In my first article on the vegetarian athlete, I tried to outline the primary dietary concerns of protein and iron intake, focusing first on protein. In this article, I'll move from macronutrients (protein, carbohydrates, and fat) to micronutrients, specifically iron and vitamin B12, as these are the most challenging to those eating a meat-free diet. Anemia is one of most common problems vegetarian athletes face, and is often a result of inadequate iron and B12, so we'll also talk specifically about that.
I want to again stress the perspective I'm writing from and remind you that I'm not a nutritionist. Bike.com has recently added former top cyclist and registered dietitian Jane Quigley to the Smart Training writing staff, and I'm hoping to learn as much from her as I hope you are. At the same time, as a vegan athlete and coach, I've made a notable investment of time over the years to research and understand what's required for my own performance and that of my clients. My goal is simply to share that with you.
Iron
I want to start with iron as I think it's the micronutrient of highest concern to vegetarian and omnivorous athletes alike. Iron's primary use in the body is by red blood cells to deliver oxygen. Very simply, 1/3 of a red blood cell is composed of a molecule called hemoglobin, and 97% of the oxygen transported by the blood is done so by hemoglobin. Hemoglobin essentially combines with or "picks up" oxygen in the lungs and then releases it in the capillaries. There are 4 iron atoms in each molecule of hemoglobin, and each iron atom can bind with one molecule of oxygen.
What does this have to do with iron in your diet? Basically, if your body doesn't have enough iron, then it can't make enough hemoglobin, and your ability to transport oxygen is reduced. Oxygen is the primary fuel source for aerobic exercise, and your performance is directly related to how quickly and in what volume you can provide it to working muscles. This process can become impaired in the form of iron deficiency anemia, or for athletes specifically, exercise induced anemia. Common causes include eating inadequate amounts of iron-rich foods, a deficiency of Vitamin B12, a deficiency of folic acid, or poor iron absorption by the body. For women, an additional concern is menstruation, which can contribute to 20-40 mg of iron loss.
We'll talk about B-12 next, but iron absorption shouldn't be a problem for the thoughtful vegetarian cyclist. The Recommended Dietary Allowance (RDA) for iron for non-vegetarian pre-menopausal women is 18 mg/day. The RDA for non-vegetarian men and post-menopausal women is 8 mg/day. Because of iron absorption limitations from plant-only sources (which I'll discuss below), the RDA for vegetarians is higher: 14 mg/day for vegetarian men and 33 mg/day for vegetarian women. Remembering that the RDA is set for sedentary people, an athlete may need slightly more, but the upper level of intake is recommended not exceed 45 mg/day. Even still, iron is widely available in both meat and plant sources, and the vegetarian athlete should be able to meet the higher standard.
In an omnivorous diet, fish and poultry are great sources of iron. Good vegetarian sources include dark green leafy vegetables, legumes, whole grains, seaweed, soy products and fortified cereals. Most well balanced vegetarian diets are actually higher in iron intake than non-vegetarian diets. The problem is in the bioavailability of that iron. In the last article I showed how protein from plant sources was actually just as available to the body, even if there was slightly less of it. Here the roles are reversed.
Iron is found in food in two forms, heme and non-heme. Heme iron, which makes up 40 percent of the iron in meat, poultry, and fish, is easily absorbed by the body. Non-heme iron, which is the other 60 percent of the iron in animal products and all the iron in plant foods, is less easily absorbed. The balance seems to come in the fact that commonly eaten vegetarian foods like beans, green vegetables, grains, and fruit often have 2-3 times the amount of iron as meat sources, as well as naturally high levels of Vitamin C, which aids the body in iron absorption.
Vitamin B12
Vitamin B12 is needed for cellular growth and nervous system development, and as we discussed above, deficiency of B12 can play a role in iron- and exercise induced anemia. At the same time, B12 deficiency is unusual, even in vegetarians. Where it can become an issue is for the complete vegan, as B12 is only found in meat, dairy products, or eggs. There are no reliable plant sources of this vitamin, and in this case the vegan athlete must turn to supplementation. This is easy enough, as many soymilks and soy analog ("fake meat") foods are fortified with B12, and the amount needed for adults (1 microgram/day) is incredibly small.
Once again, the emphasis here has to be on a varied food supply. A balanced vegetarian diet, whether you're an athlete or not, has to include a wide variety. In this case, the major micronutrient you'll likely be concerned with as a vegetarian athlete is iron. You could drink a glass or two a day of prune juice at 10g of iron per glass if you like, but a wider variety of food, including just about any bean or grains like Quinoa (which is also very high in protein), will provide you with plenty of iron in your diet, and probably be a bit more enjoyable.
In the final installment of this series, I'll discuss practical strategies for traveling and racing as a vegetarian athlete, supplements, and answer some of the questions people have sent in.