There’s a lot of hype around nutrition and running. Gluten-free, Vegan, Vegetarian, Sugar-free, Whole-Food, Paleo, Eat whatever you want, and more. Is there any (real) science behind these besides the placebo effect? I decided to dig into a few research studies to find out what fuels athletes. Combining the chemistry of nutrition and the chemical reactions that happen when one runs, it should be easy to figure out the fuel necessary right? Turns out it’s not quite that simple and nutrition is a hot topic and constantly debated. The data is ever-evolving but there are some common themes that do fall back on basic chemistry and nutrition sciences. These haven’t changed and while attempts have been made to refute them, they remain solidly irrefutable:
1) Our liver holds a certain amount of glycogen. The amount it holds is based on its weight. It will typically hold a minimum amount that stabilizes the blood sugar and other vital cell processes. It also has a maximum threshold and so can be ‘loaded.’ This is actually where carb-loading came from. When one carb loads they are attempting to bring the glycogen stores in the liver to the maximum threshold, increasing the time-limit before the depletion of the blood sugar (or ‘bonk’) in endurance running. This isn’t helpful in anything under a 20 mile distance as usually the liver holds enough kcal to fuel 15-18 miles, depending on pace, on its own stores.
2) Our muscles are also capable of holding glycogen stores, but can only use this glycogen for their own synthesis. What does this mean? The liver glycogen is ‘global.’ It can be shot out to where ever it’s needed. If your muscles are in need, it goes there, if the blood sugar is falling- bang- to the rescue. Any ailing cell will be fueled by glycogenesis being produced from the hepatic cells of the liver. The muscle glycogen, on the other hand, are completely restricted to energizing the specific muscle that it resides in. There are large amounts of glycogen stores in the muscles, depending on the muscle mass of the individual. If a person is 40% lean muscle, the muscles are holding approximately 1,650kcal of fuel in them (before loading!). Enough to propel a human body quite a distance without failing. These stores can be increased too but the process takes days vs a “night-before” carb load and has potential consequences to go with the benefits. The stores can be nearly doubled in size.
3) While glycogen is the bodies preferred fuel, if we run out, we are capable of using fat-stores to continue on. This sounds great in theory, however, this is where pain is experienced and fatigue and exhaustion come into play. When the human body starts to reach into fat stores basic chemistry comes into play. Glycogen- or glucose/sugars are very simple forms of energy to process. They are quick energy stores. Fat, on the other hand, is not. It’s a “reserve” that is only grabbed in dire times. To break down each molecule of fat requires four times as many oxygen molecules than to break down each molecule of glucose. So the body simply can’t take in oxygen and transport it fast enough to convert enough fat into energy. Breathing gets heavier, heart-rate picks up, and everything feels ‘sluggish’ during this process. The good news is, even the most lean runner has enough fat stores to run nearly 500 miles. Would they be fast or comfortable? Not likely.
Ok so that’s the gist of the tried and true 101 lesson that has been tested and proven over and over again through multiple methods that are too boring to get into. What about all the diets? What about the claims that one is better than the other and ‘my way is the only way?’ and how DOES one bring up those glycogen stores? What are the consequences of increasing the muscle stores? Benefits?
Check back as I’ve gathered the data and am working on a nice write up of answers to all of the above. Feel free to chime in with opinions, as everyone seems to have one on the topic of nutrition.