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12 Symptoms of Undereating & Underfueling

Have you been feeling like you were hit by a bus after exercising? Struggling to hit PRs or regularly feel you have difficulty recovering from your workout routine? Feel like garbage despite doing “all the right things”? If so, these may all be symptoms of undereating and this post will help you figure out if not eating enough is the primary problem.

Fatigued female runner drinking water due to underfueling.

Training for sport on any level can be a tricky thing. We all want massive strength and performance gains, yet the nutrition is far often out of alignment with those goals. As a culture obsessed with all different forms of diets, we routinely fall victim to the latest dogmatic prescriptions for what, when, and how to eat, MANY of which do not apply to athletes.

The result? The vicious cycle of undereating and overtraining ensues. 

Keep reading, because in this post we will be talking about this silent killer in the world of health and fitness that often goes undetected by even the highest caliber of athletes, consuming a hypocaloric diet. 

Like many of you, we have been there. Training the body into the ground with zero clues about the major uphill battles being fought as a result. Addressing deficits in your nutrition, aka the single most important variable in performance, starts with identifying the top symptoms of undereating.

Physical Signs of Not Eating Enough & Undereating Frequently

To be completely honest, we find more often than not our athletes have become so accustomed to surviving off lower calories that their bodies have practically learned to survive off food to feed an infant! (we do understand now after having kids, proportionally speaking, infants can eat a TON, you know what we mean 😃)

Often there is a brief period of time, we’ll call it the honeymoon period, where performance may improve a bit before a rapid decline in performance takes place. Do not be fooled, this false illusion may send you into a downward spiral of health issues that will manifest slowly but surely as a result of this increasing inflammatory load.  

Am I eating enough?  Let’s help you answer that question by covering the hallmark physical indicators that you’re not eating enough.

1.Low energy

Are you in between morning and afternoon sessions finding the thought of walking up the stairs absolutely impossible? 

Newsflash! Chronically dragging your feet or feeling unmotivated to complete daily tasks of living should NOT be chalked up to “aging” or “not sleeping enough”.

Our bodies rely on the continuous production of ATP, the body’s form of usable energy, to maintain normal biological function, not to mention exercising intensely and other non-exercise calorie expenditure such as cleaning the house or walking up and down stairs throughout the day.

The fatigue may be driven by actually undereating calories OR you may be eating ample calories with a lack of nutrient density. This will may result in micronutrient deficiencies in:

  • Thiamin (vitamin Bl)
  • Riboflavin (vitamin B2)
  • Niacin (vitamin B3)
  • Pantothenic acid (B4
  • Vitamin B6 (pyridoxine)
  • Folate (folic acid or vitamin B9)
  • Vitamin B12 (cobalamin)
  • Biotin (vitamin B7)

You may have heard in the past that B vitamins are our “energy vitamins” and this is because they help convert dietary energy (our protein, fat and carbohydrates from food) into ATP by a series of complex chemical reactions carried out by the mitochondria or “powerhouse” of the cell.

Not eating enough and working out leads to overtraining syndrome, which fatigue is a hallmark sign of.[1]

Related: Why the Standard American Diet Causes Fatigue

2. Lack of menstruation/irregular periods 

Sounds pretty clutch? Nope. Far from it. An irregular or missed menstrual cycle does not get you “off the hook”. Ladies, if you take one thing away from this article, it is this:

Your period is the single most telling sign of your health and the key to your soul.

Our menstrual cycle is truly the absolute best indicator of underlying health. If yours has become irregular or even gone completely MIA, this is a direct reflection of our bodies response to nutrition, lifestyle, exercise, environmental exposures, hormonal imbalance, or underlying health conditions.

Not to mention, you’re losing out on performance benefits since having a regular cycle regulates hormones supportive of building more lean muscle, recovering faster, and pushing with harder intensity.

Considering getting your monthly gift back? Don’t worry, it can be done! Increasing your calorie intake is the first step. 

Related: 7 Chemicals & Foods that Cause Hormonal Imbalance

3. Insatiable hunger

No matter what, how much, or how often you eat, you continue to feel unsatisfied and find yourself opening the fridge every hour without fail! Sound familiar?

While you may be eating frequently, the real question lies in what you’re eating. 

We typically come across two situations causing this symptom: 

  1. Eating like a rabbit: Maybe you’re hyper-focused on “clean-eating”, relying merely on low-calorie, high fibrous fruits and vegetables all day. While the volume may curb your cravings for a few minutes, you’re not effectively producing the proper fullness hormones like leptin that tell the body “okay, stop shoveling in the food!” 
  1. Sugar Fein: Running off bars, pre-packed snacks, or fruit alone all throughout the day? Sugar, sugar, sugar! The physiological response to sugar in your body is one that is reward-driven. In other words, the more we give it, the more it wants, resulting in continuous blood sugar spikes and consequently, insatiable hunger. 

Pro-tip: Give your body a chance to achieve satiety by consuming a balance of protein, healthy fat, and high fiber carbohydrates that are balanced in nutrients and allow the body to achieve satiety.

For example:

  • Instead of having only a banana for your morning snack, top it off with a tablespoon of your favorite nut butter
  • As a replacement for your chocolate granola bar, consider a clean protein bar that’s lower in sugar and balanced in fat and protein. 
  • If you love munching on veggies, great! Dip your cucumbers and carrots in some hummus or guacamole for increased fullness! 

Related: The 13 Cleanest Protein Bars on the Planet

4. Frequent waking during the night

Maybe you fall asleep okay, but the slumber stops there. Every other hour you’re waking, tossing, turning, and lost in ruminating thoughts. 

Glucose is the brain’s number one source of fuel, and if energy is not readily available to support your extremely active brain during the night, waking will occur as the body’s signal that it needs fuel and fast!

While we do not advise slamming a flank steak and passing out, having a nighttime snack 1-2 hours before bed will truly bring you new life (literally) by improving sleep quality and balancing cortisol levels that are likely out of whack from high stress. 

5. “Counting Macros” to a T

Finish eating and already thinking about your next opportunity to eat? We see this symptom often in those counting macronutrients. 

Individuals become hyper-focused on the precise grams of chicken or egg white needed to “hit their protein goal” and while precision has its place, we find many treat their numbers as the holy grail, refusing to diverge from that number despite their body telling them otherwise. 

Many online calculators or nutrition coaching prescribing macros are not tailoring the recommendations to the individual or considering the micronutrients that could be significantly underestimated. 

We see athletes beginning to fear and fight hunger, because they don’t want to use all their macros too early in the day, leaving themselves famished by 4:00pm. Not only is their physical stress at play, the mental and emotional impact of this type of restriction is more offensive to the body than just eating the extra scoop of rice!

For many athletes, these are real-life experiences driving inadequate calorie intake. 

Remember that your body is always giving you valuable data! It’s likely not getting what it needs to support activities of daily living alone, not to mention the energy needed to support the demands of training. 

Pro-tip: Work with a qualified functional dietitian to help you develop a plan for eating sufficient calories with a proper balance of macronutrients at your dedicated meal times. The result? You’ll likely find yourself going a full 3 hours without contemplating biting your arm off! Oh and your training will go through the roof. 

6. No appetite 

It may be hard to imagine you’re not eating enough calories but not hungry. When the diet is unbalanced and metabolism tanks from not eating enough and working out, hunger cues get thrown out of whack. 

A quick overview of our hunger hormones real quick:

Two hormones, leptin and ghrelin play a key role in regulating hunger hormones and body fat. When our cells are hungry, ghrelin is secreted to signal for hunger. We then eat food which decreases ghrelin and increases leptin, our fullness hormone.  

Two scenarios driving the tendency to undereat calories

  1. When the body signals for hunger and it does not receive food, ghrelin is suppressed as the body goes into survival food. The less food consumed, the more the body adapts and the more unregulated our natural hunger signals become.
  1. When it comes to exercise, all practices we preach about “listing to hunger cues” go out the door. This is because of resistance and aerobic training decreasing ghrelin levels and increasing levels of PYY, another hunger suppression hormone.[2] 

The result?! Athletes do not prioritize re-fueling immediately post-training. Many don’t feel hungry and end up missing this critical window of recovery when the muscles are ravenous for nutrients. Overall macronutrient consumption is key, but many athletes are not making up for those much-needed calories and end up undereating because they are fasting after workouts.

As intake increases, hunger hormones will adjust, but know that it will take time to get back up because the body is not used to having so much food in the system. 

Slowly increasing your caloric intake allows digestion to pick up, meaning better delivery of nutrients to muscle, bone and tissue. In other words, your body will begin to run more efficiently- hormones, metabolism and all!

7. Avoiding fat

Abby eating a sponful of nut butter

Skipping out on the nut butters or higher fat meats because “fat makes you fat”? We challenge you to reconsider…

There is a common misconception, particularly among athletes, that eating dietary fat equates to body fat! This could not be further from the truth, regardless of the fact that this macronutrient contains more calories per gram compared to other macronutrients. 

Commercial performance supplements are often marketed as fat-free, low in cholesterol, or “light”, hoping to capture the eyes and minds of vulnerable consumers looking to lean up. Don’t buy it.

Like any functional nutrition approach, we must consider how an individual’s genetic makeup plays a role in how we process particular nutrients, like fat.

For example, about 30% of the population’s cholesterol levels may surge with frequent egg consumption. However, scientists have extensively reviewed the scientific literature and reported that eating eggs has no discernible impact on blood cholesterol levels for approximately 70% of the population.[3]

The importance of dietary fat such as dietary cholesterol cannot be underestimated for athletes, particularly females for making hormones, protecting cells, and absorbing fat soluble vitamins A,D,E,and K.  

Infographic on the importance of cholesterol

Less obvious symptoms of undereating

8. Nagging injuries

Guess what happens when the body isn’t getting enough nutrition from food? It pulls from what it’s got…that being your bones and hard-earned muscle. 

Tissue begins to break down, inflammation increases and muscle cannot effectively repair themselves from repeated stress. The result? A host of recurrent injuries like tendinitis, muscle strains, and stress fractures.

Not only is overall protein and calorie consumption key for preventing recurring injury, but the data surrounding the concept of the importance of increasing protein supplementation for preventing and improving injury in endurance athletes is substantial.[4]

Natural anti-inflammatory supplements can be phenomenal for intermittent soreness or for immediate attention to an acute injury, but should not be used as a bandaid for the bigger issue at play when you’re not eating enough calories. 

Related:

9. No change in body composition or unable to lose weight

Eating to maintain weight means the total calories you eat will support basic functions of health as well as exercise. Many understand that to lose weight, overall calorie balance must be less than the energy expended.

BUT, when the body is chronically undernourished, all bets are off. Let’s say you’re stranded on an island with a backpack of food – You would ration every morsel of food. This is similar to how our body downregulates metabolism to conserve fat stores. Suppressed hunger will also occur as the body downregulates hunger hormones, making you feel a false sensation of satiety. 

Case in point. You’re shooting yourself in the foot by eating less and training more in an effort to lose fat and increase lean muscle because you’re fighting your own body. This is one of the most unexpected symptoms of not eating enough. 

10. Stalled strength gains 

Female crossfit athlete

As mentioned, the body will always prioritize essential functions needed to stay alive like breathing, regulating heart rate, and controlling body temperature over rebuilding muscle. This explains why strength gains are nearly impossible to come by when you’re not eating enough, because your body has neither the power output nor fuel to maximize the stimulus needed for muscle growth.

Also, undereating often results in lower levels of estrogen, which is directly sabotaging your performance at the cellular level. 

Estrogen actually affects musculoskeletal performance by facilitating regenerating muscle tissue, meaning that you’re not reaping the benefits of even your hardest sessions. 

11. Frequent illness

Can’t seem to fight that lingering cold or always dealing with repeat sinus infections? Maybe you find yourself sick more frequently and for longer than your teammates or family. Eating too few calories can lead to deficiencies in the antioxidants and micronutrients responsible for fighting these illnesses and supporting the immune system. 

For example, vitamin A and zinc regulate cell division and are crucial for a successful proliferative immune response.[5]

Combat this by eating a wide variety of fruits and vegetables along with your potatoes and chicken! If you’re hitting 3 different colors on your plate at mealtimes, you’re truly excelling in this department!

12. Caffeine Dependence

Waking up unrefreshed despite a long-night of sleep? If you’re that person who cannot entertain the thought of speaking to another human being or embarking on your daily tasks without throwing back your first cup of joe, we have a major problem.

As you may know, caffeine is an excitatory chemical that blocks our body’s sleep-promoting chemical, adenosine The result is a magical jolt of wakefulness and alertness that strategically masks your low-grade chronic fatigue, and the more we drink, the more we depend on it. 

Our challenge for you is to eliminate this morning glory for a solid two weeks without changing your diet. How do you feel? Sluggish and sickly? 

If so, this is a glaring indication that you need to look at your total intake to ensure you’re not undereating. While we all love that extra pep in our step from a dose of caffeine, it should be just that, not a means of staying afloat day in and day out. 

Infographic on the 12 signs of undereating.

What Happens if You Don’t Eat Enough Calories

Fertility issues

When you’re not eating enough your body begins fighting for life. It will use the food it is getting to maintain general foundations of health. 

Reproducing another human is not quite the priority and the body recognizes that. Our bodies are beyond brilliant and actually shut down reproductive function knowing nutrition status will not be sufficient to support a developing fetus.  

Poor intake of proteins, minerals and vitamins is associated with a reduction in reproductive performance because energy balance is altered in a way that directly reduces ovulatory function in women.[6]

Autoimmunity

When the body is deprived calorically or micronutrient wise, the immune system slowly but surely becomes suppressed eventually causing the body to go rogue. Full-blown autoimmune diseases like rheumatoid arthritis, lupus, celiac disease, inflammatory bowel disease, or type 1 diabetes to name a few have been linked to severe restriction because of changes to the level of the gut microbiota! [7]

Hormone Imbalance

As mentioned, many hormones like estrogen and progesterone, to our gut hormones ghrelin and leptin, and even neurotransmitters like serotonin and dopamine that regulate cognition/mood become disrupted when you’re not eating enough. 

Hormone imbalance is far more common than we acknowledge and manifest in other symptoms such as:

  • Inability to lose weight or improve body composition
  • Loss of menstruation
  • Lack of hunger despite eating a low-calorie diet
  • Painful period cramps
  • Irritability
  • Low sex drive
  • Mood swings 

For more on hormones check out our recent post on the top chemicals and foods that cause hormonal imbalances and our YouTube video on How to Avoid Endocrine Disruptors.

Imparied thyroid function

The thyroid gland controls essentially every function in our body, primarily overall metabolism. Both a lack of overall calories or certain micronutrients create a stressful environment for the body, meaning this beautiful butterfly cannot do its job. Cortisol levels will surge and blunt production of active thyroid hormones needed to regulate metabolism.

Studies show that prolonged calorie restriction causes a substantial reduction of our active thyroid hormone, T3. Over time, a reduction in T3 also causes many other biological functions to take a plunge.[8]

Brittle Hair and Nails

If you haven’t caught on to this theme, undereating for a prolonged duration makes for low levels of protein and vital nutrients like vitamins A, C, E and biotin that are essential for hair and nail growth. Our body is pretty darn amazing, but it just can’t do all things without a little help. 

Many of these nutrients cannot be created in the body without food sources and deficiencies in amino acids, essential fatty acids, and essential vitamins and minerals, can cause hair loss or other changes in hair color or structure.[9]

Muscle loss

Guess what happens when the cells aren’t getting the nutrients needed to support ATP production? They start pulling from what else is available…AKA your hard-earned muscles! 

“But I live on meat and protein powders to build muscle!” While protein intake is vital, particularly for strength-based athletes who are frequently breaking down muscle through weight training, the other macronutrients should not be forgotten. 

We simply cannot build or maintain muscle with solely protein intake. If the other macronutrients, i.e carbohydrates and fat are not consumed in sufficient amounts, muscle stores will be broken down to perform the roles of these macronutrients.

So, are You Eating Enough?

We hope this information was helpful for identifying whether you might be undereating and a few potential consequences of doing so long term. Many symptoms of undereating can go unnoticed, so becoming aware of whether your diet is adequate in fueling for your training and lifestyle is the first step.

Whether it be to improve your health in general or maximize performance, working with a functional dietitian to determine where your body is in terms of current health and what your individual is key!

Change is scary and adding more food into your diet can be incredibly scary. We get it.

But, the effects of not eating enough could be even scarier. Chronic dieting or intentionally/unintentionally undereating can really take a toll, especially if you’re doing it in an effort to meet your training demands. We promise you, it will not help you achieve your goals. If any of these symptoms resonate with you, adding high-quality, nutrient-filled food is an absolute must. 

You can’t expect your body to work with you if you are working against it!

Now, if you’ve challenged yourself to increase your intake yet still experience one or any of the symptoms we discussed today, there is more investigation to do.

You may want to consider reading about how an elimination diet may benefit you or learn about reducing your overall toxic burden by reading on foods that cause hormonal imbalances.

Resources

  1. https://bmcsportsscimedrehabil.biomedcentral.com/articles/10.1186/s13102-019-0132-x
  2. https://www.ncbi.nlm.nih.gov/pubmed/19233179
  3. https://www.ncbi.nlm.nih.gov/pubmed/16340654?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum
  4. https://www.ncbi.nlm.nih.gov/pubmed/28824296 
  5.  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6723551/
  6. https://pubmed.ncbi.nlm.nih.gov/18842772/
  7. https://www.frontiersin.org/articles/10.3389/fendo.2019.00041/full
  8. https://pubmed.ncbi.nlm.nih.gov/16720655/
  9. https://pubmed.ncbi.nlm.nih.gov/23159185/

About The Author

Abby Vichill

Abby is a functionally trained Registered Dietitian. She received her Bachelor of Science from the University of Dayton and completed her Master of Science in Nutrition from Case Western Reserve University, where she is an adjunct instructor. Abby has been an athlete her entire life, but never truly discovered her potential until she dialed in her nutrition from a whole-foods approach. As a high school athlete and into her college career often experienced fatigue, discomfort, and nagging injuries that held her back from excelling despite trying to eat properly. Throughout her functional nutrition education and competitive involvement in the sport of Crossfit, Abby began a more holistic lifestyle, which has significantly improved her performance and overall well-being. Abby enjoys sharing her knowledge of functional sports nutrition to help improve the lives of active individuals.

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Kylene Bogden Sports Nutrition Dietitian

Kylene Bogden Sports Nutrition Dietitian

Kylene Bogden, RDN

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