Does Calorie Deficit Make You Tired?

Always when I’m doing in a calorie deficit I notice that my energy drops, I feel unmotivated and tired. Does calorie deficit make you tired?

In general, calorie deficit does make you tired when you eat not enough calories, especially not enough proteins. Having a good amount of proteins not only improves satiety but also stabilizes your blood sugar which leads to stable energy levels.

But the proteins aren’t the only problem. In this article, I will share with you what happens when you’re in a calorie deficit, why you feel tired, and what to do to get your energy back.

Calorie Deficit Feeling Tired

In general, most of the scientific research shows that calorie restriction significantly improves mood, mobility, energy and quality of life. Also it is associated with increased vigor, better sleep and sexual drive.

So feeling tired is not directly related to the calorie deficit, but rather to food quality and nutrient composition during dieting (Martin, Corby K et al. 2016).

In other words, if the weight loss diet doesn’t have enough nutritional value, it can lead to fatigue. One of the most important macronutrient is protein.

When protein fails to meet individuals’ needs during an energy deficit, body stores are catabolized to provide energy, leading to the decrease of not only fat mass but also muscle mass (Newman, Anne B et al. 2005).

Is It Normal To Be Tired When Dieting?

Generally, it is normal to be tired when dieting, especially if you’re not getting enough essential nutrients. A balanced diet with proteins, whole grains high in fibers, mineral-rich vegetables, and omega-3 fatty acids ensures your energy levels are stable.

During a calorie deficit, the body’s need for nutrients changes. The most profound difference is in muscle protein breakdown and muscle protein synthesis.

  • Muscle protein breakdown is part of muscle re-modeling where we lose muscle mass.
  • Muscle protein synthesis is also part of the muscle re-modeling phase, which leads to muscle building.

During normal eating, muscle protein synthesis slightly exceeds protein breakdown, depending on age, gender, physical activity, etc. However, during an energy deficit, the muscle protein breakdown significantly increases and muscle protein breakdown goes up.

That’s why during the calorie deficit, the amount of proteins should be much higher than when you’re on a regular eating pattern.

A study by Dr. Stefan M Pasiakos documented that 10 days of calorie deficit (80% of total estimated energy requirements) was enough to cause a 19% decrease in muscle protein synthesis. Participants were eating 1.5 grams per kg of body weight, which twice the RDA, and still experienced muscle loss (Pasiakos, et al. 2010).

Reduced lean body mass relates to tiredness, lack of energy, and feeling of exhaustion. It also relates to fatigue difficulty in performing regular tasks during the day. Adding enough proteins to each meal together with regular strength training is often enough to make you feel less tired.

Can lack of protein make you tired? In general, lack of protein can make you feel tired because, with lower lean body mass, your metabolism drops, and you reduce the amount of oxygen getting into the cells. Also, low protein can affect blood glucose levels which cause sleepiness and tiredness.

I won’t cover here how much protein you should be eating on an energy deficit. I’ve already covered that in my other article, which I recommend you read.

Learn more: Click here to learn more about calorie deficit and protein

Calorie Deficit Exhaustion

Lack of protein in the diet while doing calorie restriction also leads to higher sugar levels in the blood. Protein has a low glycemic response which lowers the speed at which glucose enters the blood. Meals low in protein and high in carbs have a high glycemic response, which increases sugar levels.

Those constant changes in blood glucose can have an impact on your energy and mood. Protein has minimal effect on blood glucose levels, therefore, adding protein-rich food to your meals can help to balance the glucose levels and reduce exhaustion.

A study done by Dr. Mary C Gannon from the University of Minnesota documented 12 people and the effects of different amounts of proteins on glucose levels (Gannon, Mary C et al. 2003). Participants were divided into two groups:

  • High protein group with around 166 grams of protein per day (30% food intake)
  • Control group with around 84 grams of protein per day (15% food intake)

The study took 5 weeks and the results showed that the high protein group reduced their fasting glucose levels by 1/3. It also showed that adding the 80-90 grams of protein per day extra was enough to lower glycated hemoglobin by 50% and fasting triacylglycerol concentration by 20%.

Results after 5 weeks of fasted glucose levels

Can high glucose make you tired? In general, tiredness is one of the most common signs of high blood glucose. Too much sugar levels can make people feel fatigued, sleepy, and exhausted. Adding proteins into the diet balances sugar levels and can help to reduce tiredness.

Calorie Deficit Feeling Sleepy

In general, a calorie deficit can make you feel sleepy and weak when the total amount of calories is too low. People who reduce their calorie intake too low may always feel tired. The amount of calories you should consume depends on your age, gender, and physical activity.

In other words, eating too little can cause sleepiness and exhaustion. Our body can cope with a calorie deficit to some extend. However, if the number of calories is low for a long time, the body will down-regulate many metabolic functions to preserve energy.

Why do I feel weak when dieting? As a general rule, if you’re feeling weak when dieting it can be caused by not eating enough calories in your diet. Drastic calorie restriction over time slows down metabolism and can cause the body to feel weak, tired, and sleepy.

How Do You Get Energy In a Calorie Deficit?

The best way to get energy during a calorie deficit is to combine high-protein foods, together with a high volume of vitamins and microelements from vegetables and fruits. Also, reducing calories just around your BMR level ensures you’re not creating too much energy deficit.

#1: Add more protein

Eating around 0.8 to 1 gram of protein per pound of bodyweight will not only increase metabolic rate and energy expenditure but also preserve your lean muscle mass. In addition, getting enough protein with each meal helps to balance blood sugar levels.

#2: Drink enough water

In general, lack of water during a calorie deficit can make you feel tired because the body needs a certain amount of water every day to maintain basic metabolic functions. If you’re constantly feeling sluggish and tired while dieting, you may need to increase your water intake.

#3: Start exercise daily

Lack of exercise can make you feel tired during calorie deficit because a sedentary position maintained throughout the day lowers the blood flow, reduces oxygen intake, and can cause further fatigue. Also, lack of movement leads to increased muscle protein breakdown.

#4: Reduce caffeine

In general, too much caffeine can make you feel tired when you’re on a calorie deficit because of the build-up of adenosine after the caffeine wears off. Reducing your caffeine to 2-3 cups per day may be enough to increase energy levels.

#5: Reduce carb intake

Generally, carbs can make you feel tired, especially the ones with a high glycemic index. Eating too many carbs leads to higher glucose levels, which can cause tiredness and fatigue. Reducing carbs or adding proteins to your meal can be enough to help.

#6: Reduce junk food

In general, junk food can make you feel tired. Ultra-processed food that is low on fiber and high on sugar has a high glycemic index which increases your blood glucose and insulin levels. Reducing junk food and adding more fiber-rich foods can help with feeling tired.

#7: Get more vitamin D

As a general rule, low vitamin d can make you feel tired. The symptoms of low calciferol levels are tiredness, constant fatigue and depression. People who don’t have much access tot the sun may experience lack of vitamin d so adding 2000 IU to your diet can help with tiredness.


Feeling tired while being in the calorie deficit can happen, but is not due to dieting. Having your meals designed in a way to meet all nutritional requirements not only helps with better results but also maintains your energy throughout the day.

Michal Sieroslawski

Michal is an exercise physiologist (MSc) and a veteran endurance athlete. He loves to experiment and share his successes and failures to help busy men and women who want to lose weight.

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