In our culture, there’s an underlying fear of eating “too much.” This fear has led to the normalization of disordered behaviors that are supposed to prevent that from happening, like fretting over portion sizes and fixating on nutrition labels. This type of restrictive eating tends to be praised, but in reality, undereating is a major issue that carries life-altering and sometimes life-threatening side-effects—but that fact is rarely talked about.

Undereating is a symptom of most eating disorders, but it can also show up in those without an official eating disorder diagnosis. It can stem from a wide variety of causes and triggers, including maladaptive coping mechanisms, feelings of shame and guilt, or simply life circumstances. Recent research shows that undereating is especially prevalent in certain groups, such as athletes experiencing low energy availability (a condition where energy intake does not meet the demands of energy expenditure, leading to an imbalance). Some people may fall into chronic energy deficits unintentionally due to hectic schedules, high levels of physical activity, or naturally low appetites. For others, undereating may be driven by deeper issues, like body image concerns, external pressure from family or coaches to maintain a low weight, or strict internal beliefs about food.

Unfortunately, undereating—and even setting goals to eat less—is often normalized and praised, with little recognition of its negative consequences. Today, we’ll define undereating, identify its health risks, and explore strategies to help you or a loved one stop.

What does it mean to “undereat”?

Undereating happens when you don’t eat enough food to give yourself the calories or essential nutrients—or both—to function properly. “It's essentially a state where your body isn't receiving enough energy and nourishment to support its basic metabolic processes, physical activity, and overall mental and physical health,” explains dietitian Crystal Fox, MS, RDN. Humans require a significant amount of energy daily simply to stay alive, and in fact, the basal metabolic rate (the energy your body uses to maintain basic life-sustaining functions like breathing and cell repairing at rest) accounts for most of it. Then, people use additional energy—generally somewhere around a quarter of calories for a healthy person—for any sort of physical activity, whether it’s structured movement or tasks of daily living. Plus, there’s the thermic effect of food, or the energy it takes to digest and process food, which accounts for around 10 percent of a healthy person’s energy.

Energy and nutrient needs vary from person to person, and depend on several factors like gender, age, activity level, genetics, and body composition. Health status is another factor that impacts energy and nutrient needs. For instance, a person with an eating disorder is often going to have higher energy and nutrient needs than a healthy person. It may help to think of energy needs as different buckets, with some people having more or different buckets than others, depending on their circumstances. For example, a child without an eating disorder has a couple of energy need buckets: one for meeting everyday needs to support proper physiological and cognitive functioning, one for physical activity, and another one for meeting growth and development needs. A child with an eating disorder has all of those buckets along with a third bucket to support eating disorder recovery, which often requires weight gain.

It’s important to note that there are many energy need calculators available online, but these tend to be oversimplified, inaccurate, and a faulty measure of how many calories a person actually requires. They apply a one-size-fits-all formula to something that’s actually much more nuanced and complex than one equation can account for.

Dietitian Erin Kuta MPH, RD explains that undereating can “involve both intentional restriction and unintentional patterns, often influenced by the brain-gut connection,” she says. “For example, stress, overwhelm, and living in survival mode can suppress appetite and blunt hunger cues, making it hard to rely on stomach hunger alone, so I look for other signs like low energy, brain fog, headaches, mood fluctuations, and digestive issues as indicators that the body may not be getting enough nourishment, even if someone doesn’t ‘feel’ hungry.” The best way to determine whether you or your loved one is undereating and assess personal energy needs is to work with a registered dietitian who can help you both understand and meet them.

The health risks of undereating

People with and without eating disorders can experience the harmful side effects of undereating. When you don’t eat enough, it can negatively impact mental, emotional, and physical health in a number of significant ways, including:

Emotional dysregulation

Undereating can contribute to anxiety and depression due to brain chemistry changes and nutrient deficiencies. In fact, research shows low levels of B vitamins, Vitamin D, magnesium, zinc, selenium, iron, calcium, and omega-3 fatty acids can have a significant impact on the brain and nervous system, leading to depressive symptoms. Undereating can also reduce dopamine and serotonin production, making emotional regulation even harder. In my work as a dietitian, clients often report feeling more irritable, emotionally reactive, and less resilient when undereating.

Food obsession and cognitive issues

Many of my clients say they feel obsessed with food—but in reality this is not an innate “food obsession,” but the body’s survival instinct kicking in because it isn’t getting enough to eat. In the landmark study known as the Minnesota Starvation Experiment, men who were intentionally underfed became fixated on food and experienced poor concentration, slower learning, impaired judgment, and intense preoccupation with food. Additionally, one 2021 meta-analysis on anorexia shows undereating can also make daily tasks harder, contribute to brain fog, and is linked to memory issues.

Personality changes

Undereating can cause major personality shifts, showing up in ways like emotional instability, low energy, mental rigidity, social isolation, and a disconnection from your authentic values and identity. When you're not eating enough, thoughts of food take up most of your mental space, leaving little room for anything else.

Decreased metabolism

Undereating can lower your basal metabolic rate (or the energy your body needs for basic functions). When fuel is low, the body slows down to conserve energy, prioritizing survival over efficiency.

Reproductive issues

Losing your period for over three months—known as amenorrhea—is a common sign of undereating and can lead to serious issues like infertility and osteoporosis. One 2022 research review concluded that low energy availability from undereating can suppress all reproductive hormones. This is because the body conserves calories by prioritizing essential functions and shutting down other processes like reproduction

Nutrient deficiencies and muscle breakdown

Undereating can lead to nutrient deficiencies that cause a range of health issues, such as anemia, hair loss, skin problems, insomnia, bone loss, cold intolerance, and a weakened immune system. It can also slow heart rate, reduce oxygen flow, and increase fatigue, dizziness, and illness risk. Also, when the body lacks energy, it begins breaking down muscle for fuel, leading to muscle loss. Since the heart is a muscle, chronic undereating can weaken it, lower blood pressure and heart rate, and even disrupt heart rhythms, which can be life-threatening.

Digestive problems

Research shows that weight loss and malnutrition from undereating can slow the digestive tract, weakening the muscles in the stomach and intestines and slowing down digestion. This, in turn, can lead to gastrointestinal issues like gastroparesis (or slowed motility of stomach muscles), constipation, reflux, bloating, and diarrhea. Undereating also reduces enzyme production, making it harder to break down food and worsening symptoms. 

Feeling out of control

When you’re underfed, your body works hard to restore balance, which can show up as intense hunger, binge eating, or feeling disconnected from hunger and fullness cues. This can create a frustrating cycle of restriction followed by overeating, often reinforced by guilt and shame.

Lowered immune system

When you undereat, every system is affected, including your immune system. While occasional illness is normal, undereating can suppress immunity, making you more prone to getting sick, slowing recovery, and delaying wound healing. It also leads to deficiencies in key nutrients that support immune function, such as protein, healthy fats, vitamins A, C, and D, and minerals like zinc and selenium.

How to stop undereating

Starting to eat enough food after a period of undereating can be challenging—especially if you have an eating disorder—because there are often several factors at play. However, eating enough food is a necessary and foundational step towards restoring your health and well-being, and with the right tools and support, it’s completely possible. Here are ten expert-backed ways to stop undereating:

Identify the underlying issue

“It’s important to identify the root cause of the undereating and address it accordingly,” Fox says. If you have an eating disorder, undereating likely serves an emotional purpose, such as numbing or indirectly expressing difficult feelings, and is probably driven by intense eating disorder thoughts. If this is the case, it’s best to work with a therapist and dietitian to help you understand what’s driving your food behaviors. Sometimes, it’s not until after you’ve started eating enough food that you can fully understand why you weren’t eating enough.

If you don’t have an eating disorder, perhaps undereating is caused by external factors like an overpacked schedule, appetite-suppressing medication, a condition like attention deficit hyperactivity disorder (ADHD), or a combination of issues.

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Understand that everyone has different needs

As I explained above, energy needs vary from person to person and depend on several factors. “To better fuel your body, you really need to stop listening to all the noise out there of ‘only needing X amount of calories,’ because bodies are individual and each requires different levels of fueling to feel their best,” explains Equip Lead Dietitian Stephanie Kile, MS, RDN. Comparing what’s on your plate to your friend, mother, or sibling may be tempting, but isn’t helpful to getting your unique energy and nutrient needs met.

Eat consistently throughout the day

“Stick to the idea of getting in three full meals and two snacks a day, aiming to have something to eat every three to four hours during waking hours,” Kile suggests (some people may need fewer or more snacks). If you’re not able to get in all meals and snacks yet, start by eating at least something every few hours and work your way towards enough. For example, if you’re not eating breakfast regularly, start with a snack that includes carbohydrates, protein, and fat (like a banana with peanut butter) and then work towards eating a complete breakfast (like having bread and a latte or yogurt with the banana and peanut butter). “Consistency matters more than perfection,” Kuta adds.

Shoot for a relatively balanced plate

First, identify the meal’s carbohydrates, since “most of your intake should be from grain-based carbohydrates, like bread, pasta, and rice, which are the top fuel source your body needs to function optimally,” Kile explains. Then, include a protein source, like meat, beans, or fish. Next, make sure there’s some fat. “This can be in the sauce or dips you add to a meal, butter on bread, the oil you cook with, avocado, nuts, cheese, and so on,” Kile shares. Finally, include some fruits or veggies that you enjoy.

“Making sure to get all of these aspects in your meals and snacks will help to make sure you’re not undereating during the day,” Kile says. “If you’re skipping one of these nutrients, that would most likely cause you to undereat.” Keep in mind that it’s not necessary that every meal is perfectly balanced and that shooting for a relative balance is just fine.

Lean on meal plans or mechanical eating when necessary

After periods of undereating, hunger and fullness cues are often absent or unreliable at first. And if you have an eating disorder, chances are high that your eating disorder thoughts get louder as you start to eat more. If this is the case for you, a meal plan or mechanical eating (or both) could be the best route for now. “Prescriptive meal plans can be a tool to help one begin to learn their needs when they are unable to regulate it naturally,” Fox explains. Mechanical eating, or eating by the clock, is a helpful and often temporary tool to get your body out of an energy deficit and into a regular eating rhythm.

Have back-up meals and snacks

“Keep go-to meals and snacks on hand that feel doable when energy and appetite are low,” Kuta suggests. In my practice, my clients find it helpful to create a list of such meals and snacks, and then make sure they have those items or ingredients stocked in their kitchen (or stashed in a purse or bag when on the go). Some examples of simple back-up meals include peanut butter and jelly sandwiches with a side like chips and salsa or veggies and hummus, or a snack plate of cheese and crackers, grapes, cashews, and turkey or ham slices. Some snack ideas are yogurt with granola or trail mix with peanuts, chocolate and dried cranberries.

Consider logging your food

Sometimes, keeping track of what you eat can be helpful for identifying physical, emotional, or mental barriers to getting your needs met. Many of my clients like to use apps like Recovery Record or Nourishly, while others like to simply jot down their intake and insights in a journal (avoid weight loss- and calorie-focused tracking apps, like MyFitnessPal). However, be mindful about this strategy and pay attention to how it makes you feel—for some people with eating disorders, logging food can cause anxiety and distress.

Check in with yourself

Take a couple of minutes throughout the day to take some inventory of your body and mind. “Check in with your body for signs you might need food, like fatigue, foggy thinking, or irritability, even if traditional hunger isn’t present,” Kuta recommends. Perhaps you are connected to your hunger cues, and you realize you’ve been ignoring them. It can also help to notice what thoughts and beliefs are present when it comes to getting energy needs met, because sometimes societal or familial conditioning can contribute to undereating. “Remember, your body needs nourishment even when you don’t feel hungry, productive, or ‘deserving,’” Kuta adds.

Use tools during and around mealtimes

Whether or not you have an eating disorder, using nervous system regulation tools can help you slow down and feel safe enough to eat enough. “Consider pairing eating with nervous system grounding, like placing your feet firmly on the floor or taking a few slow, deep breaths to minimize overwhelm and support digestion,” Kuta says. If there are mental and emotional barriers at play, bringing coping tools from therapy in and around mealtimes can be helpful. Some examples are self-compassion, challenging black-and-white thinking, and mindfulness.

Work with a registered dietitian

Working with a non-diet dietitian is the best way to have a clear understanding of your body’s nutrient and energy needs, and to help you remove barriers to eating enough food every day. A dietitian will guide you and support you through the process, taking into account your reasons for undereating, medical and health status, and personal preferences. If you have an eating disorder, it’s best to work with an eating disorder trained dietitian as well as a therapist to help tackle emotional and mental challenges that often arise once you’re eating more food.

Eating enough food is an essential action to support your mental, emotional, and physical health and well-being, whether you’re in recovery from an eating disorder or not. Putting a stop to undereating and fully meeting your energy and nutrient needs is often nuanced and challenging, and usually requires professional guidance and support. When you’re ready, reach out to a non-diet dietitian or Equip to help you get there.