Funded By:
By Megan McCrory, C. PhD.
Excess body weight is of concern to many individuals-- with and without neuromuscular disease (NMD)-- because excess weight is considered a risk factor for diseases such as heart disease, diabetes and cancer.
Being overweight, however, presents a special problem for individuals with NMDs. Depending on the severity of the disease, it can be very difficult to carry out daily activities; and having excess weight may make it even more difficult to move around. We began to study this issue after several participants in our exercise studies asked us questions about weight control. Surprisingly, this topic has not been studied enough for us to make any recommendations based on the research. So we began to formally study this problem by first determining by how much persons with NMDs were overweight in general.
Unfortunately, "overweight" doesn't tell the whole story. For example, body builders generally weigh a lot for their height--but obviously they do not have too much fat. So what we really want to do is measure how "over-fat" one is. We can do this by determining body composition. The term "body composition" refers to the amount of fat tissue and lean tissue in our bodies. Body composition can be measured in a number of ways. The method we use in our studies is the "skinfold technique." This procedure involves taking measurements of the thickness of the fat which is just underneath the skin--thus, "skinfolds."
In our early studies on this topic, we compared a group of persons with slowly progressive NMDs (mostly myotonic dystrophy, Charcot-Marie-Tooth disease, limb-girdle dystrophy, facioscapulohumeral dystrophy, and spinal muscular atrophy) to persons without NMDs. Although these groups were equal in age, weight, and height, their body composition was different: persons with NMDs had a higher percentage of body fat than persons without NMDs. We could draw two conclusions from this study: 1) In general, persons with NMDs were indeed over-fat (that is, they have more fat tissue and less lean tissue compared to persons without NMDs;) 2) This holds true even for persons with NMDs who have a "normal" weight.
The significance of these conclusions lies in the metabolic difference between fat tissue and lean tissue. "Lean tissue" refers to all tissue in our bodies that is not fat: primarily muscle, organ, and skeleton. This lean tissue is what is metabolically active--it is what burns calories. Fat tissue is relatively inactive metabolically. Our measurements have shown that it is the muscle portion of the lean tissue which is decreased in NMD. Thus, not only is the decreased muscle mass causing weakness and fatigue, but also it is easier to put on weight because of less metabolically active tissue.
Therefore, the next issue we decided to look into was diet. What does the typical diet of a person with NMD consist of in terms of fat, carbohydrate and protein, and vitamins and minerals? (It is difficult to determine accurately how many calories a person is consuming, so this topic won't be considered here.) We carried out interviews to determine what the food choices were of persons with and without NMD. When we analyzed these diets, we found that the nutrient content of the diets of persons with NMDs were virtually identical to the diets of persons without NMD. However, when we compared these diets to recommended diets, we found they were both not up to par. Both groups consumed too much fat (about 36% of calories compared to the recommended 25-30%), and the diets were low in fiber and fruits and vegetables. The next thing we wanted to determine is what the caloric requirements are (in terms of diet) of persons with NMD. Do they differ from what is recommended for the average population? Individual caloric requirements are determined by total daily energy expenditure, or how many calories are burned in a day. The major component of total daily energy expenditure is called "resting metabolic rate," or RMR. This refers to how many calories are used if one were to lie down all day and just rest. We found that some people with NMDs tend to have a lower RMR than would be expected based on their size.
We next examined the activity patterns of this same group of persons with NMD. We carried out very detailed interviews, asking what the activities were from getting up out of bed in the morning to going to bed at night. We categorized the different activities and determined the amount of time spent in each. We found that the NMD group on average spent three hours more a day sleeping, lying down, and sitting at ease (very light activities) and one hour less per day in light and moderate activities compared to persons without NMD. Therefore, more time was spent in the lower calorie-requiring activities, and less time was spent in the higher calorie-requiring activities. Taken together, this means that on average, the total daily energy expenditure of persons with NMDs is less than that for persons without NMD. In turn, this means that the recommendations for calorie intakes of the average population may be too high for persons with NMD, since energy expenditure is less than expected.
