Maltodextrin is a flavorless polysaccharide carb that mimics dextrose (a type of sugar). While there is nothing inherently bad about maltodextrin, it does have a high glycemic index , which means that these calories get digested and injected into the bloodstream very quickly. This is no problem if you consume your weight gainer shake right after your workout, as the calories are used up in your recovery. However, taking a large amount of maltodextrin when there is no immediate need for the calories may lead to some unwanted fat gains.
Why brown rice over white? The carb content may be similar, but the body burns brown rice at a slightly slower rate because all but the outermost hull is left on the kernel, meaning there’s an extra dense layer to be digested. Since it burns slower, brown rice will help provide sustained energy through your workouts. Because the outer layers are largely left intact, brown rice is also more nutrient-rich than white. More than 90% of rice’s vitamin  is lost in the conversion from brown to white rice. Eat one to two cups of brown rice per day, limiting intake after 5 PM.