When the first wave of Covid hit the U.S., it became clear that the majority of patients being placed on ventilators had a series of underlying conditions. Among those were metabolic disorders like obesity and diabetes, both of which have been surging in the U.S. over the past few years.

A question that puzzled people at the beginning of the pandemic was: Why does diabetes make it harder to fight a respiratory virus?

First, we know that the SARS-CoV-2 virus can make blood sugar control worse in the short term and can potentially throw people with diabetes into a very dangerous blood sugar state, studies show. It does this by binding itself to the receptors found on the beta cells of the pancreas, which produce insulin.

As an allergist and immunologist, I frequently tell my patients that having diabetes means you're in a chronic low-grade inflammatory state, which taxes the body's innate immune system and makes it slower to jump on pathogens when they enter the body.

When it comes to our immune system, what we eat matters a lot. And no ingredient is more detrimental to your immune health than sugar, especially during Covid.

Sugar: The worst food ingredient for your immune system

When you have high blood sugar — which is caused by many factors, but the biggest is consuming too much of it in your diet — it starts a vicious cycle of insulin resistance and obesity that drives up inflammatory cytokines, damages blood vessels, and activates the immune system to repair those areas.

This creates a major distraction for the immune system and paves the way for dangerous bacteria and viruses to slip through our body's defenses.

If you've already been diagnosed with prediabetes or diabetes, this may sound like bad news. But it's not; Type 2 diabetes doesn't have to be permanent.

Eliminating excess sugar from your diet can not only help end this cycle, but it can reverse it completely. Dialing back your sugar consumption is one of the most effective ways to improve your immune system.

Sugar is hiding everywhere

You might be thinking: I'm not really a sweets person, so I don't need to worry about this!

But even if you don't eat donuts, candy, cakes or cookies regularly, having too many simple carbs like bread, pasta, rice, cereal or even certain fruits and juices may be silently driving up your blood sugar.

People often forget — or don't realize — that sugar is in ketchup, salad dressings and lattes, as well as in juice, yogurt, cereal and protein bars.

I'm all about preventative care, especially when it comes to an insidious disease like diabetes, and recommend that the first step you take in your nutrition journey — regardless of age — is to ask your doctor to perform a fasting hemogoblin A1c test, even if your fasting blood glucose is normal.

Hemogoblin A1c tests measure average blood sugar over the previous three months, so even if your blood sugar is normal the day you see your doctor, the test can catch underlying issues.

How to protect your blood sugar health

Once you have an idea of where you stand on the blood sugar spectrum, take the steps below for better health:

1. Cut back on obvious sugars.

This means candy, soda, cake and those seasonal flavored lattes we all love. These foods and drinks don't provide any nutritional value, and they contain massive amounts of sugar.

Instead, opt for dark chocolate, berries or another low-sugar treat. I'm not saying you have to take out all sugary foods forever. The occasional dessert is fine! But at the beginning, it's important to get to a place where your blood sugar is stable and healthy.

2. Read the labels.

Now it's time to check the amount of added sugar in every item in your pantry — and I mean everything, even things advertised as "low in sugar" or "healthy."

The average American takes in about 17 teaspoons (71 grams) of added sugar a day, but the American Heart Association recommends no more than six teaspoons (25 grams) of added sugar a day for women, and nine teaspoons (36 grams) for men.

Remember, we still get natural sugars from fruits, vegetables and grains, so we're certainly not deficient!

3. Eat more fiber.

If sugar is poison, then fiber is the antidote. Fiber not only keeps your digestion regular, it also helps slow the absorption of sugar into your bloodstream, which protects you from sugar spikes.

Lack of fiber is another reason why sodas, fruit juices and sugared coffee drinks are so detrimental to your health. They contain a ton of sugar and none of the blood-sugar-protecting fiber that fresh whole plant-based foods have.

Some of my favorite high-fiber foods are black beans and lentils, steel-cut oats, avocados, buckwheat, pears, raspberries, barley and flaxseeds.

4. Chose nutrients over calories.

Instead of worrying about cutting calories, focus on adding more nutrient-dense foods to your diet, with lots of proteins and healthy fats.

You don't need to go low-carb, just choose the "right" carbs. In fact, eating carbs in the form of vegetables, beans, whole fruits, and nuts and seeds — all mineral- and vitamin-rich foods — is a great way to keep those hunger pangs at bay.

There are several apps to help you track your intake. I have all my patients log their eating for a few days to see how much added sugar, fiber and other nutrients they're actually getting. It's often very eye-opening.

Dr. Heather Moday is a board-certified allergist, immunologist and functional medicine physician. She is also the author of "The Immunotype Breakthrough: Your Personalized Plan to Balance Your Immune System, Optimize Health, and Build Lifelong Resilience." Follow her on Instagram @theimmunityMD and Facebook.

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