Metabolic Efficiency Test – Part I

Last week I went to Fitness RX here in Louisville to have a Metabolic Efficiency Test (MET) done. I’ve been curious about having this test done for some time now. Before I get into why I wanted to have a MET done and tell you about the test procedure and my results, I wanted to take this post to explain exactly what it is how it found it’s way to endurance sports.

For the facts on Metabolic Efficiency, I will turn to the guy that developed the concept, Bob Seebohar. According to his website, Bob is a sports dietitian who loves to challenge conventional wisdom (much like myself) and always questions the “why” behind traditional sports nutrition strategies. He developed the Metabolic Efficiency concept several years ago and has coached athletes from all levels to success. Bob defines Metabolic Efficiency as simply using the nutrients that we have stored in our bodies more efficiently. We have fat and carbohydrates stored in our bodies at all times. Bob set out to determine if we can use our large amount of stored fat as fuel while conserving our limited stored carbohydrates until they are really needed. A typical athlete has between 50,000 and 80,000 calories stored as fat, but only 1,000 to 2,000 calories of carbohydrates that are available for use. Read that again…you have 40 to 50 times that amount of fat to carbohydrates to use as fuel.

Science determined long ago the you can train your body to burn fat by doing aerobic (low intensity) work. We’ve all seen the charts at the gym or on the machines showing someone’s “fat burning” heart rate zone. However, through his research, Bob has determined that through changes in training and diet, athlete’s can actually continue to burn predominately fat when exercising at high intensity. So if losing weight is not a goal, why would you care if you are burning fat or carbohydrates when you exercise? The two main reasons are long term health and race performance. Becoming more metabolically efficient has a huge impact on health by improving certain lipid blood markers and decreasing the risk of metabolic syndrome and some chronic diseases. From a performance standpoint, it can eliminate GI distress (nausea, vomiting, bloating, diarrhea, etc.) in endurance athletes. It also greatly reduces the number of calories that you need to consume per hour while competing in long endurance events such as Ironman or Ultra Marathons.

During the test (which I will explain in a later post), it is determined at what point an athlete crosses over and your body prefers to use more carbohydrates than fats to fuel your workout. This point, called a Metabolic Efficiency Point is where this shift occurs. It is determined by measuring how much oxygen you are consuming versus how much carbon dioxide you are expelling. That ratio is called the respiratory exchange ratio (RER). You will always burn a mix of both fats and carbs, but once your percentage of carbs moves above 50%, you have officially crossed over to being a carb burner. This point can move based on training and nutrition changes. It’s interesting to note that bigger changes (75%) can be achieved through dietary habits than through training changes. With eating, you can teach your body to burn fat all day long. With exercise, you only have the small window of time that you are actually moving to develop your fat burning engine. The goal with diet is to stabilize your blood sugar levels throughout the day and decrease the calories you consume before and during training. I will go into more details on how to accomplish this in another post.

So the question then becomes, how long does it take to completely adapt and become metabolically efficient? It’s not as long as you might think. If you have discipline and stick to it without exception, it can only take a few weeks to teach your body to become efficient. Once you are engaged in the diet plan and your body learns how to burn fat efficiently, you can then start to dial back the amount and type of calories per hour that you need during exercise…which will lead to less GI issues and quicker recoveries.

Part II will look at why I was so excited to have the test done and what I hoped to gain from the information gathered.

Here are the links to Parts II and III: