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CAN YOU IMPROVE POWER-TO-WEIGHT RATIO THROUGH CRASH DIETING?

Posted by Dr. Robert Portman on 8/22/2017

EVERY SERIOUS CYCLIST RECOGNIZES THE IMPORTANCE of improving their power-to-weight ratio.  A high power-to-weight ratio can translate into a significantly faster finishing time.  There are two ways to improve power-to-weight ratio.  One is increasing power output by doing high-intensity intervals, and the second is dropping weight.

A 2009 study conducted at Southern Connecticut State University compared the individual and combined effects of interval training and weight loss on the power-to-weight ratio.  They found that training or weight loss alone each produced the same improvement, about 9%.  When both weight loss and interval training were combined, there was no improvement over the 10-week study period.

The authors of the study speculated that losing weight deprived the cyclists’ bodies of the ability to benefit from doing high-intensity intervals. More specifically, inadequate protein intake from dietary restriction kept their muscles from adapting to the stress imposed by the sprints. Their conclusion was that weight loss and fitness gains are incompatible.

Because weight loss, at least up to a point, can improve the power-to-weight ratio, cyclists often obsess about their weight. Thus it is not uncommon for cyclists to embark on a crash diet before a major race.

A crash diet seems simple.  Just significantly reduce your daily calories and the weight peels off.  However, crash dieting activates the law of unintended consequences.  Here’s why. We know that a pound contains about 3,500 calories, so if we eat 1,000 fewer calories each day, more than two pounds will magically disappear each week.  And, since we are generally impatient, we push the daily caloric deficit to help us get to our goal weight faster.  For athletes, however, the consequences of reducing caloric intake by 750-1,000 calories per day can be significant.

An often-ignored observation was made almost 30 years ago by researchers at Rockefeller University.  They looked at the effect of calorie deficit on weight loss.  As might be expected, the highest caloric deficit produced the greatest weight loss.  What wasn’t expected, however, was where the weight loss was coming from.

Everyone who goes on a diet is expecting to lose body fat. But the Rockefeller researchers found that people who practiced moderate caloric restriction tended to lose the weight as fat.  Ninety-one percent of their weight loss was fat and 9% was lean body mass, or muscle.  When the subjects engaged in a diet involving severe calorie restriction, however, fat represented 48% of the loss and muscle represented 42%.  Expressed another way, the greater the daily calorie restriction, the greater the loss of muscle mass.

Ironically, moderate to severe calorie restriction, which results in loss of lean body mass, is unnecessary.  Diets that have smaller daily caloric deficits (300-500 calories) shed fat while preserving lean body mass. This was borne out in the Southern Connecticut State University study described above.  The cyclists in the weight-loss group lost about one pound per week, which translates to a daily caloric deficit of about 500 calories.

The bottom line – Here’s what we know about weight loss for cyclists:

1. Weight loss can improve power-to-weight. However:
2. Overt weight loss efforts should be separate from periods of intense training. And:
3. When weight loss is actively pursued, it should be pursued in moderation to minimize the loss of muscle mass.

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