Câu hỏi:

Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the questions

Diet and Exercise

Many people seem to believe that there is a magic diet formula that will guarantee weight loss. This is a fallacy. Most fad diet, if followed conscientiously, will result in weight loss due to the reduction in calories. However, they are nearly always too monotonous and sometimes too unhealthy to be followed in the long term. Worse, fad dieters who don't become physically active and learn to eat sensibly will eventually regain the weight they lost, and often even more.

          Some of the most popular fad diets in recent years have been low-carbohydrate programs, which work by making the body produce ketones. Ketones are normal and efficient source of energy for the human body. When the intake of carbohydrates is severely restricted, body fats are broken down into fatty acids that can be used as fuel. The fatty acids may be incompletely metabolized, yielding ketones. When your body is producing ketones, and using them as fuel, this is called ketosis. Most diets based on ketosis do not limit the consumption of protein, fat, or total calories. As a result, their fat content tends to be very high. Promoters claim that ketosis will lead to increased metabolism of unwanted fat, even if the calories are not reduced. This is not entirely true; calorie reduction is likely to occur because of the diet's lack of appealing foods. This is not conductive to forming sensible eating habits.

          The most widely used low-carbohydrate diet is the one advocated by the late Robert Atkins M.D, of New York City. Under the Atkins program, the dieter is permitted to eat unlimited amounts of non-carbohydrate foods "when hungry". The American Medical Association and many individual experts have warned that the unlimited intake of saturated fat under Atkins food plan can increase the dieter's risk of heart disease. In 2000, researchers at the University of Kentucky did a computer analysis of a week's worth of sample menus and reported several alarming findings: the diet contained 59% fat; it provided fewer servings of grains, vegetables, and fruits than recommended by most nutritionists, and while it can produce short-term weight loss, long-term use is likely to increase the risk of both cardiovascular disease and cancer. The weight loss usually doesn't last, either. As ketosis begins, weight will be shed quickly, giving the misleading impression that significant fat reduction is taking place. In fact, most of the weight loss is water rather than fat; the lost water is regained quickly when a normal diet is resumed. Appetite, which is often reduced during ketosis, also returns.

          Atkins advocated his diet for more than 30 years and claimed that more than 60,000 patients treated at his centre had used his diet as their primary protocol for losing weight. Yet he never published any study in which people who used this program were monitored over a period of several years. Besides the dubiousness of its effects in the long term, the Atkins diet shares another shortcoming of all fad diets: inflexibility. People are different, with different health problems and genetic characteristics, and no single diet is right for everyone.

          An additional downside to the recent craze for low-carbohydrate diets is that it has encouraged food companies to market low-carbohydrate foods for people who want to "watch their carbs". Most of these foods are much higher in fat than the foods they are designed to replace. "Low-carb” advertising is encouraging both dieters and non-dieters to eat high-fat foods, which is exactly the opposite of medical and nutrition authorities have been arguing for decades. Following a low-carbohydrate diet under medical supervision may make sense for some people, but a population-wide increase in fat consumption would be a public health disaster

It can be inferred from the passage that the author thinks fad diets in general ______