The food you eat provides your body with the energy it needs to function. Your body must, however, convert this energy into a form it can use. The energy your body uses is called adenosine triphosphate (ATP). As you can imagine, it takes a lot of energy to fuel your body. Just to move your arms and legs, your muscle cells require a constant supply of energy, or ATP.
How do muscles get energy?
There are a few different systems that work together to make sure your muscles always have enough energy. The first system, creatine phosphate, provides energy immediately, for about 8-10 seconds at maximum intensity. The second system, anaerobic, uses sugar, or glucose, that is stored in the muscle as glycogen. The muscles use this system at the beginning of activity, before the third system kicks in, and during intense activity. The third system, aerobic, uses sugar that is stored in the liver and sugar from food in the intestine, as well as stored fat. This third system produces the largest amount of energy, but for lower-intensity activity.
When these systems work seamlessly together, they always supply our muscles with the energy they need. For example, when Suzie goes out for a walk, her muscles initially get energy from the creatine phosphate pathway. After 8-10 seconds of activity, the anaerobic pathway steps in without her even noticing. If Suzie continues to walk at a moderate pace, the aerobic pathway takes over at about 8-10 minutes. If it starts raining and Suzie runs for cover, the anaerobic pathway ramps up again to make sure there is enough energy, or ATP, for Suzie to get out of the rain quickly.
Unfortunately, these systems don’t always work properly, as is the case in people with McArdle disease. Individuals with McArdle’s are unable to use their anaerobic system, the one that helped Suzie at the beginning of her walk and helped her to get out of the rain.
What is McArdle disease?
McArdle’s is a rare disease of muscle metabolism caused by a deficiency of the enzyme myophosphorylase. The role of this enzyme is to help breakdown sugar, in the form of glycogen, that has been stored in the muscle for energy. Without this enzyme, muscles do not have access to the anaerobic system, the one that helped Suzie to get out of the rain.
It is not known exactly how many people have McArdle disease, but in the United States it is estimated to be 1 in every 100,000 people. McArdle’s is passed down genetically; you must receive a defective gene from each parent. Because McArdle’s is rare, there are not many doctors that are familiar with it or know how to treat patients. As such, most people are not diagnosed until they are in their 30s and 40s, and when they do get a proper diagnosis, most do not have access to informed medical care.
Being unable to use their anaerobic system to produce energy for their muscles, people with McArdle’s experience an energy shortage during even the most mundane activities. As you can imagine, this happens many times throughout the day, whether a person is drying their hair, walking the dog, carrying groceries, getting dressed, or even chewing food. So, what happens when you can’t use your anaerobic system?
Once the first system, creatine phosphate, is used up, people with McArdle’s must learn to slow down or stop what they are doing, so that their muscles can rest, and more energy (ATP) can be produced. After about 8-10 minutes, the aerobic system steps in to provide energy and activity becomes easier; this is called “the “second wind.”
Since their anaerobic system is broken, if people with McArdle’s push a bit too much, their muscles will get fatigued and they will experience muscle pain and cramps, which can lead to muscle breakdown. When the muscle is damaged, a protein called myoglobin is released into the blood stream. Myoglobin can block the kidneys and can result in kidney failure.
Trying to always balance your activity to make sure your muscles don’t run out of energy can be difficult. It means taking a risk when you stop to rest in the middle of a busy road, or in the deep end of a swimming pool!
Can a low-carb ketogenic diet provide an alternate source of muscle energy?
So, what is the best way for people with McArdle’s to get energy for their muscles? Unable to access and use the sugar stored in their muscles, they need an alternative. They must either consume dietary carbohydrate – sugar – almost continuously to ensure there is always enough energy in their body, or they must draw on their fat stores for energy. Unfortunately, over time, increasing sugar intake can lead to the development of secondary conditions, such as obesity, insulin resistance, diabetes, and heart disease.
This is where a low-carbohydrate ketogenic diet (LCKD) can help people with McArdle disease. By lowering carbohydrate intake and increasing healthy fats, the body goes into a state of ketosis. This seems to provide a steady flow of energy to the muscles, similar to what happens during the aerobic system. For people with McArdle’s, this makes everyday activities easier and reduces the risk of muscle damage and the problems associated with that. It also allows people with McArdle’s to engage in exercise more easily, which helps to improve their aerobic fitness and overall health.
Patients with McArdle disease that have tried a LCKD are finding they have less trouble with completing routine tasks, can participate in moderate exercise without difficulty, keep their weight under control, and find that their quality of life has improved.
You can also read a summary of a case report, co-authored by Dr. Stacey Reason, Dr. Eric Westman, and other researchers, in the Journal of Rare Disorders: Diagnosis & Therapy, at HEALclinics.com.