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I work with an interesting population: the combative and acrobatic sports. That means wrestling, fencing Tae Kwon Do -- things with weight classes that require managing weight really closely.
On the acrobatic side, it's diving, gymnastics, synchronized swimming, all of which require a lean physique and light body weight.
For most of my athletes, weight control is all about pretty restrictive diets. Basically, everything they put in their mouth has to be monitored and thought about. We usually use a phased diet approach. Six to eight weeks out, we change from the initial diet to one with more careful considerations. They can choose to go on strict plans with portions meted out, or they can just get serving guidelines and build their own meals.