The Myth of "Carbo-Loading"
Eating large amounts of carbohydrates before a race or workout (aka "Carbo-loading") is a complete waste of time! After all, you would not assume that by sleeping 5 days straight you would now be able to stay up for 5 days straight? Why would you assume that by eating large amounts of carbohydrates 3-4 days before a race, you would fill up your glycogen stores? Most of us are cutting down our milage the week or 2 before the big race and the lighter load will create extra nutrients for your body. Adding more carbohydrates to your data will create a larger excess of glucose, which gets converted to fat. You can only increase your glycogen stores only when your body is ready to do so.
Research has shown that high levels of glucose consumed during rest does not get converted to glycogen (Am J Physiol. 1989 Nov;257(5.1):E697-703 ). How do you get glycogen, you ask? Well, only when high levels of lactate are present, through a pathway called the Cori Cycle (see below).
So what does this mean for us runners? If you want to build your glycogen store, eat carbohydrates soon (1-2 hours) AFTER you run. The consumed carbohydrate will replace the need for lactate to supply your body with the needed glucose. The glucose formed by lactate will then convert to glycogen. Therefore, the longer or harder you run, the more lactate you produce, the more potential you have to build up glycogen stores (if you eat at the right time). Real "Carbo-loading" can only happen over the course of months and not 3-5 days before your big marathon.
Additionally, the same study showed that galactose incorporated more quickly into glycogen than glucose. Thus many of those high carbohydrate drinks which contain extra glucose (as the carbohydrate source), will just be converted to fat. Galcatose is contained in many dairy products (such as milk). So, if you want to "Carbo-load", drink some milk right after you run!
