Fueling for Your Half Marathon

This week we are side-stepping from Physiotherapy and discussing nutrition in sports and I'm thrilled to introduce Casey Keane-Miller (RD, CSSD) a Registered Dietitian and Board Certified Specialist in Sports Dietetics who lives and works in the San Francisco Bay Area. Casey shares her advice about choosing the right fuels for training and race day and there are some great tips throughout this blog which can be applied to training for a marathon, half marathon and other long distance events.

Casey has previously published papers regarding eating disorders in adolescents and currently works at the Healthy Teen Project but today she is putting on her 'sports dietetics hat'. I asked Casey what her thoughts were about the popular foods consumed for running training and what message she would share with amateur runners. These are her thoughts. 


So you signed up for another half marathon? And this time you want to really compete and set your own PR? Got it. In addition to your training, proper nutrition will help you cross that finish line faster and feeling better than the last time.

Long-distance running is an endurance sport. It places high oxygen, nutrient and fluid demands on the body. Proper fueling is key to improved performance and prevention of fatigue and injury. Eating a balanced diet is essential for improved performance.

Endurance runners have increased carbohydrate and fluid requirements.


When you run, your body burns glucose (a fancy name for sugar) and body fat to use as fuel. The blood is a quick source of glucose for energy, however it’s your liver and muscles that store larger amounts of glucose for the body to tap into. These stores are known as glycogen stores.

Have you ever “hit the wall” while running? Or felt like your legs were full of lead?

Those feelings are signs of fatigue, which is most often associated with muscle glycogen depletion and/or hypoglycemia (low blood sugar).  To prevent this fatigue, it is essential to optimize glycogen stores before, during, and after a race.


Carbohydrates are the dietary form of glucose and we obtain them from grains/starches, fruit, and dairy. Consuming carbohydrates before a half marathon helps maintain blood glucose levels and top off glycogen stores that may have been depleted during a previous run and an overnight fast. Research suggests that the pre-exercise meal contain 1 to 4 grams (g) carbohydrate per kilogram (kg) of body weight, consumed 1-4 hours before exercise (1). For all you math junkies out there, 1 kg = 2.2lb so to calculate your weight in kg, divide it by 2.2 (see table 1). 

Half marathons generally start early in the morning and consuming a meal 4 hours prior to that is unrealistic for most.  Table 2 provides a more practical time frame with examples of what to eat 1-2 hours before the race. For many runners, it is helpful to break up the food into 1 meal and 1 pre-race snack. In the following example, a 150lb individual (who needs ~137 g carbs 2 hours prior to the race) would have a little more than 100g upon waking, and 30g within the hour prior to the race. Gatorade is included in this example in order to meet fluid needs as well. 

Some specific cautions about pre-race foods:

  • Avoid high fiber cereals (i.e. Fiber One, Kashi Go Lean), high fiber breads (i.e. Oroweat Double Fiber), and beans/veggies as they may increase gastrointestinal distress during the race.
  • High fat foods take longer to digest and are therefore not recommended as pre-race fuel.
  • Caffeinated beverages are safe to drink on race-day. However, due to the risk of side effects such as gastrointestinal distress and dehydration, always test out use on training runs first.


Consuming carbohydrates during exercise that lasts greater than 1 hour can delay the onset of fatigue and improve endurance.  By maintaining blood glucose levels, the body is reserving glycogen stores for the latter stages of the race (1).  The body will use up to 60 grams of carbohydrate for fuel per hour of your race. It is recommended that endurance runners consume ~30-60 grams carbohydrate per hour while running. In order to prevent any race day hiccups, try different carbohydrate sources and amounts during your training runs. Practice the fine art carrying, opening, eating, and timing those foods during your run. Table 3 suggests various fuel sources commonly used to meet carbohydrate needs during the race.


After all of that running, your glycogen stores will very likely be depleted and it is essential to fill them back up. The recommendation for post-race carbohydrate intake is 1-1.2 g per kg of bodyweight per hour for the first four hours (see Table 4) (1). It is generally recommended to start refueling immediately after the race to promote glycogen storage repletion.  Adding 15-25 grams protein to post-race meals promotes muscle repair. Sounding a bit complicated? Table 4 shows what that looks like in a 150lb individual.


The American College of Sports Medicine recommends that individuals should develop customized fluid replacement programs that prevent excessive dehydration (>2% body weight reductions from baseline body weight) (1). Since most of you are not going to weigh yourself pre- and post-run to figure out your actual fluid needs, the following list provides general tips for proper race-day hydration.  

  • Start the race hydrated (urine should be light in color).
  • Drink ~1oz of fluid per 10lb body weight about 4 hours before exercise (~15oz for a 150-pound individual).
  • To minimize unnecessary mid-race pit stops, drink pre-race fluids a couple of hours before the start of the race. This will give your body time to hydrate and will give you time to hit the porta potties before the gun fires.
  • Stop to drink at hydration stations. You will more than make up the time by staying well hydrated.
  • If prone to dehydration, drink by schedule – not by thirst

 Alright, now that you have your nutrition and fluid needs down, go practice them on your training days! Figure out what works for you and your body. You’ll thank me later!

Casey Keane-Miller 

Q & A's with Casey

Q: Can you explain the role of bananas, chocolate milk, and coconut water given after a race? 

A: Bananas offer a quick source of easily digestible carbohydrate as well as potassium (an electrolyte needed for proper hydration). Chocolate milk offers carbohydrates and protein in a palatable and easily digestible form. Coconut water contains electrolytes which promote proper hydration. All are great choices immediately post-race when you might not be ready for a full meal. 

Q: Gatorade definitely dominates the market but are there any other suitable alternatives? What about vitamin water? 

A: There are many brands of electrolyte drinks on the market, there are even recipes to make your own. I suggest you find a drink that tastes good, is well tolerated by your body, and provides adequate carbohydrates and electrolytes (primarily sodium and potassium).

Q: Are there any foods you should avoid post race which might stump your recovery? 

A: Immediately post-race, you should consume easily digestible carbs and protein (think chocolate milk, bananas, bagels with peanut butter, etc) in order for your body to quickly refill your glycogen stores. Most of those foods will be readily available at the finish line. That will tide you over until your first meal post-race which should be higher in carbohydrate. Other than that, it's up to you to decide how to celebrate your big accomplishment!

Q: Do all these principles apply during the training period and race day? 

A: Yes, if you are running > 1 hour, most of these principles apply.  

Q: Do you know of any websites that provide good resources for nutrition during running? 

A: www.runnersworld.com is a great resource

I'd like to thank Casey for her expertise and time and for sharing these tips with Rayner & Smale. Hopefully you can take them on board for your personal training regime or advise your clients how to compliment their rehab and training.



Rosenbloom, Christine A, PhD, RD, CSSD. Sports Nutrition, A Practice Manual for Professionals 5th Edition. 2012.