Wednesday, February 25, 2009

Does Nutrition Really Matter?


By Dr. Ben Miller

There are a lot of people who think taking vitamins and carrying around a bottle of filtered water all day will make them healthy. It is true that this practice may make the person healthier than if he/she did not do it, but it does not necessarily make them “healthy” if they also smoke a pack of cigarettes a day. On the other end of the spectrum, we all have that friend who eats (or even drinks) whatever he/she wants and still goes well on the bike. As I have stated before, some people are given a great set of genes, and no matter what they do, they will still go well. Going well despite a poor diet, however, does not mean that the person is going as well as he/she could. I hope this column will give you a little perspective on the importance of nutrition for cycling performance. What I hope you take away is that you can do well without proper nutrition, but you will never do as well as you have the potential for with proper nutrition.

To understand why nutrition is important, it is first important to understand how the body adapts to exercise. The basics of human adaptation are that you stress the body, the body senses the stress, and the body takes appropriate steps so that the next time the stress is imposed, the body is better suited to deal with the stress. The “appropriate steps” the body takes has to do with making proteins since proteins make up the structures of your body and directs most reactions in the body. For instance, if you perform a bout of weight training, your body makes proteins in the muscle that are better suited to generate force so that you can move that weight easier next time. This example of course is why your muscles get bigger with weight training. Not so obvious are the proteins your body makes after a long training ride since there is no physical appearance of those proteins. The proteins your body makes after a long training ride are the ones that make your muscle better suited to use oxygen for energy production, e.g. mitochondrial proteins, enzymes, and cell transporters.

The application of adaptation to exercise training has been termed the overload principle. What the overload principle states is that one must apply an appropriate stress to the body so that the body is not understressed, thus providing no stimulus for adaptation, or overstressed, causing failure and overtraining. The stress must be specific to the goal you are trying to achieve and designed for the individual person. “Specific” has many levels of complexity from cycling rather than running to get better at cycling, to doing 5 second jumps rather than 3 hours of easy riding to get better at criteriums. Individuality refers to the fact that all of us adapt to stress differently as a result of our genes, and therefore what might be right for one person may not be right for another person.

There is one more component of the overload principle that most of us know all to well and that is reversibility. What reversibility means is that if a stress is not applied for some time, the ability to deal with that stress will go away; or said another way, reversibility refers to detraining. A good question is why does the body detrain? Why do we have to go through all the work of building up resistance to stress again? The answer has to do with the proteins the body makes to help us adapt to stress. These proteins have to be built up and broken down to stay in good working order. The process of building up and breaking down proteins takes a lot of energy. In fact, while resting the making of protein is the single largest consumer of ATP in the body. Therefore, the economics becomes quite simple, if the body does not use a protein for a little while it gets rid of it so that it does not waste energy sustaining it and the body can focus its resources on other proteins that it does need. Looked at another way, a body that is not provided enough energy will get rid of proteins to maintain itself, which is why muscle wastes when someone does not eat enough.

As mentioned, the body “senses” a stress. The means by which it senses is beyond the scope of this column. What is important is that the sensing of a stress sets in motion a series of events that makes proteins. You may then ask how the body knows what proteins to make? The search for the appropriate pathways and what turns them on is a very active area of cellular biology research. For the purpose of this column, though, we will call these pathways “signaling pathways” because a sensor turns on the pathway and signals only the correct proteins to be made. For example, when people go to altitude to train, a sensor detects that there is less oxygen in the air and turns on signaling pathways that make proteins that will help make oxygen delivery more efficient (EPO is one of those proteins). Specific to cycling, the time spent on the bike doing long slow rides, sprint workouts, and intervals are the stimuli that are sensed, and turn on signaling pathways that tell the body which proteins to make so that we may do those specific tasks better next time.

Why is this column really about nutrition? As stated, when the body receives an exercise stimulus, it sends out a message to the cells to build proteins that will better help it deal with that exercise in the future. To build those proteins you need the building blocks of protein (amino acids) and energy. Amino acids and energy can only come from the diet and therein is the need for proper nutrition. I want you to think of the process of building a house. Suppose you visit the architect and have your dream house drawn up on blueprints. You then buy the perfect plot of land, stake your lot, and hire all the best contractors. Finally, the big day comes, the ground is broken and the crew gets to work. Now imagine that you only had enough money to buy second-rate construction materials, how close will that dream house really come to its potential? Will it really be a dream house with inferior building materials? This analogy is really quite simple and obvious, the blue print is your training plan, the contractors (translates blueprints to a house) are your genes (translates training stress to proteins), and the construction material is the nutrition that builds the body’s structures. Inferior building products will lead to an inferior finished project no matter how good the plan and construction crew is.

I was careful to state above that the signaling pathways tell the body what proteins to make. However, in the absence of the appropriate building blocks, the body can’t actually make the proteins. In other words, training sets in motion an adaptive potential. To take advantage of the potential, amino acids (from protein that you eat) must be provided to build the proteins you need in the body, and energy (primarily from carbohydrate) must be provided because of the energy it takes to build those proteins. As I write this, my first thought is that people will take away from this column that eating lots of protein is the most important nutrition modification you can make, which is wrong. Yes, eating protein is important, but for the endurance athlete eating enough carbohydrate is still most important. Since the body uses up energy during exercise, you need to replace it after you are done or you will not have enough energy to make the proteins you need in your body to adapt to the training. In fact, if you don’t have enough energy, your body will break down proteins that you may need without replacing them, because at that point in time, having energy to sustain body function is more important than maintaining more protein. Interestingly, scientists have recently discovered that the amount of energy in the cell is one of the “signals” that determines which proteins are made, which clearly shows that energy provision and protein requirements are tied to each other. The take away message is that eating carbohydrate and protein around your training makes available the high-quality building materials to take advantage of the message your body sent out on what to do to get stronger. Conversely, not eating correctly around training diminishes the outcome of those messages considerably.

Dr Ben Miller is Senior Lecturer in Exercise Physiology. Ben did a PhD at the University of California – Berkeley and a Post-Doc at the Institute for Sports Medicine, Copenhagen.

3 comments:

-_- said...

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