the pudding.
If you had a car with a broken gas gauge you would just pump until it overflowed… same idea here.
Over a month or so if your weight is stable then you are putting in as many calories as you burn. If you’re gaining weight, you’re consuming more, and if you’re losing weight, you’re consuming less.
It turns out the body processes different calories very differently depending on a variety of factors including: baseline genetics, time of day, menstrual cycle, prior fasting, current mineral excess/debt, gut flora/fauna biome, and the composition of previously consumed food still remaining the digestive track.
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.
I lost 130 pounds over the course of 2 years in my late 20s by skipping lunch every other day and entirely skipping breakfast. I also started tracking my calories and macros.
I don't know what to call that, but it worked and it changed my relationship with food forever (in a good way). I have since kept the weight off and switched back to eating 3 meals a day with a better understanding of how much and of what to eat.
Eat a lot more protein and way less carbs. Most meats already have the right balance of fat included, so avoid adding more. Fill up on fibrous vegetables since they don't really count towards calories and help digest all the meat you'll be eating. Drink plenty of water, sleep well, and at least hit your daily steps and heart rate targets if you're not huge on exercise. Building muscle is a good idea, but I'm lucky I've never had a problem with that and just needed to lose the body fat.
I'm now in my mid 30s and have a clean bill of health. When I was heavier I was prediabetic and my resting heart rate was 85. Now it's about 65 and blood sugar is good and doesn't spike or stay elevated all day anymore. It's good to get this stuff on track when you're still youngish.
Oh also I stopped the intermittent fasting because it was messing with my blood sugar. That was why I wrote all this and it's my argument against it.
Practical advice for people who do normal 80/20 healthy/unhealthy stuff and don't wanna think:
Now and then like twice a month, skip 2/3 meals in the day. If hard, have light juices/even fruits. Think of it as giving your digestive system "rest". Don't do it when otherwise sick.
It will make you generally healthier, no drastic changes. Those require drastic measures which differ person to person.
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.
I agree that losing body fat is the number one priority, but I wish the research would focus on that rather than the number on the scale. Losing a bit of lean muscle mass along the way is important for its own sake, and also because it's a confounding variable for what I actually want to know, which is how much fat (not weight) a person lost.
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.
Do you have source for this? Because as you write I've always read to derive protein intake from the overall weight. That would indeed be a very important distance.
I diet, on and off. Keeping fat free weight as the highest priority (I don’t want to loose hard earned muscle)!
I’ve tried all types of diets. For me, the most important for me is to save the biggest meal for late in the day. I can easily go hungry a couple of hours during the day if I know there is a filling meal coming.
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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 have never been overweight in my life but I lost ~10 kg in the first year and my weight has remained stable since then. I haven't measured it, but my body fat percentage is probably around 15%.
By the way I do moderate exercise every days. Walking at very slow speed for 3-4 hours or swimming for an hour. My muscle mass is always increasing, albeit slowly.
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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.
Soda? Chocolate? Sugar? Ice cream?
You must be eating something extremely calorie dense to be maintaining weight.
But I have found it successful in breaking bad habits, which results in weight loss indirectly.
For example, I had a bad habit of eating a large breakfast 1-2 hours within waking up. I was never really that hungry, but it was just something I did out of habit. Doing an IF routine made me realize that I’m not actually that hungry in the morning and can get by until 10-11am on just a coffee with milk.
Having any high duty-cycle behavior go from un-tracked to tracked and from (largely) unconscious habitual practice to conscious practice can be a real eye opener.
After doing intermittent fasting for a few years, I have accidentally fasted for 24+ hours multiple times. And after you do it for a while, it makes it clear that this whole modern thing of 3 meals a day, let alone with snacking, is really just weird.
The point being that rigidly sticking to IF rules is less useful than just using it as a way to reset your eating habits. (At least in my experience.)
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.
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... )
Food — not lack of exercise — fuels obesity, study finds
https://www.npr.org/2025/07/24/nx-s1-5477662/diet-exercise-o...
Your body can raise or lower its temperature. It can put energy towards cell repair or cell reproduction. It can store energy as fat, or signal to burn fat, or build muscle or catabolize muscle.
I don’t understand what’s "desperate" about IF, it’s just an easy way (for some people) to lower their calories intake. It has other benefits and some caveats but it’s one way to get healthier.
Some people operate with a goal of a caloric deficit of even something as small as e.g. 200kcal. But because all these things are impossible to measure accurately, a difference of just 10% beyond a daily BMR of 2000kcal isn't just a possibility; its the norm. You run for an hour; what if that burns an extra 50kcal that your Apple Watch did not account for? You eat a slice of bread which advertises it contains 80kcal; but it actually contains 100kcal [1]? You sleep poorly, which causes some mild systemic inflammation the next day, which raises your body temperature?
[1] https://health.clevelandclinic.org/are-calorie-counts-accura...
If you had a car with a broken gas gauge you would just pump until it overflowed… same idea here.
Over a month or so if your weight is stable then you are putting in as many calories as you burn. If you’re gaining weight, you’re consuming more, and if you’re losing weight, you’re consuming less.
Adjust accordingly.
It turns out the body processes different calories very differently depending on a variety of factors including: baseline genetics, time of day, menstrual cycle, prior fasting, current mineral excess/debt, gut flora/fauna biome, and the composition of previously consumed food still remaining the digestive track.
Whether it's IF, deficit cycles, periodic deep fast -- they all seem to have the same effect, which is just to give the body a break for a bit.
I don't know what to call that, but it worked and it changed my relationship with food forever (in a good way). I have since kept the weight off and switched back to eating 3 meals a day with a better understanding of how much and of what to eat.
Eat a lot more protein and way less carbs. Most meats already have the right balance of fat included, so avoid adding more. Fill up on fibrous vegetables since they don't really count towards calories and help digest all the meat you'll be eating. Drink plenty of water, sleep well, and at least hit your daily steps and heart rate targets if you're not huge on exercise. Building muscle is a good idea, but I'm lucky I've never had a problem with that and just needed to lose the body fat.
I'm now in my mid 30s and have a clean bill of health. When I was heavier I was prediabetic and my resting heart rate was 85. Now it's about 65 and blood sugar is good and doesn't spike or stay elevated all day anymore. It's good to get this stuff on track when you're still youngish.
Oh also I stopped the intermittent fasting because it was messing with my blood sugar. That was why I wrote all this and it's my argument against it.
Now and then like twice a month, skip 2/3 meals in the day. If hard, have light juices/even fruits. Think of it as giving your digestive system "rest". Don't do it when otherwise sick.
It will make you generally healthier, no drastic changes. Those require drastic measures which differ person to person.
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.
I’ve tried all types of diets. For me, the most important for me is to save the biggest meal for late in the day. I can easily go hungry a couple of hours during the day if I know there is a filling meal coming.
I suspect IF works in a similar way.
Wouldn't the big meal be stored as fat during sleeping?