Two foods high in magnesium/Photo by Stars Apart

Recipe: Good-for-You Brownie Thins

There’s good news for chocolate-loving triathletes this Valentine’s Day. Magnesium, one of the main elements found in cocoa, is possibly one of the most overlooked nutrients in the athlete’s diet. Even a modest deficiency in magnesium can affect oxygen uptake, proper functioning of the central nervous system, electrolyte balance, glucose metabolism, immune system functioning, and nerve and muscle functioning, to name but a few.(1) Add to that protein synthesis, bone strength, blood pressure and heart rhythm, and without magnesium, we’ve got a recipe for disaster.

You may have first met magnesium on the label of your favorite sports drink (2); as an essential electrolyte for activity, it’s often added to such beverages. Moreover, over the past few years, research has demonstrated a that magnesium is a necessary ingredient to relax the muscles during exercise. Magnesium is also behind the common post-workout Epson salt soak recommendation–it’s highly effective for relaxing sore muscles and reducing stress.

If the diet is deficient in magnesium, however, the body is forced to work harder than needed.

Although research is inconclusive in terms of the need to supplement with magnesium, in order to enhance physical performance (3,4), current research on magnesium supplementation on human subjects appears to be lacking. As an essential mineral that is slowly disappearing in the American diet, I hope in this article to at least raise awareness of the importance of magnesium in your daily nutrition regime.

Magnesium and the Athlete

As an athlete, you may think that your active lifestyle and ability to easily maintain or lose body weight reduces your risk from being one of the 35 percent of Americans who are obese (5). Unfortunately, no person is free from disease. Cited as being needed for more than 300 biochemical reactions in the body, with half of stored magnesium found in bone and the other half found inside the cells of tissues and organs, dietary magnesium is becoming more recognized for its possible role in preventing and treating conditions such as diabetes, osteoporosis, hypertension, cancer and stroke (6).

According to a recent meta-analysis of the risk of ischemic stroke and magnesium intake, Larsson and colleagues discovered that the medium dietary intake of magnesium among U.S. citizens was 242 milligrams a day, which is far from the recommended daily allowance of 420 and 320 mg/day for adult men and women, respectively (7). Furthermore, among the 250,000 people in the U.S., Europe and Asia who were followed throughout Larsson’s study, 6,500 of the initial 250,000 subjects (or 3 percent) experienced a stroke throughout the study. It should be noted, however, that for every 100 mg of magnesium that a person took in each day, the risk for blood clotting decreased by an astonishing nine percent (8).

Take chili to a whole new level by adding cocoa

As an active individual, you understand the role of nutrition and how it impacts your athletic success. Despite being able to efficiently metabolize food while partaking in daily exercise, one must not overlook the significant changes in agriculture techniques and food processing, the low-nutrient, high-calorie Western diet, and the possible correlation of magnesium deficiency associated with acute and chronic conditions. In other words, no matter how many miles a week you cover during training, if your diet is deficient in any one nutrient, short and long-term performance as well as overall health may be compromised.

Of concern for endurance athletes, research has shown an increased loss of magnesium through exercise due to the transfer of magnesium from plasma into red blood cells (8). The greater the metabolic demands placed on the body, the greater the need for magnesium in red blood cells to support activity. Despite the loss of magnesium in sweat and urine (often replaced by sport drinks), as the duration of activity continues, magnesium levels in red blood cells may continue to decrease. As long as dietary intake of magnesium is adequate, this loss will likely be compensated for.

If the diet is deficient in magnesium, however, the body is forced to work harder than needed(8). In other words, you may find yourself doing double the work and receiving half the anticipated outcome. Otherwise healthy individuals who have a magnesium deficiency may experience increased oxygen uptake, possibly due to a decrease in red blood cells, as well as an increased load on the cardiovascular system. Although there is limited research on the role of supplemental magnesium in healthy, active human subjects during activity, it could be assumed that magnesium deficiency–either through poor dietary planning or overtraining–may limit consistent performance gains among competitive athletes.

Speaking of performance limiters, athletes are very aware of fluctuating blood sugar levels throughout training, hence the tendency to eat everything in sight after a long ride. The role of magnesium and blood sugar control is promising, with research demonstrating that low magnesium levels may reduce insulin sensitivity (10). In both diabetics and non-diabetics, adequate magnesium intake appears to play a positive role on fasting blood glucose as well as affecting how the body breaks down digested carbohydrates and how the body uses insulin (10). Considering that a diet rich in fruits, vegetables, nuts, and whole grains is advised for diabetics in regulating blood sugar and insulin levels, magnesium-rich foods (which are also high in fiber) could possibly play a vital role in controlling blood sugar levels and helping athletes metabolize glycogen and fatty acids more efficiently during and after training. Recognizing that athletes are often vulnerable to crave sweet, salty, and high-fat foods after activity, foods rich in magnesium may prevent episodes of overeating and rapid drops in blood sugar as you attempt to refuel throughout the day. Perhaps that daily craving for chocolate is actually a sign that your body is in need of more dietary magnesium.

Excellent dietary sources of magnesium include plants rich in chlorophyll, which gives vegetables their green color. Magnesium can also be found in whole grains, beans, legumes, and nuts, as well as in hard water and soil.

Food sources of magnesium: (6)

Cocoa powder (25g) – 125 mg
Almonds (1 ounce) – 80 mg
Spinach (½ cup) – 78 mg
Cashews (1 ounce) – 74 mg
Soybeans (½ cup) – 74 mg
Wheat germ (¼ cup) – 69 mg
Oatmeal (1 cup) – 61 mg
Peanut butter (2 tbsp) – 49  mg
Pinto beans (½ cup) – 43 mg
Brown rice (½ cup) – 42 mg
Kidney beans (½ cup) – 35 mg
Banana (1 medium) – 32 mg
Non-fat milk (1 cup) – 27 mg

Toxicity, calcium, and bone health

Absorbed through the small intestine and regulated by the kidneys, toxicity of magnesium is rare in healthy individuals. Despite an ever-increasing deficiency in the typical “healthy” person, individuals taking diuretics, antibiotics, or anti-neoplastic medications, alongside diabetics, individuals with kidney problems and individuals with chronic malabsorption issues (ex. Crohn’s disease, celiac disease, enteritis, diarrhea) may be more at risk for magnesium deficiency and should regularly consult with a physician to discuss proper testing for magnesium status. Keep in mind that magnesium is highly concentrated in the cells (and not blood) so a blood test for magnesium may have limitations. Discuss the symptoms of magnesium deficiency with your doctor if you feel your diet is lacking key nutrients (or if you train intensely) but routinely show results within normal limits.

Lastly, athletes understand the importance of bone health in order to reduce risk for stress fractures and chronic wear and tear. Because bone health is famously supported by optimal intake of calcium and vitamin D, it is often advocated that in order to prevent osteoporosis and to increase bone strength, active individuals should increase calcium, either through dietary sources and/or supplements. However, increasing calcium to recommended levels or above, alongside a deficiency of magnesium, may be damaging to the body.

In terms of calcium intake, current research is demonstrating an increased risk of prostate cancer among men consuming a high dairy diet (>1,500 mg of dairy calcium/day)(11). However, controlled intakes of around 800-1000 mg/day of calcium (dairy or supplements) may lower the risk of new precancerous colon polyps in people who had already had one, as well as showing protection against colon and rectal cancer in both men and women (11). Considering the inconsistency of research on calcium, perhaps it is a deficiency of magnesium, and not calcium, that is affecting the role of calcium in the body.

Whereas calcium induces muscle contractions, magnesium allows muscles to relax. This may ring a bell if you tend to cramp during racing, all while consuming a high “starchy” carb diet on the days or weeks leading up to a race. (Not to mention that serving of ice cream, or cereal with milk as your ritual post-workout treats!) Without adequate magnesium, calcium (either through diet or supplementation) may collect in the soft tissues and be poorly absorbed in bones. In order to reduce the risk of arthritis, osteoporosis, muscle cramping, menstrual cramps, thyroid problems and/or premenstrual problems, I strongly encouraged you to aim for the recommended intakes of dietary magnesium while consuming a varied, whole-foods heavy diet.

Because every eating opportunity is an opportunity to provide your body with a variety of nutrients, do not overlook variety for your daily meals and snacks. If you are training for an upcoming event, trying to achieve weight loss or body composition changes, it’s time to stop worrying about what you “can’t” eat and start focusing on what you can, should, and need to eat for the overall health that powers your active lifestyle.

Recipe: Good-for-You Brownie Thins

References:

1) Laires, M.J. et al. (2008). Exercise, magnesium and immune function. Magnes Res. 21(2): 92-96.

2) Nielsen, F.H. and Lukaski, H.C. (2006). Update on the relationship between magnesium and exercise. Magnes Res. 19(3): 180-9.

3) Newhouse, I.J. and Finstad, E.W. (2000). The effects of magnesium supplementation on exercise performance. Clin J. Sport Med. 10(3); 195-200.

4) Cheng, S.M. et al. (2010). Magnesium sulfate enhances exercise performance and manipulates dynamic changes in peripheral glucose utilization. Eur J. Appl Physiol. 108(2): 363-9.

5) Katherine, M. F. et al. (2010). Prevalence and trends in obesity among US adults, 1999-2008. J of the Am Medical Assoc. 303(3); 235-241.

6) National Institutes of Health. Dietary Supplement Fact Sheet: Magnesium. Office of Dietary Supplements. Retrieved February 10, 2012 from http://ods.od.nih.gov/factsheets/magnesium/.

7) Larsson, S.C., Orsini, N. and Wolk, A. (2012). Dietary magnesium intake and risk of stroke: a meta-analysis of prospective studies. Am J. Clin Nutr. 95(2): 362-6.

8) Lukaski, H.C. (2000). Magnesium, zinc and chromium nutrition and physical activity. Am J of Clin Nutr. 72(2): 5855-593.

9) Lukaski, H.C. and Nielsen, F.H. (2002). Dietary magnesium depletion affects metabolic responses during submaximal exercise in postmenopausal women. Am Society for Nutr. Sciences. 132: 930-935.

10) Sales, C.H., et al. (2011). Influence of magnesium status and magnesium intake on glucose control in patients with type 2 diabetes. Clin Nutr. 30(3): 359-64.

11) Giovannucci, E. et al. (2006). A prospective study of calcium intake and incident and fatal prostate cancer. Cancer Epidemiol Biomarkers. 15(2): 203-10.

___________________________

Marni Sumbal, MS, RD, CISSN is a Registered Dietitian with a Master of Science degree in Exercise Physiology. She is the owner of Trimarni Coaching and Nutrition, LLC  and is a USAT Level-1 coach. Marni recently finished her 2nd Ironman World Championship race in Kona, and enjoys spending time in her kitchen coming up with vegetarian creations. If you can’t find her writing this monthly column, cooking or training, she is likely outside running with her furry best friend, Campy.