Yes your birds can get over weight on scratch if[/i] they are penned up and not allowed to work off the extra weight/ energy.. Yes there isn't much nutrition in the typical chicken scratch you would get from the feed mill/ farm store for egg production.
There are two types of Carbohydrates, Simple carbohydrates and Complex carbohydrates.
Simple carbohydrates: These are also called simple sugars. Simple sugars are found in refined sugars, like the white sugar you'd find in a sugar bowl. But you'll also find simple sugars in more nutritious foods, such as fruit and milk. It's better to get your simple sugars from food like fruit and milk.
Complex carbohydrates: These are also called starches. Starches include grain products, such as bread, crackers, pasta, and rice. As with simple sugars, some complex carbohydrate foods are better choices than others. Refined grains, such as white flour and white rice, have been processed, which removes nutrients and fiber. But unrefined grains still contain these vitamins and minerals. Unrefined grains also are rich in fiber, which helps your digestive system work well. Fiber helps you feel full, so you are less likely to overeat these foods. That explains why a bowl of oatmeal fills you up better than sugary candy that has the same amount of calories as the oatmeal.
With that being said "scratch grain" that has cracked and whole grains would be a source of complex carbohydrates and if that same "scratch grain" is coated with a molasses to cut the dust it will have both a simple and a complex carbohydrate.
When you eat carbs, the body breaks them down into simple sugars, which are absorbed into the bloodstream. Insulin is needed to move sugar from the blood into the cells, where the sugar can be used as a source of energy.
Chris