Five key genes influence an individual's tastes and appetite, affect the body's tendency to store fat, adjust calorie-burning ability and determine response to exercise, explains Barnard (Foods that Fight Pain; etc.), a physician and genetic researcher; however, he argues, we can manipulate our fat genes and our thin genes (yes, everyone has both!) by implementing diet and lifestyle changes. Instead of a low-calorie diet, which he predicts will lead to later bingeing, he emphasizes a diet high in fiber (whole grains, legumes, vegetables and fruits). Moreover, Barnard claims, carbohydrates are not the enemy we think they are; instead, it's the butter, sour cream, oils or other fats people slather them with that are the problem. In a nutshell, it's not how much but what we eat that makes the real difference. To wit, he eschews animal products, including dairy, because of their fat content, and opts for a vegetarian diet to maintain both good health and proper weight. Putting his theory to the test, Barnard closes his compassionate, clearly written and well-argued book with a three-week ""gene-control program"" that features enticing menus and recipes. (Feb.) Forecast: Barnard's name and fat-fighting program is about to burst onto the national stage--alongside the likes of Dr. Atkins and Barry Sears--with a 33-city tour and major TV and radio publicity. Although many readers may prefer a non-vegetarian diet, Barnard's distinctive marketing advantage--his unique insight into how we can control certain genes--offers something no other diet book does.