I can only base my opinion on personal experience. I feel that my body absorbs these minerals in the forms I have used. I have had changes in my skin, my eyes, and my muscles which have occurred repeatedly in conjunction with suppplementation with these minerals. I have read many peoples' comments that because these supplements are not from foods, that our bodies do not recognize or use them. However, I have to disagree. I feel even so-called health conscious people do not give our bodies due credit. The body is capable of transforming material into what it may need, and it can expel what it doesn't by transforming that, as well. Admittedly, it may be forced to work harder to extract nutrients from certain sources, but when the need is great enough, the body finds a way.
I do believe that it serves the body better to receive nutrients through food sources so that more nutrition can be gained from the processes than just one or two nutrients, and so that the body does not have to sort and excrete unnecessary binders and fillers. And if someone has been successful in improving or maintaining health just with food, then I would not suggest switching to supplementation. However, when faced with chronic nutritional deficiencies, in combination with poor digestion and assimilation, in general, I do feel that supplementation can be beneficial, and that it has helped me to regain my health.