Do you get sick easier when in a calorie deficit?

October 18, 2025 •

4 min read

According to a 2006 study, the effect of undernutrition on viral infections depends on the host's nutritional reserves at the time of infection. This highlights the complex relationship between your energy intake and immune function, especially when questioning if you get sick easier when in a calorie deficit.

Quick Summary

Severe or prolonged calorie restriction, particularly when coupled with poor nutrient intake and high stress, can weaken your immune system, increasing your risk of illness. However, a moderate and balanced calorie deficit does not necessarily compromise immunity and can have anti-inflammatory benefits.

Key Points

Severity Matters: Extreme calorie restriction, rather than a moderate deficit, is the primary cause of a compromised immune system during dieting.
Nutrient Deficiencies: Insufficient intake of key vitamins and minerals, like A, C, D, and zinc, can severely hamper immune function.
Stress Response: Drastic calorie deficits can increase stress hormones, such as cortisol, which directly suppresses the immune system.
Energy Prioritization: In a severe deficit, the body conserves energy for basic survival, leaving less fuel for the energy-intensive processes of the immune system.
Gut Health: Diet impacts the gut microbiome, which is closely linked to immunity; poor nutrition from extreme dieting can negatively affect gut health.
Moderate Deficits: Healthy, moderate calorie deficits (e.g., 300-500 calories) are generally safe for immune function and can even offer anti-inflammatory benefits.
Best Practices: Maintaining immune health during weight loss requires a balanced diet, adequate hydration, stress management, and sufficient sleep, in addition to a moderate calorie reduction.

For many, weight loss means a calorie deficit, but this process can have profound effects on the body's defense mechanisms. While a moderate and sensible approach can lead to health improvements, an extreme or poorly managed deficit can leave you more susceptible to illness and infection. Understanding the distinction between healthy, sustainable weight loss and dangerous restriction is crucial for protecting your immune system.

The Immune System's Energy Demands

The immune system is a complex network of cells and processes that requires a significant amount of energy and nutrients to function correctly. When your body is fighting off a pathogen, its metabolic demand increases to fuel the rapid production and mobilization of immune cells, such as T-cells, B-cells, and natural killer (NK) cells. In a state of calorie deficit, particularly an extreme one, the body's energy reserves are lower. It must prioritize energy expenditure for vital functions, and immune function can be deprioritized.

The Impact of Nutrient Deficiencies

A critical factor linking severe calorie restriction to compromised immunity is nutrient deficiency. When you drastically cut calories, it becomes difficult to consume a sufficient quantity and variety of foods to meet your needs for essential vitamins and minerals. Key nutrients vital for immune health include:

Vitamin A: Important for the development and function of immune cells.
Vitamin C: A powerful antioxidant that supports various cellular functions of the immune system.
Vitamin D: Crucial for modulating immune responses.
Zinc: Essential for the proper function of immune cells.
Iron: Necessary for immune cell proliferation.
Protein: Provides the amino acids needed to build and repair immune cells and antibodies.

Without an adequate supply of these nutrients, the immune system's ability to mount an effective defense is significantly hampered, making you more vulnerable to common infections.

Moderate vs. Extreme Calorie Deficits: A Comparison

The way you approach a calorie deficit matters immensely for your immune health. Here is a comparison of how different approaches impact your body:


Feature	Moderate Calorie Deficit	Extreme Calorie Deficit
Calorie Reduction	Gentle, typically 300–500 calories below maintenance.	Severe, involving drastic, unsustainable cuts.
Nutrient Intake	Focused on nutrient-dense foods to ensure sufficient vitamins, minerals, and protein.	High risk of nutrient deficiencies due to severely limited food variety and quantity.
Weight Loss Rate	Slow and steady (e.g., 1 pound per week).	Rapid and unsustainable.
Metabolic Impact	Can lead to gradual metabolic adaptation, but is manageable with healthy strategies.	Often causes a significant drop in metabolism and muscle mass.
Immune System	Generally does not compromise immune function and can lead to anti-inflammatory benefits.	Compromised immune function, increased susceptibility to illness and delayed recovery.
Energy Levels	Stable energy levels, with mindful hydration and sleep.	Fatigue, low energy, and sluggishness.

The Role of Stress and Hormones

Intense dieting is a form of stress on the body. This can trigger the release of stress hormones like cortisol. While a normal part of the body's response to stress, chronically elevated cortisol levels can suppress the immune system. This hormonal response, combined with the lack of sufficient energy and nutrients, creates a perfect storm for a compromised immune system. This effect is particularly pronounced when a calorie deficit is combined with strenuous physical activity, as seen in some studies on athletes.

The Gut Microbiome Connection

Your gut health is deeply intertwined with your immune system, and your diet plays a crucial role in shaping your gut microbiome. Severe calorie restriction and poor dietary diversity can negatively alter the composition of your gut bacteria, potentially compromising your immune defenses. Conversely, a balanced and nutrient-rich diet, even in a moderate deficit, can support a healthy gut microbiome, which in turn benefits immune function.

How to Maintain Immune Function in a Calorie Deficit

To ensure your weight loss journey doesn't come at the cost of your health, follow these guidelines:

Prioritize a moderate, slow deficit. A deficit of 300-500 calories is safer and more sustainable.
Focus on nutrient-dense foods. Prioritize lean proteins, fruits, vegetables, whole grains, nuts, and seeds to ensure adequate nutrient intake.
Stay hydrated. Dehydration can be mistaken for hunger and impairs bodily functions. Drinking plenty of water is essential.
Manage stress. Incorporate stress-reducing activities like meditation, yoga, or spending time in nature. Chronic stress elevates cortisol, which weakens immunity.
Get enough sleep. Poor sleep quality is a significant risk factor for a weakened immune system. Aim for 7-9 hours per night.
Avoid extreme or rapid weight loss. If a diet promises rapid, dramatic weight loss, it is likely unhealthy and will put your immune system at risk.

Conclusion

In summary, the answer to whether you get sick easier when in a calorie deficit is not a simple yes or no, but rather depends on the how. A severe or extreme calorie deficit that leads to nutrient deficiencies, hormonal imbalances, and increased stress will almost certainly weaken your immune system and increase your risk of illness. However, a moderate, well-planned deficit that emphasizes nutrient-rich foods and healthy lifestyle habits can be pursued safely and may even have overall health benefits. The key is to listen to your body, choose a sustainable approach, and prioritize nutrition alongside your weight loss goals.

For more research on the intersection of nutrition and health, consult reputable scientific sources like the National Institutes of Health (NIH).

Frequently Asked Questions

A healthy and sustainable calorie deficit is typically 300 to 500 calories below your maintenance level. This approach promotes slow, steady weight loss (about 1 pound per week) and reduces the risk of negatively impacting your immune system.

Ensure your diet includes foods rich in vitamins A, C, D, and E, as well as minerals like zinc and iron. Lean protein sources are also essential for building and repairing immune cells.

Yes, especially if the exercise is strenuous and combined with a severe calorie deficit. Some studies on athletes have found that intense physical activity paired with low energy availability increases stress on the body and can suppress immune function.

Not necessarily. When managed properly and ensuring adequate nutrient intake, moderate calorie restriction may not suppress immunity. Some research even suggests moderate restriction in humans can improve certain markers of immune function.

Dieting can increase the body's stress response, leading to elevated cortisol levels. Chronically high cortisol is known to suppress the immune system, making it harder for your body to fight off infections.

Yes. A healthy calorie deficit reduces the risk of immune compromise but does not eliminate it. Factors like exposure to pathogens, sleep quality, and underlying health conditions still play a major role in whether you get sick.

Warning signs of an overly extreme calorie deficit include extreme fatigue, frequent illness or slow recovery from sickness, constant hunger, hair loss, and mood swings.