I'm not into fad diets. Calories in < calories used = weight loss. The laws of physics don't change. If gimmicks help you make that happen, more power to you. At least one doctor that was recommending intermittent fasting did their own study which showed it was on par, or worse, in general, compared to consistently eating the same average calorie deficit (I'd link but it's been a while since I looked it up last so I don't remember her name). Others show some positives for it. The general medical advice out there is still that moderate caloric deficit is the most healthy way to lose weight from all the doctors I've talked to/read. So that's what I stick with when losing weight.
It's not quite that simple, as the body has "set point" weights where it likes to stay.
This means that if you are at a set point, simply cutting 100 calories a day won't result in losing 10 lbs a year. (Conversely, adding 100 cals a day won't make you gain 10 lbs either.)
At a setpoint in both directions, it takes a lot more calorie changes because of the body's efficiency in changing food to heat, or whatever.
I've learned quite a few things like this in my 40-something years on the planet. It's pretty fascinating. What works for person A won't necessarily work for person B. What works for person A when they are 20 might not work when they are 40, and that might not work when they are 60. Meds, hormones, stress. Also, the type of calorie matters too. I can eat more calories if I eat more fat/ fewer carbs, and maintain weight. (As a woman in my late 40s.)
When I was in my early 30s and losing weight, I was using weight watchers. Simply cutting calories worked wonders for me, and worked far better for me than my friends in their 60s. But eventually, I got to my goal weight. I added calories. I started dropping weight EVEN FASTER. Added more calories, eventually found the right number to gain a few lbs back to a comfortable spot and maintain my weight.
My most recent discovery = wheat. I started having digestive problems with wheat a little over a year ago. When I eliminated, I dropped about 8 lbs. I was already at a healthy weight. I did not cut carbs - I replaced the whole wheat with other carbs, like oats, rice (brown and white), potatoes, corn tortillas.
Back to the OP, intermittent fasting. It's not really for me. I've done it here and there, but it's really hard on my body and my brain. I get light headed and cranky. Studies show that IF doesn't always work the same for women as men.
Little brief on the setpoint, with a link to the original study.
https://www.foodpolitics.com/2010/01/how-many-extra-calories-cause-weight-gain/
YES YES YES! Are you me? Boy, is this true! I was plump, but not overweight, in my teens (5'4" 128-130lbs on a small boned frame). I didn't eat a lot of food, but I ate a lot of crap when I did eat, and I didn't exercise. Then I went to college and still ate a lot of crap for a couple years, but exercised regularly and lost a ton of weight. In my late 20s and 30s, I was an inconsistent exerciser, but got much healthier with my eating. Weight fluctuated, but still seemed to generally follow a pattern... if I lapsed into eating more sugar/simple carbs, I gained a bit. If not, weight was stable.
Then came my 40s. All of a sudden, I could NOT maintain weight eating like I had been. Unless I dramatically increased sugar/carbs, I lost weight. Exercise actually made me gain weight if it built muscle, but without that I had to eat like a teenage male wrestler to stay above 100 lbs, which was physically impossible b/c my digestion is so slow. At the same time, I completely lost my hunger response. I almost never felt hungry. I forced myself to eat, even when I had no appetite. In desperation, I started adding TONS of fat calories to my diet to avoid adding sugar and carbs. A calorie is a calorie is a calorie, right? Wrong, not with my body! I was glopping quarter cups...QUARTER CUPS! of olive or nut oils on my food, adding butter, etc....and I COULD NOT GAIN WEIGHT.
My body stayed stuck at 100-101lbs no matter how many calories I poured on, or how much aerobic exercise I did or did not do. Light weight training could bump it to 103/04lbs, but I had to struggle to maintain that muscle mass.
This continued for 3 full years. It was kind of scary. Especially because I have overweight friends and family who I am absolutely certain regularly ate lower calorie than I did, and they couldn't LOSE weight.
Individual bodies most definitely are unique and process food differently.
After about 3 years, I gave up with the oil. I couldn't take it anymore and went back to eating lower calorie, with moderate fat, high fiber/veggie, moderate protein, low sugar/carbs, just like in my 20s and 30s. Nothing happened for several months...I didn't gain weight or lose it...I stayed stuck at 100-101 lbs. Then randomly, with NO CHANGE IN HABITS, I suddenly gained 9lbs in 10 days! That's almost 1 lb/day! With zero change in diet or exercise habits!
I mean, WTF?
A calorie is a calorie is a calorie is only true once your body actually uses it, and my body definitely uses different types of foods differently. In my case, what I've found is that adding tons of fat calories seems to send my metabolism into hyper-compensation to the point that it then burns calories to a counter productive extent. Adding the equivalent calories in sugar or simple carbs OTOH, will eventually cause me to gain weight, but because I have a sugar processing endocrine disorder, this is not an option for me. I think a combination of my personal body chemistry, plus hormonal/endocrine disorder, just makes my body run strangely.
So I'm constantly worrying about every damn mouthful of food, and weighing myself daily, just like I did during the periods of my life when I was young and 25lbs heavier. I was on vacation recently for only 5 days. I did eat somewhat fewer calories than usual, but the problem was that I ate almost 0 carbs/sugar. I exercised LESS than usual. Result? I DROPPED 1 lb per DAY, and had to struggle for 3 weeks afterward to force my body back up to its healthier, 109lb set point.
I really envy people whose bodies just lose or gain based on any old type of calorie they add or cut. That would make my life would be a hell of a lot easier.