8 Harmful Effects of Excessive Calorie Restriction

Published on May 13, 2024
8 Harmful Effects of Excessive Calorie Restriction

People aiming to lose weight usually decide to eat fewer calories.

This method is actually prescribed by nearly every commercial diet program available today, sighting reducing calories, counting points, or watching portion size as the best way to lose weight.

However, restricting your calories, especially too severely, can lead to a variety of metabolic and chronic health problems.

This article will outline three potentially harmful effects of calorie restriction.

What’s A Calorie?

Scientifically, a calorie is defined as the amount of heat energy needed to raise the temperature of one gram of water by 1°C (1.8°F).

However, most people are more likely to think of calories as the amount of energy your body gets from the foods and beverages you consume.

Metabolizing these nutrients will produce calories that can be used to power three main processes (1, 2): 

1. Basic Metabolism

The body will use most calories to provide energy to your brain, heart, lungs, and kidneys. The amount needed to support these basic functions is referred to as your basic metabolic rate (BMR). This makes up the biggest proportion of your total daily requirements (1).

2. Digestion

The body will use part of the calories to help you digest and metabolize foods. This is called the thermic effect of food (TEF), which may vary depending on what you eat. Protein, for example, requires more energy to be digested, while fat demands the least. Approximately 10-15% of the calories you get from foods will be used to support the TEF (3).

3. Physical Activity

The rest of the remaining calories will fuel your physical activity. This includes your daily tasks and exercises. The count of calories needed to cover this category may vary on a daily basis and from one person to another. 

Theoretically, eating more calories than your body needs will cause you to gain weight, while eating fewer calories than your body requires leads to weight loss. 

This calorie balance concept, which is pushed on us by the commercial dieting industry and reinforced by the media, is why people who want to lose weight repeatedly try to restrict their calorie intake. 

However, science clearly shows us that restricting calories, especially too much, may harm your weight loss potential and overall health.

How Can Excessive Calorie Restriction Harm You?

Too much calorie restriction may cause the following: 

1. Slow Metabolism 

Regularly eating fewer calories than your body needs can cause your metabolism to automatically slow down.

Studies show that low-calorie diets can decrease the number of calories the body burns by as much as 23 percent. And what’s more, this lower metabolism can persist long after the calorie-restricted diet is stopped (4, 5).

In fact, researchers believe that this lower metabolism may partly explain why more than 80 percent of people regain weight once they go off of their calorie-restricted diets. (6).

One of the ways that calorie-restricted diets slow your metabolism is by causing a loss in muscle tissue (7, 8).

This loss of muscle mass is especially likely to occur if the calorie-restricted diet is low in protein and not combined with exercise (9, 10).

To prevent your weight loss diet from affecting your metabolism, make sure that you never eat fewer calories than are required to sustain your BMR. Also, slightly increase your protein consumption and add in some resistance training exercises to your workout routine (11).

Severely restricting your calories can decrease your metabolism and cause you to lose muscle mass. This makes it more difficult to lose and maintain your weight loss over the long term.

2. Fatigue and Nutrient Deficiencies

Regularly eating fewer calories than your body requires makes it quite challenging to meet many important daily nutrient needs. For instance, calorie-restriction may not provide sufficient amounts of iron, folate or vitamin B12 which can lead to anemia and extreme fatigue (12, 13, 14).

Additionally, calorie-restricted diets may limit other vital nutrients as well, including:

  • Protein: Not eating enough protein-rich foods like meat, fish, dairy, beans, peas, lentils, nuts, and seeds may cause muscle loss, hair thinning, and brittle nails (15).
  • Calcium: Not eating enough calcium-rich foods like dairy, leafy greens, calcium-set tofu, and fortified milks may reduce bone strength and increase the risk of fractures (16).
  • Vitamin A: Not eating enough vitamin A-rich foods like organ meat, fish, dairy, leafy greens, or orange-colored fruits and vegetables may weaken your immune system and lead to permanent eye damage (17).
  • Magnesium: An insufficient intake of magnesium-rich whole grains, nuts and leafy greens may cause fatigue, migraines, muscle cramps and abnormal heart rhythms. (18)

To prevent fatigue and nutrient deficiencies, avoid restricting your calories below metabolic stimulation (1000 calories per/day) and make sure you eat a majority of your diet from whole, unprocessed or minimally processed foods.

Restricting calories too severely can lead to fatigue. Maintaining this calorie restriction for too long can also lead to nutrient deficiencies.

3. Weak Bones 

Consuming too few calories can weaken your bones. That’s because calorie restriction can reduce estrogen and testosterone levels. Low levels of these two reproductive hormones are thought to reduce bone formation and increase bone breakdown, resulting in weaker bones (19, 20, 21).

In addition, calorie restriction, especially when combined with physical exercise can increase stress hormone levels. This may also lead to bone loss (22).

Bone loss is especially troublesome because it is often irreversible and increases the risk of fractures (23, 24).

4. Less Lean Muscle Mass

When your body is out of fuel (or calories) it will begin to use it’s own muscle and collagen for energy. It will also begin to use your fat stores which increases your likelihood of starvation and triggers bingeing. This will lead to muscle atrophy or shrinking, which can dramatically impact the quality of your life.

5. Fertility Problems 

Restricting calories too dramatically can negatively affect fertility. This is especially true for women, as the ability to ovulate depends on hormone levels.

More specifically, an increase in estrogen and luteinizing hormone (LH) levels is needed in order for ovulation to occur (25, 26). Interestingly, it was found that LH levels partly depend on the number of calories available in a woman’s diet.

Accordingly, studies show that reproductive function is suppressed in women who eat 22–42% fewer calories than are needed to maintain their weight (27).

An insufficient calorie intake may also reduce estrogen levels, which is thought to have lasting negative effects on bone and heart health (28, 29).

Signs of reduced fertility may include irregular menstrual cycles or a lack of them. However, subtle menstrual disturbances may not have any symptoms, so they may require a more thorough medical examination to be diagnosed (30).

Researchers believe that severe calorie restriction may also affect men’s reproductive function, but few studies exist on the topic (31).

6. Mood Swings

Food makes us feel good! It gives us energy, keeps us healthy and makes us happy! However, when we are taking in the necessary amount of calories each day our mood will begin to take a turn. You may notice you feel more stressed, more easily agitated, short-tempered, depressed, and more. You may also notice a difference in your memory and have more episodes of tears or emotional outbursts.

7. Immunodeficiency 

Restricting calories may increase your risk of infection and illness. This especially applies to viruses like the common cold and appears to be especially true when it’s combined with a high level of physical activity (32, 33).

For instance, one study compared athletes in disciplines that put a strong emphasis on body leanness, such as boxing, gymnastics or diving, to those in disciplines less focused on body weight.

The researchers reported that athletes in disciplines that required leanness made more frequent attempts to lose weight and were almost twice as likely to have been sick in the previous three months. (34).

In another study, taekwondo athletes who were dieting to reduce their body weight in the week before a competition experienced reduced immunity and an increased risk of infection (35).

The effects of calorie restriction in non-exercising individuals are less clear, and more research is needed before strong conclusions can be made (36).

Calorie restriction, especially when combined with strenuous physical activity, may lower your immune defenses.

8. Binge Eating

When your body is in need of calories it wants food! People who have a tendency to restrict calories normally place a “black and white” label on foods. When an urge to have “bad” food kicks in, instead of having a small serving it will be an all-out food fest! Then the vicious cycle of restriction and bingeing starts over. Restrict from a binge, binge from restriction. If a binge happens, instead of restricting, heal the healthy way.

Eat the Right Number of Calories!

Caloric intake varies from person to person due to factors such as age, sex, height, weight, body composition, and physical activity level.

Determining the number of calories that’s right for you will reduce your likelihood of developing the negative health consequences outlined above.

There are various ways to estimate your own calorie needs. However, the easiest method consists of three simple steps:

  1. Determine your BMR: Use this BMR calculator to estimate the minimum number of calories your body requires per day. Aim to never consume fewer calories than this (37).
  2. Estimate your daily requirement: Use Calorie Calculator to estimate the number of calories you may need to maintain your current body weight (38).
  3. Determine your calorie needs for weight loss: If weight loss is your goal, aim for a daily calorie intake falling between the amount required to sustain your BMR and the amount needed to maintain your current body weight.

In addition, make sure you record what you eat in an online food journal, at least in the beginning of your weight loss process. Tracking your diet will help you ensure that you continue to reach your daily recommended nutrient intakes.

Use the method above to estimate the daily calorie intake that’s right for you, in addition to an online diet journal to ensure that your diet covers your nutrient needs.

Best Foods to Eat When Restricting Calories

Cutting calories without considering the foods you eat is usually not a healthy and sustainable weight to lose weight. Though it may work for some people, most will end up starving and eventually give up on their diet. 

For this reason, you have to make sure that every calorie counts. It is very important to choose foods that are nutrient-packed and filling but are low in calories. Here are 5 common examples:

1. Oats

Oats can certainly be an excellent addition to a healthy weight loss diet. They are not just low in calories but also contain high amounts of protein and fiber to help keep you feeling full. 

A ½ cup serving of dry oats has less than 150 calories but packs 3.8 grams of fiber and 5.5 packs of protein. These can have a significant impact on your appetite and hunger. It has been proven to be effective in increasing feelings of fullness and reducing hunger and calorie intake at the next meal.

Another study found that instant and old-fashioned oatmeal can significantly improve appetite control for 4 hours compared to a bowl of ready-to-eat breakfast cereal.

2. Greek Yogurt 

Greek yogurt is also a good source of protein that can help reduce cravings and promote weight loss. Though the exact numbers may differ between brands and flavors, a 2/3 cup serving of Greek yogurt can provide approximately 130 calories and 11 grams of protein.

Evidence found that women who ate yogurt instead of crackers and chocolates experienced less hunger and consumed 100 fewer calories at dinner. Also, another study suggested that high-protein Greek yogurt is more effective in creating feelings of fullness compared to lower-protein snacks.  

3. Eggs 

Eggs contain several vital nutrients minus the calories! One large egg contains 6 grams of protein, a wide array of important vitamins and minerals, and just 72 calories.

Evidence found that consuming eggs in the morning can help reduce hunger and promote fullness. They are even better than bagels. They can help you consume 105 fewer calories later in the day.

Other studies observed that a high-protein breakfast can limit snacking, slow the emptying of your stomach, and decrease levels of ghrelin, the hunger hormone.

4. Berries 

Who doesn’t love berries? Which is your favorite? Do you like strawberries, blueberries, raspberries, or blackberries? Anyway, whichever you choose, they are equally nutritious! All are loaded with antioxidants, vitamins, and minerals that can promote overall health. They are also rich in fiber, which can control hunger and boost weight loss. 

A single cup of blueberries can supply 3.6 grams of fiber and just 84 calories. Berries are also an excellent source of pectin, a type of dietary fiber that has been proven to be effective in delaying stomach emptying and increasing feelings of fullness in both animals and humans. This can greatly help cut calorie consumption to aid weight loss. 

Another evidence noted that a 65-calorie snack of berries can help decrease calorie intake later in the day compared to a confectionary snack containing the same amount of calories.

5. Apples 

Fruits are an important part of a nutritious diet. Several studies showed that eating fruit is associated with lower calorie intake and may contribute to weight loss over time.

In particular, apples have a very high satiety index score. They contain pectin, a soluble fiber that naturally slows digestion to help you feel full. They are likewise over 85% water, which adds volume and improves satiety without adding calories. 

It is very important to remember that whole, solid fruits can increase satiety more than juice and purees. Evidence showed that those who ate solid apple segments took 91 fewer calories than those who had applesauce and 150 fewer calories than those who enjoyed apple juice.

The Bottomline

When it comes to long-term weight loss, patience is the key. It’s best to stay clear of diets that require you to severely restrict your calories.

Instead, opt for a diet that is focused on quality whole, unprocessed or minimally processed foods that encourage you to make sustainable lifestyle changes.


(1) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3302369/

(2) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3401553/

(3) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC524030/

(4) https://pubmed.ncbi.nlm.nih.gov/27136388/

(5) https://pubmed.ncbi.nlm.nih.gov/23404923/

(6) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3673773/

(7) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3943438/

(8) https://pubmed.ncbi.nlm.nih.gov/7632212/

(9) https://pubmed.ncbi.nlm.nih.gov/17684207/

(10) https://pubmed.ncbi.nlm.nih.gov/24092765/

(11) https://pubmed.ncbi.nlm.nih.gov/17684207/

(12) https://www.nap.edu/read/11537/chapter/26

(13) https://www.nap.edu/read/11537/chapter/37#329

(14) https://www.nap.edu/read/11537/chapter/19

(15) https://www.nap.edu/read/11537/chapter/14

(16) https://www.nap.edu/read/11537/chapter/32

(17) https://www.nap.edu/read/11537/chapter/17

(18) https://www.nap.edu/read/11537/chapter/38

(19) https://pubmed.ncbi.nlm.nih.gov/14974441/

(20) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3971652/

(21) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2901252/

(22) https://pubmed.ncbi.nlm.nih.gov/23415825/

(23) https://pubmed.ncbi.nlm.nih.gov/24022502/

(24) https://pubmed.ncbi.nlm.nih.gov/23536179/

(25) https://pubmed.ncbi.nlm.nih.gov/9451615/

(26) https://pubmed.ncbi.nlm.nih.gov/12519869/

(27) https://pubmed.ncbi.nlm.nih.gov/25352438/

(28) https://pubmed.ncbi.nlm.nih.gov/17227959/

(29) https://pubmed.ncbi.nlm.nih.gov/15572426/

(30) https://pubmed.ncbi.nlm.nih.gov/19945961/

(31) https://pubmed.ncbi.nlm.nih.gov/24620037/

(32) https://pubmed.ncbi.nlm.nih.gov/18185032/

(33) https://pubmed.ncbi.nlm.nih.gov/19846424/

(34) https://pubmed.ncbi.nlm.nih.gov/18185032/

(35) https://pubmed.ncbi.nlm.nih.gov/19846424/

(36) http://www.fasebj.org/content/28/1_Supplement/40.4

(37) http://www.fasebj.org/content/28/1_Supplement/40.4

(38) https://www.calculator.net/calorie-calculator.html

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