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Diets And Metabolism

What are the effects of dieting on metabolic rate?

One particular problem that occurs with dieting is a significant reduction in metabolic rate. If your metabolic rate decreases then your body requires less energy for normal functioning and therefore unless you restrict your calorie intake, still further, you will be likely to fail to loose more weight or even put the weight back on. With severe dieting the metabolic rate may decrease to around of normal – this would have a very negative effect on weight loss.

If we use the example of a woman who reduces her calorie intake, by more than 1000 calories, to just 900 calories a day. Initially she looses a lot of weight – although most of the weight she looses is just stored water and glycogen which she will quickly put back on as soon as she returns to a normal diet – but after a while her metabolic rate slows to the point where she only needs 1000 calories a day. In this case even though she is consuming around 900 calories a day, her body now needs just 1000 calories a day to maintain normal body size and she is unlikely to loose a significant amount of additional body weight.

Your metabolism remains low after dieting and is slow to return to a normal level

An additional problem, is that her metabolic rate will not quickly return to normal, when a dieter returns to a normal calorie consumption (e.g. 2000 calories/day) they will be consuming 1000 calories more than what her body actually needs. Consuming around 1000 extra calories a day, would lead to a 2 pound gain in weight over a week. However, the actual weight they would put on, when returning to a normal diet would be even higher as they would quickly put on all the weight that was lost from water and glycogen early on in the diet. This is why people who come of strict diets may put on as much as 6 pounds in one week once they return to their normal eating habits.

Reductions in muscle mass and the effect on metabolism when dieting

Another factor to consider is that highly restrictive diets will lead to a reduction in muscle mass. Since lean muscle is metabolically active, any reduction in muscle mass will lead to additional reductions in the metabolic rate and make dieting less successful. A reduction in muscle mass, occurs through dieting because the body breaks down muscle tissue to use as an energy source because it isn’t getting enough energy supplied through the diet. Therefore the lower dietary intake the greater the loss of muscle mass will be.

A less restrictive controlled diet is more effective in the long run

By using a controlled diet – reducing your calorie intake by around 500 calories a day – you will be less likely to lower the metabolic rate, or lose muscle mass, and therefore will be more successful in the long run. A controlled dieter could expect to loose 1-2 pounds of fat per week.

Diets and metabolism summary:

  • Diets can significantly affect metabolism by reducing metabolic rate and compromising weight loss
  • Metabolism is slow to return to normal following dieting which can lead to dieters rapidly gaining weight if they stop the diet
  • Diets can also lead to reductions in muscle mass which can lead to additional reductions in metabolic rate
  • Less restrictive diets have less of a negative effect on metabolism and are more succesful in the long run.