What Happens If You Eat Too Few Calories

Usually, if you burn more calories than you eat, you’ll lose weight. But before skipping meals, you need to know what happens if you don’t eat enough.

Woman eating a small leafy salad

When we wake up begging the bloat to go away and pant as we try to fit in our pants, it can make us want to wormhole the web to find the quickest diet fix. But before starving yourself silly, it's important to understand the sabotage that happens when we don’t eat enough. Learn how cutting too many calories can be dangerous and damaging to your metabolism and health.

Making sense of metabolism

Metabolism is what regulates how many calories we need daily. It is defined by all the chemical reactions that happen inside our body to keep us alive and functioning normally (1). This includes breathing, cell function, and even eating food. We also burn calories by moving about our days and doing physical activity. 

In general, if we eat less energy (calories) from food than we burn, we’ll lose weight. And the reverse goes that if we eat more in comparison to what we expend, we’ll most likely gain weight. However, each of us burns calories differently as a result of our family background, sex, gut bacteria, muscle mass, and state of health.

Cut calories with caution

Cutting too many calories over time can change how efficiently our metabolism works. Our bodies are designed to keep us surviving and thriving. This means that when food is scarce, it will adapt by decreasing the amount of energy we burn through a slower metabolism, less activity, and increased hunger.  

Slower metabolism 

Restricting calories is known to lead to a short-term dip in how many calories we burn at rest (2). Some research has shown that a decreased metabolism can last beyond st a restrictive diet and is most likely related to weight regain (3). A slower metabolism means that we require fewer daily calories to maintain our weight.


Fatigue affects both the mind and body. Since calories provide energy, if we don’t get enough to cover basic functions, our body will slow down activity and thought processes to help preserve them. Eating too little can be linked to low energy whether sedentary or active (4). This even includes standard daily activities such as cleaning and walking.

“Hangries” and hormones 

Even in the short term, a reduction of calories can increase appetite hormones which signal when we are hungry or full. These hormones have been shown to stay elevated even a year after a restrictive diet (5). It also has been shown to increase cortisol, a stress hormone that can contribute to weight gain (6).

Nutrient deficiencies 

Eating a minimal amount of calories makes it very difficult to get all the essential nutrients we need. Nutrient deficiencies can impact anything from how effective our bodies functions, such as immunity and mental health, to the way we look. For instance, not eating enough over time can result in hair loss and poor quality of the skin (7). 

How to boost metabolism

Regardless of the metabolism you were born with, or what you have done to impact your current level of burn, you can still increase your metabolic rate through healthy habits. 

Eat more whole foods 

Eating whole foods versus their processed versions can actually lead to burning more calories (8). This is because whole foods are “more work” for our bodies to break down and digest. Just think about the comparison of drinking one cup of orange juice to eating three oranges. They both have similar total calories but the orange juice takes a lot less effort than the oranges to eat. 

Get moving 

Exercise and movement can help contribute to weight loss. Exercise burns calories during the activity. Some activities such as high-intensity interval training (HIIT) or weight training also lead to an afterburn effect. Having more muscle mass versus fat mass, which can be increased by exercise such as strength training, can also contribute to an increased metabolic rate (1).

Drink enough water 

Drinking enough water has been suggested to have an impact on metabolism. In a study of 50 overweight girls, those who drank an extra 6 cups (1500 ml of water) had decreases in body mass index and body composition (9). Keep in mind that the effects may be negligible, so it's just another factor in the metabolism picture. It can be helpful to keep track of daily water intake. 

Remember to rest

Consistently missing out on quality sleep can impact hormones that are involved with the metabolic process (10). People who get about eight hours of sleep a night reduce stress and have and can double the chance of losing weight (11).

Recipe of success

If your goal is to lose weight, a successful approach includes a long-term strategy that works best for you. So rather than just focusing on calories, it's important to find foods that keep you satisfied, focusing on whole foods, and a schedule of eating that works for your lifestyle.

Start your day right with this delicious, protein rich breakfast bowl from the Lifesum app:

All of the content and media on Lifesum is created and published for information purposes only. It is not intended to be used as a substitute for medical advice or treatment. Users should always consult with a doctor or other health care professional for medical advice.

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All of the content and media on Lifesum is created and published for information purposes only. It is not intended to be used as a substitute for medical advice or treatment. Users should always consult with a doctor or other health care professional for medical advice. If you have or think you are at risk of developing an eating disorder, do not use the Lifesum app and seek immediate medical help.