During the 2009 H1N1 influenza epidemic, more people with obesity were admitted to hospital than people with a normal BMI. The same seems to be true for the current COVID-19 pandemic.
How does obesity impair the immune system, and is there anything you can do to improve your immune response?
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Obesity is a complex disease and the immune system is a complex system so there is still a lot we don't know about the relationship between these two. We do, however, know that the effect of obesity on the immune system is a negative one.
Obesity leads to low-grade, chronic inflammation in body fat tissue which means your immune system is permanently switched on. Constant inflammation isn't good for your body as it can interfere with your immune response when you have an infection.
Inflammation is your body's normal reaction to injury or infection. It is the immediate response your immune system kicks off when faced with a problem – whether that's a twisted ankle or a virus. A twisted ankle typically swells up and turns red which means it is inflamed.
What may not be as commonly understood is that inflammation also occurs on the inside of your body.
In a normally functioning body, inflammation is a response to a problem. However, in the last decade scientists have observed that overweight and obese people often have chronic, low-level inflammation in tissue that is otherwise healthy.
For a long time, it was believed that fat cells (adipocytes) did little else than store and release energy. What we are beginning to understand is that the fat cells play an active role in defending themselves.
The problem, though, is that in obese people the fat cells act as if under attack by an infection or other foreign substance and send out false distress signals. The immune system then responds by activating inflammation in the fat tissue.
As mentioned earlier, constant inflammation isn't good for your body. Among other complications, it is believed that it can lead to metabolic diseases such as type 2 diabetes and cardiovascular disease.
But the chronic inflammation can also interfere with your body's response to infections. During the 2009 H1N1 influenza epidemic, doctors noticed that a disproportionate number of patients admitted to hospital were overweight or obese. The same seems to be true of the current COVID-19 pandemic.
A study from France found that among patients admitted to hospital with COVID-19, obese patients were more likely to present with severe symptoms and much more likely to have critical symptoms of the disease requiring intensive care.
We also know that obesity leads to higher rates of vaccine failure and a greater risk of complications from infection after surgery.
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You've probably heard of plenty of products meant to fight inflammation in your body but, as a starting point, you can eat fewer foods that cause inflammation. Foods that cause inflammation are also otherwise generally considered unhealthy, such as foods high in saturated fat and/or refined carbohydrates (processed meats, white bread, pastries, cakes, cookies, sugar, highly processed snacks).
Conversely, an overall healthy diet with plenty of fruit and vegetables is also an anti-inflammatory diet. Think tomatoes, fruit, nuts, olive oil, leafy greens and fatty fish.
In the long run, if you're overweight or obese, losing weight can have a positive effect on your immune system.