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What is Metabolic Efficiency and Why Do I Need It?

Posted by  blog  Nov 30, 2014

By:  Ashli Collins, MD

Bob Seebohar, noted sports dietitian to professional athletes and Olympians, spent years of his career trying to interpret data and text books to understand the inner workings of our body-both physically and nutritionally-to make athletes more efficient at burning fat. The theory of “burning more fat” certainly sounds appealing but not to the detriment of our athletic goals. Many athletes are lean, mean, fighting machines and feel that they have no fat to give. But through Bob’s years of research and field testing, he has shown that by proper nutrition and training we can train our bodies to use our internal fat stores as our main source of nutrition while training.

It is surprising to know that even the leanest of athletes are estimated to have 30,000 to 50,000 calories of fat available for energy at any given time. Some athletes, like myself, may have a few more than that. It is estimated that the average person has 80,000 calories of fat whereas they have only 1,000-2,000 calories available in the form of carbohydrates. Many of us “train” our bodies to be carb burners. We are constantly feeding, and often with high carbohydrate choices. In our testing at FitnessRx, we have already seen a number of athletes be tested that are carb burners who are super lean and super fit. That means that almost the minute they start to workout, they immediately flip their engine to burn carbs, when there are THOUSANDS of calories available in the form of fat. Wouldn’t most of us prefer to have a body that uses fat as a fuel instead of constantly having to ingest sports drink after sports product to keep our engine fueled by carbs?

Metabolic efficiency is just that. Teaching our body to be more efficient at using our innate fat stores than rely on carbohydrates-both endogenous and exogenous. Becoming more metabolically efficient also has a goal, through diet changes, of helping maintain blood sugar levels at a more steady state level than the typical peaks and valleys that we feel after a sugary snack and the subsequent “crash”. A metabolically efficient diet typically tends to be lower in carbohydrates, while increasing our protein and fat intake. By not taking in tons of carbs, thus decreasing the release of insulin, we see stabilized blood sugars. That, in turn, is now starting to show significant decreases in the symptoms associated with metabolic syndrome. The other huge benefit is lessening GI distress (bloating, vomiting, diarrhea) by needing to overfuel during training or racing.

Coming up with a plan to be more metabolically efficient generally starts with being tested to see where you really are as far as fat burning vs. carbohydrate burning at rest and/or in exercise. Testing preferably should be done at a facility that has someone trained in evaluating the data as well as having adequate equipment to provide that data. The machine that is used is called a metabolic cart and it is considered a medical or exercise physiology device. The client being tested will have to wear a headpiece and have a mouthpiece in to capture your exhaled CO2 and O2. On Bob’s protocols, you have a slow, easy warmup on either a treadmill, bicycle (computrainer) or rower. After a nice warmup you begin incrementally increasing your effort every five minutes. Data will be pouring out every fifteen seconds including your percentage of fat calories burned, carbohydrate calories burned and your heart rate. On typical VO2 Max testing you continue to increase until you cannot go anymore. The metabolic efficiency test is considered “submaximal” in that you will not have to push until you feel like you are going to drop.

After your test is completed, the data will be analyzed. The goal of the data output is to show several things. One, is whether you have a “crossover point” or that point at which you switched from being a fat burner to a carb burner. Some people have one, and some people as I said, are carb burners and never even begin to use their fat stores. The data also lets us evaluate through other numbers your personalized heart rate zones. Many athletes use these numbers to set their zones for training and or racing. If you are not using heart rate zones, data will also be collected throughout the test to determine your training zones based on perceived effort. Many people are just interested in the calories burned at different paces/efforts to help them pinpoint their nutrition for training or racing days. Whatever your interest, this data is uniquely yours and can give you great insight into what your body is doing at say a 10:00/mile pace vs. an 8:30/mile pace vs a 7:00/mile.

The other benefit to the test aside from learning all of this information is to give an athlete a road map of where they are and where they could be if they became more metabolically efficient. For example, if my “crossover point” occurred at 10:00 per mile, that means slower than 10:00/mile pace I am burning fat. But as soon as I speed up, I crossover and start burning through my limited stores of carbs. That may be ok for a shorter run but if I want to train for a marathon or half marathon, wouldn’t it be great to be able to do that on fewer calories at a faster pace. By working on my nutrition, Bob has shown that I can significantly change my crossover point to allow me to run faster, for longer, on fewer calories because I can use my internal stores of fat. Awesome. See below for an athlete’s “after” MET. Initially, her crossover point was at 9:55min/mile. Through diet and exercise changes, she can now run any pace slower than 8:55 (see star) and burn mostly just her own stores of fat!