10 Ways Restricting Calories Can Be Harmful

by Ahmed Zayed, MD on September 30, 2020
Last updated on May 23, 2021

What is the first thought that comes to your mind when you think of losing weight? Cutting down on calorie consumption, right? Well, you are not the only one. 

10 Ways Restricting Calories Can Be Harmful

Almost everyone thinks that slashing their calorie intake will help them to lose weight immediately. But what you don’t know is low-calorie content isn’t a joke, and it can do a lot of damage to the body. 

Calorie restrictions can lead to many health problems. People try to cut down on fat (1), and carbs which is why they only consume 200-300 calorie meals 3-4 times a day. To avoid carb, they only eat lean proteins, salads, and non-dairy items. They also get rid of fruits from their diet. Some even skip meals to prevent calorie intake, thinking the lesser the intake, the better. 

Well, that is where most people are wrong. We need calories to be alive. Food that contains calories (2) is necessary for the proper functioning of the kidney, heart, lungs, brain, etc. 

In this article, we are going to tell you about the potentially harmful impacts of calorie restriction. By the end of this article, you will know how a calorie deficit diet isn’t right for you. 

But first, learn about our body’s calorie requirement. 

How Much Calorie Does Your Body Need?

Calories are the amount of heat energy required for increasing the temperature of one gram of water by 1 degree centigrade. Nevertheless, we take it as the amount of energy the body gets from the food it consumes. 

The body needs calories to perform adequately. It uses calories to sustain the following three processes:

  • Basal Metabolic Rate (3): It refers to the calories required to sustain regular functions of the brain, heart, kidneys, nervous system, and lungs.
  • Physical Activity (4): It is the number of calories required for powering everyday tasks.
  • Digestion (5): The body uses a specific number of calories for the digestion and metabolism of the food you are consuming. It is also called the food’s thermic effect.

Simply put, consuming more calories (6) will cause you to gain weight, usually in the form of fat. Taking fewer calories causes the body to lose weight. It is the primary reason people resort to a calorie-restrictive diet. 

Restricting Calories Can Be Harmful

While there’s a possibility of you losing weight with calorie restriction, overdoing it can be harmful. Listed below are some reasons why a calorie-restrictive diet might not be good for you.

1. Loss of Nutrients

When you follow a low-calorie diet (7), not only do you limit the number of calories your body needs to perform its regular function, you are also going to deprive the body of essential nutrients. 

A calorie-restrictive diet is going to limit the consumption of other diets too. Let’s take a look at these: 

  • Protein (8): Not having sufficient protein-rich food such as fish, meat, peas, beans, dairy, nuts, and lentils can lead to hair thinning, muscle loss, and even brittle nails. 
  • Biotin and Thiamine (9): Low intake of legumes, whole grains, nuts, dairy, eggs, and seeds can also limit the intake of Vitamin B. Due to this, you can develop weak muscle and scaly skin. It can also cause you to lose hair. 
  • Calcium (10): A diet rich in calcium, including calcium-set tofu, leafy greens, dairy, and fortified milk can reduce bone strength and increase the risk of fractures.
  • Magnesium (11): Not taking magnesium-rich leafy greens, whole grains, and nuts can cause fatigue, muscle cramps, migraines, and unusual heart rhythm. 

All these nutrients are important for the regular functioning of your body. Not getting enough of them will lead to low energy and fatigue.

2. Causes Fatigue

Apart from consuming food low in calories leading to nutrient deficiency (13), not having food for long stretches to reduce calorie intake can decrease your blood sugar level. It will cause a steady drop in your energy level too. 

You might be thinking, how does this happen? Well, your brain and body require calories to function adequately. If you cut them too low, it might be difficult for you to focus. 

So, to feel better and full of energy, you need to make sure your body is getting enough calories. Otherwise, you’ll spend the day lumbering around due to low blood sugar and fatigue.

3. Slows Down Metabolism

This is one of the obvious effects of low-calorie intake. Many studies have shown that eating fewer calories will slow down your metabolism (14). 

People following a low-calorie diet can cut down the number of calories that the body is burning by as much as 23%. What’s more, low metabolism will persist even if you stop with your calorie-restrictive diet. 

According to some researchers, low metabolism is one of the reasons why 80% of people tend to regain weight when they come out of their calorie-restrictive diet regime. 

A calorie-restrictive diet also leads to muscle loss. It initially causes a loss in weight but as soon as you stop; you’ll start regaining weight. 

You will see a loss in muscle mass if you are following a calorie-restrictive diet that runs low in protein and isn’t accompanied by exercise. If you want your weight-loss special diet to not affect your metabolism, you have to ensure that you aren’t eating fewer calories than you need to sustain your body’s BMR. 

Increase your protein intake and add exercise and workout to your regime.

4. Burns Muscle Mass

With a reduced intake of calories, your muscle mass can also fluctuate with your metabolism. Muscle functions to make your move. Thus, they take in a lot of energy. 

According to a study by the University of Mexico (15), 1 pound of muscle burns 4.5-7 calories every day. Muscle comprises 40% of the body. Thus, a 150-pound individual can burn up to 420 calories in a day without performing any additional activity. 

While you are trying to lose weight by consuming low-calorie food, you tend to lose muscle.

5. Reduces Fertility 

As you follow a calorie-restrictive diet, your fertility can bear the burn of it, especially among women. Women’s ovulation depends on their hormonal levels. To be more specific, an increase in the luteinizing hormone (16) and estrogen is required for ovulation to take place. 

But the LH or luteinizing hormone levels depend on the number of calories one consumes. As per studies, the reproductive function gets suppressed in women who eat about 22%-42% fewer calories than what is required to maintain their weight. 

Insufficient calorie intake can also lead to a drop in the estrogen levels. It makes a serious impact on your heart and bone health. 

Signs of suppressed fertility include irregularities in menstrual cycles or complete cessation. Nevertheless, subtle menstrual discrepancies don’t fall under these symptoms. Hence, reduced fertility requires a thorough examination to be diagnosed. 

Experts think that a calorie-restrictive diet can also harm the reproductive function of men. However, more studies are needed to ascertain this.

6. Gallstones and Constipation

You might not realize, but a calorie deficit diet can lead to other serious side effects, including gallstones. 

If you are cutting down on your calorie intake and losing weight at a rapid pace, your liver will start to secrete extra cholesterol. This increases cholesterol content in the bile, which can cause gallstones.

Gallbladder stones (17) can cause:

  • Nausea
  • Pain in the back and upper abdomen
  • Vomiting
  • Indigestion, bloating, gas, and heartburn

Not getting enough calorie-rich food can also disrupt the normal functioning of your digestive system. This, in turn, can cause constipation. 

If you have less than three bowel movements in a week, you can develop constipation. In such a case, even if you don’t have enough food and you are losing weight, you will not feel happy. 

A low-calorie diet means consuming so little food and fewer carbs. You’ll also miss out on the recommended daily fiber requirement. This also causes constipation. 

One way to prevent this is to include fiber-rich vegetables (18) and fruits in your diet or find out a fiber supplement.

7. Weakens the Bone

Consuming less than the required dose of calories can also weaken your bones. It is because restricting calorie intake reduces testosterone and estrogen (19) levels in the body. Lower levels of these hormones in men and women can reduce bone formation and will augment bone breakdown. This ultimately leads to weaker bones. 

Are you still working out while restricting calorie intake? This may also increase stress hormone levels. Thus, it leads to bone loss. Bone loss is a cause of concern since it is hard to rectify. It can increase the risk of fractures.

8. Causes Feelings of Depression

Cutting down on calories to lose weight can increase your symptoms of depression (20).  

People who consumed fewer calories and lost about 5% of their body weight were 78% more likely to be depressed than the ones who consumed the required number of calories. 

The reason behind this is the lack of nutrients. If you lose weight by consuming fewer calories, you are more likely to be depressed and may require the help of a psychologist.

9. Lowers Immunity

Following a calorie-deficit diet can increase the risk of illnesses and infections. It applies to all viruses, including the common cold. Your risk increases when you combine it with a high level of physical activity. 

Evidence shows that athletes following a regime that needed them to be lean lost more weight but are more likely to be sick in the next few months. 

Another study that focused on taekwondo athletes dieting (21) to cut down their body weight before a competition saw a reduction in immunity. This led to an increased risk of infection. 

So, it can be said that less consumption of calories can cause low immunity.

10. Triggers Binge Eating

When your body requires calories, you’ll feel hungry. So, you will start looking for food even when you have had your fair share of food. It is particularly due to the hormone known as leptin (22). 

As you are consuming fewer calories, your body’s level of leptin increases. This will make you hungrier. It makes people binge eat unhealthy food. It can reverse the effect of losing weight. So, you start gaining weight as rapidly as you lose it. 

The vicious cycle of restriction and binge eating begins. Thus, it is better to restrict in a healthy way instead of just following a diet that is too low in calories. 

Counting the Right Dose of Calories

To reach a healthy weight loss goal, it is important to count the correct number of calories you need in a day. The calorie count varies from one person to another since it depends on sex, age, height, current weight, and physical activity. 

Consuming the correct amount of calories daily will help prevent the side effects that were listed above. 

To make the right estimation, you will have to follow a few metrics. Let’s take a quick look at them. 

  • Estimate the Daily Requirement: You can use an online tool to calculate the number of calories you need every day appropriate for your body weight. 
  • Determine Your Body’s BMR: To calculate the calorie count you need; it is necessary to know your BMR. 
  • Determine the Calorie Required for Weight Loss (23): In case losing weight is your ultimate goal, make sure you consume calories between the amount necessary for sustaining BMR and the amount required for maintaining your present body weight. 

Experts say that you should consume less than 1000 calories in a day unless otherwise instructed by your physician. Keep track of your diet as it helps you reach the daily requirement for nutrients. 

Final Words

If you want to lose weight, there are several better options than opting for a low-calorie diet. So, other than controlling your calorie intake, you should do the following: 

  • Build muscle through weight training
  • Take part in physical activities
  • Include cardio exercises in your weight loss regime
  • Eat at regular intervals and have unprocessed foods
  • Get enough sleep 
  • Avoid crash dieting

It is better to stay away from diets that restrict calories. You should go for diets that include nutritious food and help in making sustainable lifestyle changes. To lose weight, you have to be patient. 

You cannot expect to see results within just a few days. By taking nutritious food, you are proving that you care about your health and can keep it under control. That is the first step to getting a better and well-maintained body. 


PhentermineDoctors has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.
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  2. https://www.ncbi.nlm.nih.gov/books/NBK499909/
  3. https://www.healthline.com/health/what-is-basal-metabolic-rate#:~:text=Basal%20metabolic%20rate%20(BMR)%20is,burns%20while%20it’s%20at%20rest.
  4. https://www.ncbi.nlm.nih.gov/books/NBK221839/
  5. https://pubmed.ncbi.nlm.nih.gov/3287896/
  6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5639963/
  7. https://pubmed.ncbi.nlm.nih.gov/11707556/
  8. https://www.ncbi.nlm.nih.gov/protein/
  9. https://www.ncbi.nlm.nih.gov/books/NBK169615/#:~:text=Treatment%20of%20manifestations%3A%20Biotin%20(5,Symptoms%20typically%20resolve%20within%20days.
  10. https://www.ncbi.nlm.nih.gov/books/NBK56060/
  11. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4455825/
  12. https://www.ncbi.nlm.nih.gov/books/NBK482362/
  13. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2585731/
  14. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2897177/
  15. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2866261/
  16. https://www.ncbi.nlm.nih.gov/books/NBK539692/
  17. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3899548/#:~:text=High%20biliary%20protein%20and%20lipid,bilirubin%20precipitation%20and%20gallstone%20calcification
  18. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3614039/
  19. https://pubmed.ncbi.nlm.nih.gov/18030175/
  20. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3181882/
  21. https://www.sportsdietitians.com.au/factsheets/food-for-your-sport/food-for-your-sport-taekwondo/
  22. https://pubmed.ncbi.nlm.nih.gov/17212793/
  23. https://www.healthline.com/nutrition/how-many-calories-per-day#:~:text=The%20average%20woman%20needs%20to,this%20depends%20on%20numerous%20factors.

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