Can diet affect our ability to ward off the flu?
You’ve heard the old wives tales about chicken soup curing everything and an apple a day keeping the doctor away, but does diet really play that big of a role in protecting you from the flu? As we prepare to enter the sugar-laden Christmas season, I think it’s worth exploring how diet (especially eating too much sugar) can impact your risk of getting the flu this year.
Studies on how sugar impacts the immune system have been going on since the 1940’s when Dr. Benjamin Sandler looked at sugar and the susceptibility to Polio1. Dr. Sandler found that higher sugar diets made patients more likely to get the polio virus. The proposed mechanism was by affecting insulin response. The constant high intake of sugar lead to an increase release of insulin which lead to an over correction and much lower blood sugars than desired. Dr. Sandler proposed that these drastic swings in blood sugars decreased the cells ability to mount up adequate immune response and increased risk of developing the virus.
Another proposed mechanism deals with your gut microbiome (the bacteria in your gut)2. These bacteria either can help protect you or harm you depending on what you feed it. High sugar diets feeds bacteria that can be harmful for the body. This increase in harmful bacteria can put you at risk of being more susceptible to certain viruses and bacteria. One study found that certain bacteria in the gut could increase the risk of developing Polio 500%. Other studies showed similar effects with other viruses, including measles.
Another big concern with high sugar meals, is that neutrophils (the part of the immune system responsible for destroying foreign bacteria and viruses) are slowed down after consuming a high sugar meal3,4. High sugar intake also slows down macrophage activity (the part of the immune system that “eats” foreign invaders and helps to destroy them)5. Meaning, if you eat that whole pecan pie ala mode and then Aunt Sally sneezes on you- your immune system is in a sugar coma and can’t start attacking the invaders as efficiently. I always like to think about the family football game after Thanksgiving. If you’ve eaten that huge meal, you’re more likely to let Uncle Brian slip through your defenses and score a touchdown because you just can’t quite catch up to him and you’re feeling too sluggish to try anything too exciting. However, take that same scenario before eating that Thanksgiving meal- Uncle Brian, you’re going down! The good news in all of this, eating complex carbohydrates (things like veggies and whole grains) don’t have the same immune slowing impact.
Excessive sugar has been also associated with increased damage to cells6. Excessive sugar can bind to the protein in your arteries, joints, muscles, and organs (a process called glycation). This can lead to nerve damage, organ failure, and thickened arteries. Even in children, there is significant increase in cell damage by the age of 3 with higher sugar intake. Keeping in mind that we need these healthy cells to be able to fight off any viruses that we are exposed to.
As a dietitian, I encourage people to focus on nutrient dense, high quality diets. High intake of sugar displaces these necessary nutrients to help support your immune system. There is a complex mechanism controlling fullness and hunger mostly controlled by blood sugars7. Your body thinks it’s getting what it needs and is “full” when you eat high sugar meals, yet you are missing the vitamins and minerals your body needs to function optimally. Often, I see people that are over-fed, but under-nourished. Take a classic sugar cookie. You’re going to get a nice dose of sugar but not much else. It is devoid of vitamins and minerals, yet your body thinks it had enough calories to meet its vitamin and mineral need for that snack. On a side note, there is a recent study showing that you might be doing harm to your immune system by completely limiting carbohydrates8. In general, I would much rather you get an appropriate amount of carbohydrates from things like fruit, whole grains, and sweet potatoes rather than high processed sugar foods like cookies, pies, and candies.
A sugar cookie here and there isn’t going to derail you. BUT it is important to not overdo the sugar this holiday season AND make sure you are getting nutrient dense foods along with your sugary treats.
A couple of tips to help make this Christmas season most successful for your immune system:
- If you receive a bunch of sweets at work (I’m looking at you teachers)- pick a few that you are excited to enjoy, and then pass that blessing onto someone else. You don’t have to keep and eat everything.
- Make sure you’re not skipping meals. If you’re hungry- you’re more likely to overindulge in sugar-laden foods. This goes for Christmas day. Don’t wait for that massive Christmas dinner to eat- eat something for breakfast and lunch so you’re not starving by the time you get to that meal (and are more likely to overdo it).
- Similarly, make sleep a priority. It is harder to say no to sugar when your body is sleepy. This also weakens your immune system.
- For the love of everything- eat your veggies. Please. Just put something green on your plate (that green Jello casserole does not count).