8 Signs You Might Be Undereating

True Protein Blog Avatar Fallback reviewed by our Nutrition Team 14 April 2022

While the issue of overeating is discussed frequently, undereating can be just as standard, and the severity of the risks can be on par with that of overeating. Read on for eight signs that you might be undereating.

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8 Signs You Might Be Undereating

While the issue of overeating is discussed frequently, undereating can be just as standard, and the severity of the risks can be on par with that of overeating. Food is fuel, and undereating can have a range of adverse effects on one’s health and wellbeing. Our bodies require food to function correctly, and even more so if we live an active lifestyle and participate in regular exercise. While eating in a calorie deficit is a suitable and effective way to lose weight, severely reducing calorie intake can be dangerous. The human body will start to show signs that something is wrong. Here are eight signs that you might be undereating. 


 1.   Fatigue 

Fatigue and constantly feeling tired are probably the most apparent signs of undereating. We get our energy from the food we consume, and the human body requires a certain amount of calories to function correctly. We need the energy to engage in intense exercise, but our bodies also require calories to complete essential bodily functions such as breathing and digesting food. This is known as your basal metabolic rate (BMR) and requires the largest amount of energy your body expends daily – between 50-80% of your calories. 

The amount of energy our body needs each day depends on many factors, including gender, age, activity level, and body composition. When a person is undereating, it has a drastic effect on energy levels and can result in physical and mental fatigue. This can harm one’s daily functioning and impair their quality of life. Studies have also shown that undereating and high levels of fatigue can lead to poor sporting performance and hurt physical fitness (1). 


2. Weakened immune system 

Undereating and not eating a balanced diet can lead to our bodies not getting the essential nutrients it needs to maintain a healthy immune system and fight off colds and illnesses. It also means that colds may stick around for long as the body is already in a weakened state and doesn't have the strength to fight infections (2).

3. Poor hair, skin and nail health 

When we restrict calorie consumption and, therefore, energy intake, the body uses the small amount of energy it has to fulfil vital bodily functions and neglects other less essential things like maintaining healthy hair, skin and nails. Specific vitamins and minerals are vital for hair, skin and nail health and without a balanced diet, these areas will reflect deficiencies by becoming brittle, dull and dry.


4. Difficulty losing weight 

While undereating may result in a significant decrease in weight quite quickly, this is not sustainable and can negatively affect your health long-term. After an extended period of undereating, the human body goes into energy-conservation mode, storing food as fat if it needs to turn to use it for energy later. This will lead to difficulty losing body fat and improving body composition in the long term. 


5. Constipation / Poor digestion 

Constipation is defined as having three or fewer bowel movements per week. When a person undereats, there is less food in the digestive tract, and therefore less waste is passed. Undereating combined with a poor diet can lead to stools that are hard to pass, slowing the metabolic rate, resulting in constipation.  


6. Difficulty sleeping 

During sleep, the body undertakes various processes to repair the body physically and mentally. Undereating can result in restless sleep and waking up often during the night as the body doesn’t have the resources to undertake repairs. Therefore, instead of feeling well-rested in the morning, you may feel groggy or unrefreshed as the body is unable to complete its nightly restorative processes. 

7. Cold body temperature 

Your body needs to be fueled to maintain an average body temperature. Reducing calorie intake results in a lower level of a particular thyroid hormone responsible for body temperature maintenance (3). If you’re finding yourself constantly cold, it may be time to up your daily cals! 


8. Moodiness / Irritability 

We have all heard the term hangry, but undereating takes it to a whole new level. Studies have shown that prolonged undereating has been linked to increased levels of irritability and moodiness. The brain needs fuel to regulate emotions, so moodiness may indicate that you are undereating. If the most minor things have been irritating you lately, you might want to review your daily calorie intake. 



Although it isn't discussed as often as it should be, undereating is a prominent issue, mainly since social media has contributed to glamorising diets and restrictive eating. If you think you may be undereating or are intrigued to find out how much you should be eating, you should speak to a qualified health professional who will be able to assess your individual needs. 


Fuel up using some products from our Protein Powder or Snack range.


Key Takeaways: 

  • Food is fuel, and eating less than your body requires can have significant adverse effects on your health and wellbeing. 

  • It is essential to know how many calories your body needs as a base level to fulfil basic physiological functions. 

  • Engage a health professional to find out whether you are undereating and are experiencing any of these signs as a result. 



  1. El Ghoch, M., Soave, F., Calugi, S., & Dalle Grave, R. (2013). Eating Disorders, Physical Fitness and Sport Performance: A Systematic Review. Nutrients, 5(12), 5140–5160. https://doi.org/10.3390/nu5125140 

  2. https://journals.co.za/doi/epdf/10.10520/EJC48520 

  3. https://therenegadenp.com/blog/are-you-eating-enough 


IMPORTANT INFORMATION: all content provided here is of a general nature only and is not a substitute for individualised professional medical advice, diagnosis or treatment and reliance should not be placed on it. For personalised medical or nutrition advice, please make an appointment with your doctor, dietitian or qualified health careprofessional.