My good friend Chris wrote a nice post about nutrition - one which I am very much in agreement with, and I thought I'd use it as a jumping-off-point to put down some thoughts I've had for a while.
One of the problems in talking about this stuff is that there's a paradox in how you eat as an athlete. Sometimes you should eat really well, and other times you should do the opposite. But I had a thought recently.
It all revolves around blood sugar. The whole goal of performance diets is to keep a constant blood sugar level, but the way you do it depends on the circumstances.
It starts with your base diet - what you eat normally. You want to keep your blood sugar constant, which means avoiding the things that will cause your blood sugar to move quickly. Which means refined sugar, flour, rice, etc. - anything that has a high glycemic index.
If you eat it, your blood sugar goes up really fast, your body releases insulin, and the sugar gets converted to fat and stored. And your blood sugar drops, and you get hungry again. Which is what is behind the "chinese food" syndrome, where you eat a meal with lots of white rice, and then get hungry again a few hours later.
It's not quite that simple, however. It turns out that the absorption of carbs - and therefore their effect on blood sugar - is moderated by the presence of other foods. If you have fat, protein, or fiber, it will slow down the spike in blood sugar.
So, to keep your blood sugar constant and your hunger in check, you want to have some fat, some protein, some fiber, and any carbs of the less-refined variety. If I had to pick a popular diet that's close to this, I'd pick something like South Beach.
That will moderate blood sugar normally, but it doesn't work when we are exercising. During exercise, we are burning carbs in conjunction with fat, and over time - if we exercise long enough - we will totally run out of carbs, leading to the dreaded "bonk". Even if we don't totally run out of carbs, we will end up with very depleted carb reserves. Which means, at the end of the ride you'll be very hungry, and likely to overeat, or at the very least, not eat very well.
You also may not be able to fill up those carb reserves in time for your next workout.
So, we need a way to keep your blood sugar up during the workout. If you can do that, not only will your carb reserves last longer, but you will be less hungry at the end of the workout.
And how can we do that? Well, we could eat more of our normal healthy diet, but that has a few problems. It's fairly hard to digest, and you probably don't have enough blood supply to spare from your muscles to send to your stomach to digest. It's also pretty bulky, and you don't really need any extra fat during exercise - there's plenty in your fat stores.
So, we need something that's easily digested, and will support our blood sugar. That's exactly the simple, refined carbs that we are avoiding in our normal diet. We don't get an insulin response because we are burning enough carbs that we aren't going to spike the blood sugar.
And finally, when we're done exercising, we haven't quite refilled our carb stores, so we can take in some extra simple carbs and protein, and that will let us refill those carb stores.
How does this work if we are trying to lose weight? We might burn 1500 calories on that 3 hour ride, but if we are taking in 250 cal/hour of carbs, we'll only net a 750 calorie debt. So, if we don't eat at all, we'll lose more weight.
But remember the blood sugar thing. Sure, we'll have a 1500 calorie deficit at the end of the workout, but we'll have to work hard to not to eat more than that when we're done. Or, we can burn 750 calories of fat, replace the carbs, and - because we've kept the blood sugar constant - not replace the fat.