One of the most common myths that I debunk is the idea that sugar is a common cause of vaginal yeast infections.
Whenever I write about this subject there is always one (but often more) person who becomes enraged and tells me “how dare” I write this because they get a yeast infection “immediately” after one bite of cake.
I would like to take the time to point out that it takes 15 minutes or so for ingested carbohydrates to make it into the blood stream and at least 24 hours, but more likely 48-72 hours, for any low levels of yeast to overgrow so any immediate symptoms can’t possibly be yeast. Immediately symptoms are a nocebo effect, essentially a negative placebo effect.
Most women have some yeast in the vagina. At any given time we might detect it in 20–30% of women by culture, but it is just hanging out part of the microbiome. Using more sensitive techniques for testing (like DNA amplification) that number is probably much higher, maybe even close to if not 100% . Why this normal yeast over grows and causes symptoms is not well understood. Sometimes it may be the lactobacilli (good bacteria) is failing to keep the normal yeast in check. Sometimes it is due to skin trauma, micro tears from sex or hair removal can allow yeast to enter the skin. For others the yeast may become more virulent and causes inflammation and symptoms more easily (basically at lower levels). However, if you do not have diabetes it is NOT what you are eating.
The vagina normally has sugar in the form of glycogen. This is what feeds the healthy bacteria (lactobacillus). The epithelial cells (vaginal lining) are full of glycogen and when they die they release their glycogen into the vagina to feed the good bacteria. The cells are then shed as part of the vaginal discharge. The vagina is basically built for sugar.
If healthy women without diabetes have a large load of sugar by mouth it does not change the level of vaginal glucose. We know this because A) if you do not have diabetes you will not have a pathologic spike in blood sugar and B) this has been tested. Most of the vaginal discharge comes from the vagina itself (cervical mucous and from the lactobacilli). Only a very small amount of fluid is transudate, meaning something that actually could transmit glucose from the blood stream to the vagina. And minute amountsof sugar in trasnudate (and this would be minute beacuse we are talking about < 1 ml of fluid) would be far less than the sugar from the glycogen that is constantly being dumped into the vagina.
It is true that women with diabetes are more likely to have vaginal colonization with yeast and that there is a relationship with vaginal and vulvar yeast infections for these women with regards to longer-term control of blood sugars. The prevailing thought as to how this happens is that it is due to the high levels of glucose in the urine. High levels of blood sugar spill into the urine, not the vagina. When we empty our bladders there is a microscopic (and sometimes a macroscopic) plume of urine that gets on the skin. If there is chornically a high level of glucose in the urine this could can cause increased adherence of yeast and bacteria to skin and mucosa, thus increasing the risk of both yeast infections on the vulva and in the vagina as well as bladder infections. Many women who have elevated blood sugars due to diabetes do not get yeast infections, so there are likely other factors that are also involved, such as immune system changes.
While I think there are many reasons to limit refined sugars (i.e. don’t eat them every day), fear of yeast for someone who does not have diabetes should not be one of them. A beer or a glass of wine, a well-buttered roll, or a slice of cake because is not going to upset your vagina. Anyone who says otherwise hasn’t bothered to learn the biology.