It's key in how he summarizes it at the end: "it's not easy, but it's very simple."

Losing weight isn't complicated. Eat less, move more. That's it.

Losing weight is extremely difficult. The drive to eat is a fundamental instinct. That instinct isn't calibrated for constant easy availability of food. We inherently want to eat more than is good for us in an environment of abundance. Fighting that requires a great deal of willpower, which is a limited resource.

Successful weight loss comes down to figuring out how to reduce your intake and increase your movement without requiring more willpower than you can actually muster. This is really hard. But losing weight is still simple.

To give it a car analogy, it feels like the weight loss discussion is asking: "Why are there so many automobile accidents?" Then come a lot of replies in that say "When you hit the brake, the car will slow down!" I feel like there are multiple things going on at different levels that so many people don't/can't hit the brake at the right time. That doesn't make the calorie-in-out statement false, and any solution will certainly involve reducing calories in. But, it suggests to actually get the weight of the overall population down, we need to look a bit more broadly.

"Simple, not easy".

You track your calories, you track your weight. If you're not losing weight you reduce your calories until you are. This method compensates for peoples differing metabolism and activity levels.

One of the most insightful studies I've read on dieting is that people trying to lose weight underestimate how many calories are in the food they're eating. It's not surprising once you start logging everything you eat -- you'll see that a lot of common foods are extremely calorific.

I can't find the exact study but here are two on the matter

http://www.ncbi.nlm.nih.gov/pubmed/16954358

http://www.bmj.com/content/346/bmj.f2907

obesity rates are high because people don't try hard and consistently to lose weight. people lead busy lives, diets are not fun, and its very easy to eat a high calorie diet. diets don't work because people don't stick to them, not because diets don't work.

Exercise is good for you and it seems to be pretty damn simple, but we are way too sedentary. Would you similarly suggest that exercise therefore must in fact be a lot more complicate than it appears?

I would suggest people are overweight because the steps to lose weight are unpleasant, or require willpower, rather than being too complicated and mysterious.

I think "other factors" could well include the reluctance of the average human mind to undergo consistent discipline, and the reluctance of health food corporations to concede that it pays off if successful.