Diet to lose weight, exercise to keep it offStudy shows benefits of working out after dieting
Most people who lose weight by dieting eventually put the weight back on. A new study suggests that there may be good scientific reasons for this, and that exercise can play a key part in maintaining a reduced weight.
Effects of dieting
At the most basic level what we weigh is the difference between what we eat and the energy we expend. But the study points out that the underlying physical and mental processes are much more complicated than this. In most animals, eating is controlled by physiological signals that may suppress appetite or arouse the desire to eat, but in humans these signals are normally quite weak.
But after a period of weight loss caused by a diet, these physiological signals can become more dominant. A feeling of persistent hunger can drive dieters to overeat, which results in the weight gain so often seen after dieting.
How exercise can help
Some people are of course able to maintain weight loss after a diet, and studies have shown that regular exercise is one of the main factors in this success. Now it seems that there are good reasons for this. The study investigated how exercise affects the body’s physiology to minimize weight regain.
About the study
The study, carried out at University of Colorado Denver, involved a group of obesity prone rats. For the first 16 weeks, the rats ate a high-fat diet, as much as they wanted, and remained sedentary. They were then placed on a diet. For the following two weeks, the animals ate a low-fat and low-calorie diet, losing about 14% of their body weight. The rats maintained the weight loss by dieting for eight more weeks. Half the rats exercised regularly on a treadmill during this period while the other half remained sedentary.
In the final 8-weeks, the relapse phase of the study, the rats stopped dieting and ate as much low-fat food as they wanted. The rats in the exercise group continued to exercise and the sedentary rats remained sedentary.
Compared to the sedentary rats, the exercisers:
- regained less weight during the relapse period
- developed a lower 'defended' body weight
- burned more fat early in the day, and more carbohydrates later in the day
- accumulated fewer fat cells and less abdominal fat during relapse
- reduced the drive to overeat
- enhanced the ability to balance energy intake with energy expended
During feeding, the sedentary group preferentially burned carbohydrates while sending fat from the diet to fat tissue. This preferential fuel use stores more calories because it requires less energy to store fat than to store carbohydrates. In addition, burning away the body’s carbohydrates may contribute to the persistent feeling of hunger and large appetite of the sedentary animals.
Exercise blunted this fuel preference, favouring the burning of fat for energy needs and saving ingested carbohydrates so that they could be used later in the day. Taken together, the exercise led to a much lower appetite and fewer calories ending up in fat tissue.
Finally the researches found that exercise prevented the increase in the number of fat cells observed with weight regain in sedentary rats.
The study was published in The American Physiological Society.
This article was published on Wed 2 September 2009
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