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How do I know if I'm underfueling my running?

Feb 07, 2024

Are you feeling tired, moody, performing poorly, or lacking motivation in your running? It's time to check your fuel intake! For various reasons, many runners sometimes underfuel themselves. Keep reading to discover the consequences of underfueling, symptoms to watch out for, and strategies to become a properly fueled runner who can achieve optimal performance.

What is underfueling?

Underfueling exercise refers to inadequate nutritional intake prior to and during the activity. This term also encompasses low energy availability, which occurs when the amount of calories or kilojoules consumed is not enough to meet daily energy requirements for both living and training. Prolonged low energy availability can lead to Relative Energy Deficiency in Sport (RED-S), which can cause declining athletic performance and negative health outcomes. Often, underfueling is a result of insufficient energy intake due to lack of carbohydrates.

The consequences of underfueling can have both short-term and long-term negative effects on training response, capacity, and health. It can lead to fatigue, inhibit recovery, and affect performance outside of exercise. Additionally, it can suppress metabolism, reduce bone density, and increase the risk of psychological and health issues, such as depression, gut dysfunction and respiratory tract infections. Athletes experiencing low energy availability are more prone to stress fractures and illness-related missed training days. Forty percent of athletic and recreationally active females are at risk of low energy availability, and distance runners are particularly vulnerable due to a variety of reasons, including:

  • failing to increase calorie intake with increased or hard training loads
  • poor appetite after hard and long training sessions
  • trying to lose weight during high training loads
  • restricted intake due to gut symptoms during running such as nausea or diarrhoea
  • excessive focus on weight and body fat by coaches and media
  • disordered eating behaviours in yourself or your training group
  • inadequate food availability due to poor meal planning and lack of time
  • diets high in fibre and low in energy density
  • a lack of knowledge about nutritional requirements

What are the symptoms of underfueling?

The symptoms of underfueling can range from transient poor performance and fatigue, through to serious long-term health consequences such as bone injuries and poor mental health. If you notice any of the following symptoms in yourself, it’s time for a fuel check!

  • Reduced training capacity
  • Loss of muscle and strength
  • Repeated injury or illness, particularly upper respiratory tract infections
  • Delayed or prolonged recovery times
  • Change in mood, e.g. depression, anxiety, irritability, poor stress management
  • Failure to lose weight
  • Reduced or low bone density
  • Reduced libido (sex drive)
  • Cessation or disruption of menstrual cycle
  • Excessive fatigue
  • Changes in appetite, either constantly hungry or lack of interest in food
  • Reduced sleep quality, e.g. difficulty falling asleep and/or staying asleep, not waking feeling rested
  • Gut dysfunction, e.g. constipation, diarrhoea, frequent bloating and/or gut discomfort

How do I avoid underfueling?

To avoid underfueling, consuming enough calories to meet your body's energy needs is crucial. It is important to follow a balanced diet including enough carbohydrates, protein, and healthy fats. Your daily calorie and nutrient needs depend on factors like age, sex, weight, height, and activity level. Dropping your energy intake below your resting metabolic rate (typically 1400-1800 kcal/day for most runners) is not recommended. Runners with high training loads may require as much as 4000kcal/day. Working with an Accredited Sports Dietitian can help determine the right calorie intake and macronutrient balance for you.

To boost energy intake you can increase portion sizes, add mid-meal snacks, and focus on fueling before, during, and after training. Aim to include carbohydrate and protein-rich foods at main meals and at least 1-2 snacks per day. Healthy fats such as extra virgin olive oil, avocado, nuts, and seeds, and oily fish like salmon provide long-lasting energy and are essential for overall health.

Allowing enough recovery time between exercise sessions and getting at least 8 hours of sleep per night can also prevent underfueling. It's important to monitor how you feel throughout the day and during exercise to ensure you're on track. Improvements in symptoms can often be noticed within a few weeks of following these guidelines.


There are many reasons why runners may underfuel, which can lead to symptoms such as decreased training capacity, more frequent injury or illness, mood swings, poor sleep quality, and even changes in menstrual cycle. To ensure that you are consuming enough calories to meet your body's requirements, work with an Accredited Sports Dietitian who can advise you on the right balance of macronutrients for your needs. Lastly, don't forget to take care of yourself. Get plenty of sleep, take breaks between workouts, and check in with yourself often. With a little love and fuel, you'll be crushing your runs and feeling your best in no time!

Book your FREE Performance Strategy Call here to explore your goals and the EXACT steps needed so you can perform at your best!


Coyle EF 1994, 'Nutrition for distance athletes'. In: Wilmore JH, Costill DL, Kenney WL, eds. Physiology of Sport and Exercise. 3rd ed. Champaign, Ill: Human Kinetics, pp. 445-461.

Logue DM et al 2019, 'Screening for risk of LEA in athletic and recreationally active females in Ireland', Eur J Sports Science, vol. 19, iss. 1, pp. 112-122.

Melin K et al 2019, 'Energy Availability in Athletics: Health, Performance and Physique', Int J Sport Nutr Exerc Metab, vol. 29, iss. 2, pp.152-164.

Mountjoy et al 2018, 'IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update', Br J Sports Med, vol. 52, iss. 11, pp.687-697.

Thomas DT, Erdman KA, Burke LM 2016, 'Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance'. J Acad Nutr Diet, vol.116, iss. 3, pp. 501-28. doi: 10.1016/j.jand.2015.12.006. PMID: 26920240.

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