Slow Carb, but legumes and vegetables have carbs

The Catch is Insulin

Carbohydrates are Sugar chains. The longer the sugar chain the more Complex it is.

Well, If you look at the Carb breakdown on beans and brocolli

http://www.wolframalpha.com/input/?i=nutrition+in+1+cup+black+beans

http://www.wolframalpha.com/input/?i=nutrition+in+1+cup+broccoli

A large portion of those carbs are indigestible dietary fiber. The sugars are also extremely low. Meaning the rest of the carbs are complex carbohydrates which take the body much longer to break down.

The diet works on the principle of moderating insulin levels to avoid spikes. Insulin is the Big hormonal trigger for glucose to be metabolized by fat cells. When insulin spikes It works by stopping fat cells from dispersing energy and opens up the pores to feed them glucose.

Simple sugars are already broken down and prepped for the body to metabolize quickly. While the more complex carbohydrates take more processing to be put into a form efficient enough for metabolic use.

When you eat complex carbs solely you are creating slow drip of sugar into the bloodstream keeping insulin stable and your fat cells consistently metabolizing their energy to fill gaps where needed. This is why you lose fat on extremities first and belly last. They are simply further down the line on the blood vessel highway and your organs need the energy more than your hands and feet. So the fat on them is used because of proximity. Once you lose most of the fat on your extremities the arms and legs are going to start needing energy and the only place to get it is the belly. That is why tremendous results are achieved after week 8 or so when everything starts accelerating.