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Question of the Month!
I am training for a marathon this summer and my trainer wants to eat a high protein diet. How much protein do I need?
To answer this question, let’s start with the basics! The dietary reference intakes (DRIs) are the nutrition recommendations set by the Institute of Medicine (IOM). They include the recommended dietary allowance (RDA) and the acceptable macronutrient distribution range
(AMDR). These include the amounts of protein that the general healthy public should be eating.
So how much protein is recommended for the general healthy public? The RDA for protein is 0.8 grams/kilogram.
Let’s look at an example of how to calculate the protein needs for a person that weighs 165 pounds.
1.
Change pounds to kilograms by dividing by 2.2. a.
165 lbs/2.2 = 75 kilograms
2.
Multiply the kilograms by 0.8. a.
75 kilograms X 0.8 = 60 grams of protein
You can also figure out protein needs based on your daily calorie intake. The AMDR for protein is 10%-35% of your total calories. This is the range for the amount needed. Let’s look at an example for a person eating a 2,000 calorie diet.
1.
2,000 kcals X .10 = 200 kcals a.
200 kcals / 4 grams per kcals = 50 grams of protein
2.
2,000 kcals X .35 = 700 kcals a.
700 kcals / 4 grams per kcal= 175 grams of protein
So why would a trainer suggest eating a high-protein diet when training for a marathon?
One of the major roles of protein is building and repairing muscles. Proteins can help repair the damaged muscles that running causes. Many athletes think because of this they need to increase their protein intake. So is the protein recommendation the same for athletes? Or do they have an increased need?
The answer is yes they have an increased need, but the more complex question is to how much more is needed. Studies have been done to figure out the optimal amount and the dangers of eating too much protein. However, there have been no specific answers to either question.
Nitrogen balance is the difference between protein intake and protein breakdown. One study found that for athletes it is usually balanced when a person eats 1.2 grams of protein per kilogram. This can be compared to the 0.8 grams per kilogram in the general healthy public.
The Academy of Dietetics and Nutrition also recognizes that athletes have a nitrogen imbalance by only eating 0.8 grams per kilogram. They agree that there is an increased need for athletes.
Based on current research, the Academy gives the recommendation for endurance athletes to be getting 1.2-1.4 grams of protein per kilogram.

Let’s see how much protein an endurance athlete weighing 165 pounds would need.
1.
Change pounds to kilograms by dividing by 2.2. a.
165 lbs/2.2 = 75 kilograms
2.
Times the kilograms by 1.2 - 1.4. a.
75 kilograms X 1.2 – 1.4 = 90 - 105 grams of protein
As you can see, this is only 30 – 45 more grams of protein then what is suggested for the general healthy public. In fact, researchers in one study stated that the average protein intake in the
Western countries is 15–16% of total calorie so most people are already getting plenty of protein anyways.
Little proof of the dangers of too much protein has been found. However, the concern with eating too much protein is that it begins to replace the carbohydrates in the diet. Carbohydrates are the body’s main source of energy. They are very important in a marathon runner’s diet. If the body does not have enough carbohydrates available to use for energy, then the body must use proteins.
Using protein for energy takes them away from their other roles such as helping repair damaged muscles. The AMDR maximum of 35% of total calories was set to help keep the balanced diet.
A healthy diet for a marathon runner should consist of 55-65% of calories from carbohydrates,
10-15% from protein, and 25% from fat. For more information about tips for eating healthy as a marathon runner, I would recommend reading Nancy Clark’s Food Guide for Marathoners.
References

American Dietetic Association. Position of the American Dietetic Association,
Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance. J AM Diet Assoc. 2009;109:509-527.
 Clark N. Nancy Clark’s food guide for marathoners. Oxford. Meyer and Meyer Sport
(UK) Ltd; 2007.

Fox E, McDaniel J, Breitbach A, Weiss E. Perceived protein needs and measured protein intake in collegiate male athletes: An observational study. J Int Soc Sports
Nutr. 2011;8:9.

Phillips SM. Dietary protein requirements and adaptive advantages in athletes. Br J
Nutr. 2012;108:S158-S167.

Poortmans JR, Carpentier A, Pereira-Lancha LO, Lancha Jr A. Protein turnover, amino acid requirements and recommendations for athletes and active populations.
Braz J Med Biol Res.

Sizer FS, Whitney E. Nutrition concepts and controversies. 12 th
ed. Belmont, CA:
Wadsworth Cengage Learning; 2011.

Tipton KD. Symposium 2: Exercise and protein nutrition efficacy and consequences of very-high-protein diets for athletes and exercisers. Proc Nutr Soc. 2011;70:205-
214.