Fueling and Starving

One of the things I learned this past year was that I shouldn't be tempted to eat like world-class ultrarunners. I don't train like them (no 140 mile weeks yet!), so why did I think that fueling was the same? I'll try to cover the old way of thinking, then what was wrong and how my thinking has changed.

First, the Tarahumara when running subsist on pinole, a form of roasted corn which converts all its starch to maltodextrin. Their diet is 75% carbs, 15% protein, 10% fat. If one looks at the data from the 1960's of the world's longest-lived people, their diet was also 75-15-10. More recently, the best studied long-lived people are the Okinawans and their diet is quite similar (I endorse both the Okinawan diet and the Mediterranean diet, though they are very different from each other), as is the diet of the vegan Seventh Day Adventists of Loma Linda, CA (according to "The Blue Zones"). Diets of under 10% fat have been shown to reverse heart disease (according to Dr. Dean Ornish), the problem being that no one can stand to live on such diets for long, unless their lives depend on it. According to "The Lore of Running," Yiannis Kouros's diet during a six day race was 98% carbs; the data suggests that it was closer to 75-15-10. This looked like the way to go.

The idea behind the high carb diet is that muscles prefer using the sugar glucose for energy and use it exclusively for anaerobic exercise. The muscles store glucose in the form of glycogen. When glucose levels are low, the liver supplies it either by breaking down its own glycogen or by gluconeogenesis, which can convert lactic acid, most amino acids and the glycerol moiety of fats into glucose. Red blood cells can use only glucose for their energy and the brain uses glucose exclusively, except during starvation and diabetes (more on that later). The plan is: when running, one takes in enough glucose to supply the muscles with their needs and this means that one doesn't have muscle protein breakdown problems.

The problem comes in supplying the body with glucose. A 24-hour 100 miler means taking in 400-500 calories per hour in the form of glucose, maltose, maltodextrin or other high-glycemic load foods (potatoes, for example). This is a lot of food and monotonous food. My tastebuds rebel eventually, though I don't have nausea problems.

So, when one drops below the adequate amount of glucose, one suddenly becomes like the classic marathoner hitting the wall. One gets dead legs and shuffles.

The first thing to recognize is that in runs over half an hour, if not run hard enough to be breathing hard, one is burning more fat than glucose in one's muscles. One takes in glucose, the glucose level in the blood rises, the muscles take in whatever they require - and the rest goes to fat cells, which then convert fats to fatty acids, which get transported to the muscle cells for use. One has enough fat reserves that this isn't necessary.

When one runs very long distances, one's burning fat. One need take in only enough glucose for normal functions. Training causes one to burn fat earlier in the run, to burn it at faster speed of running and eventually, to decrease muscle protein degradation.

This decreased protein degradation is what happens in starvation, so think of long runs, where one is burning more calories than one is ingesting, as similar to starving. In starvation, the body's first goal is to keep the brain working and that means making glucose and it does that by breaking down protein. By six weeks of starvation, however, the body destroys much less protein, as muscle is also needed for survival. It does this by having the brain switch from burning glucose to burning ketone bodies, which are created by the burning of fat (and some protein).

So, six weeks of heavy training decreases the amount of glucose needed.

There is another interesting twist to this, which is the sugar fructose, found in most fruits and vegetables. Your body doesn't use fructose the way it uses most things to provide "glucose energy." The level of fructose in muscles appears to be negligible (I cannot find good data on this and I've really tried). It gets burned in two different ways. In the liver, fructose gets turned into fructose-1-phosphate, which in turn gets converted through a number of steps into dihydroxyacetone phosphate and glycerol 3-phosphate. These are the same products that glucose becomes, but using a different pathway. If there isn't an immediate need for energy, fructose can then be converted back into glucose and then glycogen for storage.

In fat cells, fructose gets turned into fructose-6-phosphate, something glucose also becomes, but can't be converted back to glucose, because fat cells lack a necessary enzyme.

The upshot to this is that diets like the Paleo diet, which exclude starches, can provide adequate sugars through the ingestion of fruit (high protein diets like Atkins do it through breaking down ingested protein rather than muscle protein, though this has some complications). One's muscles wouldn't store enough glycogen for a world-class marathon, but most people don't have to worry about that.

So, suddenly, the idea of ingesting some protein during long runs starts to make sense, though the whole 4:1 ratio of carbs to protein is still completely meaningless.

I'm not advocating the Paleo diet nor the Paleo Diet for Runners, though. The latter isn't terrible, but creates a bunch of "rules" to follow that are meaningless. Sometimes people are right, though their reasons are wrong. An example in the Paleo Diet is the "alkaline balance." One side of one's stomach lining is 10000 times as acid as the other; one's body has a remarkable way of compartmentalizing acids and bases to meet its needs and one's diet has no effect on it at all (except in some disease states).