Protein, Carbs & Endurance Running: Finding the Right Balance

by Nancy Clark MS RD CSSD


If you are curious about how to best fuel for endurance runs, here are some tips presented at the 27th Annual SCAN* Symposium, April 2010. The information was presented by Asker Jeukendrup PhD, Professor of Exercise Metabolism-Univ. Birmingham in England and Nancy Rodriquez RD PhD, Professor of Nutritional Sciences-Univ. Connecticut. (*SCAN is the Sports Nutrition group of the American Dietetic Assoc.;


Carbohydrate Update

Mararhoners commonly wonder what’s best to eat during long runs that last more than 60 to 90 minutes. The answer depends on your personal tolerance. Some runners enjoy the convenience of engineered sports foods such as Clif Chomps, PowerGels, and Sports Beans. Others prefer the taste (and price) of standard supermarket foods, such as dried pineapple, twizzlers and gummy candy. All are equally effective. And because we're talking about “survival” more than “good nutrition” during endurance exercise, you need not tsk tsk yourself for enjoying candy. That's what your body wants—sugar! (FYI, gels and sports drinks are also “just sugar.”)


Does it matter if you get your energy from an energy bar as opposed to a sports drink?

No. Both solid foods and liquids (i.e., sports drinks) get burned at the same rate when you are exercising at a pace you can maintain for more than half an hour. Your job is to experiment during long training runs to learn—

1) what settles best in your intestinal tract, and

2) what tastes best to you during extended exercise.


Consuming enough calories is more important than the form of the calories. With endurance athletes, research suggests the faster finishers consume more calories than the slower finishers. (Ironman Champ Chrissie Wellington consumed about 335 calories/hour when she won at Hawaii.) The challenge is to train the intestinal tract to manage that much fuel. If you are a marathoner, part of your training program is to practice your fueling so you can train your intestinal tract as well as your heart, lungs and muscles.

How much should you eat to maintain good energy when you’re running for longer than 60 to 90 minutes?


The standard recommendation for fueling during endurance exercise has been to target 1 gram carbohydrate/minute of exercise (60 g carb per hour for a 150-lb person, the equivalent of 240 calories). The research, originally done with just glucose, indicated consuming more than 60 grams of glucose/hour offered no benefits. The body has a limited number of glucose transporters and can carry only 60 grams out of the intestines, into the blood and to the muscles.


More recent research indicates consuming as variety of sugars (that is, more than just glucose) allows more fuel to become available per hour. That's because different types of sugars (carbs) use different transporters. Generally, runners consume more than just glucose. (Sports drinks, for example, tend to be glucose+fructose.) Let's say you eat a banana that consists of many different types of sugars and uses many different transporters. Your muscles will have access to more fuel (up to 90 g carb/hour; 360 calories) than if you consume just one kind of sugar. Variety is a wise idea!


In general, the recommendations for fueling during exercise are:

• If you are exercising for less than 45 minutes, no need for fuel during exercise. (As always, enjoy a pre-exercise snack.)

• For 1-2 hours of exercise, target ~30 g carb/hour (120 calories).

• For 2 to 3 hours of exercise, target ~60 g carb/hr (240 calories).

• For more than 2.5 hours of exercise, target ~90 g mixed carbs (i.e., (360 calories of sports drink, candy, dried fruit, pretzels).


Some serious marathoners wonder if they should train first thing in the morning without having eating before or during exercise. Doing this from time to time may teach the body to burn more fat and spare limited glycogen stores (glycogen depeletion is associated with fatigue). But it’s grueling and the verdict is unclear if this will enhance competitive performance because an athlete cannot train as hard when underfed. Stay tuned!


What happens if fueling during long runs creates intestinal distress?

You might want to “swish and spit.” When research subjects just swished and then spat out a sports drink, they improved their performance as compared to swishing and spitting just plain water. How could that be? Receptors in the mouth are linked to the brain. When the mouth gets a swish of sports drink, the brain gets the signal energy is on the way; it's OK to work harder.


Protein Update

Protein requirements are hard to define because the amount of protein your body needs depends on how many calories you consume. That is, if you are restricting calories to lose undesired body fat, you require more protein than when you eat adequate calories; the protein gets burned for fuel. Dieting runners should target at least 1 g protein/lb (2 g pro/kg).


Note: If you are dieting to lose undesired body fat, you are unlikely to lose only body fat and build muscle simultaneously. Building muscle takes energy; dieting restricts energy.


The protein recommendations for non-dieters who consume adequate calories are:

Healthy adults: 0.4 g Pro/lb 0.8 gm Protein/kg

Strength athletes: 0.5 to 0.8 g Pro/lb 1.2 to 1.7 g Pro/kg

Endurance athletes: 0.5 to 0.6 g Pro/lb 1.2 to 1.4 g Pro/kg.


Because the typical runner’s diet contains more than enough protein, most runners do not need protein supplements. A protein-rich food with each meal and snack can do the job.


Sports Nutrition Guidebook

During long runs, should you choose a sports drink with protein?

Not unless you prefer the taste; it does not offer performance advantages over a standard sports drink. The better time to consume protein is after exercise. That is, carbs+protein (as in chocolate milk, fruit yogurt, or spaghetti & meatballs) enhances muscle repair.


Consuming some carbs+protein before you workout, as a part of your pre-run meal (such as cereal+milk, fruit+yogurt) is another option to bolster the supply of protein that will be available both during and after exercise for recovery. Note: Athletes generally don’t burn much protein for fuel during exercise unless their glycogen (carb) stores are depleted.

The bottom line: Meals and snacks with carbs as the foundation and protein on the side offer the right balance for endurance performance.


Nancy Clark, MS, RD, CSSD (Board Certified Specialist in Sports Dietetics) counsels both casual and competitive athletes in her practice at Healthworks, the premier fitness center in Chestnut Hill MA (617-383-6100). Her Sports Nutrition Guidebook and food guides for new runners, marathoners and cyclists are available via also

Copyright: December 2009



Jeukendrup, A. Sports Nutrition: From Lab to Kitchen. Meyer 7 Meyer Sport, 2010

Mettler S, N Mitchell, K. Tipton. Increased protein intake reduces lean body mass loss during weight loss in athletes. Med Sci Sports Exerc. 42(2):326-337, 2010.

Rollo I. M. Cole, R. Miller and C. Williams. Influence of mouth rinsing a carbohydrate solution on 1-h running performance. Med Sci Sports Exercise 42(4):798-804, 2010.