Blood Sugars and Fertility: Glycemic Index, Glycemic Load and Insulin Resistance

blood sugars and fertility

One of the key reasons that it’s important to have the right amount and type of carbs when TTC is the relationship between blood sugars and fertility. We know that consuming a moderate amount of carbs – preferably whole grains– is probably the best option for fertility.

As well as choosing whole grains, it seems that the glycemic load of the carbs we eat is also really important. 


Glycemic Index and Glycemic Load

Before we look at the evidence on blood sugar and fertility, let’s get some definitions out of the way. Here’s how Harvard explains glycemic index and load: 

Glycemic index (GI) assigns a score to a food based on how drastically it makes your blood sugar rise. Foods are ranked on a scale of 0 to 100, with sugar given a value of 100. The lower a food’s glycemic index, the slower blood sugar rises after eating that food.

But the glycemic index tells just part of the story. To understand a food’s complete effect on blood sugar, you need to know both how quickly it makes glucose enter the bloodstream and how much glucose per serving it can deliver. A separate measure called the glycemic load does both — this gives you a more accurate picture of a food’s real-life impact on your blood sugar. Watermelon, for example, has a high glycemic index (80). But a serving of watermelon has so little carbohydrate that its glycemic load is only 5.

Blood Sugars and Fertility: How Does GI/GL Affect Fertility?

In The Nurses Study researchers looked at the main carb sources in the group with ovulatory infertility. Overall, they found that high glycemic index foods (such as cold breakfast cereals, white rice and potatoes) were associated with infertility. Low glycemic index foods (such as brown rice, pasta and dark bread) were associated with a reduced risk. But this was not consistent across all foods they looked at. However, in general, dietary glycemic load – rather than the glycemic index of specific foods-  was associated with a higher risk of infertility due to anovulation.

A more recent study looked at two groups trying to conceive, one in the US and one in Denmark.  Over both groups they found that when women with the highest glycemic load, the couple had a 14% lower chances of becoming pregnant than when the woman had the lowest glycemic load. 

A high GL diet may also increase the chance of pregnancy complications. One study found that a pre-pregnancy diet with high glycemic load was associated with an increased risk of gestational diabetes in pregnancy.

Blood Sugars and Fertility: Why is Low Glycemic Load Important?

It all comes down to our blood sugars and the relationship between our reproductive hormones and another hormone, insulin. 

Insulin is a hormone that regulates the amount of glucose (or sugar) in our blood. When our cells don’t respond properly to insulin, this leads to insulin resistance, where we see high levels of both insulin and glucose in the blood. This can be the early stages of diabetes or pre-diabetes. 

Too much insulin in the blood also messes with our reproductive hormones. Lots of evidence suggests that insulin sensitivity may be a key factor in ensuring ovulation and maintaining fertility. It may also affect our egg health. Animal studies show insulin resistance contributes to oxidative stress and disrupts mitochondrial function in oocytes (eggs).

A huge study, with over 2 million women, looked at blood sugar levels and found that women with higher blood sugar levels had an increased time to pregnancy, even if they didn’t have diabetes. 

The food we eat, in particular, the amount and type of carbs, has a huge impact on blood sugar levels and over time, insulin resistance. We know that low GL diets improve blood sugar levels and insulin sensitivity and high GL diets lead to increased blood sugar and insulin resistance.

Blood Sugars and Fertility: How To Manage Your Blood Sugars?

  • Make sure your portion of carbs makes up about ¼ of your meal, a fist sized serve of carbs is a good aim, with the rest of the meal be made up of ½ low starch veggies and ¼ protein 
  • Generally whole grains have a lower GI than refined grains
  • Heavily processed food is almost always higher GI than something you make yourself
  • Fibre, fat, protein and acid are known to slow digestion of carbs and so help to make your blood sugar levels rise more gradually. If possible include some or all of them in all meals and snacks
  • Eating the protein, low carb vegetable or fat part of a meal prior to the carbs can help blood sugars rise more gradually. For example, starting your meal with a salad (including acid in the dressing and some healthy fats and protein, like nuts or cheese) can make sure your blood sugar levels rise gradually

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