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Your Body Weight and Your Immune System

Last week, we looked at how a healthy diet can strengthen your immune system. This week we go to the next step to consider your body weight and your immune system. Body weight is one of the eight fundamentals of a healthy immune system, but it may be particularly important when you are at risk for respiratory diseases like Covid-19.

Infection causes your white blood cells (macophages) to release inflammatory proteins called cytokines. Cytokines are good, because inflammation is your friend when it comes to infection. But inflammation is also what produces your symptoms when you’re sick. Fever? Cough? Runny nose? Muscle aches? Those are all the result of inflammation. With ordinary cold or flu, you just have to get through it. When the infection is eliminated, the inflammation subsides and you get back to normal. But what if the inflammation didn’t subside?

The Trouble with Fat

It turns out that fat, particularly belly fat (as opposed to subcutaneous fat) secretes cytokines, even without the presence of macrophages. That means it does this whether or not you have an infection. When you have excess belly fat, your body can be in a constant state of low-grade inflammation.

There is a relationship between fat, inflammation, and the immune system. A 2010 study of gastric banding patients provided direct evidence of the relationship. Researchers found that weight reduction leads to a reduction in hormones secreted by fat cells, including immune reaction hormones and cytokines. This shows that obesity leads to inflammation, and weight reduction leads to less of it.

Body Weight and Your Immune System

In another study, Canadian researchers examined 12 years of flu season records in Ontario. They reported in 2011 that “severely obese individuals with and without chronic conditions are at increased risk for respiratory hospitalizations during influenza seasons.” It seems that the chronic inflammation caused by severe obesity compromises the immune system and reduces your ability to fight off infection.

What’s the difference between normal weight, overweight, and obese? The CDC defines normal weight as having a BMI (body mass index) of 18.5 to 25. Overweight is 25 to 30. More than 30, and you’re considered obese. Severe obesity is 40 or higher, and the CDC says people in that group are at risk of severe illness with Covid-19. If you don’t know your BMI, the CDC has a calculator online to help you figure it out. You put in your height and your weight, and it gives you the number.

Just last week, a large study of Covid-19 patients in a New York hospital system found a relationship between obesity and the severity of Covid-19 symptoms. Patients with a BMI of 30 to 34 were twice as likely to be admitted to acute care and 1.8 times as likely to be admitted to critical care compared to patients with a BMI under 30. All patients were less than 60 years old. The authors concluded that “obesity appears to be a previously unrecognized risk factor for [Covid-19] hospital admission and need for critical care.”

Your Ideal Weight

BMI is a good way to categorize patient populations. But my advice is to treat your BMI only as a starting point to determining your ideal weight. When it comes to your immune system, BMI by itself may not mean much. What should concern you is the proportion of fat in your body. According to Healthline, there are 10 ways to measure your body fat. Many of them involve sophisticated, expensive machines. But there are calculators on the web that can get you in the ballpark, such as this one, which uses a formula developed by the U.S. Navy. All you need is your height, weight, and a tape measure.

Beyond essential fat (10-13% for women, 2-5% for men) the American Council on Exercise specifies three healthy ranges of body fat, depending on your athleticism and fitness. Athletes and fit people tend to be leaner than ordinary people. Since they would mess up the scale for “normal” people, they get their own ranges. For men, good health lies under 24%. For women, you can go up to 31%.

Start with the tape measure and calculator to get an idea of where you are. You probably have a fairly good idea of where you stand just by looking at your waistline. If you have the money, you can always line up one of the more accurate measurement methods after the emergency is over. But if you think you could stand to lose some fat (and if you’re a normal person, you probably could), get to work on your diet and exercise. Because of the relationship between fat and the immune system, if you get your weight on track, you’ll likely strengthen your immune system as well.