Every study ends with something along the lines of:

Longer duration trials are needed to further substantiate these findings.

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.

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'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.

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.

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.

After briefly looking into it, my assumption is intermittent fasting works great for people that are eating throughout the entirety of the day.

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:

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 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.

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’m curious whether taking the oral form of Ozempic at a lower dose could have effects similar to intermittent fasting, given that it may lead to skipping a meal as well.

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.

I suspect IF works in a similar way.

It surprises me how often the basic physiology still gets overlooked.

Hunger is driven by hormonal signals designed to defend a set point. Even if you consciously fast for most of the day, your brain will push you to make up the difference once you start eating. When it comes to fat loss, it still boils down to maintaining a caloric deficit — timing alone won’t keep your appetite in check for long. We’ve known this for years.

IF may have other potential benefits — better insulin sensitivity, longevity, or improved adherence for some people (since avoiding food most of the day can be psychologically easier) — but none of that is “new” anymore.

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.

N=1 but in 2017 I lost over 100 pounds in 8 months by changing to a keto diet and I've kept it off. The results come fast. I lost 10 pounds in 10 days and 20 pounds the first month. At around six weeks I became 'fat-adapted', a long-term metabolic transition to primarily burning fat instead of carbs (glucose) for energy. Around that point I sort of fell into intermittent fasting because it just felt right. I'd heard about IF but never had it as a goal and it seemed impossible since I'd been hungry my whole life. But limiting carbs with keto controlled my blood sugar to the extent I was almost never hungry which made IF easy. It was also more convenient to just do one larger meal a day and I also noticed I felt better on IF.

The combination of Keto+IF worked so well for me, for a while my calorie tracking switched from the usual preventing eating too many calories to ensuring I was getting enough, which was certainly never on my bingo card. After a lifetime of being a slave to hunger it was liberating to suddenly feel effortlessly in control of diet and my relationship with food changed completely. Then at around 90 days my palate shifted, meaning I even lost my taste for carbie foods. If I tried a small bite of something carb-laden that I'd loved my whole life, it didn't even taste particularly good to me anymore. I also became hyper-sensitive to sugar. Sugar-soaked foods just taste poisonously over-sweetened (which they kind of are). A slice of apple now tastes as sweet as I'd ever want, like a dessert that has extra sugar-added.

In the 8th month I reached below my ideal 'dream' weight and even saw abs appear for the first time in my life! I transitioned to maintenance mode but stayed keto because being in a blood sugar controlled state felt so amazing and not just physically but also mentally and emotionally. At around a year I went from strict keto to low carb for life which I still am 8 years later. When I started that was unimaginable. I saw Keto as an onerous regimen that I'd endure if it worked and stop the moment I was no longer overweight. But during the journey my metabolism, palate and food preferences changed so dramatically, I was basically a different person when I arrived. Those first few months when I was rigorously tracking every calorie in an app and managing intake with measuring cups and a kitchen scale felt like a burden but were actually invaluable training. Of course, after a few months all that process became automatic so I didn't need to constantly track and eventually I got to the point where I don't even consciously think about it. That early rigor helped me get so in-sync with my body and able to sense where my metabolism is in its natural cycles that now I just eat when necessary and convenient for my schedule. This often ends up being IF but it's not an intentional thing.