A. Jeffrey Blumberg, PhD, director of Tufts HNRCA Antioxidants Research Laboratory, answers: Because of the way most people chew whole nuts, about 10%-15% of the calories from eating them is not absorbed due to the resistance of the plant cell walls to microbial and enzymatic degradation. The cells in the nuts that are not ruptured during chewing then pass through the gastrointestinal tract without releasing the oil they contain (or the calories therein). When nuts are processed into butters, most of the cell walls are broken, and therefore much more energy is available per gram than from whole nuts. Of course, it is important to note that nuts and nut butters are both rich in good fats-monounsaturated and polyunsaturated fatty acids-as well many essential minerals and fiber.
