Carbo-loading is a nutrition system that first came into vogue during the 1970's. It starts by attempting to deplete glycogen reserves early in the training phase. This is accomplished by limiting carbs. Next, you load carbs late during your taper. The idea is to hit the race with super-saturated glycogen (stored carbs) reserves . This silver bullet is supposed to pull you through your race with fuel to spare.

It doesn't work. This is because the human body can only store enough glycogen to take us through 2 to 3 hours of high-intensity work.

Worse yet, carbo-loading can cause you some race-day woes. Ever wonder why there are all those porta-lets spaced out along the race? To accommodate all those heavy and bloated carbo-loaders, many of whom have to stop multiple times with GI distress? These athletes did not race like they trained.

So what's a marathoner to do? Read on.

The answer lies in the way we run a marathon. We run our race at lower energy levels, where both glycogen and fat burn simultaneously, in addition to those calories we take in during the race. Exercise at lower levels allows us to use a higher proportion of fat along with our 2-3 hours of stored glycogen (carbs).

At 65 to 75% of our maximum heart rate (MHR), we can derive 50% or more of our energy from fat. Find your 65-75% heart training rate (HTR) as follows: 220-agex65-75%=HTR. So for a 54 year old runner, 220-54=166x65/75%= an endurance HTR of 108 to 125.

At that level of exertion, even the leanest of us has enough fat (3250 cal/lb) to get us to 26.2.

The average marathon runner will burn about 250 calories per hour. Since hydration trumps nutrition for events under 5 hours, you really need only fluids and a couple of gels or energy bars. Experiment with these to find the one that suits your taste and gastric constitution. Might be as little as one bottle with 50/50 dilution of a tasty sports drink and 2 gels/energy bars.

If your running in the heat, hydration must increase correspondingly. If it's hot, keep an eye on your sodium (salt) intake to avoid the hyponatremia and it's accompanying nausea, headache and vomiting. Since water is almost always provided on the course, your fanny-pack just got lighter. Way lighter.

Marathon runners are always looking for a nutrition and hydration advantage (due in no small part to aggressive advertising of these products) and are anxious to venture onto the race course so lightly provisioned. Look at the race veterans, maybe not the elite athletes, but those who regularly run marathons. The hydration/nutrition system described above works for them when they run at the 65-75% HTR pace.

As with many things in life, healthy marathon hydration and nutrition is fairly simple. Try this system and see if it works as well for you as it has for me. I'm not the fastest runner in the race, but my butt-pack is definitely one of the lightest.

Run fast (and light!). See ya at the race. George