Massachusetts General Hospital (MGH) researchers have found that the amyotrophic lateral sclerosis (ALS) patients who were mildly obese survived longer than who were normal weight, underweight or even overweight.

"We have long known that being underweight shortens survival for ALS patients, and several studies in an animal model have shown that weight gain is associated with increased survival," said Anne-Marie Wills, of the MGH Neurology Clinical Trials Unit, senior author of the report.

"Our study was designed to investigate how cholesterol levels affect survival. We were surprised to find that body mass index or BMI - a measure of weight adjusted for height - made a large difference in survival. Patients with a BMI of 30 to 35, who would be considered mildly clinically obese, lived the longest; and patients who were overweight, with a BMI of 25 to 30, lived the second longest," she added.

ALS is a progressive neurodegenerative disease affecting motor neurons in the brain and spinal cord. Death of these nerve cells stops the transmission of neural impulses to muscle fibers, leading to weakness, paralysis and usually death from respiratory failure. During the course of their disease ALS patients usually lose even more weight than can be attributed to the loss of muscle mass caused by nerve destruction and the related muscle inactivity. Studies have shown that ALS patients burn more calories than would be expected from their limited physical activity, but the mechanism for this metabolic change is currently unknown.

The study will appear in the journal Muscle and Nerve and has been detailed online.