Many individuals are positively embracing the “good food revolution” that brings people back to relying on small farms for wholesome foods for their family and trying to prepare recipes from scratch while decreasing their intake of highly processed food. This is obviously a great idea for improving health and preventing many diseases.
However, for the active individual, an important nutrient may be missed in the process. Recently, a cyclist came to me struggling with stomach upset, exhaustion, cramps and occasional vomiting after trying to increase her distance. She has made positive attempts with improving her food intake and noted that previously she could ride for 1.5 to 2 hours with no problem. But, after trying to do a 4+ hour race, recognized something wasn’t right when she struggled with being able to finish the race. She wondered if she needed to increase her carbohydrate intake (which seemed impossible to her given the nausea she was experiencing)? When asked about her fluid intake, she explained she drank a LOT of water along with a sports drink on her rides so didn’t believe she was dehydrated. What should she do?
Along with eating well, most athletes are aware of the need to stay well-hydrated and replace fluids lost due to sweat during exercise. However, the role of salt, or more correctly, sodium replacement is often overlooked resulting in muscle cramps, heat illness, inability to rehydrate after exercise, and an increased risk for hyponatremia (low blood sodium). And, for the recreational athlete who continues to improve their athleticism while eating “healthier” (most likely with reduced sodium intake), this risk becomes even more apparent.
Salt consists of sodium and chloride with sodium being a critical nutrient that the body needs to work properly and maintain fluid balance. However, many people believe that a high-sodium diet is always unhealthy, and indeed, The Dietary Guidelines for Americans suggest that healthy adults limit their sodium intake to 2,300 milligrams (mg) per day (roughly the equivalent of 1 teaspoon of table salt). The average dietary sodium intake in the United States is estimated to be 3400 mg per day and chronic over-consumption of sodium can lead to health concerns, including high blood pressure, heart disease and/or kidney problems.
Although the typical American diet contains more sodium than is needed, this may not be true for every athlete. The amount of sweat loss during athletic activity can be significant, especially for those who practice or compete in hot or humid conditions, for a long duration, or over consecutive days.
A case of low sodium:
So, back to my cyclist hoping to compete in a 4 hour race – without cramps, nausea and vomiting. We discover that she loses about 2 pounds of body weight (so one liter of sweat) after an hour riding in hot, humid conditions. We also note that she is a “salty sweater” (evidenced by an accumulation of salt on skin or clothing after training). Her sweat is estimated to have 1000 mg of sodium per 1 liter of sweat. Therefore, during a 4 hour event she may lose over 4 liters of fluid which means her sodium losses could be almost 4,000 mg for the duration of the event.
If she were to follow the recommended guidelines of less than 2300 mg/day of sodium, her intake would be insufficient to replace what she lost during the event. Additionally, if she consumed a large amount of water to replace fluid losses, she may very likely suffer from symptoms of hyponatremia (headache, vomiting, swollen hands and feet, confusion, restlessness and irritability).
Developing a sodium replacement strategy:
There is significant variation in both sweat rate and sweat sodium concentration among individuals making it difficult to recommend a guideline for fluid and sodium replacement that applies to everyone. Therefore, the following calculations may be helpful in estimating sodium needs based on average sweat concentrations.
1) Calculate a sweat rate: Weigh yourself before and after a 1-hour exercise session (accounting for fluid intake and urine output during this hour). One liter of sweat is equal to 2.2 pounds of body weight. It is not uncommon for athletes to sustain sweat rates of 1-2 L/hr in hot environments, or a 2 to 4 pound weight loss.
2) Estimate sodium needs: A liter of sweat contains, on average, about 1000 mg sodium (Sawka et al., 2007). Therefore, if an athlete loses 2 L of fluid per hour, the athlete would need to replace 2000 mg of sodium per hour of exercise.
3) Plan to replace sodium lost during exercise. During prolonged exercise lasting greater than 2 hours, consume sodium-rich foods and beverages at regular intervals. Foods and snacks high in sodium include pretzels, saltine crackers, tomato juice, pickles or pickle juice and broth (see table below). Sports drinks also contain sodium and may be used for fluid replacement instead of plain water; but typical sports drinks are more water than sodium and won’t protect against hyponatremia. Adding 0.5 tsp of table salt to each 32 fluid ounces of a sports drink will increase sodium concentration without adversely affecting taste or absorption.
4) Understand typical dietary sodium intake. Consider reading food labels to get an idea of your typical sodium intake, especially if following a vegan diet. Consuming sodium-containing foods (along with water) in the days before and after training is important to ensure adequate rehydration after exercise, which can only be achieved if the sodium lost in sweat is replaced along with the fluid lost.
5) Before increasing sodium intake, speak to a sports medicine doctor or dietitian. For those who have sustained a low sodium intake for a long period of time, such as for vegan eaters, increasing sodium intake slowly will be important to provide time for the body to adjust. Also, for those with high blood pressure or kidney problems, a dietitian can help you determine an intake appropriate for your overall health.