Well, a recent systematic review, that is, a study of other studies, found that a lower carb diet for obese or overweight women with PCOS prior to pregnancy seems to reduce pregnancy complications. It’s thought that both the weight loss that came from the low carb diets and the effect on hormones of reducing carbs lead to the positive effects. But it’s unclear if a similar effect would have been seen with reduced calories from other macronutrients.
The authors of the review also recommend that the diet be undertaken in the earlier stages of conception rather than immediately before, due to potential affect on oocyte (egg) health.
One study found poorer egg quality with a low carb diet, even when it achieved weight loss. They believed it was likely the result of ketosis harming the eggs. And we know that in mice, a ketogenic diet negatively affects maternal fertility, leading to both a decrease in pregnancy rates and litter size.
We don’t really have enough evidence on it the affect of a low carb diet on fertility. If you’re getting adequate energy and still consuming plenty of whole grains and fruit, a moderately low carb diet is likely to be okay, and maybe even good for fertility due to its affect on blood sugar levels.
On the other hand, it’s likely a very low carb, ketogenic type of diet, is going to harm fertility. Especially if it’s not providing adequate energy for ovulation.
The Nurses Study looked at lots of different aspects of carb intake and how they affected ovulatory fertility.
They found women with the highest carbo intake had a 78% greater risk of ovulatory infertility than women with the lowest. This increase was seen in a dose response manner, meaning the more more carbs you had, the more infertility risk.
But it’s not quite that simple, as they also found that total carb intake was only associated with ovulatory infertility if the carbs were increased at the expense of fats. So if people were having a high carb diet with a bit less protein it didn’t seem to affect fertility. This just highlights why it’s important to get enough fat for fertility.
A more recent study looked at two groups trying to conceive, one in the US and one in Denmark. In the US group there was a slight decrease in fertility with increasing carb intake but little association in the cohort from Denmark.
Both these studies suggested that not all carbs are created equal. Whether you’re consuming refined or whole grain carbs as well as the glycemic load of your carb intake can have the biggest impact on fertility.
It’s a boring answer but a moderate or moderately low carb diet is probably best for fertility! What’s really important seems to be the having the right amount and type of carbs to keep your blood sugars stable. Whole grains and fruit have added benefits and added sugars and soft drink seem to do harm.
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I help people trying to conceive to ovulate, so they can get pregnant faster.
Tweaking your diet *before* you get pregnant not only improves your cycles and fertility, it also ensures that you have the healthiest pregnancy possible.