Symptoms of undereating: What happens when you don’t eat enough
Do you often feel like you’ve been "hit by a bus?” Struggling to get a good night’s sleep? Not seeing the progress you want in your training? These could all be early signs that you’re not eating enough.
Calories from food fuel every function of your body, from essential processes like breathing to the energy needed for playing sports. It makes sense that a lack of calories will interfere with how your body functions.
Undereating doesn’t always mean you’re deliberately cutting calories. It can result from misunderstandings about your energy needs, loss of appetite, or high energy expenditure from intense exercise that outpaces your intuitive eating habits. Additionally, it’s normal for appetite to be suppressed after exercise. For someone who trains regularly or trains before regularly-scheduled meals, this could contribute to missed meals and unintentional undereating.
Eight signs and symptoms of undereating
Undereating is much more common than people think, especially in active populations. The following are signs that someone may not be eating enough food, though keep in mind that each sign can have other causes, too.
Fatigue. Because food is the only source of energy for the human body, it makes sense that someone might feel fatigued or lethargic when not eating enough food. This person may find that no amount of sleep alleviates their fatigue. They may also find it difficult to focus on tasks at work or simply lack motivation to exercise.
Constipation and other digestive issues. In order to have healthy and firm bowel movements, there must be enough food – and fiber – to create “bulk” in the stool. Someone who doesn’t eat enough food may not have daily bowel movements, or the bowel movements may feel incomplete. Other symptoms that may occur from undereating include diarrhea, nausea, bloating, and loss of appetite.
Dizziness and lightheadedness. Studies show that women with low energy availability may experience low blood pressure, especially when standing after sitting or lying down. Dizziness can also happen because of low blood sugar from a low calorie or carbohydrate intake.
Missing or irregular menstrual cycles. The prevalence of menstrual cycle disorders is higher for women in sports compared to the general population. In 2022, a study discovered that as many as 61% of female athletes experience issues with their menstrual cycle. Periods can disappear when the hypothalamic-pituitary-ovarian (HPO) axis is suppressed due to undereating, over-exercising, and/or stress in a condition known as functional hypothalamic amenorrhea (FHA). While it may feel convenient to not have a period, the resulting low estrogen can lead to serious complications for bone and heart health, contribute to mood disorders, and cause infertility. More immediately, low estrogen can cause hot flashes and night sweats.
It's important to know that periods don’t have to disappear overnight to be an issue. Oftentimes, periods become irregular over time before disappearing altogether. This means that being aware of changes in the menstrual cycle – including period frequency and length – creates an opportunity to prevent FHA before it happens.
Poor sleep quality. Individuals who have low energy availability tend to suffer from poor sleep quality. They may also find it difficult to fall or stay asleep, and they may wake up hungry in the middle of the night. If someone suddenly finds that sleep is more difficult after increasing training, then diet is a great place to start.
Training plateaus and poor recovery. The human body needs calories to recover from and adapt to exercise. Without it, someone may feel like they lack strength and endurance, fail to progress in training (plateau), and experience excessive or long-lasting muscle soreness. Muscle may be more sore than usual for someone who is new to exercise or starting a new exercise program, but in general, muscle soreness should not interfere with daily life functions. In addition to plateaus, someone who does not eat enough food may be more susceptible to injuries.
Unrelenting thoughts of food and sugar cravings. Those who feel like they can never stop thinking about food or have strong sugar cravings might want to take a look at their overall energy intake! Thinking of food is an early hunger signal, and it’s good to check in with yourself when this happens. Sugar cravings can also signal that someone needs carbohydrates in particular. Of course, sometimes we just want a sugary snack, and that’s okay, too.
Feeling out of control around food at night. Feeling out of control around food at night is a strong signal that you could be restricting during the day. This is similar to the unrelenting thoughts of food mentioned above. Most people are taught to ignore hunger signals or even stay a little hungry, but it’s great to challenge these beliefs and learn to listen to your body.
Iron deficiency and undereating
Low iron status can create symptoms similar to those of undereating even if a person is eating enough calories. Symptoms of iron deficiency include fatigue, headaches, dizziness, and decreased exercise tolerance. Menstruating women, pregnant women (or women who were recently pregnant), vegetarians, and endurance athletes may be more susceptible to iron deficiency. It’s extremely important to test iron levels before supplementing as excess iron can be harmful.
What is REDS?
Unfortunately, undereating can have negative consequences, and it can lead to a condition known as relative energy deficiency in sport (REDS), which refers to the negative health consequences resulting from “low energy availability.” Low energy availability happens when an individual doesn’t eat enough food to support the physiological functions that maintain health and performance. While low energy availability may be tolerated for short periods and not all cases of undereating progress to REDS, it’s important to realize that chronic undereating is a detriment to your health and performance.
REDS vs. the Female Athlete Triad
REDS is essentially an updated version of the Female Athlete Triad. Compared to the Female Athlete Triad, REDS is not gender-specific, and it expands to complications beyond menstrual dysfunction and bone health including other hormonal effects, cardiovascular issues, immune system disturbances, gastrointestinal issues, and more.
Low carbohydrate availability
Low carbohydrate availability describes a low carbohydrate intake before, during, and/or after exercise. It can occur alongside low energy availability, and it can also amplify the negative health effects of REDS.
What’s the difference between over-training and undereating?
Over-training and undereating share symptoms like fatigue and under-performance, and both have the potential to be diagnosed as over-training syndrome (OTS) or REDS. Because REDS and OTS present similarly and both conditions are diagnosed upon exclusion of other factors, it can be difficult to differentiate between the two. Indeed, symptoms of training overload or even diagnosis with OTS could stem from poor recovery due to undereating and low energy availability. Because of this, it’s important to take a holistic approach and consider all areas of a person’s life, including calorie and carbohydrate intake, training load, sleep, and stress.
Hormonal changes in women from undereating
Though both males and females can be impacted by REDS, females tend to be more sensitive to low energy availability and may experience hormonal changes as a result.
Hormones that tend to decrease in low energy availability include:
· Estrogen
· Progesterone
· Luteinizing hormone
· T3 (active thyroid hormone)
Hormones that tend to increase in low energy availability:
· T4 (inactive thyroid hormone)
· Cortisol
Because hormones like estrogen and luteinizing hormone fluctuate even as they gradually decrease from undereating, it can be difficult to catch low levels if a hormone happens to surge when testing.
In men, low energy availability can result in low testosterone levels. Low testosterone symptoms in men include reduced muscle mass, poor physical performance, reduced libido, erectile dysfunction, decreased energy, depressed mood, difficulty concentrating, difficulty sleeping, and increased body fat. Finally, both men and women may have low insulin levels.
If someone is experiencing the above hormonal changes or one or more of the signs of undereating, they may want to consider if they’re eating enough food to support their active lifestyle. “Red flag” habits for undereating include intermittent fasting, restricting carbohydrates, restricting any food without medical or cultural necessity, and even a “clean eating” mindset, which often translates to a focus on low calorie foods.
What to do if you think you might be undereating
If you suspect that you might be undereating – even if you don’t yet feel the health effects – it's essential to take action to support your health and performance. Begin by seeking support from a qualified healthcare professional, Certified Nutrition Specialist (CNS), or Registered Dietitian (RD) who specializes in working with athletes. When you meet with a nutrition expert, you can explore your eating habits, address any underlying issues, and develop a customized plan to ensure you’re eating enough to support your body and active lifestyle. Remember, it’s never too early to seek help!
If you need more support in overcoming undereating, I help clients learn to match their nutrition to their training and address many of the health issues from undereating. Here is more information about my background and nutrition counseling services. Always feel free to reach out to see if we’re a good fit to work together!
If you think you may be suffering from an eating disorder, don’t hesitate to reach out for help. The National Eating Disorder Association has resources including a private screening tool and helplines.
Are you an athlete struggling with undereating and want to know how much to eat to support your goals?
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