The endocrine aspects of DMD are not well understood and have only recently been the subject of focus for DMD. Affected boys and young men use steroids and also struggle with weight gain due to inactivity which can contribute to elevated glucose levels. The body responds to higher glucose levels by flushing excess sugar through urine leading to thirst. There are also affected individuals who have been diagnosed with Type I or Type II diabetes.
It is wise to consult your son's physician if thirst seems unquenchable, especially if accompanied by fatigue, sudden weight loss or complaints of blurred vision. What is less understood is whether those affected by DMD also are more prone to Glucose Intolerance (Insulin Resistance). Prolonged periods of elevated glucose levels can affect vision and lead to other medical problems. Fasting blood tests (Not eating for 8 hours before test.) are used to diagnose glucose intolerance.
Diet can exacerbate glucose intolerance. Certain foods have a high Glycemic Index meaning they cause glucose levels to rise quickly triggering the body to produce more insulin to metabolize sugar. The sudden rise in Insulin is followed by quick digestion and soon after a sensation of being hungry despite consuming adequate calories. This can lead to weight gain and elevated glucose levels. Foods that are highly processed, white bread, white potatoes and foods containing high levels of sugar trigger this response. These foods should be avoided and replaced with whole grains, fruits and vegetables and less processed foods which take longer to digest leading a sensation of being full longer and moderate glucose levels. A balanced diet is crucial.
Speaking with a nutritionist or physician familiar with DMD and diet needs can help with planning such a diet. There are many commercial diets advertising the benefits of their plan, yet a meal plan can be developed without spending money on these programs. In a Glycemic Index diet foods are rated based on glucose with higher rated foods are avoided and lower rated foods used more frequently. I have a meal plan given to my family by a Nutritionist from Cincinnati Children's Hospital I am able to e-mail to anyone interested (firstname.lastname@example.org).
Again, seeing your son's doctor is important when he has excessive thirst and before modifying diet to ensure appropriateness.