Do You Burn More Calories When Sick? Understanding How Illness Affects Your Metabolism

When you’re sick, it’s common to feel a loss of energy, weakness, or fatigue. You may also experience changes in appetite, making you wonder if your body is burning more calories than usual. After all, when you’re under the weather, your body is working hard to fight off an illness. But does this mean you burn more calories when you’re sick?

In this article, we’ll break down how your metabolism reacts when you’re sick, and whether or not your body burns more calories during illness. From the effects of fever to the role of your immune system, we’ll explore what happens to your body during sickness and how it affects your energy needs.

How Your Body Burns Calories

To understand whether you burn more calories when sick, it’s important to first understand how your body burns calories in the first place. Calories are the units of energy your body uses to perform various functions, including breathing, digesting food, and maintaining body temperature.

Your body’s metabolism is the process by which it converts food into energy. The rate at which your body burns calories is known as your basal metabolic rate (BMR). BMR is influenced by a variety of factors, including age, gender, muscle mass, and overall health. When you’re sick, this rate can fluctuate, depending on the type of illness and how it affects your body.

How Illness Affects Calorie Burn

When you’re sick, your body goes into “defense mode” to fight off infections. This requires more energy and, in turn, can cause an increase in the number of calories burned. The effect varies based on the type of illness you have, but common factors include:

1. Fever

Fever is a common symptom when you’re sick, and it can increase the number of calories your body burns. When your body temperature rises, your metabolism speeds up to help fight the infection. This increased metabolic rate is partly responsible for burning more calories when you have a fever. A study published in the Journal of Clinical Investigation showed that a fever of about 1.8°F can increase calorie burn by as much as 10-13%. So, if you’re running a fever, you are likely burning more calories than usual.

1. Infections

When you’re fighting an infection, your body’s immune system is working overtime to protect you. This can also lead to an increase in your calorie expenditure. The body produces more white blood cells to fight off bacteria and viruses, and this process can burn extra energy. For example, common illnesses like the flu or cold can result in slightly higher calorie burn due to the immune response.

1. Inflammation

Infections and other illnesses can trigger inflammation in the body. This process requires energy, and the longer the inflammation lasts, the more calories your body may burn. This is why chronic illnesses or prolonged illnesses can lead to higher calorie expenditure compared to short-term sicknesses.

Do You Burn More Calories When Sick with Cold or Flu?

When you have a cold or the flu, your body has to work harder to fight off the virus. In addition to fever, you might also experience chills, muscle aches, and a feeling of fatigue. While this doesn’t necessarily mean you’re burning significant extra calories, it does indicate that your body’s metabolism is working overtime.

During these types of illnesses, your body requires more energy to generate heat (in the case of chills) or to fight off the virus. However, you’re also more likely to experience a reduced appetite and a decrease in physical activity, both of which could offset the additional calories burned.

How Your Body Responds to Different Illnesses

Not all illnesses result in the same increase in calorie burn. The type of illness and its severity can have a significant impact on your metabolism. Some illnesses can cause a slight increase in calorie burn, while others may cause a more substantial rise. Understanding how different illnesses affect your body’s energy expenditure can help you manage your health better and understand the importance of proper nutrition and hydration during illness.

1. Cold and Flu

A cold or flu can increase your calorie burn slightly, especially when you have a fever. A fever raises your body temperature, forcing your body to work harder to regulate it, which in turn increases your metabolic rate. The body uses more energy to fight off the infection, resulting in the burning of extra calories. However, many symptoms associated with the cold or flu, such as a sore throat, congestion, fatigue, and body aches, may reduce your activity level and make it harder to maintain a high level of physical activity. This can counterbalance the increased calorie burn. Despite the rise in metabolism, it’s important to allow your body time to recover. Resting and staying hydrated are essential for supporting the immune system and ensuring the body has enough energy to fight off the infection. While you might be burning a few more calories than usual, overexerting yourself during illness can slow recovery.

1. Stomach Illness (Gastroenteritis)

Stomach illnesses, such as gastroenteritis or food poisoning, can lead to an increase in calorie burn, but often in a less efficient way. When you’re battling nausea, vomiting, and diarrhea, your body is working hard to flush out the infection and stay hydrated. The body uses more energy to fight the infection, but the lack of appetite and inability to keep food down can make it challenging to provide the necessary nutrients for recovery. In these cases, the slight increase in calorie expenditure may be outweighed by the lack of fuel, which can cause the body to lose weight rapidly. While your metabolism may be slightly elevated due to the body’s immune response, the absence of proper hydration and nutrition can slow down recovery and deplete energy reserves. Therefore, it is crucial to stay hydrated with fluids like water, electrolyte drinks, and broths to replenish lost nutrients and aid the healing process. Resting is also important so that the body can direct energy toward fighting the illness rather than being diverted by activity.

1. Chronic Illness (Cancer, HIV/AIDS, etc.)

Chronic illnesses such as cancer, HIV, and other long-term conditions can have a much more significant impact on your calorie expenditure. When the body is battling a chronic illness, it often experiences a prolonged inflammatory response, which can lead to a substantial increase in calorie burn. In many cases, the body enters a state of accelerated metabolism, known as cachexia, which leads to unintentional weight loss. This is especially common in cancers, where the body’s energy demands rise due to both the disease and treatments like chemotherapy. Similarly, HIV/AIDS can cause significant weight loss due to the body’s continuous battle to fight infection. During these times, the body burns more calories to support its constant fight against the disease and repair damaged tissues. This metabolic increase is much more pronounced than during a short-term illness like the flu. Because of the higher energy needs, individuals with chronic illnesses may experience a faster rate of weight loss. Proper nutrition becomes even more crucial to counterbalance the calorie loss and maintain strength. In such cases, a careful balance of nutrient-dense foods and adequate calorie intake is required to avoid malnutrition and muscle wasting.

Calorie Burn and Weight Loss While Sick

While you might burn more calories when you’re sick, it’s not always a good thing if you’re trying to maintain or gain weight. Being sick can lead to a loss of appetite, and if you don’t eat enough to match the calories you burn, you may lose weight.

If you’re already underweight or concerned about losing too many calories while sick, it’s essential to focus on eating nutrient-dense foods that provide energy without overloading your system. Foods high in vitamins, minerals, and healthy fats can help support your immune system while ensuring you get the calories needed to recover.

Does Being Sick Affect Muscle Mass?

While you may burn more calories when you’re sick, there is a risk of losing muscle mass if your illness causes extended periods of inactivity or a lack of nutrients. Muscle mass can begin to decrease when you’re not eating enough or engaging in physical activity for a long time.

If you are bedridden for an extended period, it’s crucial to maintain protein intake to prevent muscle loss. Your body will use stored proteins for energy if you’re not consuming enough, which can lead to muscle breakdown.

How to Manage Your Calorie Intake While Sick

When you’re sick, it’s still important to eat balanced meals to fuel your body, even if you don’t feel like eating. Here are some tips for managing your calorie intake while sick:

• Stay Hydrated: Illnesses like fever, vomiting, or diarrhea can dehydrate your body. Drink plenty of fluids like water, herbal teas, and broths to stay hydrated.

• Eat Smaller, More Frequent Meals: If you’re struggling with appetite, eating smaller meals throughout the day can help ensure you’re still getting the nutrients you need.

• Focus on Easy-to-Digest Foods: Choose easily digestible foods, such as soups, smoothies, or plain crackers, that can provide essential nutrients without irritating your stomach.

• Prioritize Nutrient-Dense Foods: Even if you can’t eat large amounts, aim for foods that are rich in vitamins and minerals to support your immune system and overall health.

The Impact of Illness on Metabolism in Older Adults

As we age, our metabolism naturally slows down, which can make it more difficult for older adults to burn calories efficiently. This slower metabolism is due to factors such as reduced muscle mass, hormonal changes, and less physical activity. Muscle tissue, being more metabolically active than fat, plays a key role in calorie burning, so as muscle mass declines with age, calorie expenditure decreases. When older adults become sick, their metabolism may not increase as much as it would in younger individuals, leading to a smaller boost in calorie burn during illness.

Additionally, older adults may face challenges in maintaining their nutrition during illness, such as reduced appetite or difficulty eating, which can further complicate the issue. This can result in weight loss, which is especially concerning as it can exacerbate existing health problems, such as muscle weakness or malnutrition. The combination of a slower metabolism, decreased muscle mass, and potential issues with eating means older adults may struggle more during illness, making recovery slower and more difficult. Therefore, proper nutrition and care are crucial for helping older adults maintain their health and support their metabolism while sick.

How Hydration Affects Calorie Burning When Sick 

When you’re sick, hydration becomes even more essential for maintaining your body’s natural functions, including metabolism. Water plays a vital role in almost every bodily process, from digestion to circulation. Without enough fluid intake, your body’s ability to burn calories and metabolize food efficiently decreases. Dehydration can also cause fatigue, making it harder for your body to perform essential tasks like fighting off infection or maintaining an active metabolic rate.

Drinking enough fluids while sick helps regulate your body temperature, aids digestion, and supports the circulatory system, all of which can enhance energy expenditure. When properly hydrated, your body can more effectively break down nutrients and produce energy, thus improving the efficiency of calorie burning. This is especially important when you’re sick, as your body requires more energy to heal. Additionally, hydration can help you feel better overall, keeping your energy levels up and potentially preventing unnecessary weight loss associated with illness. To ensure optimal recovery, it’s crucial to drink water, herbal teas, or electrolyte-rich beverages regularly while sick to maintain your metabolism and keep your body functioning at its best.

Conclusion: Do You Burn More Calories When Sick?

In short, yes, your body can burn more calories when you’re sick—especially if you have a fever, infection, or inflammation. However, the increase in calorie burn may not be as significant as many think, and it can be offset by reduced physical activity and lack of appetite. It’s important to balance your calorie intake to ensure that you’re still nourishing your body during illness, even if you aren’t as active. If you’re concerned about your weight or how an illness is affecting your metabolism, consider consulting a healthcare professional for advice on managing your nutrition during recovery.

By understanding how your body burns calories when you’re sick, you can make better decisions about food, hydration, and rest to ensure a smoother recovery.