By nature, we're wary of books announcing ""A Whole New Approach to Losing Weight,"" offering excessive good cheer (""Every Day Is Your Birthday!""), and promising new scientific breakthroughs: ""Most people can go on eating the same foods they are eating now, and lose weight if they will just eat them earlier in the day."" Enter Chronobiology: ""When you eat during the day can be almost twice as important as the total number of calories you eat."" The ""twice"" comes from a set of statistics taken from one experiment in which people ate one high-calorie meal a day. Those eating only breakfast more often lost more weight; those eating only dinner usually lost less weight or gained a little. Oh, exercise (especially jogging), enough fiber, and attitude are important, and a balanced diet matters too, but biorhythms get top billing here. Gatty writes a slippery prose and manipulates all the dietary catchwords in good time. But passing this off as conclusive scientific evidence is misleading: it's hardly revolutionary, and what's noteworthy could fill a pamphlet.