Meet the Systems Biologist Series - Mary Ellen Harper

Posted on Wednesday, May 16, 2018

pic of Mary Ellen Harper

Mary Ellen Harper


Slow Muscles Rock!  Dr Mary Ellen Harper’s work on how the mitochondria impacts our weight is beginning to unravel the mysteries of weight and why your weight is just not a reflection of what you eat.  To learn more about Mary Ellen’s research program and the power of slow muscles, read  4th year Translational and Molecular Medicine student Kelsey Pitre’s article:  Obesity isn’t Rocket Science.  It’s more complex than that!


We all have that one friend who can survive on a regular diet of Big Macs and still fit into size two jeans. Most of us also know someone who, despite best efforts at dieting and exercise, is constantly battling to lose weight.

There is a common misconception that obesity is a choice. However, research is showing that not all humans are created equal – at least not in the weight loss department. Mary-Ellen Harper, a Professor in the Department of Biochemistry, Microbiology and Immunology at the University of Ottawa, has focused her research on uncovering the myriad of mitochondrial factors that contribute to obesity in order to combat weight-related stigma.

We all know mitochondria as the powerhouses of the cell and the central hubs for converting food into a form of energy that our body can use, ATP (or adenosine triphosphate). Dr. Harper describes our cells as cars. Just as moving cars burn fuel, our exercising bodies burn the energy from the foods we eat. And, like how an idling car continues to burn fuel, our resting muscles also continue to burn fuel, and the amount of fuel burned at rest varies from one person to the next. But why do muscles at rest still need fuel? It turns out that this idling energy expenditure keeps the mitochondria (car engine) running properly by preventing the buildup of molecules called Reactive Oxygen Species (ROS). ROS can damage the proteins and fats that make up the mitochondria – essentially mucking up the car engine. This can interfere with pathways in cells, ultimately increasing processes of cellular aging, and increasing our risk for diseases, like diabetes.

So what actually happens when we eat a meal? Well, food is broken into various forms of fuel that can be used by the body. Some of the fuel is stored as glycogen in the muscles and liver, which is similar to filling a small fridge with food. When that fridge becomes full, some of the food must be stored in a freezer, or in the case of our bodies, stored as fat. Fat is a great store of fuel, and is necessary for good health, but having too much of it can be harmful.

Different types of muscle are more easily able to break down fridge (glycogen) vs. freezer (fat) fuel. When we think of movement, our body has two main types of muscle: slow and fast. It may seem counterintuitive, but slow muscles burn fat more efficiently. On the other hand, fast muscles rely on readily accessible “fridge” energy, or glycogen. In short, more slow muscles means more fat burned! Dr. Harper’s lab has found that some people have greater amounts of slow muscle, and that they burn more fat than other people. These lucky folks have slightly different car engines, which affect how well the muscles can burn fat.

To complicate matters, mitochondria aren’t the only factors at play when it comes to obesity. Hormones can also affect weight loss and gain.  Specifically, the thyroid hormone controls how much energy your body uses at rest. Hyperthyroidism is a condition in which the levels of thyroid hormone in your blood are higher than average. This causes your body to use more fuel at rest – so you can eat more and still fit in those size 2 jeans. On the other end of this spectrum, hypothyroidism occurs when you have lower levels of thyroid hormone. So, at rest, your body does not burn as much fuel, making you more prone to obesity.

In a nutshell, those who are looking to lose weight are waging war against much more than just their desire to binge on tasty food. Dr. Harper and her colleagues are working to understand how various “bad guys” prevent weight loss and how we can equip our bodies to fight back. Not to say that all of your efforts to exercise and eat well are futile, but next time you get on the scale, remember that a multitude of factors are affecting the number you see.

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