Calories When Sick (How many do you burn and what to eat)

Being sick isn’t fun. It makes you feel weak, fragile, and vulnerable. In this article, I will explain does your body burns more calories when sick, and help to clarify nutrition and calorie requirements.

As a general rule, you do burn more calories when sick because during the period of sickness or infection the body increases resting metabolic rate and raises oxygen consumption. It also increases the use of proteins as an energy source and elevates heat production, which all comes with higher calorie burn.

Keep reading to learn how much energy you need, what to eat, and how many calories you burn.

Calories When Sick

Overall, calories do matter when you’re sick because the body has to use more calories to be able to combat the sickness and recover faster. Having enough energy increases the chances of fighting off the virus.

On the other hand, not enough calories may cause a lack of energy and extends the sick time.

But before I answer should you eat more calories when sick, first I want to show you a fascinating study done by Dr. Leah MacDonald from La Trobe University in Melbourne Australia.

She documented that 25-50 percent calorie restriction was able to suppress sickness (MacDonald et al. 2011). Calorie restriction was documented in the past to alter cytokine levels, but this was the first time to show that calorie intake also matters in sickness.

Does being sick burn calories? As a whole, being sick burns calories because during sickness the viruses and bacterias dramatically modify cellular metabolism. This starts a cascade of metabolic processes, increases metabolic rate, and elevates core body temperature to fight against the viruses.

Do you need more calories when sick? Overall, your body does not need more calories when sick. In fact, studies have shown that eating just below calorie maintenance was associated with better outcomes, including shorter hospital stay, ventilator dependence, use of antibiotics, and even mortality.

However, there is a fine line between less and too little because inadequate calorie and protein intake during sickness often leads to poor recovery (Yamamoto et al. 2020).

How Many Calories Do You Lose When Sick?

On average, you can lose 100 to 200 calories for every 0.5°C increase in core body temperature when sick. During sickness, the body elevates its basal metabolic rate by around 7% for every half-degree Celcius. The estimate will be influenced by total body temperature and calorie intake.

Another thing that influences calorie expenditure will be body weight and lean body weight as heavier people need more energy to increase core body temperature (Heyland et al. 2011).

How many calories do you need when sick? On average, you should be getting around 2000 to 3000 calories when sick, depending on your age, gender, and current body weight. It also depends on things like your physical activity, lean body mass, and the type of food you eat.

In other words, it depends.

Being sick is a perfect time to focus on a healthy diet. Adding protein, fresh fruits, and vegetables maybe won’t significantly shorten your sickness, but at least make you feel better.

Should you count calories when sick? In general, if you’re used to counting calories, you should continue doing it when you’re sick. This can help to control calorie intake, especially if you want to reach your desired weight goal. However, people who never count calories and don’t have any weight goals in mind should avoid calorie counting.

Should you restrict calories when sick? In general, you should only restrict your calories when sick when you have a weight loss goal or bodybuilding competition that you train for.

Calories and Fever

Fever is a symptom of having a higher than normal body temperature, which can be caused by several factors.

Does having fever burn calories? As a whole, you do burn more calories when you have a fever because fever triggers the thermoregulatory part of the hypothalamus to increase the core body temperature above 36.6°C. This process increases resting metabolic rate and as a result, the body burns more calories.

Of course, apart from body temperature, there are other physiological changes going on like:

  • Metabolic adaptations
  • Sleep/wake cycle changes
  • Hormonal changes

And all of them play a role in your appetite and how the body will use energy.

How many calories does having a fever burn? Overall, the fever can burn around 20% more calories comparing to a homeostatic state because during fever the body increases basal heat production by 20 to even 50 percent. Also, During fever, the body switches energy sources from using glucose to using protein and fat.

Glucose is a great medium for bacterial growth, therefore, the body halts utilizing it.

Infection and Calories

Infection can happen for a variety of reasons. It usually happens because of the bacteria, viruses, yeast, fungi, or other microorganisms spread in the body.

Do you burn more calories when you have an infection? In general, you do burn more calories when you have an infection. During the response to illness and infection, the body elevates metabolism and initiates the number of metabolic changes that contribute to the maintenance of body homeostasis.

Does fighting infection burn calories? As a whole, fighting infection does burn calories because more energy is needed to combat germs and bacterias. Studies have shown that infection without sufficient calorie intake often leads to weight loss and often malnutrition.

What To Eat When You Are Sick

As a whole, infection and sickness increase the need for nutrients in the body like proteins, vitamins, and electrolytes.

What’s the best thing to eat when sick? Overall, the best thing to eat when sick are foods that are high in protein and anti-inflammatory compounds like ginger, curcumin, and garlic. Also, drinking plenty of water and soups that are high in electrolytes helps to stay hydrated.

What’s the worst thing to eat when sick? As a whole, the worst thing to eat when sick are foods high in fat because excess fat consumption during the infection time can trigger the immune response and be perceived as foreign objects.

Here is the list of things you should pay attention to when sick:

  • Proteins

During inflammation time, glucose isn’t used for energy, therefore, the number of amino acids from dietary proteins needs to be higher than usual.

This means, with each meal you should include large amounts of proteins. For men that should be two palms of high-protein dense foods, and for women one palm.

One way to add more protein to the diet, without adding too many calories is by drinking protein shakes. My favorite protein shakes are from the company Optimum Nutrition available on Amazon. Details here.

(if you buy through links on this page, I may earn a small commission).

  • Water with electrolytes

High body temperature can quickly dehydrate the body, which will make it harder to move pathogens out of the body.

  • Vitamins and minerals

Vitamins and minerals play a critical role in the strength of the immune system. Making sure your diet is rich in vitamins A, C, D, E, B12, B6, and B9 can prevent depressing the immune system.

From minerals, magnesium, copper, zinc, and iron also strengthen your immune system.

So limiting fat intake during the illness, and increasing protein can balance and speed up recovery. I take vitamins from the company called Nordic Naturals, available on Amazon. Click “here” for the full list and prices.

Appetite When Sick

Overall, being sick affect your appetite because of many changes in the body. Depending on the sickness, some people may notice an increase in appetite, where other may feel like they appetite has lowered.

Does your appetite increase when sick? In general, your appetite can increase when you’re sick because during sickness the bacterial infections increase the pro-inflammatory cytokines that increase metabolic rate. However, the most common is suppression of appetite during sickness.

Upper respiratory infections, diarrhea, and fevers can suppress appetite and food intake by 15-20%. Some of the illnesses like measles, mumps, or rubella can suppress appetite even more (source).

When I was younger I remember joking that when I was sick, I always lost weight. This was true because when you’re sick, not only you don’t wanna eat, but your metabolism is higher so you burn extra calories.

But that’s not the smartest way to lose weight.

Why does your appetite decrease when you are sick? As a whole, your appetite does decreases when you’re sick because during the inflammatory response of fever, headache, myalgia, and malaise, the TNF cytokine starts long-term immune reactions that create changes in appetite and energy intake.

The immune system takes up a lot of energy to combat infectious diseases. So halting digestion, suppressing appetite, and moving all the resources to the battle seems like a logical move.

Nevertheless, eating nutritious food during times of sickness can add many benefits and speed up the recovery process (source).

But how you can eat if you don’t feel like eating?

Here are some tips to eat more while being sick

How To Eat When You Are Sick And Have No Appetite?

There are 4 ways to eat when you are sick and have no appetite:

  • Choose foods that you like

Start by choosing your favorite meals. This is not the time to diet or being in a calorie deficit. Also, tell people around what you like.

  • Eat small and often

Small and often means you want to graze throughout the day. If a cooked meal seems like a challenge, have yogurt or cereals.

  • Eat snacks

Snacking during the day may be helpful. A nice variety of snacks can improve your sensory-specific satiety. This means the more variety we have, the more appetite we get. My favorite snack that is packed with proteins is Jack Links from Amazon. You can check out the prices “here“.

  • Try smoothies

Having a smoothie is a great choice because it can be delicious, nutritious, and easy to eat. Being creative and adding some fruits, milk, dark chocolate, and nuts can make your meal a really exciting part of the day. Try to avoid ready-to-eat smoothies with plenty of simple sugars.

Calorie Deficit While Sick

Calorie deficit while being sick can slow down the recovery process. Lack of appetite during sickness, poor absorption, loss of water, increased metabolic rate, and increased body temperature increases the demand for nutrients.

Can calorie deficit make you sick? Overall, the calorie deficit can make you sick, especially if you’re doing it for too long and with unhealthy foods. Not eating enough calories triggers a lot of metabolic adaptations, and without sufficient nutrients, the body can get sick.

During sickness the body experience lack there is a high demand for nutrients due to elevated metabolism, loss of water and low calorie

Some studies show that “calorie restriction” while being sick alter cytokine levels and enhance anti-inflammatory pathways. This however doesn’t modify sickness behavior.

Which means it is not recommended to diet while being sick (source).

During low-calorie intake:

  • Immune system defence mechanisms are lower
  • Defence against pathogens is compromised

However, reducing carbohydrates can help.

A high carb diet and high glycemic foods alter the white blood cells’ function and reduce their anti-inflammatory functions.

This means reducing foods that have a lot of simple and processed sugar and increasing foods that are high in proteins.

Calorie Deficit and Immune System

A strong immune system needs a sufficient amount of calories to work in its optimal way. A calorie deficit is great for fat loss, but over time it can start to affect other important departments in the body.

Does calorie deficit weaken the immune system? In general, calorie deficit does weaken the immune system because long-term calorie restriction creates several physiological changes that affect metabolism. Plus, long-term calorie restriction also increases susceptibility to a variety of parasites and infections.

The main caveat of scientific papers about calorie restriction, immunity, and infections is that majority of research is done on rodents in a laboratory setting (source).

So again, it depends.

Is dieting bad for your immune system? Overall, dieting isn’t bad for the immune system, as long as it’s done correctly. Reducing too many calories and not having enough essential micro and macronutrients can lead to malnutrition and can compromise immune system function.


Being sick is not fun. And depending on what you have, your body will burn slightly more calories at rest, comparing to the normal state.

But this shouldn’t be the motivating factor to lose weight. When sick, you should focus on improving your strength by adding plenty of protein-rich foods, whole foods, and even some supplements, if necessary.

Michal Sieroslawski

Michal is an exercise physiologist (MSc), nutrition coach, Ashtanga teacher, and fitness blogger. He shares his successes and failures to help busy men and women squash down 20, 50, or even 100 pounds of fat without leaving their home.

Leave a Reply

Your email address will not be published.

Recent Posts