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The Role of Functional Nutrition in Preventing Overtraining Syndrome & Optimizing Athletic Performance

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The Role of Functional Nutrition in Preventing Overtraining Syndrome & Optimizing Athletic Performance

Anyone looking to improve their physical fitness and athleticism understands how important it is to consider your lifestyle outside of your workout or sport. A hallmark of an athlete - and anyone looking to get stronger, faster, or fitter- is the desire to improve performance and gain a mental edge.

Functional nutrition can be extremely useful to those looking to take their physical fitness to the next level. Paying attention to nutrition can help improve performance, recovery, and stamina, fueling the body to adjust to training.  


What is Functional Nutrition?

Functional nutrition is a subset of functional medicine that is based on a holistic perspective of the body - physical, spiritual, and emotional - and uses healthy, whole-food nutritional interventions to address the root causes of illness and support optimal gut health. Instead of focusing only on “calories in, calories out,” functional nutrition also pays attention to the micronutrient density of food as well as each person’s lifestyle habits, environment, genetics, stress, and other factors. 

Considering all of these factors allows a functional nutritionist to tailor recommendations to each person’s specific goal. Functional nutrition also emphasizes bio-individuality, meaning that each person has specific needs and specific physiological considerations when it comes to their nutrition and overall health. 

Functional nutrition provides a way to help people understand how their food, environment, stress, and overall lifestyle impact their health status and how they feel and perform. As a result, functional nutrition is a piece of personalized lifestyle medicine that continues to thrive in today's healthcare landscape as more and more people look for health advice tailored to their unique needs.  

Signs of Overtraining Syndrome (OTS) in Athletes

Generally speaking, athletes train to improve performance - to meet higher training loads, run faster, cycle longer, and so on. Overtraining syndrome sometimes referred to as underperformance, can have a variety of signs and symptoms, including: 

  • Depressed mood
  • Fatigue
  • Hormonal changes
  • Poor recovery time
  • Loss of motivation
  • Bradycardia or tachycardia
  • Insomnia
  • Irritability
  • Heavy, sore, stiff muscles
  • Anxiety
  • Brain fog
  • Weight loss and/or muscle loss
  • Amenorrhea in women
  • Decreased physical performance in the sport

Possible Causes of Overtraining Syndrome in Athletes

Overtraining syndrome in athletes is often multifactorial in nature, though there are several possible causes that may contribute to a higher risk of overtraining syndrome.


Adequate hydration plays an important role in athletic performance, recovery, and overall injury prevention for active individuals. This holds true for both endurance athletes as well as strength and power athletes, limiting an athlete’s ability to generate power and keep up with continued physical demand.   

Excess Inflammation and Oxidative Stress

While some inflammation and oxidative stress are desirable for athletes to help with training adaptations and cellular repair, excessive build-up (whether due to inadequate recovery or another reason) can lead to muscle fatigue, soreness, and inhibited performance. In fact, studies of overtrained, underperforming athletes show higher resting rates of oxidative stress markers. 

Alterations to The HPA or HPG Axis 

Hormonal changes have been seen in studies of various endurance athletes, indicating that the hypothalamic-pituitary-adrenal (HPA) and/or the hypothalamic-pituitary-gonadal (HPG) axes may be altered in cases of OTS. Compared to healthy athletes, athletes with OTS symptoms have a less-sensitive HPA axis response to the stress from training, leading to earlier fatigue and poorer glucose regulation during performance. Understanding an athlete's hormone levels can be an important piece in designing a personalized nutrition and recovery plan to help optimize performance.  

Alterations to The Gut Microbiome

In endurance athletes, the gut microbiome may play an important role in regulating oxidative stress and inflammatory response to training, as well as playing an integral role in ensuring adequate nutrient digestion and absorption to meet an athlete’s dietary needs. Ongoing stress can change the composition of the gut microbiome, leading to changes in mood, metabolism, and inflammation that may impact an athlete’s performance.   

Central Fatigue

Athletes experiencing overtraining syndrome often exhibit symptoms such as changed mood, sleep, and behavior. Serotonin plays a role in all three of these areas, so examining serotonin metabolism and that of its precursors can be helpful in identifying biochemical factors contributing to overtraining syndrome. Levels of serotonin precursors have been found to be altered with excessive exercise as well.   

Micronutrient Deficiencies 

Vitamins and minerals are essential for athletic performance and recovery, as these are essential for basic metabolic functions and hormone production and to help with muscle recovery and repair. In particular, zinc, magnesium, iron, and B vitamins are important for athletes to track. Without adequate micronutrient intake to meet the high demands of training, athletes may be at risk for poor recovery and higher inflammation that can lead to underperformance if left unchecked. Understanding levels of these micronutrients can help fine-tune training and recovery needs and guide any supplementation during high training periods. 

Functional Nutrition Labs to Help Improve Athletic Performance

Functional nutrition labs can help identify nutrient deficiencies, electrolyte imbalances, inflammatory markers, and other biomarkers indicative of an athlete's need for personalized nutritional support.   

Comprehensive Metabolic Panel

A metabolic panel evaluates an athlete’s metabolic markers, including electrolytes, blood glucose, protein levels, and liver/kidney function. Ensuring an athlete has a well-functioning metabolism helps bring to light any extra stress on the basic metabolic pathways that can occur due to overtraining or poor recovery.  

Oxidative Stress and Inflammation

Evaluating levels of oxidative stress markers can help identify if an athlete is experiencing excessive oxidative stress load that may be contributing to overtraining syndrome. Additionally, an omega-3 index can provide insight into the state of inflammation of an athlete and can help guide recovery plans to support optimal performance. Omega-3 fat levels are important to help keep inflammation from a high training load at bay and have also been linked to better recovery and lower post-training soreness in athletes.

Neurotransmitter Testing

Assessing levels of neurotransmitters such as serotonin can help provide insight into potential factors leading to some of the mood, sleep, and behavioral changes that can occur in athletes who are underperforming.  

Comprehensive Hormone Testing

Overtraining, particularly in combination with poor recovery and lack of adequate caloric intake, can result in relative energy deficiency in sports, or RED-S, which is characterized by a higher risk for injury, illness, and hormone dysfunction, especially in young female athletes. Understanding sex hormone levels can help reduce the risk of RED-S and ensure an athlete's training, recovery, and nutrition align with their performance goals. 

Thyroid testing is essential for athletes to optimize their performance, as low thyroid function has been linked to reduced exercise capacity and endurance performance. The thyroid is also sensitive to prolonged stress and overtraining, and suboptimal thyroid hormone ranges can indicate a need for better recovery methods. Additionally, chronically elevated cortisol can occur with high levels of training stress (particularly without adequate recovery) and increases an athlete's risk of fatigue, trouble with weight control and maintaining muscle mass, poor sleep, and injury. Testing cortisol is, therefore, also important.

Micronutrient Panel

Vitamins and minerals are essential for athletic performance and recovery, as these micronutrients are essential for basic metabolic functions and hormone production and help muscles recover. In particular, zinc, magnesium, iron, and B vitamins are important for athletes to track.

Comprehensive Gut Microbiome Testing

Since the gut microbiome plays an important role in controlling oxidative stress and inflammation levels in athletes, evaluating the health of the gut microbiome can be beneficial for athletes who are experiencing symptoms of overtraining syndrome. If the gut microbiome and overall gut health are not optimal, it puts an athlete at risk for poor nutrient absorption and stress modulation, both of which can be problematic in cases of OTS.  

Functional Nutrition Approach to Improving Athletic Performance

Using the data from functional blood testing as well as a thorough understanding of a given athlete’s training structure and recovery needs, athletes can bring a layer of precision into their nutrition, recovery needs, and any supplements they may need to optimize their performance. 

Nutrition For Optimal Athletic Performance

A functional nutrition protocol that includes nutrient diversity and plenty of nutrient-dense whole foods and that meets the caloric needs of an athlete’s training load is a central tenet of any holistic plan for optimal athletic performance. Functional nutrition testing can help bring to light any deficiencies in specific micronutrients (such as iron or vitamin D) so that an athlete’s personalized nutrition plan can emphasize their specific needs.

Protein intake is perhaps the most important consideration for athletes, as this macronutrient is essential for muscle repair and recovery (or training adaptation), maintaining muscle mass, and favorable body composition. Inadequate protein intake can lead to a higher risk of injury during training, loss of muscle mass, strength, and power, and an overall decrease in athletic performance - early fatigue or poor endurance. Too little protein may also lead to low iron levels, changes in various steroid hormones, and issues with thyroid function, as protein is essential for the formation of hormones

Generally speaking, athletes require higher amounts of protein than the general population, with some studies suggesting up to 2 grams per kilogram of body weight to support optimal performance. Adequate intake of amino acids, the building blocks of protein, is also essential for neurotransmitter production, meaning too little protein may lead to alteration in mood, sleep, and behavior.  

Optimal carbohydrate intake to maximize performance and power can vary depending on an athlete’s sport and training regimen. A long training day (for example, those typical of Ironman athletes or other endurance sports) may require three times the amount of carbohydrates that a light recovery day may require (often 2-3 grams per kilogram of body weight). Too low of a carbohydrate intake can lead to deficits in muscle strength and power, poor endurance, early fatigue, and fluctuations in blood labs such as cortisol or thyroid hormone levels. Functional nutrition labs, as well as each athlete’s personal preferences, can help a practitioner create a plan that includes specific carbohydrates rich in various vitamins and minerals to ensure an athlete’s nutritional supply is meeting the demands of their sport.

Last, adequate fat intake is also paramount for athletic performance, especially due to the impact of dietary fat on inflammation and hormone production. Moderate fat intake has been linked to more ideal testosterone levels, while an emphasis on omega-3 fats can help reduce inflammation and support recovery. For those athletes who need to cut their body fat percentage quite low for their sport, supplementation with omega-3 fats can help them achieve the aforementioned benefits.

Supplements and Herbs That Help With Athletic Performance 

Supplements are used by 40-59% of athletes, depending on their specific sport, competition level, and recovery needs. By using functional medicine blood testing as a part of an athletic training program, an athlete can gain personalized insight into what supplements may be needed to support their training and performance goals.  

It should be noted that some supplements can negatively impact post-training adaptations - for example, high doses of antioxidant supplements such as vitamin C or E can impact levels of muscle damage that are actually favorable for certain sports, such as bodybuilding. Ultimately a food-first approach to performance nutrition, with supplementation guided by blood work, is the most evidence-led approach for most athletes.  

Below are a few common supplements that may help athletes improve performance and recovery, decreasing their risk of overtraining syndrome.


Athletes commonly use electrolytes to help stave off dehydration. Electrolytes can help to maintain total body water, as even mild dehydration deficits will increase cardiovascular strain and limit aerobic performance. Consuming electrolytes pre, during, and post-training have been linked to better retention of minerals like sodium, calcium, and magnesium as compared to plain water or caffeinated sports drinks, helping ensure not just better athletic performance but better recovery as well.

Omega-3 Fish Oil

Omega-3 fat levels are important to help keep inflammation from a high training load at bay and have also been linked to better recovery and lower post-training soreness in athletes. Studies have shown that athletes using fish oil supplementation have also experienced positive effects on cognition and have had lower inflammation overall.

Supplemental Protein

While total calorie intake and protein intake in the long term plays the most crucial dietary role in facilitating adaptations needed for optimal athletic performance, protein supplementation pre- and post-workout is useful to optimize physical performance and positively impacts the recovery process for both resistance training and endurance sports. With the use of supplemental protein such as whey protein, studies show there can be a significant rise in muscle protein synthesis and an increase in levels of essential amino acids and branched-chain amino acids, driving more fuel to the muscles that have been working hard.  



Functional nutrition can provide another layer of personalization to an athlete's training, nutrition, and recovery plan to help optimize athletic performance. Using functional nutrition testing to understand an athlete’s baseline metabolism and nutrient needs can help guide recommendations, ensuring that an athlete will be meeting the high demands of training for their sport through a well-balanced diet created for their specific needs.

The information provided is not intended to be a substitute for professional medical advice. Always consult with your doctor or other qualified healthcare provider before taking any dietary supplement or making any changes to your diet or exercise routine.
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