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Why You Aren’t Losing Weight: The Link Between Undereating and Weight Gain

Yvonne Mahl, MHSC, RDN, LDN, IFNCP

Published in Weight Loss

9 min read

November 16, 2021
December 7, 2023
a person eating a green salad, looking unsatisfied
a person eating a green salad, looking unsatisfied

Have you been trying to shed a few pounds to no avail? Do you find it challenging to manage your weight no matter how much—or how little—you eat? If you’re cutting down on calorie intake and portion sizes and still don’t see the results reflected on your weighing scale, you may be undereating! 

We know that overeating and cutting healthy foods out of our diets can be an issue for weight loss, but undereating is less commonly addressed. One of the signs of undereating is finding that you’re not only not losing body fat, but you may actually be seeing some weight gain. Shocking, right? You may also notice a loss of lean muscle mass. 

So what counts as undereating and can you still gain weight in a calorie deficit? Read on for the answers to these questions, plus expert advice on how you can determine the right caloric intake for you and your weight loss goals.

What is Undereating?

a girl eating a salad
Source: Mikhail Nilov

Undereating refers to the practice of consuming insufficient calories or nutrients to meet your body's basic energy and nutritional needs. People undereat for various reasons, and the motivations can be complex and multifaceted, including factors such as:

  • Intentional caloric restriction for weight loss
  • A lack of access to an adequate food supply
  • Underlying body image concerns or eating disorders
  • Stress and emotional factors
  • Cultural or social influences

Long-term undereating or extended calorie deficits, especially paired with overexercising, can lead to nutritional deficiencies, fatigue, weakness, and other health complications. This can also be the reason some people can't shed the pounds, no matter how hard they try. 

When it comes to weight loss, a certain level of calorie restriction can be helpful. However, a temporary moderate calorie deficit is not the same as undereating. When you consistently undereat, you’re not consuming enough calories or nutrients to sustain your daily metabolic functions, like breathing, digestion, and temperature regulation - among many others. 

Striking a balance between calorie intake and energy expenditure is crucial for maintaining overall well-being and supporting the body's essential functions. Whatever your diet, weight loss, and fitness goals look like, it’s essential to ensure your body gets all the nutrients it needs to function optimally. If you aren’t sure how to do this in a safe, healthy manner, consider working with a registered dietitian or nutritionist for support.

Can You Gain Weight From Not Eating Enough?

If you’re on a weight loss journey and have been eating in a calorie deficit for several weeks or months without seeing any progress, you may find yourself asking, “why am I not losing weight even though I’m not overeating?”

After all, if you’re in a calorie deficit, shouldn’t it help you to lose weight? The answer is yes, and no. While a caloric deficit is typically promoted to support weight loss, reducing calories may not help everyone lose weight. There are many other factors that can affect someone's ability to lose weight, such as:

factors that can hinder weight loss
  • Activity levels
  • Chronic health conditions
  • Genetics
  • Lifestyle habits, including dietary choices

So why might you be gaining weight in a calorie deficit? One of the primary reasons that undereating can lead to weight gain is because consuming too few calories can cause your resting metabolic rate to slow down. This means you may burn fewer calories throughout the day. 

According to findings from researchers Jasper Most and Leanne Maree Redman or the Pennington Biomedical Research Center, a slower metabolic rate that can come as a result of calorie restriction can make it more difficult to lose weight. Working with a qualified nutritionist or healthcare professional to raise your caloric intake, nourish your body adequately, and add appropriate levels of exercise into your lifestyle can help combat these effects.

As with anything else, remember that each person may have a different response to dietary changes, calorie deficits, and changes in activity levels. Before making drastic changes to your food intake, consult a qualified nutritionist or dietitian for personalized guidance. Monitoring how certain foods affect your blood glucose levels with a CGM can also be beneficial before making any changes to your diet. 

What Are The Symptoms of Undereating?

symptoms of undereating

Here are some of the potential symptoms and side effects to look out for if you're worried that you may be undereating. 

Dysregulated Glucose Levels

Although rare in individuals without diabetes, undereating could also cause hypoglycemia or low blood sugar. If you experience dizziness, sweating, or sugar cravings, you may want to consider a blood test to check your glucose levels. Wearing a CGM can also help you determine if your glucose levels are in abnormal ranges throughout the day.

Energy Loss and Chronic Fatigue

Do you feel tired no matter how much you sleep? One of the earliest signs you’re not eating enough is having less energy than usual. Nutrient deficiencies may contribute to fatigue in a variety of ways.

If you undereat for a prolonged period, you can develop chronic fatigue and may begin to notice that even your normal, daily activities are tiring you out. If you are experiencing regular or significant energy dips, consider a visit to your doctor and dietitian for guidance. 

Unhealthy Hair and Nails

Undereating sometimes leads to malnutrition, which can begin to show through physical signs. Your hair and nails rely on protein, healthy fats, and a number of micronutrients to grow strong and healthy. Without enough of those things, your hair may start to lose its shine, and your nails may become brittle or discolored or structurally distorted. As malnutrition intensifies, you may even experience hair loss.

Mood Imbalances

a girl looking distressed in bed
Source: Unsplash

Serotonin, dopamine, and norepinephrine are neurotransmitters in the body that help regulate your mood and cognition. All of these are made in the body from precursor amino acids and require nutrient building blocks for enzyme function. Insufficient nutrient intake may contribute to poor neurotransmitter production and regulation. 

When your glucose levels are too low, which can occur from factors such as undereating, it can also make it difficult for your body’s stress-response regulation. This can cause a cycle of mood swings and irritability. Undereating can quite literally make you “hangry!” 

A Slower Metabolic Rate 

Eating too few calories can cause your metabolic rate to slow down, meaning you may gain weight more easily. Your body requires energy when you walk, work out, think, breathe, just about everything else!

When you deprive your body of the fuel it needs, it will begin to store food and enter a sort of “survival mode.” So even when you exercise, your body will protect the fat that it has stored, and you may not be able to lose the weight you want to lose. 

Food Obsessions and Cravings

During WWII, the University of Minnesota conducted a study showing that people experiencing a prolonged caloric deficit think about food constantly. Known as The Minnesota Starvation Experiment, the test found its subjects became obsessed with food over time.

Undereating for a prolonged period of time can create an unhealthy obsession with food that can put you at risk of developing eating disorders. If you start to notice these feelings, consider consulting a registered dietitian for support in crafting a personalized eating plan.

Muscle Loss

a girl looking skinny
Source: Unsplash

When your body goes too long without the appropriate amount of calories it needs to function, it can stop recognizing the difference between fat and body tissue. It will begin to burn lean body mass for fuel. Muscle loss may also occur simply from lacking adequate nutrients, like protein and vitamin/mineral cofactors, for muscle protein synthesis (MPS).  

Sufficient protein and exercise have shown to help prevent muscle deterioration and preserve lean body mass, so being in an extreme caloric deficit can also be detrimental for things like muscle growth

The Chills

Do you ever reach for a sweater while everyone else is still in a t-shirt? Do you feel unnaturally cold, even on a warm day? This could be due to a lack of nutrients in your diet, which may be because you’re not eating enough.

Thermogenesis is the dissipation of energy in the body, which occurs through heat production. When you don’t ingest enough calories, your body isn’t producing as much energy. So, the next time you feel chilly and can’t explain why, make sure that you’re getting enough to eat so that your body can regulate its temperature.

How to Regain a Healthy Caloric Intake if You’ve Been Undereating

tips to regain caloric intake

Caloric deficits may help many people reach their target weight and achieve their health goals. But as always, remember there’s no one-size-fits-all when it comes to staying healthy. And focusing on calories alone is unlikely to give you sustainable weight loss results. 

You have to make sure that whatever changes you make, you’re eating enough food for your body. The best way to regain a healthy caloric intake while still addressing your dietary and weight loss concerns is to get a nutrition coach (like a registered dietitian or qualified nutritionist) to help with your specific needs. 

Here are some other tips to help you regulate your diet and boost your metabolic rate:

Sleep Well

Sleep is crucial to maintaining a healthy metabolism as well as healthy hormonal levels. As you reintroduce more calories into your diet, make sure you’re forming a regular sleep routine.

Try to create an environment in which you can sleep well through the night. Simple things like keeping the room dark, minimizing technology use, and not eating too close to bedtime can help you sleep better

However, it’s often the case that your poor sleep is influenced by what you are (or aren’t) eating. Your diet can have a big impact on your sleep. Sometimes that means that making the necessary healthier changes in your diet can help you naturally improve your sleep more over time. 

Track Your Blood Glucose Levels

the nutrisense app and a coffee

Does reintroducing an adequate amount of calories, protein, carbohydrates, and fats into your diet sound too intimidating if you still have weight loss in mind? Do you find it difficult to balance healthy eating with your goals? One helpful tool for additional metabolic insights can be a CGM.

CGMs track your blood glucose levels in real-time. So, when you eat and exercise, you have trackable data to see what foods and activities your body responds well to. This can help you get back on track in a way that keeps you in the driver’s seat when it comes to your health and weight loss goals.

CGMs are not weight loss devices and achieving balanced glucose levels isn’t all that you’ll want to focus on in your weight loss journey. However, obesity and insulin resistance have close ties and understanding how your body’s glucose levels respond to your current habits may be one additional bit of useful insight along your weight loss journey.  

Eat Smaller Meals More Frequently 

As your body readjusts to having a healthy caloric intake, eating small meals throughout the day can keep your glucose levels stable. It can also help your body understand that you’re no longer in “survival mode" and make it feel more manageable to reintroduce extra calories if you’re worried about increasing your food intake. Prioritizing protein with these small meals is very important!  

Introduce Gentle, Frequent Movement to Tolerance

If you are struggling with chronic fatigue, this may be something to hold off on until you are feeling stronger and have begun more foundational repair work with your nutrient intake. Pushing your body harder with exercise in the face of inadequate nutrition can spell disaster for your health. 

However, there is a time when some gentle movement to individual tolerance can help your body grow stronger, including improving lean muscle mass growth. If you’re looking for a way to tailor your fitness approach to your unique needs, consider working with a sports dietitian who can help you understand how to properly fuel your body and workouts for best results. 

Get Advice From a Personal Nutritionist

chat with a nutrisense nutritionist

Sometimes we all need a little extra help and encouragement to reach our health goals. A personal nutritionist can help you do a deeper nutrition assessment, understand your metabolic needs, and even help interpret glucose data if you’re using a CGM. An expert you can trust, like a Nutrisense nutritionist, can help you meet your weight loss goals by creating sustainable healthy eating practices. 

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Engage with Your Blood Glucose Levels with Nutrisense

Your blood sugar levels can significantly impact how your body feels and functions. That’s why stable blood glucose levels can be an important factor in supporting overall wellbeing.

With Nutrisense, you’ll be able to track your blood glucose levels over time using a CGM, so you can make lifestyle choices that support healthy living.

When you join the Nutrisense CGM program, our team of credentialed dietitians and nutritionists are available for additional support and guidance to help you reach your goals.

Ready to take the first step? Start with our quiz to see how Nutrisense can support your health.

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Kara Collier, RDN, LDN, CNSC

Reviewed by: Kara Collier, RDN, LDN, CNSC

Kara Collier is the co-founder and VP of Health at Nutrisense, one of America’s fastest-growing wellness-tech startups, where she leads the health team. She is a Forbes 30 under 30 recipient, frequent podcast guest & conference speaker.