DECREASED THYROID OUTPUT
Hormone T3 is the most active thyroid hormone and is responsible for managing blood glucose levels and metabolic function. We also have rT3 (reverse T3) which inhibits the production of T3. When we don't have enough carbs, not only does our T3 production slow down, but rT3 increases and blocks the capacity of the T3. The result is that metabolism slows with the decrease of T3 production, making carbohydrates an important factor for the production of the peripheral metabolism of thyroid hormones.
Thyroid function is not only important for weight loss, but also for overall health and energy levels. Without adequate carb intake, energy levels will plummet and your training will suffer.
INCREASED CORTISOL OUTPUT
Cortisol is our stress response hormone released by the adrenal glands, which sit directly on top of the kidneys. As an important system for our “fight or flight” mode, cortisol is vital for keeping us out of harm's way, as well as playing an important role in blood sugar regulation. As athletes, we put ourselves into a “stressed” state through exercise, which is healthy in certain doses. However, when combined with a low-carb diet, cortisol output increases, leading to HPA-axis dysfunction, commonly referred to as adrenal fatigue. In women, this can lead to hypothalamic amenorrhea.
In conjunction with increased cortisol output, low carbohydrate intake can lead to decreased testosterone levels. Glucose is a precursor for gonadotropin-releasing hormone (GnRH), responsible for triggering the release of testosterone. It’s also important to remember that testosterone is important for everyone regardless of gender, as testosterone gives us the ability to grow our muscles and function actively, as well as promote bone strength. The combination of these two hormones being out of sync leads to negative effects in performance and the ability to recover since carb intake prevents a drop in testosterone levels post-exercise.
When you're exercising, the goal is to typically break down muscle and then rebuild it to build new muscle fibers and strength. When you aren't eating enough carbs, however, your muscles break down and are unable to rebuild themselves. As we mentioned earlier, carbs are required to create glycogen stores in muscles, but in order to build muscle, insulin must be released into the bloodstream to shuttle glucose to cells to replenish those glycogen stores. When your muscles deplete glycogen stores with being replenished, your body is also unable to repair muscle fibers and develop new muscle fibers. The result is a consistent process of breaking down muscles through exercise, without allowing them to rebuild and repair.
HOW TO UTILIZE CARBOHYDRATES AS AN ATHLETE