I talk a lot about exercising but not much about fluid replacement during and after. Fluids are always needed, more so now that summer is upon us. As there are a host of sport and energy drinks available, what really is necessary?

Most energy and sport drinks are not needed for the average gal or guy. They won’t necessarily harm you (although high-fructose corn syrup may contribute to metabolic syndrome, a precursor of diabetes), all you really need is water. The lone exception is if you are engaging in continuous, strenuous activity for more than an hour; then some electrolyte replacement may be necessary. What are electrolytes? They are ions which carry either a positive or negative charge. Potassium (K+), sodium (NA-) chloride (CL-), magnesium (Mg2+), and calcium (Ca2+) are some of the more notable ones.

K+ and NA- are responsible for maintaining fluid balance inside the cell and in the extracellular fluid. Ca2+ helps to regulate muscle (including the heart) contraction, and Mg2+ helps to relax muscles and nerves. Sodium is the electrolyte most easily lost through sweat. How do you know if you need to replace it? I use these two rules; 1) does your skin taste salty or are there white sweat stains on your workout clothes, and 2) do you crave salty foods afterwards? Either eat something salty or a sport drink will work. The most K+ you lose during a workout is ~450 mg; eat a banana. bananas contain 500-600 mg of K+. Don’t worry too much about Mg2+ or Cl-, they are rarely lost in appreciable amounts in sweat unless you’re Lance Armstrong.

Drink plenty of water before; a little coffee (caffeinated) is great too as it helps to free up fats for energy use.

Stay well, John R Blilie, M.S.