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5 Undereating Effects On Your Workouts

I would say about 75-80% of the clients that come to me for sports nutrition are underfueling, or not eating enough for their workouts.

And it’s not always intentional. Running a lot of miles requires eating a lot of food. 

Most people don’t know what an adequate amount of food looks like because diet culture isn’t showing them that.

What is Diet Culture?

First, let’s review, what is diet culture?

Essentially, diet culture is the food environment we live in. There are messages coming at us constantly about foods being “good” or “bad” (foods have no moral value), foods being “fattening” or “too high in sugar.”

All of these thoughts and terms have created a fear-mongering and food police of food, and we’ve forgotten how to eat normally or enjoy our food and make peace with food.

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intuitive eating ebook

Instead, the culture is showing small portions, empty plates, mostly fruit and veggies, no sugar, low carbohydrate diets, etc.

So, as a result, people have come to think that this is all normal when in reality it’s far from normal eating

This is one reason why I created the ebook, The Runners Guide to Intuitive Eating. I want you to learn how to fuel adequately for your sport!

I used to share a day of meals on the blog, but I’ve moved away from that because I don’t want my day to be compared to your day of meals. They may look very different.

Occasionally, though, I’ll post meals I’ve eaten recently as a meal inspiration post, but it’s not meant to compare and generally, the post isn’t limited to just things I ate that day. 

What Happens If You Underfuel Your Workouts?

Underfueling your workouts, both consciously (through food rules and diet culture) and unconsciously, can lead to a condition known as relative energy deficiency in sport, called RED-S, for short. 

RED-S affects many aspects of health including physiological, emotional, mental, relational and overall health. It also has a devastating impact on athletic performance, leading to an increased risk for injuries, loss of menstruation, cognitive difficulties and more. 

If you’re training for a full or half marathon and you don’t have a marathon nutrition plan in place, you’re in trouble. This can also happen with new runners not understanding needs, which is why I wrote a whole post on sports nutrition for new runners

black running shoes with road ahead | Bucket List Tummy

Undereating Effects and Symptoms

Here are some of the main signs that you may not be eating enough to support your workouts. Maybe all of these apply to you – maybe just a few?

1. You’re Not Recovering

Are you constantly tired and sore from the previous day’s run or workout, or wondering “Why am I not recovering from workouts?”

This is normal after long runs or hard, fast workouts, but shouldn’t be the norm on the regular. Especially if you’re including adequate rest days, your body should be able to recover. 

Not recovering could relate back to poor muscle function and decreased muscle strength, increased injury risk, and a decreased training response. All of these are side effects of undereating. 

Here’s a little bit about nutrition for injury recovery.

avocado and peanut butter toast with eggs on white plate for breakfast

If not, it may be time to evaluate what you’re eating, and also how much you’re training.

Are you engaging in compulsive exercise or are you actually enjoying it?

2. You’re Tired All the Time or Your Sleep is Disturbed

I’m sure you’ve been in the camp wondering, ‘”WHY am I always tired?” I’m sleeping well. Maybe I need to take more vitamins!” 

No, you don’t need more vitamins. You likely need more food. AND you can get vitamins through your food! You may just be overtrained and/or under fueled.

This can translate to a lack of energy when running.

woman bent on knees suffering from stomach pain after running | Bucket List Tummy

The mechanism behind this goes like this. Low blood sugar from undereating can act as a stressor on the body, therefore waking you up. You also won’t sleep well if you feel hungry. 

Studies have linked undereating with a reduction in deep sleep.

Deep sleep is important because that’s when your body is repairing muscle and organs, and helps improve recovery, cognitive function and more.

Undereating also decreases sleep quality, so although you think you may be getting eight hours of sleep, the quality of that sleep is very poor. Energy restriction often leads to fragmented sleep. 

brain with pink and yellow lines coming out of it

This is likely due to the hypometabolic state (aka burning less calories during sleep) that then affects body temperature and sleep patterns (Karklin, 1994.).  

Inadequate sleep will also alter your hunger hormones and affect hunger and fullness levels, cravings, and can also increase the risk of injury, among other things.

There is hope with improving sleep when you regain nutrition, though.

A 2004 study published in the journal, Sleep Medicine, found that at least partial weight restoration resulted in more deep sleep (Lauer, Krieg, 2004). 

We interviewed sleep expert and RD, Amy Bender, on the Nail your Nutrition podcast. It’s worth a listen as she gives great recommendations to improve sleep hygiene and quality.  There’s some great nuggets in here!

infographic for the Runner's Guide to Intuitive Eating

3. You’re Thinking About Food Constantly

Thinking about food is not a sign of food addiction, as diet culture may have you think. Instead, it’s a natural and biological response for survival.

When you’re not getting enough food, of course you will continue to think about it! Our bodies tend to focus on what we don’t have enough of, or what we tell them not to focus on. 

This is why you may crave ice cream more when you tell yourself you can’t have ice cream or it’s off-limits.

Not eating enough will also lead to nutrient deficiencies. Iron deficiency is a big one as iron for runners, especially females, may fall beneath recommendations.

Knowing how much protein athletes need is important too!

woman in yellow tank top looking into open refrigerator to decide what to eat

Think about how you feel when you actually do eat food that makes you feel full.  You probably stop thinking about food until you feel hungry again.

Imagine being chronically hungry – of course, your mind is always thinking about food.

To begin to fix this, I usually have clients on a set eating structure until they are able to relearn some of their own cues for hunger and fullness. 

4. You’re Getting Injured More Often

We often think about stress fractures when we touch on injuries for running. However, it makes sense that there would be a higher risk for injury when you’re restricting or underfueling. 

girl in pink tank top running around track grabbing her hamstring

When losing weight, we never lose just fat – we also lose muscle. Therefore, being in an energy deficient state leads to decreased muscle strength and bone repair, impaired judgment and decreased coordination (which can also increase the risk of injuries), and decreased training response, among other things. 

As you can imagine, under eating and exercise can be dangerous. 

As described in a journal article published in The American Journal of Sports Medicine:

“An energy deficit, defined as an inadequate calorie intake relative to exercise energy expenditure, sustained over a period of weeks or months can lower leptin,e stradiol, and insulin-like growth factor-1 and can increase cortisol. These hormone disruptions can decrease osteoblast activity and increase bone resorption, yielding an imbalance in bone turnover that can in turn, lower the capacity to lay down newly formed bone and reduce the ability to repair microdamage.”

Barrack et. al, 2014
a visual representation of how RED-S can affects physical performance in athletes from the IOC

I love this graphic from the International Olympic Committee for visually seeing how many body functions can be affected. 

5. You Aren’t Menstruating

Another name for this is amenorrhea. There are two types of amenorrhea, and this is specifically referring to secondary amenorrhea, or hypothalamic amenorrhea (HA). 

Let’s review a little bit about why this happens. Amenorrhea = loss of menstruation.

A chronic energy deficit causes the body to start to conserve fuel for critical body processes. If there’s not enough energy coming in, the body essentially has to delegate which processes it will choose to fuel.

Obviously, it chooses to fuel processes that are essential to survival – like the heart pumping, lungs breathing. Having a period is not an essential mechanism for the body to survive. So, simply put, the body does not prioritize menstruation or reproduction. Also, insufficient energy suppresses the release of ovarian hormones.

All of this is controlled by the hypothalamus in the brain, which plays a central role in maintaining body systems. It determines whether it secretes or does not secrete hormones that affect organs and processes, such as reproduction.

One of my favorite easy-to-read resources about this is No Period, Now What.  Nicola Rinaldi also has several resources for understanding this. 

No period Now What book up close

Essentially, high levels of cortisol (stress that can result from undereating) can prevent the hypothalamus from releasing reproductive hormones. 

So, that’s why it’s called hypothalamic amenorrhea. If you google “hypothalamus-pituitary axis,” you can see some visuals as to why these pathways are affected. 

An important point that I like to make here is that HA can happen even when weight is not extremely low. People can be undereating and restricting in a larger body and still have hypothalamic amenorrhea.

I hope this post helps you to understand just how important eating enough is, not only for your sport, but for so many other functions and processes in the body. If you don’t know what “enough” looks like for you, schedule a free consultation with me to see if we’d be a good fit for working together.  


  • Barrack MT, Gibbs JC, De Souza MJ, Williams NI, Nichols JF, Rauh MJ, Nattiv A. Higher incidence of bone stress injuries with increasing female athlete triad-related risk factors: a prospective multisite study of exercising girls and women. Am J Sports Med. 2014 Apr;42(4):949-58. doi: 10.1177/0363546513520295. Epub 2014 Feb 24. PMID: 24567250.
  • Karklin A, Driver HS, Buffenstein R. Restricted energy intake affects nocturnal body temperature and sleep patterns. Am J Clin Nutr. 1994 Feb;59(2):346-9. doi: 10.1093/ajcn/59.2.346. PMID: 8310984.
  • Lauer CJ, Krieg JC. Sleep in eating disorders. Sleep Med Rev. 2004 Apr;8(2):109-18. doi: 10.1016/S1087-0792(02)00122-3. PMID: 15033150.
  • Mountjoy M, Sundgot-Borgen J, Burke L, Ackerman KE, Blauwet C, Constantini N, Lebrun C, Lundy B, Melin A, Meyer N, Sherman R, Tenforde AS, Torstveit MK, Budgett R. International Olympic Committee (IOC) Consensus Statement on Relative Energy Deficiency in Sport (RED-S): 2018 Update. Int J Sport Nutr Exerc Metab. 2018 Jul 1;28(4):316-331. doi: 10.1123/ijsnem.2018-0136. Epub 2018 May 17. PMID: 29771168.

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