Tuesday 9 August 2011

Nutrition and Athletic Performance: Part 1

What about Pizza?
Recently, I have had quite a few people ask me about various components of nutrition and its role in athletic performance.  The good news is that there is a huge amount of research on this topic, and the basic principals are very well understood.

Proper nutrition is extremely important in any sport, but undoubtedly becomes more important the longer the event lasts.  When I think back, it is almost comical when I count the number of races and training sessions that I have struggled through due to poor nutrition.  For instance, once during my cross-country days in university, I was busy with school and thus made the incredibly intelligent decision to skip eating to save time.  Then, when 3:30pm rolled around, I suddenly realized that,  "hey, I will need some calories to get me through the 4:00pm workout."  Well, my then 18 year old brain analyzed the situation, and came up with a seemingly flawless solution: 2 slices of greasy pizza (with copious amounts of dipping sauce, of course), and a coke.  Needless to say I bonked hard, barely finished the workout, and was left baffled.  Why did this nutrition strategy not work nearly as well as anticipated? 

Fortunately, since then I have learned exactly what it takes to optimize performance, especially in endurance sports.  Since it is a complicated issue, today I will talk about only one important component: carbohydrates.

How Much Should I Eat?
For endurance activities, carbohydrates are vital as they function as your primary source of fuel.  The amount of carbohydrates you consume during a regular training regimen is obviously quite variable depending on the training volume.  A general rule of thumb though is that you should ingest 6-10 grams of carbs per kg of body weight per day.    So, for me, I am about 71kg, so I need to ingest up to 710grams of carbohydrates per day.  That is about 32 pudding cups- delicious!

To get a more specific idea of how much and when you should be eating, first let's go through where your energy is coming from.   

When You Use What
Disclaimer: If you're bored by science, skip this section! 
It is important to understand that depending on how long your sport lasts, you utilize different sources of energy from within your body.  Here is a breakdown of when each fuel source kicks in: 
  1. Activities lasting 1-3 seconds (i.e. golf swing): Your body uses ATP already present.  ATP is essentially energy waiting to happen, ready to be used virtually instantly.
  2. Activities lasting 4-7 seconds (i.e. short sprint): You body again uses ATP along with the help of creatine phosphate (which basically helps to replenish depleted ATP levels)
  3. Activities lasting 10-30 seconds (i.e. hockey shift): Again ATP and creatine phosphate is used, but this time fast glycolysis is also used.  Fast glycolysis is the process of breaking sugar down that is readily available in your blood.
  4. Activities lasting 1-3 Minutes (800m run): Now your body not only utilizes sugar already in the blood, but it also taps into your glycogen stores.  Glycogen is essentially chains of sugar stored in your muscles and liver, waiting to be mobilized and used for energy.
  5. Activities lasting 3 minutes or more: You still are using sugar and glycogen, but you also start to tap into fat stores.  I will talk about this more in a future blog.

How To Eat Carbs Days Before
From above, it is clear that for any activity lasting more than 10 seconds, carbohydrates are extremely important.  In addition, any activity lasting over a minute, glycogen becomes a valuable source of energy.  For longer events (i.e. vigorous activity lasting 40-150 mins), about 70% of your energy comes from glycogen.  Thus, it only makes sense to pack as much glycogen into your muscles as possible prior to a competition.  This is the best way to do it:
  1.  During regular training, consume carbohydrates at a proportion of 60-70% of your daily caloric intake (this may go up to 80% if you train very long hours, i.e. for cycling).
  2. 4 days prior to competition, exercise to exhaustion while consuming a low carb diet (i.e. force yourself to completely deplete your carb stores).  This will not be fun!
  3. In the next 3 days, train easily, and consume a carbohydrate rich diet (up to 80% of your total diet).
  4. Do not train the day before competition.
This method has been shown to induce a phenomenon called super-compensation.  By implementing this method of carb loading, research has shown that the muscles are effectively able to hold 200% of the glycogen they normally contain.  Thus you have more glycogen, more energy, and as a result a longer lasting level of high performance.

How to Eat Carbs on Race Day
So after you have completed the perfect carbohydrate load by following the sequence above, now the question becomes; how do I eat the morning of a competition?  While there are many different things to consider, the one universal rule that should be followed is: eat your last large meal at least 3 hours prior to competition.  So, if your race is at 8am, make sure you are done breakfast by 5am.  Here's why:
  1. When you eat, the hormone insulin is released into your blood.
  2. Insulin's job is to signal the body to store the food that was just ingested (either in fat or glycogen).
  3. This is BAD for performance, because we need to access those energy sources as quickly as possible, but insulin is working against us, trying to store that food.
  4. However, in 2.5-3 hours post meal, the levels of insulin drop off, and the hormone will no longer inhibit your ability to access the carbohydrates 

So again, eat at least 3 hours prior to competition.  Well, at least now we know it was not my fault for being terribly slow post-pizza...it was entirely insulin's fault.

How to Eat Carbs During
During an endurance activity, muscle breaks down carbohydrates at a rate of about 1g per minute.  Thus, consuming 30 g of carbs every 30 minutes is ideal.  Great sources of carbohydrates include sports drinks and power gels.  The reason why these sources are so effective is because they are composed of simple sugars that are quickly absorbed and subsequently utilized.  This is the one time in your life where sugar is the best thing you can possibly have, so take advantage of it.  It is important to stay away from fibre and fat as they both slow intestinal absorption of food, while fibre encourages water retention in the intestinal tract.

It is important to note that after your race begins, you should wait 30-40 minutes prior to ingesting any carbohydrate containing foods or liquids.  The reason for this, once again, is related to my arch-nemesis: insulin.  Essentially, if you eat too soon, your body will act as if it is in a fed state, and thus be reluctant to release glycogen and fat stores.  

The key things to remember from this article include:
  • Exercise to exhaustion and then carboload to maximize glycogen stores for competition
  • Do not eat within 3 hours of competition
  • After the first 30-40 minutes, consume 30g of carbs every 30 minutes during activity
  • A delicious greasy pizza consumed 30 minutes before training may feel right at the time, but apparently science says it is quite the opposite
There will be more to come on nutrition and athletic performance, next week I will discuss the importance of protein (probably).


 Burke L.M.  et. al. 2006. Energy and carbohydrate for training and recovery. J Sports Sci. 24:675–85. 

 Meschino, J.,  2010. Nutritional Aspects of Athletic Performance. Pages: 1-10

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