Protein In Your Diet

Contributed by Dr. Steven T. Devor – Director of Performance Physiology for MIT and OhioHealth, and Associate Professor of Exercise Physiology, Department of Human Sciences, and Department of Physiology and Cell Biology, The Ohio State University

There is little doubt that many Americans consume far too much protein in their diets, and this is especially common in power sport athletes.  More recently this has become a problem for endurance athletes as well, and a diet that is too high in protein will have a very large negative influence on your training and racing performance.

A frequent problem for endurance athletes is they lack the stored energy required for quality training and racing.  A contributor to this problem is the very common misconception that protein is a good primary fuel source for strength training, muscle building, intense exercise, and endurance exercise.  Indeed it is hard to find a body builder who does not rely on some form of protein or amino-acid supplement, and also attributes their success to these products.  These athletes in particular consume much more protein than they need.  However, over consumption of protein is not a problem that is exclusive to power sport athletes.  Increasingly I have questions from endurance athletes regarding their protein intake, and I am frequently surprised at how much protein they consume when I evaluate their diets carefully.

A higher than necessary consumption of protein can offset the intake of other essential energy nutrients (carbohydrates and fats), so it is not surprising that many athletes struggle with low energy during a workout.  All nutrients (carbohydrates, fats, and protein) get converted to energy in the form of adenosine triphosphate (ATP), but each nutrient has unique properties that determine how it gets converted to energy.  I believe it is critical to understand that protein is not a ready source of energy, and understand the real value of protein: muscle recovery.

Carbohydrate is the primary fuel source for moderate to high-intensity exercise, while more fat (though not exclusively fat) is utilized for lower intensity exercise. Once the stored carbohydrate in your body is fully depleted, which is known as glycogen depletion, an athlete will “hit the wall” or “bonk”.  During training or a race situation, hitting the wall can be avoided by simply replenishing carbohydrate stores; for example, consuming easily digestible carbohydrates during exercise that lasts more than 90 minutes.  However, glycogen depletion can and does occur after several days of limited carbohydrate intake.  When this happens it is like going into your workout or race with an empty tank of fuel.

Limiting carbohydrate intake in your daily diet will force your body to rely on fat metabolism for energy production when you are training or racing.  And using fat for energy production is far less efficient and will absolutely limit performance.  The main function of protein is to maintain and repair body tissues and your body will rely on protein as a fuel source only as a last resort in order to satisfy energy requirements.  As long as you have stored fat, your body will not utilize protein as a fuel source.

Dietary protein is comprised of building blocks called amino acids. Once dietary protein is broken down into amino acids, they join together to synthesize the particular protein the body needs such as hair, nails, hormones, enzymes, and muscles.  The liver is the central processing unit of protein, monitoring the needs of the body and synthesizing the particular proteins from the amino acids.  The by-product of protein synthesis is nitrogen in the form of ammonia, which is converted to urea by the liver and extracted from the body by the kidneys in urine.

The consumption of too much protein has a negative impact. As ammonia builds up it is removed as urea, which disturbs the pH balance of blood creating an acidic environment.  The kidneys are subsequently forced to work overtime, using body fluids to flush the nitrogenous ammonia from the blood in order to stabilize the blood pH. This process is a potential problem for endurance athletes as it greatly increases the risk of dehydration.  Excess dietary protein has also been shown to cause an excretion of calcium in the urine.  Both dehydration and loss of calcium are detrimental to endurance performance.

With regard to a pre-training meal generally, a low fiber, low fat combination is recommended as a pre-workout fuel source as it is digested more quickly and thus reduces the risk of gastrointestinal distress.  Protein digestion is much slower than carbohydrate, so a high protein meal may not be fully digested, causing water to be rapidly absorbed into the intestinal track.  This increases the risk of gastrointestinal distress during exercise, so it is important to avoid a large protein meal several before your train or race.

Research has shown that protein consumed with carbohydrates shortly after exercise does help the body recover faster by initiating muscle repair and growth. Adding protein to a recovery meal does not enhance the ability of the muscle to store energy, but it does stimulate the muscles to repair and rebuild.  Relatively small amounts of protein are required for muscle repair.  Therefore, athletes should consume a combination of carbohydrates and protein immediately post-exercise.

Carbohydrates are used to refill the muscles with fuel, while protein is used to help build and repair muscle tissue. Within the scientific community, the be all and end all optimal ratio of carbohydrates to protein in the recovery process is still debated.  However, based on the majority of research available a ratio of 3:1 carbohydrate to protein appears to work best.

Endurance athletes are more commonly relying on liquid shake mixes for recovery meals, they are convenient and the 3:1 carbohydrate to protein ratio is frequently formulated in many over the counter pre-made recovery mixes.  However, if you prefer to refuel with solid food, here are some healthy options: 

    • Half of a whole wheat bagel with 1/4 cup cottage cheese or a tablespoon of peanut or some other nut butter
    • Yogurt smoothie, berries and a tablespoon of protein powder
    • Medium sweet potato and two egg whites
    • Medium banana with a tablespoon of peanut or some other nut butter
    • Small turkey sandwich on whole wheat bread
    • Bran cereal with skim milk and a few nuts
    • Protein bars (many specially formulated with the 3:1 optimal carbohydrate to protein ratio)

    Best wishes for your continued training success.

    Dr. Devor
    Steven T. Devor, Ph.D., FACSM

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