It's funny too, because I have perfectly logged data showing that the weeks I eat fewer than about 1800 calories reliably, (because I have an incredibly sedentary lifestyle) reliably and predictably lower my weight.
I've literally got a science experiment in my own body that shows reducing calories in, without reducing the actual design of my meals, reduces my body mass.
I'm willing to accept that there are some minor irregularities and difficulties that make "Calories in == Calories out" not 100% accurate, but I'm betting the effect size is closer to +-10%, and therefore easily discarded for approximations, even though they are scientifically significant and could create a more accurate model.
I agree that the CICO is a model that works, but it is at least somewhat complicated by the fact that CO is a function of CI. I.e., what you eat takes different amounts of energy to metabolize so it also contributes to what you burn. If I eat 1800 kcal of protein I may have higher CO than if I ate 1800 kcal of simple carbohydrates.
There's already a lot of uncertainty when most people measure their calories (very few people actually weigh their food) and this just adds another layer of uncertainty. I have a feeling those all combine to make it inaccurate enough in practice for some people to claim the CICO model doesn't work.
No. A healthy diet is a diet that provides you with the right amount of nutrients without leaving you hungry or unsatisfied.
By not being hungry and unsatisfied you'll then stop overeating (surprise!).
"My diet is OK, I just eat too much" is all wrong: there is a complex relation between caloric intake, which foods are eaten, hunger, satisfaction, energy, mood etc.
Many fad diets "work" even if they are not grounded in any scientific fact and are even unhealthy in the long term (low fat, low carb, keto, gluten-free, all-meat).
They artificially restrict the variety of food one person can eat and this indirectly encourages people to eat less. And when people stop overeating they feel better and believe the fad diet is sound.
There were even a diet where you can only eat foods in a given meal from the same group... by color. Same trick.
Talk about generalising. How is gluten-free unhealthy in the long term. Do you actually believe that wheat in particular is required for health?
Just above you said a diet needs to be nutritionally complete. Low carb, keto, gluten free, hell even low fat can be nutritionally complete and satisfying, though the latter one will not feel really good in the long term.
Your body stores calories you eat, and it's really good at it. If you eat too much of anything (that contains more calories than the calories required to digest it), you will gain weight. Eat too much fried chicken, gain weight. Eat too many oranges, gain weight. Eat too many beans, gain weight. You can probably gain weight from eating too much broccoli, although I'd get sick of broccoli before that happened.
I've literally got a science experiment in my own body that shows reducing calories in, without reducing the actual design of my meals, reduces my body mass.
I'm willing to accept that there are some minor irregularities and difficulties that make "Calories in == Calories out" not 100% accurate, but I'm betting the effect size is closer to +-10%, and therefore easily discarded for approximations, even though they are scientifically significant and could create a more accurate model.