All food that we eat turns into sugar in our diges

All food that we eat turns into sugar in our digestive tract. That converting of foods to sugar is how the body absorbs the calories to make energy.
The simple carbs are more basic forms of sugars.
The complex are just that. More complex versions of the sugars.
The starches are easy targets to convert to sugars. That is why these foods are used to make alcohol.

Broccoli is a carb. Because of its make up it burns clean with little sugar content and rich in vitamins.
The potato is starchy and thus can be converted to sugar quickly. From an exercise standpoint, the starchy carbs are burned immediately for energy, or stored. Thats called carbo loading!

So, you can eat all the veggies you want, limited fruits due to sugars, and small amounts of protiens to help support soft tissues.