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The Truth about Weight and Infertility

Updated: Nov 3, 2021

Weight is a tough topic, especially when it comes to fertility. The mere suggestion that weight loss could improve your chances of conception and a healthy pregnancy outcome may feel the world is blaming you for not getting pregnant. Self-deprecating thoughts may fly through your head. You begin to tell yourself that if you only “worked harder” at losing weight, you might get pregnant. You worry that other people are thinking this too.

But deep down, you know you’ve given it everything you’ve got. You’ve counted calories, tried Whole 30, joined a cross fit gym. But for some freaking reason, your body holds on to this weight. So, after spending years experimenting with all kinds of weight loss techniques, it feels like an absolute slap in the face when your doctor tells you that you need to lose weight to conceive. Gee, thanks. Never thought of that. I’ve just been eating Halo Top for the last year because I love the taste of expensive low-calorie air.

Some influencers capitalize on your resentment. They tell you weight doesn’t matter and BMI is bullshit. Well, here are my thoughts.

BMI is not very helpful when applied to an individual because it doesn’t take into account several nuances, like muscle vs. fat mass, and where fat mass is distributed on your body, which actually makes a big difference in terms of health outcomes. However, BMI is a decent public health tool. It helps us make generalizations in studies about large groups of people. When your doctor gives you advice based on your BMI, they are usually referring to the generalized results of large studies.

For instance, several studies have found that there is a J-shaped curve between BMI and infertility. Women who are underweight (BMI <19 kg/m2) and overweight (BMI 25-29.9 kg/m2) have a similar chance of struggling to conceive. One study found that underweight women spend an average of 29 months trying to get pregnant, compared to women within the “normal” BMI category who taken an average of 6.8 months to conceive. Women with a BMI over 30 kg/m2 have been found to have 2 times the risk of ovulatory disorders. In women who still ovulate, trying to conceive without reproductive assistance, the likelihood of conception decreased 5% for each BMI unit over 29 kg/m2. Women who are obese have a higher chance of menstrual disorders, miscarriage, poor egg quality, poor uterine receptivity, poor in-vitro outcomes, and poor pregnancy outcomes.

There are dozens of potential mechanisms that can explain these results. One being the associations between BMI and insulin resistance and insulin resistance with fertility. Another explanation can be the endocrine function of our fat cells. Our fat cells actually secrete chemicals and hormones that can affect fertility. Our weight is also linked to our gut health and the type of microorganisms in our intestines.

I know reading this f*@#ing sucks. Especially when you feel like your weight should be in your control, but maybe previous failed attempts at weight loss have proven to you otherwise.

Here’s the thing though- losing weight isn’t an action you can take. It’s a result. It’s a result of genes, the environment, lifestyle and sometimes strategic, targeted action. You may struggle with weight because of PCOS, genes, angry gut microbes, eating disorders, stress, chronic inflammation, etc. You can’t force these things to change by going on a diet. Weight loss isn’t just about willpower. For many people, willpower has absolutely nothing to do with it. Because you can’t will yourself to be a certain weight, I prefer to focus on actions, because those are factors that you can control.

I like to look into root causes and try to determine if there’s anything we can do to change how that underlying cause is affecting your body. Then, based on those findings, I prefer to focus on small, attainable, behavior-based goals that put you back in the driver’s seat.

So even though research does show that weight is influential in fertility, this doesn’t mean you should blame yourself for your weight or struggle to conceive. This blame overlooks the complicated spider-web of issues that can go into problems with weight and fertility. Weight loss is not simple because the causes of weight gain are not simple. Give yourself a break, because this is hard and you’re doing your absolute best.

Gaskins AJ, Chavarro JE. Diet and fertility: a review. Am J Obstet Gynecol. 2018;218(4):379-389. doi:10.1016/j.ajog.2017.08.010

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