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The link between RED-S and carbohydrate consumption

Relative Energy Deficiency in Sport (RED-S) has become a common nutrition concern among athletes and sports dietitians over the last few years, and nutrition experts and sports physiologists have been working to learn more about the condition and its causes. Recently, sports nutrition researcher Louise Burke revealed that RED-S is not simply caused by a lack of overall energy, but specifically by a lack of carbohydrates in athletes’ diets.

RED-S and energy availability

Until now, most nutrition experts agreed that RED-S was caused exclusively by low energy availability (i.e. a lack of calories). In other words, if an athlete’s overall calorie intake does not match their calorie output, they’ll be at risk for developing RED-S, and their performance and health will suffer.

While this isn’t entirely wrong, Burke’s research reveals that it isn’t entirely right, either. According to her findings, athletes who consume enough calories but don’t consume enough carbohydrates are still at risk for the condition.

The study

The goal of Burke’s study, published in the journal Medicine and Science in Sports and Exercise, was to understand how a short-term, low carbohydrate/high fat (LCHF) diet and a low-energy-availability diet affected endurance athletes’ immune, inflammatory and iron-regulatory responses to exercise.

To do this, she recruited 28 elite male race walkers and had them complete two, six-day diet and training phases. The first phase was a baseline phase, in which all athletes consumed a high-carbohydrate, high-energy-availability diet. In other words, they ate adequate calories and carbohydrates to fuel their training.

In the second phase, athletes were split into three groups. One group continued to follow a high-carb, high-calorie diet, the other followed an LCHF diet, and the other followed a low-energy-availability diet. During both phases, athletes completed a 25K race walk, walking at about 75 per cent of their VO2 max. Burke and her team collected blood samples before and after exercise during both phases to measure immune, inflammatory and iron markers.

The results

Although the phases were very short, Burke and her team could already see the negative effects of an LCHF diet on athletes’ iron levels, immune and stress responses to exercise. In contrast, they didn’t see any notable changes to the athletes health who followed the other two protocols, even those who followed a low-energy-availability diet.

This led Burke to the conclusion that “short-term restriction of CHO (carbohydrates), rather than energy, may have greater negative impacts on athlete health.” In other words, if you consume enough total calories but that number comes predominantly from another source (like fat), you’re still at risk for developing RED-S.

This is yet another addition to the ever-growing list of reasons why runners should not restrict carbohydrate intake. If you’re concerned about both your health and performance, make sure you’re eating enough carbohydrates to fuel your training. If you’re not sure what an adequate amount of carbohydrates looks like, talk to a sports dietitian, who can help you understand what a healthy diet looks like for you.