Moderate amount of protein in low-carb beverage improves aerobic endurance: Report

Compared to a standard carbohydrate supplement, a low-carbohydrate beverage with added protein leads to longer endurance times in cyclists, reports the October issue of the The Journal of Strength and Conditioning Research, official research journal of the National Strength and Conditioning Association. The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health, a leading provider of information and business intelligence for students, professionals, and institutions in medicine, nursing, allied health, and pharmacy.

Depending on exercise intensity, a low-carb beverage with a moderate amount of added protein can improve aerobic endurance—even though it contains half the carbohydrates and less than one-third the calories of standard sports drinks, according to a study by Lisa Ferguson-Stegall, M.S., and colleagues of The University of Texas at Austin.

Cyclists Go Longer on Low-Carb, Added-Protein Supplement
In the laboratory study, 15 trained endurance cyclists performed two long rides: three hours, followed by an intense ride—up to 85 percent of aerobic capacity (VO2 max)—until exhaustion. On one ride, the athletes were given a standard six percent carbohydrate supplement. On the other ride, they received a three percent carbohydrate supplement (containing a mix of carbohydrates) with 1.2 percent added protein. On each ride, the cyclists were given 275 mL of their assigned beverage every 20 minutes.

Overall, there was no significant difference in endurance times. Average time to exhaustion was 26 minutes with the standard supplement and 31 minutes with the low-carb plus protein supplement.

However, the difference became significant for athletes exercising at or below their ventilatory threshold (VT)—the point at which breathing starts to become increasingly difficult. For the eight cyclists in this group, average time to exhaustion was 45 minutes with the low-carb plus protein beverage, compared to 35 minutes with the standard carbohydrate drink.

Thus endurance improved by about 28 percent in cyclists exercising at or near their VT. For the seven athletes exercising above their VT, there was no significant difference in time to exhaustion—about 15 minutes with both supplements.

Studies have shown that carbohydrate-containing beverages increase endurance exercise performance, compared to water and placebo drinks. Supplements containing protein in addition to carbohydrates bring further performance benefits. "However, many athletes and recreational exercisers desire a lower carbohydrate, lower caloric content alternative when maintaining or reducing body weight...in addition to improving fitness and endurance," Ferguson-Stegall and coauthors write.

The new results suggest that a drink containing a lower amount of carbohydrate, plus a moderate amount of protein, leads to improved endurance performance in trained long-distance cyclists. The low-carb drink increases performance "despite containing 50 percent less total carbohydrate and 30 percent fewer calories relative to a higher carbohydrate beverage," according to the researchers.

The difference is significant only for athletes exercising at or below VT. The ability to exercise for long periods at or near VT is a "critical component of performance in long events such as marathons, longer cycling races, and long-distance triathlon," according to Ferguson-Stegall and colleagues. Thus the low-carb, added-protein supplement may be "more effective in extending endurance and delaying fatigue...around the exercise intensity at which prolonged endurance performance is crucial."