It's Time to Drop BMI From the Fertility Conversation

This is Nike (M)

Stressing about your weight while trying to conceive totally sucks—and may not be necessary. Learn what to focus on instead.

Last updated: 21 November 2022
6 min read
  • What you've heard about BMI may not be accurate—especially when it comes to fertility. And obsessing over this arbitrary number could be counter-productive.
  • Restricting your calorie intake is not helpful for fertility.
  • As long as you don't overdo it, movement is great for physical and mental health when trying to conceive. If your routine needs a refresh, check out the Nike (M)ove Like a Mother program in the NTC App.

Read on to learn more …

Why You Shouldn’t Focus on BMI When Trying to Conceive

*This content is designed to inform and inspire, but it is not meant to diagnose, treat or give specific medical advice. Always check with your health care provider about how to stay healthy and safe before, during and after pregnancy.

Fertility can be kind of a mystery. There are so many factors that influence a person's ability to conceive and maintain a pregnancy: genetics, medical history, the shape of their uterus, not to mention the fertility of the person doling out sperm. One particularly tricky—and controversial—factor? Body mass index.

If you're rolling your eyes, us too. BMI was never intended for medical use. It's a mathematical formula (weight ÷ height² × 703) invented by 19th-century statistician Adolphe Quetelet as a tool for gauging the average body size of (white, male, Western European) populations. It was only adopted as a uniform measurement to assess body weight sometime between the 1970s and 1990s, and only because it was deemed slightly better than other available options. Even now, researchers—and the Centres for Disease Control—note that "it does not diagnose the body fatness or health of an individual".

So what does this seemingly random formula have to do with your uterus? Many fertility practices refuse to treat patients above a certain BMI until/unless they lose "enough" weight, a controversial policy that can frustrate both patients and practitioners. But while it's true that BMIs above or below a "normal" range (again, controversial) are correlated with decreased fertility for various reasons, "people can be fertile at a lot of different weights", (and infertile at "normal" weights too), says Lora Shahine, MD, a reproductive endocrinologist and obstetrician-gynaecologist at Pacific NW Fertility in Seattle and the host of the podcast Baby or Bust. "To put somebody in a box and say, 'Your BMI is too high or too low, that's why you're not getting pregnant' is just not looking at the full picture".

It may be part of the picture, but focusing on weight alone can do more harm than good. Studies show intentional weight loss is typically temporary and can backfire, commonly leading to weight-cycling and increasing the risk of stroke, cardiac diseases and diabetes—in other words, messing with your health overall. And overall health is a big deal for reproductive health, says Dr Shahine.

So instead of stressing over "some arbitrary number", as Dr Shahine puts it, here are some other—uncontroversial—actions to take when trying to conceive.

Why You Shouldn’t Focus on BMI When Trying to Conceive

1. Eat. Maybe more than you think.

Food restriction is such an accepted social norm that many people, whether they're "doing keto" or "eating clean", don't realise they're doing it. And it's not helpful for fertility, says Willow Jarosh, RDN, a dietitian in New York City. Jarosh encourages people who are trying to conceive to step away from a diet-based mentality to ensure they're getting adequate caloric and nutritional intake—which mostly comes down to simply eating regular, satisfying meals.

Jarosh's other concern when it comes to fertility is eating for blood sugar stabilisation. This is especially important for people with insulin-resistant polycystic ovarian syndrome (PCOS), one of the most common causes of infertility in women, according to the CDC. While PCOS affects fertility in complex ways and there's no quick fix, eating for stable blood sugar is pretty simple: "try to incorporate protein, carbohydrate and fat at each meal", says Jarosh. Snacks are also a great way to keep blood sugar stable and to round off your diet with nutrients and food groups you might not always get at meals.

As for the specific foods you choose? Jarosh says not to over-think it. Dr Shahine backs her up, noting that some patients struggling with fertility can become fixated on nutrition and swept up in popular health trends. "Everyone wants to be told, 'Cut out gluten and you'll get pregnant next month'. It's just not one-size-fits-all" (of course, if you have conditions or allergies that require specific dietary changes, it's best to discuss them with an RD one-on-one).

2. Try not to stress about stress. Cope with it.

Yes, stress may throw off your cycle and affect fertility. But if it made conception impossible, there'd be no more people … anywhere". I talk to my patients a lot about how you cannot eliminate stress, but you can work on coping mechanisms to decrease its impact", says Dr Shahine. Now, stress isn't inherently bad. That fight-or-flight response can be a lifesaver. But when your body is busy trying to save your life, says Dr Shahine, it's not going to bother with the baby-making hormones. Say a bear is chasing after you. "Are you going to ovulate? Or are you going to try to run away from the bear?" asks Dr Shahine.

Look, if there's a bear, you can't exactly ignore it. But when you're in the midst of a mental bear attack, you can talk with friends, take a walk, roll out your yoga mat, watch movies that make you literally LOL, make lists or do whatever helps you feel calmer. Again, this isn't make-or-break. As Dr Shahine notes, people get pregnant in all kinds of stressful situations (cavemen definitely procreated with animals on the prowl). But there's no downside to getting better at managing stress.

3. Move your body. Don't exhaust it.

Exercise was once considered off-limits for those trying to conceive. Now we know movement is generally helpful for everyone, including those hoping to get pregnant. In fact, some research indicates that physical activity can improve fertility and menstrual function regardless of body size or weight change. But exercise is a broad category, and whether you have a current routine or want to start one, chat with your doc first.

As with mental stress, your body's ability to recover from the physical kind is key. "When you're putting your body into a stressful state, whether it's physically or emotionally, it's going to be pumping out things like endorphins and cortisol, and it's going to shift away from reproduction", says Dr Shahine. That's why doctors typically advise patients not to begin a new intense workout routine while trying to conceive. For those who already have one, Dr Shahine often suggests moderating it slightly or trying lower-intensity alternatives. She advises even her hardest-core patients not to exercise to the point of exhaustion or a negative calorie state, which may cause hormonal and ovulatory problems. Other than that, Dr Shahine says, "movement is good".

At the end of the day, you may never know what made it hard to get pregnant. But if you can learn to take good care of yourself (diet culture be damned), you'll have a solid foundation for whatever life brings you.

Words: Kelsey Miller
Photography: Vivian Kim


Want more guidance as you navigate all the stages of motherhood? Start the expert-vetted Nike (M)ove Like a Mother program in the Nike Training Club App for workouts, wellness advice and more.

Originally published: 17 November 2022

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