Someone with a (big enough) caloric deficit will lose weight, sooner or later

Someone with a (big enough) caloric surplus will gain weight.

Big enough is because the body will adapt its metabolism to small (and one shot) caloric surpluses/deficits.

But what happens beyond that is very interesting. And so beyond the 'food pyramid' and "conventional knowledge" it's not funny.

Oh and by the way, protein diets (usually) work. Why? Caloric deficit (of course) promoted by modified hunger sensation (that's another piece of the puzzle).

Outside the lab where they are free to revert to gluttony they also typically revert to their original weight (exactly as harris/benedict predicts).

Cals in/cals out works fine. But only if you actually work it. I've successfully used it myself to modulate my weight in both bulking and cutting cycles, as well as reducing my weight from obese to healthy back in the day.

That is possible if it's a small reduction of calories and you're not very far off your ideal weight.

Otherwise is a thermodynamical impossibility.

And yes, losing weight is one problem, keeping it off is a different matter.

Reducing calories causes the body to reduce its calorie usage and starts pumping hormones that cause fat to be retained and your desire to eat to increase, until the hormonal system forces an "override" where you have to eat more. Sure, there are some people who manage to overcome the hormonal override, but they are by far the exception and not the rule, and any weight loss program that tries to override the body's built-in protections against starvation (which go back who knows how long and exist in pretty much any animal) is a recipe for failure.

The keys to the whole hormone cycle are insulin and leptin. Any successful weight loss regimine will have to address those hormones, which calorie reduction "inflames" rather than "pacifies".

But there's an absolute minimum of calories the body need to operate, even at 'low gear' (I'm not sure, but this is around 1000kcal per day), so if you're really limiting the calories below a certain point you will lose weight.

Apart from that, if you're trying to lose weight, but not actually consuming less calories, of course you may have a weight gain.

1. This is a review of 31 studies that comes to the same conclusion: http://mann.bol.ucla.edu/files/Diets_don%27t_work.pdf

2. My anecdotal story, I tried restricting calories for 15 years with the result of hitting 350+ pounds. Seven years after a gastric bypass, I've found low-carb to be the only way I can maintain my weight. Even with the gastric bypass, I can't limit myself to the 1200 calories or less a day I would need to maintain (and I feel like crap). Low carb, I never have to even think about the number of calories (I trade one number for another :) and my energy goes up.

I was experimenting with this and, when the results were positive, it really drove me to understand why the results are positive. I'm (slowly) starting to get an understanding of the biochemistry involved (that is a lay understanding, for sure!).

The relatively recent acknowledgement of the role of the insulin response to refined carbohydrates is a major example of how "calories in - calories out = weight gain" is far too simplistic a view.

No, I think it's an excellent demonstration that for most people 'calories in' is the primary driver of weight gain.

There's not an epidemic of people getting fat from eating 2,500 kcal per day but which is mostly refined carbs.

Most people who are overweight are eating far more calories than that, usually as sugar or fat. They have problems with portion control, and recognising just how much they are eating.

I'm being careful to say 'most' because as this research shows there's a small number of people who might be affected by other things.

As another poster points out elsewhere in this thread - that's like saying that fuel consumption is the primary cause of auto accidents.

They have problems with portion control, and recognising just how much they are eating.

Nutrition is about far more than calories in. Controlling cravings through controlling the insulin response is enormously important. The types of foods that make up calories is enormously important.

Not a single one of them defined low carbs as 5%, in them low carb was like 30%.

30% carbs will make anyone fat with enough calories (exactly what you said was demonstrated.

I'll wait for the 5% carbs version.

You're also making the assumption that less fat results in a healthier human being. that is also something that depends entirely on the nutrient content of your food. You can lose weight by eating nothing but small portions of white rice, but it's not going to result in a healthy individual.