When we eat a meal, blood sugar levels rise, peaking 1-2h postprandially (post-eating) & normalizing by 3-4h postprandially. Sugar in the blood is problematic so insulin rises after eating to help shunt glucose out of the blood & into the tissues.
Much of what we know about sugar & immunity comes from looking at diabetes - a condition where hyperglycemia (too much sugar in the blood) is a defining feature. Sustained high blood glucose (for example in poorly controlled diabetes) can cause a dysfunction of many components of the immune system increasing risk for several inflammatory conditions, more frequent infections, complications & reduced recovery.⠀
There are numerous mechanism by which hyperglycemia has negative effects on immunity:
1️⃣Enhanced virulence of infectious germs by changing molecules on our cells surfaces ex. Advanced Glycemic End (AGEs) products: sugars stick on our own proteins disrupting their function & trigger unruly inflammation.
2️⃣Dicarbonyls are breakdown products of glucose that interfere with infection-controlling antimicrobial immune molecules called β-defensins. Beta Defensins are small proteins that function in antimicrobial defense by penetrating a microbe's cell membrane and cause microbial death in a manner similar to that of antibiotics
3️⃣Immune responses are energetically costly & have varying needs for different metabolic fuels (proteins, carbs & fats) depending on what function they are carrying out. Blood sugar needs to be able to get into immune cells so they can carry out their function. But if insulin control of blood sugar is not working properly, then energy can’t get from blood to cells & immunity can be compromised.
4️⃣Increased oxidative stress, a disease-causing mechanism that links elevated blood sugar & insulin resistance with the dysfunction of certain crucial protective mechanisms in the body, which over time leads to inflammatory disease e.g. heart disease.
These are just SOME of the problematic mechanisms at play with poor glycemic control. But what if you are not diabetic? Glycemic control is still really important to overall health. But before you say ‘sugar is bad’ consider that this doesn't make sense unless you also consider what your overall diet looks like. Context matters.