That's exactly his point. The approach of merely counting calories ignores the fact that some foods such as diet soda are low in calories but can have an effect on body composition.
You shouldn't just "eat less" you should "eat better", and that means eating an appropriate amount of healthy good.
Research has shown that, among dietary and health guidelines, switching soda for diet soda is the most effective guideline that exists.
Eating better is obviously preferable, but the reason most people fail their diet is because it is too hard for them to comply with it. This is where the "switch to diet soda" is so effective; people can actually do it.
I wasn't comparing regular soda to diet soda, I was comparing having diet soda to not having diet soda. Diet soda affects gut flora and insulin levels. Calories are not the whole story.
That has only been demonstrated in mice, however, and only with semi-unrealistically large dosages of sucralose, if memory serves me right.
In humans, we have a lot of evidence that shows that the source of calories does not matter, for fat loss. Long term health is another issue, of course.
IMHO, putting focus anywhere but on calories is doing oneself a very big disservice, except for some athletes and bodybuilders for whom other factors are important as well.
What effect on body composition is that? Artificial sweeteners don't cause insulin resistance, so they should be fine for you.
The acid in Diet Coke is real bad for your teeth, but fruit juice is more acidic and has more sugar than diet soda and yet you probably think it's healthy, right?
