Facebook Pinterest Twitter Email
Image 12-9-18 at 1.54 AM.jpg

Share the knowledge

Nutrition For Training and Competing in Endurance Sports

February 2, 2019

In early 2017 I signed up for a half Ironman triathlon that would test my abilities: though I lived at sea level, I opted to race at 5,430 feet elevation (Boulder, CO) in August. For any non-USA residents, this tends to translate to brutal heat.

I woke up early that morning, had some breakfast, and went the race site. After setting up my transition station (more on that later), I hopped in the water, then onto the bike. The first half of the bike course was flat and fast, and I was feeling pretty good. I took the occasional sip of water and some Pedialyte, but suddenly noticed the course started to get harder.

Or did it? Undeniably, it’s a long race. But I felt other factors at play. Suddenly I was feeling delirious, weak, and a bit unaware of my surroundings. I was lucid but noticed that instead of using my bike handlebars to control my bike, I was using them to lay on. These were symptoms of the dreaded “bonk”, or simply the word used to describe running out of fuel for your body and brain.

I drug myself through the final few miles but was both wobbly and miserable. Then it hit me, I had to do a half marathon next. It was about 11am and not a cloud in the sky. To make matters worse, it was over 90 degrees Fahrenheit and there was no shade on the course.

Endurance sport and triathlon nutrition is not a concept entirely synonymous with eating healthy, following a diet fad, or eating a well-balanced meal. While a nutrition can and should certainly be healthy, this type of nutrition is a concept unto its own.

It’s about eating to fuel your training, recovering, hydrating to stay healthy and perform well, and timing nutrition and meals in accordance with training and racing. Fueling on race day is the easy part; it’s only a chunk of a single day. But the bigger picture is perhaps more important.

The Science

First off, let’s talk a bit about the science behind nutrition and endurance sport fueling and hydrating.

In her book Sports Nutrition for Endurance Athletes, Monique Ryan R.D. points to glycogen as being the most accessible energy source for endurance athletes. When you properly increase the amount of carbohydrates you are consuming prior to a race or on a daily basis to support training, these are stored as glycogen in the muscles and liver and are your energy source.

By this same token, if you have not consumed enough carbohydrates then your body turns to fats for the next-best energy source. Since these are not as accessible, the body takes some time convert fats into energy. The “bonk” described above can also be related to glycogen depletion, causing you to hit the metaphorical wall earlier than you wish.


Dr. Allen Lim, PhD in Exercise Physiology and Skratch Labs founder, wrote a comprehensive research article titled “Hydration Science and Practice”. In his piece, he discusses the specifics of why a sports hydration mix is important and provides both general and detailed discussion of electrolytes.

When we sweat from exercise, our body loses electrolytes. Of the electrolytes lost, Lim notes that sodium is the most important one as it “supports the delicate electro-chemical cellular balance key to life and thirst regulation”.

This thirst regulation mechanism signals to the body to drink water lost through exercise, replenishing the fluid levels without overdrinking and keeping your sodium balance optimal. Otherwise, becoming dehydrated can be destructive to your body, cause a drop in weight, and adversely affect performance.

Sports hydration options like Skratch contain sugar as well (a non-electrolyte) as they help speed up rehydration.

Finally, a very important note on water vs. sports drinks for rehydration. While water is obviously a healthy component to any athlete’s race preparation or day-to-day, it is not suitable in race.

When we exercise, Lim notes that it is estimated that we lose anywhere between 700-1,400mg of sodium per liter of sweat. Trying to rehydrate with water will only dilute the sodium that is left in our body, leading to hyponatremia.

Unsurprisingly, the characteristics are similar to bonking: confusion, decreased ability to think, nausea, poor balance, seizures, and coma. Make an effort to always rehydrate with sports drinks (more below on this).

What should I consume when training for endurance sports?


The daily diet of an athlete will depend on training volume and training intensity. Getting enough food into your system will help you to store glycogen and recover.

In a normal day, an endurance athlete should strive to get calories from each macronutrient group - carbohydrate, protein, fat -  with the bulk of their calories coming from carbohydrates. Let’s break this down a bit:

Triathlete and writer Christopher Tull suggests the following sources and breakdowns:

  • 50% of your meal should come from fruits (a simple carbohydrate) and vegetables (a complex carbohydrate), with about a 40/60 split, respectively. He suggests apples, oranges, pears, bananas, and grapes; and broccoli, carrots, celery, cucumbers, frozen mixed vegetables, salads, and green beans.

  • 25% of your meal should come from a whole grain, like whole-grain bread, cereals, rice, pasta, oatmeal, and quinoa.

  • 25% of your meal should come from a lean protein, like chicken, turkey, eggs, fish, tofu, or beans. You can round out meals with a protein powder or yogurt if needed.

  • Complement your meals with healthy fats, including avocado, olive oil, nut butters, or cheese.

For recovery, board certified sport dietician (and excellent triathlete and coach) Marni Sumbal recommends a protein-rich drink and high glycemic foods for post workout recovery.

Since high fiber and high fat foods can slow food passage to the intestines, you can speed up glucose transport to the muscles by prioritizing glycogen-replenishing foods such as bananas, raisins, corn chex cereal, pasta, pineapple, melon, beets, brown rice, cereal, potatoes, white rice, corn, honey, corn, peas, pasta, oatmeal, sweet potatoes, saltines and oranges

As a rule of thumb, she recommends 7-10g of carbs per kilogram of body weight. A 45g carb recovery meal could be a banana and 1.5 cups of milk.


You should also prioritize hydration throughout the day. As Lim notes in the above passage, there is a distinction between water and sports drinks, the former providing a base hydration and the latter of which replaces electrolytes.

You probably know by now that you are largely made up of fluids and water. The US government’s “Water Science School” study notes that muscles are made up of 79% water, bones 31%, and heart 73%.

Try aiming to get most of your water intake from plain water while also getting it from watery fruits and vegetables. Also count the times you go to the bathroom to determine if you’re getting enough water. As a rule of thumb, Sumbal says you should fully empty your bladder 4-5 times a day.

For recovery after training, Lim underscores the importance of getting electrolytes into your system as a part of your recovery routine. There are many external factors that may affect your fluid loss during a workout, including weight, gender, weather, geographical location, and workout intensity.

However, after workouts the water in your body has indeed decreased and this could contribute to any number of post-workout discomfort symptoms. Aim to consume around 24 ounces of a sodium-dense drink.

Techniques and Products

You now have read about the science and logic behind consuming certain food and drink for your training and racing.

Another aspect to take into account is fueling in race or in training. Different distances and circumstances require different fueling, but this section will suggest a few techniques for you to consider.

You can also apply the following information on long-distance racing to shorter distances. Just use the calculations to tailor your training or racing fueling strategies.

Long-Distance Triathlon, Run, or Bike

A long race requires more than hydration. Calories are going out and your body requires that calories also come in to keep up the intensity and achieve your desired outcome. While rehydration is one goal, a twin goal in a long race is calorie replacement.

There are two ways to approach calorie replacement: liquid calories or solid foods. If competing in either a half or full Ironman distance race, then it’s critical that you begin taking in calories on the bike portion, preferably starting about 10-15 minutes after you are on the bike.

Some nutritionists believe it to be perfectly fine for calorie replacement to come in liquid form while others advocate for eating real food. This is something that you need to practice in training. In either case, there are basic tenets that you need to follow as you begin to experiment:

  • Eat foods that are high in carbohydrates

  • Make sure intake is low in fiber

  • Place an emphasis on finding foods that are low in ingredients

  • Replace about half the calories that you have burned per hour

A general Internet search on the topic typically advises anywhere between 150 to 350 calories per hour. But Lim specifically differentiates between rider body types, making rules of thumb like this less relevant. Take the following two cases, which assume riders at a moderate sweat rate (75-80 degrees F) during a five hour ride:

  • Rider 1: Amateur cyclist in good shape; riding 150 watts/hour on the bike; burns 594 calories an hour with around 1,500 calories stored as glycogen

  • Rider 2: Professional cyclist; riding 250 watts/hour on the bike; burns 990 calories an hour with around 2,000 calories stored as glycogen.

Lim does the math for us, taking into account glycogen and fat stores, and determines that Rider 1 could rehydrate and fuel with 160 calories an hour while Rider 2 would need to fuel with 292 calories an hour.

When estimating your needs, you need to be realistic with your intensity level and use your training tools (like watches, bike computers, heart rate monitors, or others) to estimate how many calories you are likely to burn.

You also do not need to be exact in your nutrition. For instance if you were to do the math presented above and determine you need 292 calories, you would be well off going to around 320 just to be sure.


For every training run longer than 45 minutes, I make sure to carry a run belt with flasks of Skratch hydration product. To keep calories and carbs up, I will complement hydration with products like Skratch fruit chews. Another favorite among endurance athletes are Honey Stinger waffles, though I find these more difficult to eat than the fruit chews. They are also less focused on hydration and electrolyte replacement.

In a standalone half marathon, most runners are able to go without a run belt. Since it’s a race, it makes sense to run up to the point of glycogen depletion and recover properly. The belt is extra weight and discomfort/awkwardness in such a situation.

By contrast, if you are doing a half or full Ironman distance triathlon, your nutritional needs are different as you’ve already been losing water and body weight and using glycogen stores. I always wear a hydration belt in a half Ironman.

Comment Form is loading comments...

Share if you like!

New eBook coming out soon on Race prep and nutrition! Sign up to get notified!


Skratch Labs   electrolyte replacement sports drinks are a very popular choice among athletes seeking a superior product with great taste.

Skratch Labs electrolyte replacement sports drinks are a very popular choice among athletes seeking a superior product with great taste.

Facebook Pinterest Twitter Email