By Carly Waldman, MS, RD, and Connor Huntoon

I would like to extend my sincere thanks to my intern, Connor, for his exceptional hard work and dedication in researching and compiling this blog.

Get to Know the Guest Author: Connor Huntoon

Connor Huntoon is a junior at West Chester University, working toward a B.S. in Nutrition with the goal of becoming a Registered Dietitian. He is set to graduate in Spring 2026 and is actively gaining hands-on experience both inside and outside of the classroom. Outside of his studies, Connor enjoys hiking, weightlifting, and staying active. After graduation, he plans to pursue a career in sports nutrition, helping athletes optimize their performance and achieve their full potential.

In today's world, diet fads, social media, and misinformation have convinced many people that under-consuming calories is the key to achieving their 'ideal' body. But what if I told you that constantly restricting food could actually do more harm than good? Research shows that undereating is not only harmful but also an unsustainable approach to weight loss and fitness. Yet, countless people fall into this trap, only to end up feeling exhausted, hungry, and frustrated with the process, ultimately leading to a cycle of weight gain and extreme restriction all over again.
Here’s why eating enough calories is essential. In this post, you'll learn about the importance of proper fueling, discover how many calories you actually need, and hopefully feel more confident and empowered to nourish your body in a way that supports your goals and well-being.

What are Calories?

A calorie is simply a unit of measurement for the energy found in food. Your body relies on calories to power essential functions like breathing, circulating blood, and moving throughout the day. In times of illness, your body may even require extra calories to fight off infection and recover properly.

Now, knowing how vital calories are for keeping your body functioning, would you really want to deprive yourself of the energy it needs?

Why are Calories Important?

To perform at our best, our bodies require an adequate intake of calories. When individuals drastically reduce their calorie intake, they put themselves at risk for both short-term and long-term health problems. This underconsumption doesn’t just stress the body physically, but also down to the cellular level by depriving it of essential nutrients, but it also impacts our mental well-being. Over time, this can lead to slowed cognitive function and, surprisingly, even weight gain. Properly fueling your body is crucial for both physical and mental health.

5 Calorie Misconceptions Debunked

Less Food Always Equals Weight Loss:
Undereating can actually slow down your metabolism, making it harder to lose weight in the long run. The body adapts to fewer calories by conserving energy, which can stall progress.

Severe Calorie Deficits Will Work Long-Term:
While extreme calorie restriction may lead to initial weight loss, it often results in fatigue, energy crashes, cravings, and nutrient deficiencies—none of which are sustainable for long-term health.

You Will Not Gain Muscle If You Eat Too Much:
Adequate calorie intake is essential for building or maintaining lean muscle mass. Eating too little can actually lead to muscle atrophy, making it harder to gain strength or size.

Skipping Meals Boosts Fat Burning:
Skipping meals can cause major energy dips throughout the day, disrupting your metabolism and making it harder for your body to burn fat efficiently.

To Lose Weight, You Have to Give Up Your Favorite Foods:
One of the most important things I remind my clients is that balance and control are key. You don’t have to give up the foods you love. In fact, allowing yourself the occasional treat can help you stay on track and prevent feelings of deprivation.

The Power of Social Media & Calories

Social media has a massive influence on how we view nutrition, but unfortunately, it’s also a source of widespread misinformation. With so many conflicting messages, it's crucial to verify the facts before blindly following advice that could harm your health in the long run. In today’s world, unrealistic expectations about body image are all too common, and when influencers promote myths about calories and dieting, many people feel compelled to follow suit. A lot of this comes down to a misunderstanding of how calorie consumption really works, leading to confusion and potentially harmful habits.

How Many Calories Should You Consume?

Calorie needs are unique to each person and depend on whether you want to gain, maintain, or lose weight. The five main factors that determine your ideal calorie intake are gender, age, height, weight, and activity level. Each of these plays a role in calculating how many calories your body requires just to maintain its current state. For example, someone who is active will need more calories than someone who leads a sedentary lifestyle. Men generally require more calories than women due to differences in lean muscle mass and metabolism.

To estimate your daily calorie needs, you can start by calculating your Basal Metabolic Rate (BMR), which is the number of calories your body burns at complete rest. Once you know your BMR, you can adjust it based on your activity level using the Total Daily Energy Expenditure (TDEE) formula.

BMR, using the Mifflin-St Jeor Equation:

Men: BMR = 10 x Weight (kg) + 6.25 x Height (cm) - 5 x Age + 5
Women: BMR = 10 x Weight (kg) + 6.25 x Height (cm) - 5 x Age - 161

Adjusting to find your TDEE:

Sedentary (little or no exercise): BMR × 1.2
Lightly active (light exercise/sports 1-3 days/week): BMR × 1.375
Moderately active (moderate exercise/sports 3-5 days/week): BMR × 1.55
Very active (hard exercise/sports 6-7 days/week): BMR × 1.725
Extra active (very hard exercise/physical job): BMR × 1.9

Before placing yourself in any calorie deficit, it’s always a good idea to consult with a dietitian or healthcare professional to ensure you’re meeting your unique needs safely and sustainably.

Here is a link to help you discover how much you need

Cons of Not Consuming Enough Calories

Between busy schedules, diet culture and just not feeling hungry at times, it’s easy to underfuel your body. Getting caught up by skipping meals, or trying to “eat clean”, but just end up restricting yourself too much. Social media makes it always seem like less is better, but often your body will disagree with that opinion. Your body needs energy to function, build muscle and keep you feeling the best. Even stress and medications can change your appetite, but the bottom line is this. If you're feeling tired, out of it, and struggling to hit health goals, it is time to check if you're truly eating enough.

Short-Term Effects of Underconsumption:

Nutrient Deficiencies: When calories are drastically restricted, it becomes much harder to meet your body’s essential nutrient needs. Research shows that people who chronically undereat are more likely to be deficient in key nutrients like vitamin B, iron, and folate, all of which are critical for energy production and overall vitality. Inadequate intake of both macro- and micronutrients can slow metabolism, disrupt sleep, impair cognitive function, and reduce physical performance. Your body depends on these nutrients to function optimally, and without them, everything starts to decline.

Mental Health: Undereating doesn’t just affect the body—it takes a toll on the mind as well. A sharp drop in calorie intake can elevate cortisol levels, the body’s main stress hormone, which can leave you feeling anxious or on edge. Without enough fuel, the brain struggles to regulate stress, often leading to burnout and anxiety. Cognitive functions also begin to slow, making it harder to concentrate, remember information, and think clearly.

Weakened Immune Response: Not getting enough calories not only leaves you feeling tired, but it can also compromise your immune system. When the body is under-fueled, it prioritizes energy use and often deprioritizes immune function. Research from the National Institutes of Health shows that prolonged calorie restriction can impair the body's ability to fight illness or recover from infections. Even if undereating is driven by good intentions or a desire to be healthier, it can actually make you more susceptible to getting sick, staying sick, and feeling chronically run down.

Your body is never working against you, it’s always doing its best to protect and support you. Give it the nourishment it needs to function at its best. Calories are not the enemy; they are fuel that powers your immune system, supports your brain, and builds the foundation for long-term health.

Long-Term Effects of Underconsumption:

Hormonal Issues: Prolonged undereating can significantly disrupt hormone levels, especially in women. Research shows that low-carb and low-calorie diets can throw off estrogen and progesterone balance, often leading to missed periods, mood swings, and even fertility complications. Over time, these imbalances can result in more serious health issues. Men are also affected—chronic calorie restriction has been linked to lower testosterone levels, which can reduce energy, impact mood, and hinder lean muscle maintenance. Fatigue, decreased strength, and difficulty building or preserving muscle often follow. The body interprets restricted caloric intake as a stressor, and hormones are typically the first systems to be impacted.

Muscle Loss: Consistently consuming too few calories can lead to a loss of muscle mass, which negatively affects overall health and physical strength. When your body doesn’t receive enough energy from food, it begins breaking down muscle tissue to meet its energy needs. This results in decreased muscle strength and function. Severe calorie restriction also impairs muscle protein synthesis—the process your body uses to build and repair muscle. Over time, this can increase the risk of injury and reduce your ability to perform physically. To maintain or rebuild muscle mass, it’s important to eat enough protein and calories and engage in regular resistance training.

Slowed Metabolism: Your metabolism relies on adequate fuel to convert food into energy efficiently. When you consistently undereat, your body senses the energy shortage and slows down your metabolic rate to conserve energy—an instinctive survival mechanism. This contradicts the common belief that cutting calories will boost weight loss. In reality, fewer calories are burned at rest, making weight loss more difficult and weight regain more likely. According to experts at the Cleveland Clinic and Harvard Health, severe calorie restriction can also cause muscle breakdown, which further slows metabolism, since muscle tissue burns more calories than fat. Supporting your metabolism with adequate nutrition and consistent movement is key to maintaining a healthy weight and overall vitality.

Nutrient Deficiencies: When you undereat for an extended period, you're not only lacking in calories but also likely falling short on essential nutrients. Deficiencies in vitamin D, B12, and other critical vitamins and minerals can lead to fatigue, weakened bones, impaired concentration, hair loss, and even long-term damage to the heart and nervous system. According to eating disorder specialists, restrictive eating habits often fail to meet basic nutritional needs, even when someone’s weight appears to be “normal.” The best way to support your health is by nourishing your body with adequate energy and a variety of nutrient-dense whole foods. This approach promotes sustainable wellness and realistic, long-term health goals.

Pros of Eating in a Healthy Calorie Range

When you nourish your body properly, you'll start to feel the difference in how you function. Getting enough calories helps maintain steady energy levels throughout the day, meaning no more mid-afternoon crashes after lunch. It also supports a better mood and improved mental clarity by giving your brain the nutrients it needs to stay balanced and focused.

Fueling your body efficiently promotes better metabolic health. Proper nutrition helps regulate blood sugar, cholesterol, and hormone levels, which, over time, reduces the risk of chronic diseases like heart disease and diabetes. On top of that, eating enough calories supports muscle growth and repair, which is important not just for aesthetics but for long-term strength, mobility, and healthy aging. Maintaining lean mass becomes especially important as you get older. The takeaway is simple: eating enough and choosing quality, nutrient-rich foods helps your body thrive, from your brain to your metabolism.

Eating within your optimal calorie range plays a major role in preventing disease and protecting your long-term health. When the body is underfed, it becomes more vulnerable to illness and less capable of functioning efficiently. A balanced diet helps regulate key health markers such as blood pressure, blood sugar, cholesterol, and inflammation, all of which are critical for reducing the risk of chronic conditions. A well-nourished body built on whole, balanced foods is better equipped to manage stress, repair damaged cells, and stay strong and resilient.

How to Spot and Address Calorie Deficiencies

Underconsumption doesn't always come from a strict intention to eat less. It can sneak in through everyday habits like skipping meals due to a packed schedule, not understanding portion sizes, or following a low-calorie trend you saw on Instagram. Simply relying on “healthy” packaged foods can be misleading, too. Many products are labeled as clean, low-fat, or healthy, but more often than not, this is just marketing. These foods may fall short in meeting your body’s actual nutritional needs.

Although these habits may seem harmless in the moment, over time, they can leave you feeling drained, low on energy, and stuck in a cycle of under-fueling. The first step to correcting this is awareness. When you start giving your body enough nourishment, you’ll notice improvements in both energy and mood.

Symptoms of Undereating

Undereating can reveal itself through a wide range of symptoms. While constant hunger and exhaustion are the most common, there are other signs to watch out for:

● Trouble focusing
● Rapid weight loss
● Muscle loss
● Hair thinning
● Mood swings
● Loss of menstrual cycle (in women)
● Weakened immune system

These symptoms are your body’s way of telling you, “I need more calories!” It's important to make sure you're eating enough to maintain or lose weight at a healthy, sustainable pace rather than pushing for rapid weight loss, which can lead to harmful effects.

How to Correct Undereating

If you realize you’ve been undereating, don’t panic. There are simple, manageable steps to get back on track and support your body’s needs. Start by learning basic portion sizes and tracking your intake so you can understand what you're actually eating. Focus on nutrient-dense, calorie-rich foods like nuts, healthy fats, whole grains, and lean to moderate-fat protein sources.

From there, begin building balanced meals that include protein, carbohydrates, and healthy fats. This combination ensures your body has a steady, reliable energy source. Don't shy away from eating more often, either. Adding in snacks and gradually increasing portion sizes over time can make a big impact, without feeling overwhelmed. These small but consistent steps will lead to long-term change and lasting health benefits.

Not sure what “enough” looks like? Your hands are a built-in tool for estimating portions—no scales or measuring cups required. Here’s a quick visual guide:

● Protein (chicken, tofu, fish): the size of your palm
● Carbohydrates (rice, pasta, potatoes): a cupped hand
● Fats (nut butter, oil, avocado): the size of your thumb
● Vegetables: two fistfuls

This method isn’t about being perfect. It’s about giving yourself a simple, intuitive way to build balanced meals without overthinking it. Your body needs all types of nutrients in the right amounts to feel good and function at its best.

Fuel Your Body, Don’t Fight It

At the end of the day, you should never fight against your own body. Your body is something to support and nourish every single day. Eating the right amount of calories isn’t just about losing weight or cutting back drastically. Whether your goal is better health, improved energy, greater fitness, or simply feeling safe and at home in your own body, underconsumption won’t get you there.

There’s a lot of noise in the world: diet trends, influencers, and unrealistic expectations. But real health starts with consistently fueling your body with whole, nourishing foods. Listen to what your body is asking for, and trust science over social media. Never be afraid to seek guidance from a qualified professional.

Eat well, feel strong, and live fully. Let food be your fuel, not your fear.

The Importance of Consuming Enough Calories