So I follow a pretty crazy diet that moves between low carb, keto, and extended fasting, would I recommend it to others? No I follow the diet because I have found that it works the best for me given my various medical problems, but it is unlikely that it is the right diet for most other people. The diet world seems full of all or nothing thinking, as well as a fundamental supposition that is just untrue which is that we are all the same and there is a “best diet”. Now there are probably diets that are universally not the best, ones with lots of fat mixed with processed carbs and sugars in a delicious and convenient package. (What do Bill Clinton, Bill Gates, Warren Buffet, and Donald Trump have in common? A genuine love of McDonalds, let’s not pretend the food doesn’t taste good to most when some of the richest men in the world still eat it, plus it is easy and cheap).
So while there are some near universals(not everyone eating a “bad diet” will face negative health consequences) the truth about diet science is that it is very very complicated and very very over simplified.
Genetically we are all pretty similar, but we are far from the same. There are all kinds of differences in how our leptin (a hormone that has much to do with fat and hunger, mice bred without leptin will be fat, if you underfeed them they will be fat with underdeveloped organs) glucose metabolism, and well everything else that relates to food and diet. So it stands to reason that even though some advice might be universal (sugar is, at best, probably not great for you) the best diet should vary by person. So long as it is safe, try out a diet measure your results see how you feel (blood work is a plus) and if you find success good for you, but remember the same might not be true of everyone else so there is no need to become an evangelist. If it doesn’t work, keep looking.
-Calories in calories out
To lose weight you need to take in fewer calories than you expend, to gain it you must take in more calories than you expend. This is just thermodynamically true, but that doesn’t necessarily make it useful when discussing diet. If you eat less then you expend you will lose weight, you breath in oxygen you breath out CO2 that carbon came from the stuff you ate, don’t eat stuff and bam by definition you have to be exhaling carbon that came from you. So if I fast for 10 days I might lose 15 lbs (I exercise a lot when I do long fasts) but within a month of unrestricted eating I will be right to my steady state weight with my current diet which is about 150lbs. My steady state weight back when I could eat anything, and anything turned out to largely consist of pasta my steady state weight was around 185 lbs. It makes much more sense to look at things from the perspective of why someone is taking in more or less calories then they are expending, and seems to have a lot to do with the composition not just caloric quantity of the diet.
Lets also try to not moralize so much about weight and fat. People who are skinny are very unlikely to be exerting intense willpower everyday to maintain a state of hunger, that isn’t how it works, that isn’t how anything works. People have a much easier time staying skinny usually when they are younger, is it that as you get older you lose willpower? Not to say that no willpower is ever involved as avoiding the stuff you really want to eat isn’t always easy, and some have more cravings than others. But in all likelihood fatter people probably exert more willpower and feel more hunger when it comes to attempts at caloric restriction than do thin people.
Low carb works for a lot of people, certainly if you have problems with glucose regulation (or you know don’t produce insulin and have to rely on slow external insulin) it might be a really good idea to try to see if it works for you to help you regulate blood sugars. It can also help many lose weight. But I highly doubt given ancestral diets and all the different variations there exist in glucose metabolism that it is the best for everyone.
I promise you that if you went on an all you can eat potato diet you would most likely lose weight despite your diet being almost all fairly rapid carbs. Just plain potatoes mind you, no salt, no pepper, no butter, just boiled. By the end of a week or two your brain will be so utterly bored of food that you will naturally eat less. That is what a good diet really needs to do at the end of the day, nourish you while at the same time naturally making you want to eat around the right amount of calories for your body. Insulin spikes certainly can play a role in this, as can many other factors.
Diet and human metabolism are complex. Simple solutions sell but they never tell the whole picture. The obesity crisis is quite recent, carbs are essentially what has been the foundation of the human diet for the last ten thousand or so years.
The goal is finding a diet where you can
A. Stick to it
B. Feel good
C. Naturally have the desire to eat calories consistent with a healthy weight for you (please know in terms of healthy weight, being underweight is actually worse than being overweight!)