So-called yo-yo dieting‘losing weight, putting it back on, losing it again and so on’is bad for your health. If you suddenly reduce your food intake, you body, because it is designed for survival, will slow down your metabolic rate in order to store energy more efficiently. This is why people on a diet crave snacks like chocolate, which gives a quick boost to their energy levels, and why weight loss slows down dramatically after the first couple of weeks.