Regardless of what anyone's emotional opinion of diet is, the bottom line is that the first law of thermodynamics cannot be negated. Yes, there are other factors--not becoming glycogen depleted, taking in adequate protein for muscle building, thermic effects of protein vs other nutrients, rebound blood sugar effects, satiety and the fat flushing effect of fiber--but there is no negating calories out vs net absorbable calories in, period.
Anything that tells you otherwise is an attempt to sell you a program. If you get your nutrients in the needed quantities and don't take in more calories than you need, and eat frequently enough to avoid glycogen depletion, AND are on a sound exercise program, you will not gain extra body fat. This isn't my opinion--it's science.
I know some people are passionate about "clean diets" but it all still comes back to calories out vs calories in. If you take more calories in the form of lean protein, fibrous veggies, cookies, cake or anything else, than you expend, you will gain body fat. Sure, it's harder to eat too much of the less calorie dense and higher fiber or protein foods, but it is possible.
Again, nobody's negating the benefits of healthy eating--to the contrary, what Annette and I have said time and time again is everything in moderation. For the record, both Annette and I are 41, so if anyone has the idea that we're young with rapid metabolisms, it isn't the case.
I've worked with people with eating disorders for years as well as recovered from one myself. The quickest path to boredom, sabatoge, and disordered eating is to forbid yourself any type of food on an ongoing basis. There's nothing that should be a total no-no, including junk food and treats--but you can't eat them, nor anything else in unlimited quantities, nor can you eat treat foods in quantities that mean you have to limit other foods to the point that your nutritional needs go wanting.
If some of you love the idea of having to stick to a "clean" diet for the rest of your lives, go for it. But realize that the science behind factual information regarding weight loss is strictly a matter of caloric intake vs caloric expenditure. I would be glad to demonstrate how what someone might think to be the magic of clean eating boils down to just that in terms of weight control.
Maribeth