Researcher blogs

Ah, the holiday season. A great time to take some vacation, spend time with family and friends, open presents, and, of course, enjoy a nice meal.

However, while the succulent meats and sugary desserts taste really good, it doesn’t mean that they’re good for us. They can wreak havoc on all sorts of body systems, but one in particular that I would like to consider is your immune system. In particular, these little cells called CD4 T helper cells.

What are CD4 T helper cells?

T helper cells, which can be recognized by the CD4 molecule on their surface, are white blood cells that “help” direct your immune system in an appropriate way. Their importance can be found most dramatically in diseases where they are absent, such as human immunodeficiency virus (HIV) or in the case of the “bubble boy.”

CD4 T cells come in various “flavors.” To keep inflammation down, regulatory “Tregs” teach your cells to tolerate unharmful things such as food and pollen. On the other hand, effector CD4 T helper (Th) cells such as Th1, Th2, and Th17 cells are pro-inflammatory and help protect your body from infections. A balance of these cells needs to be maintained in order to avoid excessive tolerance and inflammation. Tregs, for instance, can suppress anti-cancer immunity, whereas Th17 cells drive inflammation in several autoimmune diseases.

Several studies have found that the “Western-style” diet found in countries such as Sweden can affect CD4+ T cells. A Western-style diet contains high levels of saturated fats, cholesterol, simple carbohydrates, and alcohol. Your holiday dinner table will likely contain most (if not all) of the following four components. May this blog post be a guide to what you should consider before making your food choices.

1. Fat

High fat diets (HFDs) have earned their bad reputations. These diets (which are defined by a diet in which 35% of all calories come from fat) have been associated with weight gain, high cholesterol levels, increased risk of cardiovascular disease, and more. Interestingly, many of the negative effects of a HFD can be linked to changes in the immune system. The proposed cause of cardiovascular disease, for instance, has changed from clogging of arteries with saturated fats to a chronic inflammatory condition.

Diets high in saturated (but not polyunsaturated!) fat led to more pro-inflammatory CD4 T cells in mice. In addition, mice fed a HFD have fewer Tregs and develop worse colitis than those fed a normal diet. Thus, animal studies associate HFDs with increased inflammation that are at least partly explained by changes in CD4 T cells.

This holiday season, it’s worth taking a minute to consider if that delicious chicken skin or fried potatoes are really worth it, or if they can be replaced by healthier, low-fat options such as roast potatoes.

2. Cholesterol

The connection between cholesterol and health is complicated. While diets high in cholesterol have gotten a bad rep, a common confounding factor has been that high cholesterol foods often also contain high levels of saturated fats. Saturated fats affect how your body processes cholesterol and can thus lead to high cholesterol levels in the blood. Cholesterol is naturally made in the liver and medical experts are increasingly realizing that the amount of cholesterol you eat doesn’t actually make a huge impact on your cholesterol levels. In fact, cholesterol from the food you eat barely makes it to your bloodstream.

Some biological processes that rely on cholesterol include building cell walls and making hormones among others. Since T cells rely on membrane-membrane interactions, it is not surprising that cholesterol levels can have a big impact on their activation and function.  

The data on cholesterol and T cells suggest that cholesterol can actually be anti-inflammatory. For one, cholesterol sensing is essential to control the number of activated T cells during homeostasis. Cholesterol leads to an increase in Tregs in both the liver and spleen as well as a decrease in inflammatory molecules.

Unfortunately, which cholesterol may not be so bad for you or your CD4 T cells, the number of foods that have high cholesterol but low saturated fat contents is rare. It might be worth considering replacing some of that red meat and sausages with shrimp or one of these healthy egg recipes.

3. Sugar (simple carbohydrate)

In addition to high amounts of fats, Western-style diets contain a shift in carbohydrate sources that have been linked to disease. The easily-absorbed simple sugars found in candy bars has largely replaced the undigestible fiber found in fruits. This change has impacts on our bodies in several ways, from changing our healthy gut bacteria to, you guessed it, altering our CD4 T cells.

Mice fed a high sugar diet had changes in the bacteria found normally in their guts. This study also found the intestines of these mice to be more permeable and thus prone to disease.

People with high blood sugar levels have been shown to have weakened immune responses but higher levels of an inflammation marker in their blood. In addition, a high sugar diet has been associated with greater risk for developing autoimmune diseases.

Apparently, at least some of the effects sugar exerts on the immune system can be traced back to how to changes in CD4 T cells. CD4 T cells cultured in vitro are more activated when cultured in media containing high sugar levels. Intriguingly, diets high in glucose tips the balance away from Tregs and towards Th17 cells, resulting in worse disease outcomes in mouse models of colitis and encephalitis. Thus, changes to CD4 T cells following excess sugar found in Western-style diets may explain the increase in autoimmune diseases found in developed countries.

Thus, it might be better to skip the simple and try adding instead the more complex carbohydrate explained below.

4. Fiber (complex carbohydrate)

Fiber, on the other hand, is a type of carbohydrate that is digested by our gut bacteria into short chain fatty acids (SCFAs) and leads to reduced inflammatory conditions. SCFAs can directly affect CD4 T cells and lead them to become anti-inflammatory Tregs. In addition, SCFAs themselves have been found to reduce intestinal inflammation in animal models.

While the seasonal cookies and cakes are difficult to avoid, perhaps a fun fruity alternative could be just as tasty for you and keep your CD4 T cells happier.