Dean, a question I’ve had in the back of my mind is whether low body fat can impact performance in longer events. Generally my body fat has always been low. It maxed out at 20% when I was sedentary and dropped to the 5% range since I started back running. Yesterday it was measured at 3%.
I’ve always wondered whether this impacts my performance in my long races as essentially I have no fat to burn once the other energy sources have been consumed. I certainly feel that way in the races.
I’ve done some initial reading and found this study on ultra-endurance events that I found of interest. Athletes do burn fat, so it does seem that it could be an issue if you don’t have any to burn. http://www.iutasport.com/files/articles/Decrease%20in%20body%20fat.pdf
This then leads to another question. If you don’t have fat to burn are they ways to compensate with nutrition during the race. Clearly elite marathoners have low body-fat, in the 5-7% range. I haven’t been able to find anything that specifically discusses elite nutrition DURING the race. I don’t see them eating gels. I’m very interested in any information that you may have on this and specifically how it might be applicable to me –Rob
The Article Comments
Rob, thanks for the article. It’s thought provoking for sure.
This topic is not as straight-foward as you think. The article is interesting and points to some interesting findings. As I began reading the article one immediate problem I was thinking about was dehydration was not being addressed. In their discussion on the last page the admit this. This is a major flaw since hydration status impacts calculations of fat content. The second point I have with this is that though it may apply to extreme ultra running that does not automatically mean that it applies to any races shorter than this.
I also found it interesting that one conclusion is that HIGHER not lower intensity revealed more fat loss. That is contrary of course to most “fat burning” advocates. I decided to research online what “expert coaches” and “expert health advisors” advocate. The range was from 33% to 65% of VO2max! Yet this study specifically says there is more fat burning taking place at higher (65-75%) NOT lower intensities!
Fat and Elite
Now let’s address your more core question about body fat as it relates to marathoners. Let’s review the issue for runners running from just over two hours to four or so – and not 45 hours of continuous running as in the study.
Elite marathoners – male and female – dip under 5% body fat often. However, elite men are running just barely over two hours. Women run about 15-20 minutes longer. The reason you don’t see them taking all kinds of gels and energy bars is that they do not need them. They are running so intensely the only thing they get down is fluids with carbohydrate mixtures in them. [Elite men average 4:45-5:00/mile and women are running 5:15-5:30/mile.] Therefore, in some ways what they do may not really give too much guidance to slower runners.
What it does most likely mean is that their reliance on fat as an energy source is low. They need carbohydrates for immediate use at that level of effort. And for what little they need fat for energy, their bodies have been trained to metabolize it fairly efficiently compared to us mortals. This also means that extra body fat for elite runners only means excess weight to carry around.
[Before anyone gets weird on me – of course there are unhealthy low levels of body fat. I am not saying to lose weight to be faster. I am addressing elite runners for whom a few extra pounds of fat weight is a disadvantage competitively – and not a source of energy reserves. Of course if you have EXCESS fat on your body it will not enhance your running and in fact will act as a sort of anchor – slowing you down.]
Fat, Energy and the Rest of Us
The truth is that the slower the athlete the longer the athlete will be running. Therefore, the higher the reliance on fats as an energy source.
Now Some Math
One pound of fat is about 3500 calories. If you way 150 pounds this is only .67% of your body. So, even at say 6% total body fat this will drop you to 5.34% by the end of the race IF you used an entire pound of fat for energy. But, wait, 26 miles only requires approximately 2500-3000 calories… NOT even one pound. Furthermore, you’ll burn predominantly carbohydrates for the majority of the race. I’m only guessing here so bare with me but you may only be using 1000 calories from fat in a marathon. That means it might only be 3/10ths of a percent of your body weight. My bottom line is that unless you are pathologically thin, you do not need more fat to run long distances better. You need a better hydration and nutrition plan.
- The most accurate measure of body fat is a DEXA scan. All other methods skew results. Hydration status also effects calculations. So take results with a grain of salt.
Use of fat as an energy source must be trained. That does happen through longer runs in training. So a sound training program with the right mix of longer runs and goal paced [higher intensity] long runs will facilitate this. That’s it. You took care of the fat issue.
Now your focus has to be on how do you get carbohydrates into your body and digested. That’s it. (I know I make it sound so simple.)
Your hydration and nutrition plan has to be practiced. Everyone is unique and even the science and nutritionist recommendations are just guidelines. Every runner has to experiment with what works for the individual.