Endurance Eating

By Dr. John M Berardi, Ph.D.
First published at www.fitdv.com, May 2002.



Success in endurance activity is a result of a multitude of genetic and physiological factors. While many of these factors are out of our control, one major player in the success of the endurance athlete is fluid and nutrient intake in and around training and competition. Therefore in this article I'll describe a few strategies for eating and drinking for a big race.

Fuel Utilization

During endurance activity the body uses muscle glycogen, blood glucose, muscle triglycerides, and free fatty acids from adipose tissue to provide the ATP to fuel performance. The relative ratio of these substrates utilized is dependent on exercise intensity and exercise duration as well as availability of each substrate. As exercise intensity increases during an endurance bout, more carbohydrates are used. However, since carbohydrates are limited in supply, as the exercise continues (and the body's carbohydrate stores diminish) more stored fats are used. Unfortunately the metabolism of fat is less metabolically efficient; therefore when carbohydrates become limited, exercise intensity must diminish. Since the body typically contains enough stored fat to fuel several marathons, the focus of eating for endurance activity should be on the carbohydrate content of the diet.

Before The Event

Eating a relatively calorie dense meal 2-4 hours before a race or several smaller meals between 2-5 hours before a race is absolutely essential for topping off muscle glycogen levels as well providing blood glucose for the intense activity ahead. By eating this meal, the activity will be fueled by the nutrients provided during the meal and will therefore be able to exercise for quite some time before the body is forced to use stored energy. This can end up delaying fatigue and improving performance. On the other hand, if you fail to eat or eat far too long before a race, your body will have used up all the nutrients from the last meal and even have dipped into stored energy well before you ever step foot on the racecourse. This can lead to premature fatigue and poor race performance.

While it's important not to wait too long between meals before an event, it's equally important not to eat too close to the event. Eating this big meal within 1.5 - 0.5 hours before a race can lead to one of two problems. The first is gastrointestinal distress. You'll simply feel too full or even sick as a result of eating too close to the event. The second is something known as "rebound hypoglycemia". Immediately after eating carbohydrates the hormone insulin is released. Insulin's function is to clear the blood of the ingested carbohydrates and to deliver them to storage sites such as the muscle, the liver, and the adipose tissue. Therefore eating causes hyperglycemia and in response to this, insulin comes along to cause hypoglycemia. Since insulin is the storage hormone, it opposes nutrient mobilization, locking those carbohydrates in the cells for as long as it's hanging around the body.

Now, when eating well before a race, the body is able to clear the blood of carbohydrates, store the nutrients, and get rid of insulin well before it's time to compete. However, if you eat too soon before the race, insulin will still be clearing the blood so that when you start to race, the body will have very few blood carbohydrates (this causes a lethargic feeling) and it will have a hard time mobilizing the stored fuel (this causes early fatigue). Therefore, by eating a big meal 2-4 hours before the race or eating several smaller meals between 2-5 hours before the race, you'll be able to fuel the body's energy needs without causing premature fatigue and hypoglycemia. If you couple this eating strategy with a sound carbohydrate loading strategy (see sidebar), you can be sure that you'll enter your race full of high octane carbohydrate fuel.

Here is an example of what the pre-race meal should contain:

* Adequate water (1L)
* 4-5g of carbohydrate (300g for a 70kg individual)
* A small amount of protein (20-40g)
* A small amount of fat (10-20g)

While this may seem like a lot of calories, keep in mind that you don't need to eat it all at one sitting. Spreading this meal out over the course of 2 or 3 hours may make it more palatable for you.

* 2 whole eggs
* 3 slices of whole wheat bread
* 2 cups of fresh orange juice
* 2 bananas
* 3 cups of raisin bran
* 1 cup of low-fat milk

During The Event

Although eating as directed above will allow you to top off glycogen stores coming into the event, you're not in the clear yet. You still have to contend with two potential enemies: 1) dehydration and 2) rapid glycogen utilization and depletion. Let's start with the glycogen situation.

While it is very important to start a race with muscle glycogen stores topped off, it is also important to note that the body tends to use carbohydrates much more quickly when there are more available. Unfortunately, even if you're topped off, muscle glycogen depletion can still occur. In order to prevent this from happening you should be consuming sports drinks or gels during your entire race. Since the body can only use about 60g of carbohydrate per hour during exercise, one to two servings of a drink like Gatorade or Powerade (or 1-2 servings of sports gels) per hour should do the trick for carbohydrate supplementation.

While the above recommendations take only carbohydrate needs into account, we should now consider fluid needs. During hot and humid days, the body can lose up to 2-3 liters of water per hour. This water loss corresponds to an unacceptable 4-6 lb of weight loss per hour. This loss of water is detrimental to performance as a weight loss as small as 1-2% of body mass (1.5 - 3.0 lbs for a 150lb runner) can lead to impaired blood volume, stroke volume, cardiac output and oxygen consumption. Therefore it's very important to keep fluid intake quite high during exercise. To this end, you should focus on consuming 2L of water per hour to prevent dehydration.

Here are a few examples of how to hydrate and feed the body during competition:

* Drink 2L of water per hour while consuming 2 servings of a Powergel-type product

OR

* Dilute 2 servings of a powdered Gatorade or Powerade-like product in 2L of water

After The Event

Once you've crossed the finish line, the nutrient battle is not over; you have one more responsibility to your body. Endurance exercise, much like strength exercise, causes depletion and damage of skeletal muscle. Therefore after such exercise, it's important to begin repletion and repair immediately after the race. For a more detailed description about this topic, please see my previous article about post workout nutrition (insert link here). To summarize my recommendations, however, since the post exercise period is the optimal time to replenish and repair damaged muscles, this is the time to consume easily digestible liquid carbohydrates and protein. Your post exercise strategy should contain:

* 0.8g/kg carbohydrate (56g carbohydrate for a 70kg runner)
* 0.4g/kg protein (28g protein for a 70kg runner)

Some examples of what to drink/eat during this time are as follows:

* A specifically formulated recovery drink such as Biotest Surge - (305 calories) - 25g Protein, 50g Carbohydrate, 0.5g Fat
* A homemade recovery drink containing 1 serving whey protein + 2 servings Gatorade - (369 calories) - 25g protein, 66g Carbohydrate, 0.5g Fat

Then, every two hours after this for the remainder of the day, be sure to consume a meal containing protein and carbohydrate.

Why Carbohydrate Load?

Intense endurance exercise performance is often fueled by a combination of stored carbohydrate (glycogen in the liver and the muscle) and stored fat (triglycerides in the muscle and adipose tissue). While fat burning can contribute significantly to an endurance athlete's fuel needs, there are a few reasons why it's not the best source of energy during intense activity. First, the rate of fat metabolism is slow compared to the rate of carbohydrate metabolism. Therefore, during intense exercise, when the body demands the quick provision of energy, fat metabolism cannot provide energy quickly enough and the body must slow down. Secondly, metabolizing fat is more oxygen costly than metabolizing carbohydrate; making fat metabolism more inefficient than carbohydrate metabolism.

So, I hope it's clear that without adequate carbohydrates in the body, the endurance athlete will suffer at the hands of the infamous "bonk". You see, since body's carbohydrate stores are limited (a 70kg individual may store about 400 total grams of carbohydrate), endurance events lasting greater than 90 minutes may deplete muscle glycogen to low levels, leading to early fatigue (and thus being passed by someone's grandmother). Since the carbohydrates in the body are consumed preferentially to fats, are used rapidly during intense exercise it's clear that any attempt to increase the body's carbohydrate stores during longer duration events may help with performance. One such attempt to try to boost the body's glycogen stores is the pre-race carbohydrate loading scheme. By following a carbohydrate loading protocol as such, carbohydrate stores can increase significantly (in some cases, muscle glycogen has doubled) and this may provide greater fuel for the latter portions of the race. So, if you're about to compete in long duration endurance events, you owe it to yourself to give carbohydrate loading a chance.

How Do I Carbohydrate Load?

Over the years there have been several carbohydrate loading schemes proposed. Original schemes were based on the fact that following a 3-day, ridiculously low carbohydrate diet (<50 grams) causes an increase in muscle glycogen storing enzymes. Therefore, starting 6 days from your event, "depleting" muscle glycogen with this 3-day low carb diet (exercising intensely on all 3 days as well), you can set your body up for a "rebound" of carbohydrate storage during the 3 days immediately prior to the event. For those next 3 days, you simply rest, eat a very high carb diet (10 grams of carbohydrate per kg of bodyweight), and watch your muscles swell up with energy. One problem, though, with these original schemes is that they were very difficult to follow for athletes accustomed to regularly eating carbohydrates. In addition, the 3 days of carbohydrate depletion led to such low energy levels during these 3 training days that performance suffered on these days. Although performance would ultimately "rebound" along with the glycogen stores, this phenomenon wreaked havoc on the athlete, causing psychological distress. Think about it. The last three practices before race day were their worst performances! So other schemes were devised. Here is a more modern scheme for carbohydrate loading that's nearly as effective as the one discussed above, but much more manageable:

Day 6 - Training Day - Low carbohydrate diet (<200g carbohydrate)*
Day 5 - Training Day - Low carbohydrate diet (<200g carbohydrate)*
Day 4 - Training Day - Low carbohydrate diet (<200g carbohydrate)*
Day 3 - Recovery Day - High carbohydrate diet (>10g/kg carbohydrate)**
Day 2 - Recovery Day - High carbohydrate diet (>10g/kg carbohydrate)**
Day 1 - Recovery Day - High carbohydrate diet (>10g/kg carbohydrate)**
Event Day

*During the low carbohydrate days, you must increase your consumption of good fats (omega 3 fatty acids and monounsaturated) as well as complete protein sources in order to keep your energy intake the same. Therefore carbohydrate will make up only a small percentage of your daily intake.

**During the high carbohydrate days, decrease your fat and protein consumption as your diet should be >80% carbohydrate.