Recently so-called liquid diets start to find popularity. Their essence consists that you should eat only liquid products: soups, juice, kissels, probably liquid porridge. Such diet helps to dump quickly weight, however it conceals many dangers in itself. The matter is that our digestive system is adapted for digestion of firm food. The firm food is gradually entered into a diet of children already on the first year of life. Refusal of firm food for long time at adult age isn’t always defensible aspiration to grow thin. After all we want not only to grow thin but also to keep our organism healthy. Therefore before choosing a similar kind of a diet or to refuse it, it is necessary to understand why it is necessary to eat firm food.