The Hidden Link Between Energy Availability, Carb Intake, and Bone Stress Injuries
As an endurance athlete, you're no stranger to pushing your body to its limits. Whether you're running marathons, cycling long distances, or swimming in triathlons, your body endures a great deal of physical stress. But what if I told you that inadequate fueling could make one of your most essential structures—your bones—more vulnerable to injury?
In this post, we’re diving into the often-overlooked connection between energy availability, carbohydrate intake, and bone health. If you’ve been battling bone stress injuries or struggling with fatigue, this key player could be the missing piece of the puzzle. Let's break down how energy deficiencies affect your bones and how you can protect them to stay strong and injury-free.
What is Energy Availability, and Why Should You Care?
Energy availability refers to the amount of energy your body has available to perform all of its necessary functions after accounting for the energy you expend during exercise. Simply put, it's the balance between the calories you eat and the calories you burn. When you're in a state of low energy availability, your body doesn't have enough fuel to support all its vital functions—this includes hormone production, bone maintenance, and recovery from training.
As endurance athletes, it’s common to focus on fueling for performance, but if you’re not eating enough to meet your energy needs, you're putting your bones at risk. Even small, chronic energy deficiencies can lead to hormonal disruptions and weaken bone structure over time. This is where the risk of bone stress injuries comes into play.
The Link Between Carbs, Hormones, and Bone Health
Carbohydrates are one of the most important fuel sources for endurance athletes. When consumed, they are broken down into glucose, which fuels both your muscles during exercise and your body’s basic functions. But carbs do more than just fuel your workouts—they also play a crucial role in bone health.
Carbs and Bone Turnover
Bone turnover is a natural process in which old bone is broken down and replaced with new bone. This process is essential for maintaining bone strength and preventing fractures. However, when your body is in a low-energy state due to inadequate caloric or carb intake, your body conserves energy by reducing bone turnover. In other words, your body slows down bone rebuilding to redirect resources elsewhere, making bones more fragile and prone to stress fractures. While eating enough energy is key, if you’re falling short on carbohydrates your bone health can still suffer.
Hormonal Imbalance and Its Impact on Bones
One of the most concerning consequences of low energy availability is hormonal disruption. When your body doesn’t have enough fuel, it produces less of key hormones such as estrogen, testosterone, and IGF-1 (Insulin-like Growth Factor 1)—all of which are critical for maintaining bone density and strength.
For women, low estrogen levels can significantly reduce bone density, increasing the risk of stress fractures. In men, testosterone plays a similar role in protecting bones. Both men and women also rely on IGF-1 to stimulate bone growth and repair. Without enough energy, these hormones become suppressed, making it harder for your bones to rebuild after the wear and tear of endurance training.
The Cortisol Connection
In addition to hormonal suppression, low energy availability causes an increase in cortisol, the body’s stress hormone. While cortisol is essential in short bursts (such as in response to acute stress), chronically elevated cortisol levels contribute to bone breakdown and inhibit bone-building activities. This leaves your bones even more vulnerable to injury and slower to recover.
How to Protect Your Bones and Stay Strong
Now that we understand the risks associated with inadequate fueling, let's explore how you can protect your bones and keep them strong during training. The key is to ensure you're getting enough energy and carbohydrates to support both your performance and bone health.
1. Fuel Properly Before, During, and After Training
Endurance training puts a significant amount of stress on your body, and you need to fuel it accordingly. Training in a fasted state or not eating enough before, during, or after your workouts can lead to energy deficits and increase your risk of bone stress injuries.
Before Training: Have a meal or snack containing carbohydrates, about 1-2 hours before your session. Not sure where to start? Check out this blog on pre-run fueling.
During Training: If you're training for more than an hour, it’s recommended to consume carbohydrates during your workout. Aim for 60-90 grams of carbs per hour for endurance sessions lasting longer than 60 minutes. This could be in the form of sports drinks, gels, or food like bananas or energy bars.
After Training: Refuel with a mix of carbs and protein to help replenish glycogen stores and support muscle recovery. Eating within 30-60 minutes post-workout is ideal.
2. Prioritize Daily Carb Intake
Carbohydrates are the cornerstone of fueling for endurance athletes. Not only do they fuel your muscles, but they also protect your bones by helping maintain hormonal balance. Aim for 3-5 grams of carbs per pound of body weight, depending on your training intensity and duration.
Whole Grains: Oats, quinoa, brown rice, whole wheat pasta and whole wheat breads are excellent choices.
Fruits and Vegetables: Berries, apples, and sweet potatoes are great sources of natural sugars and vitamins.
Dairy: Greek yogurt and milk provide a combination of carbs and protein, making them ideal post-workout snacks.
Legumes and Starchy Vegetables: Beans, lentils, peas, and squash are excellent sources of complex carbohydrates.
Sports Products: Use faster-digesting carbs like sports gels, drinks, or white bread immediately before or during workouts to maintain energy levels.
3. Listen to Your Body
Your body is incredibly intuitive, and it can give you clues when something is wrong. If you're experiencing frequent injuries, persistent fatigue, or irregular menstrual cycles, it could be a sign that you're not fueling enough. These are red flags that you may be in a state of low energy availability and need to reassess your nutrition.
If you notice these signs, it's important to take a step back and focus on restoring energy balance. This might involve adjusting your training load, increasing your calorie intake, or consulting with a sports dietitian to help you develop a fueling strategy that meets your energy needs and supports optimal performance.
Conclusion: Fuel for Bone Health and Performance
Your bones are a critical foundation for your endurance training, and protecting them should be a top priority. By ensuring you're eating enough to meet your energy needs and prioritizing carbohydrate intake, you can support bone turnover, maintain hormonal balance, and reduce your risk of bone stress injuries.
If you're struggling with bone stress injuries or just want to ensure you're fueling properly to stay strong and injury-free, let's talk about strategies to keep you fueled and fracture-free. Book a session with me today to start fueling for success!
PMID References: 35523419, 35869933, 37655940.