Elizabeth Somer. Holt, $23 (336p) ISBN 0-8050-6335-8

"Genetically speaking, our bodies need the same amount of nutrients that were needed by our Paleolithic ancestors," Somer claims. Registered dietician, health writer and self-described "research junkie" (she spent the last 20 years reading thousands of nutrition and anthropological studies), Somer (Age-Proof Your Body; Nutrition for Women; etc.) takes a novel approach to the age-old problem of dieting and recommends readers get back to their evolutionary roots, literally, and conscientiously maintain a diet of countless fruits, vegetables, roots, water and some animal meat (although she does not favor red meat). Somer presents a workout plan that's specific, gradual and measurable, as well as recipes, menus, a shopping list and plenty of coaching, motivation and inspiring tips (e.g., people should avoid drinking alcohol when eating out because doing so makes them eat more, but for those who prefer to, she recommends that they drink two glasses of water for every glass of alcohol). It's a demanding program for weight loss and maintaining that loss for the long term, but what she says makes sense-and is convincing. Somer's program is a diet for people willing to make a definite commitment, but, as she explains, readers can make significant improvements in their overall health and fitness by implementing even some of her advice. Agent, David Smith. (Jan. 3).