You spend a lot of your training focused on heart rates, pacing, and mileage. All of which helps drive a higher VO2max, a faster lactate threshold pace, or greater running economy and glycogen efficiency (which is hard to quantify, of course). But if you are out to squeeze every minute out of your marathon PR, are you overlooking one key attribute that stares right back at you from the mirror every day?
No, I’m not talking about the mental aspects, though those are important. I’m talking about something that is easier than anything in the world to measure. It’s your body weight.
Run Faster by Weighing Less
You may well think that, as someone running high mileage, you can eat whatever you want and your weight will take care of itself. And to some extent, this is true, if your goal is simply to lose “a little weight” or roughly maintain what you presently weigh. But if you want to deliver your best marathon performance, finding and maintaining your right weight is a significant factor.
How much does it matter, and why? To answer the second question first, obviously carrying less weight around means you have to do less work (burn less calories) to hold a given pace. But additionally, even if you think in terms of VO2max, note that it is expressed as ml/kg/min (and, as a reminder, this is the volume of oxygen the body uses, per kg, in one minute at maximum effort). This means that, for a given VO2max, the more you weigh, the “thinner” the oxygen is spread, and the less effective you will run.
There is a calculator buried in a set of Runner’s Projection Utilities (more on this spreadsheet in future posts) that helps you predict your marathon time at given weights, assuming all else remains equal. In my case, I believe my weight was roughly 170 lbs. for the Akron Marathon in 2010, and around 162 lbs. at last year’s Towpath Marathon. The calculations on this sheet would suggest that 7 minutes of the 8 minute PR I achieved was strictly due to weighing less!!! In fact, considering that Akron was a hilly course and the Towpath was flat, I may well have been in better shape (or, at least, had a higher VO2max) in 2010.
Of course, “all else remains equal” is a bit of a broad caveat. Weight loss is good until the point that you begin to lose muscle and thus hurt your running economy (how efficiently you turn energy into forward progress). And taking in enough calories to meet your training needs is obviously critical.
So how do you go about defining your ideal weight? There’s no perfect formula for doing so – some target a low BMI (observing that most elite marathoners are in the 18-20 range), but this may not be realistic for your body structure. It seems the best bet is trial and error, finding the weight at which your calorie intakes are sufficient to support your training needs without gaining weight – after having lost weight initially.
The Runner’s Diet – A Simple Approach
This can be very difficult to manage, no doubt – when you are running even 50 miles weekly, this is roughly the equivalent of requiring two extra days worth of meals needed each week. Calorie tracking applications like My Plate from Livestrong can help, if only to make you more conscious of the amount and types of calories you are taking in.
The principles of a good diet for runners (or anyone else) are really pretty simple:
- Calories in need to be less than calories out (it takes 3500 calories deficit to lose a pound) – it doesn’t really matter whether these are fat, carbohydrate, or protein calories. As a runner, your bias should be towards protein to help promote muscle repair and growth.
- Don’t seek to lose more than a half-pound per week – anything more than that is likely to leave you a bit weak for key workouts.
- Keep the same kind of balance you’d use if you weren’t running (ideally) – don’t make up the gap with “empty calories” like many snack items.
- Use whatever strategy works for you – maybe it’s “grazing” through the day (though that has largely been discredited), or maybe it’s 3 squares a day. Again, it’s mostly about calories in minus calories used.
That’s really it – most of the other advice you’ll hear on low fat diets, or low carb diets, or running in the fat-burning zone really don’t work in the long run, if you can’t keep the calorie balance in mind. And for an extra minute of time in the marathon per pound lost, isn’t it worth doing so?