Fueling the Finish Line: The Surprising Impact of Low-Carb Diets on Endurance and Bone Health

Introduction

For recreational runners, the journey to better performance often involves experimenting with nutrition to gain an edge. One hot trend in the endurance world is the low-carbohydrate (low-CHO) diet, widely promoted for boosting fat metabolism and energy efficiency. But while these diets may sound promising, emerging research reveals a potential downside: they might also come with unexpected impacts on bone health and injury risk. Let's dive into recent findings that could help you make more informed decisions about fueling for the long run.

Understanding Low-Carb Diets in Endurance Sports

Low-carb diets, especially in endurance sports, have gained traction due to claims of improved metabolic flexibility, allowing the body to utilize fat as a primary energy source. For athletes, this can mean longer-lasting energy without as much reliance on stored carbohydrates (glycogen). Yet, while elite endurance athletes might benefit from a finely-tuned low-carb diet, recreational runners face unique challenges and may need to weigh the risks against the benefits.

Key Findings: Low-Carb Diets and Bone Health

Raleigh’s study sheds light on how common low-CHO dietary practices are among elite endurance athletes, but also highlights a concerning connection between these diets and bone health issues. Here are some of the major takeaways:

Prevalence of Low-CHO and Fasted Training: About 28% of surveyed athletes reported following a low-CHO diet, and 38% engaged in fasted training. Fasted training—exercising on an empty stomach—was associated with a higher rate of bone injuries, with athletes who used this method 1.6 times more likely to suffer from bone injuries than those who didn’t.
Nutrition Knowledge Gaps: Many athletes showed limited understanding of sports nutrition, especially around carbohydrate needs. Raleigh’s study found that athletes often under-consumed carbohydrates and overconsumed protein, potentially leading to energy deficits that impact overall health and recovery.
Impact on Bone Remodeling: The study also examined how the macronutrient content of pre-exercise meals (carb-heavy vs. carb-light) affected bone metabolism markers. Though short-term low-CHO intake didn’t immediately harm bone formation, prolonged low-carb or low-energy diets might lead to long-term bone health issues, particularly stress fractures common in endurance athletes.

Why This Matters for Recreational Runners

For recreational runners, the takeaway is clear: while low-carb diets can be tempting, they come with risks that are particularly relevant if you're not carefully monitoring your nutritional intake or aren’t as equipped as elite athletes to handle intense training on lower carbs.

Here are some tips to maintain a balance:

Consider Carbohydrate Periodization: Rather than going low-carb all the time, balance high-carb days around intense workouts and long runs with lower-carb days during lighter training. This allows you to maximize glycogen stores when needed while still supporting fat adaptation.
Don’t Skimp on Fuel: If you’re doing a long run or intense workout, fuel adequately! Low energy availability (not eating enough to meet your energy expenditure) can harm both performance and bone health.
Keep Learning: Sports nutrition is complex, and the science is evolving. Raleigh’s study emphasizes that a tailored approach, backed by proper guidance, is essential. If you’re interested in a low-carb approach, consult a sports dietitian who can help create a balanced plan tailored to your needs.

The Bottom Line

While low-carb diets may hold potential for endurance athletes, recreational runners should approach them with caution. Raleigh’s research reminds us that bone health and injury risk can be significant factors in long-term running performance. Fuel smartly, listen to your body, and stay informed—so you can keep hitting the road safely and effectively.

Citation

Raleigh, C. (2024) ‘An exploration of low carbohydrate dietary intake in endurance athletes: prevalence, knowledge and the potential effect on bone health and remodelling’, available: https://doi.org/10.34961/researchrepository-ul.27377160.v1.