Ray Kurzweil is a 'futurist', making his reputation particularly with the concept of the 'Singularity' - the point at which computers become genuinely smarter than human beings (a bit closer than you think). At this point, the game becomes a different one for all of us grunts. Ray's interest in advanced future techncology has led him to believe (and he makes a strong argument in this book) that we are close enough to a point where medical solutions and interventions will allow us if not to live forever (some hyperbole is allowed) but a LONG time - perhaps 1,000 years. Much os this technology is around (think of intraocular lens replacement, new knees) now and part of the path towards much wider use is for it to achieve a critical mass and get out of the lab and into the consumer; analagous to the early days of personal computing. The trick, says Kurzweil, is to live long enough to be around when then time comes for the technology to come together so you are here to live forever. This might not be too much of a stretch. But you need to have the tools at hand and the knowledge to know how to make it.
Grossman's part of this is to help us go through the basic science and understand enough biology and medical science to know what we should be doing while we wait for the technology to catch up. So after Chapter 1 has made the argument that "immortality is within our grasp" and Chapter 2 has explained that "we are in the early stages of multiple profound revolutions spawned by the intersection of bilogy, information science and nanotechnology" much of the remainder of the book is a hard look at some of the basic mechanics of the machine that we live in - the body. Chapter 4 deals with food and water,, Chapter 5 with carbohydrates and the glycemic load (which worried me A LOT); other chapters deal with fat and protein, the digestive tract, weight, insulin, heart disease, 'methylation' (yes, its important!) and so on right through the entire User's Manual (23 chapters in all). This is NOT an easy read and you may have to go beyond high school biology, but it IS worth the effort. In some ways you end up knowing more than you ever wanted to...and it does change your perspective.
The authors are obviously fanatics about their subject - they really want you to live forever, and they truly believe you can. But the effort to follow all their prescriptions is enormous and expensive - by the way Grossman runs a longevity clinic in Colorado (http://www.fmiclinic.com/) so he has something of an interest in being enthusiastic. But if you followed Kurzweil's regime (there are chapters describing each of the author's approach to life). you would be routinely testing dozens of blood levels; not cheap.
This seems to be a key issue the authors gloss over. The economics of living forever are a major hurdle. But of course this was true wit computing. even so, for a while it will be the rich in developed countries that are able to availa themselves of this techncology. whwre that goes is beyond the scope of this nevertheless excellent book.