“I have a high BMI and my fertility doc is telling me I need to lose weight. Am I being fat shamed, or is there actual evidence that this could affect my chances of getting pregnant?”

I’m hearing this more and more. People are being turned away (or delayed) from fertility treatments because of a high BMI and it’s causing a lot of stress. First of all, let’s talk about BMI …

How does BMI affect fertility?

The Body-Mass Index is a measurement based on your height and weight that most physicians use to help flag individuals that are underweight, “normal” weight, overweight, or obese.

I say it’s “used as a flag” because it can’t actually tell us how much body fat and lean tissue are there, and these are the components that affect your hormones. Instead, it’s a value used to screen people for reproductive challenges such as being underweight or overweight.

The body’s fat tissue, also called adipose tissue, can give you some sexy curves, but these adipose cells do a lot more. They are hormonally active. Yes, that’s right: your body fat contains key hormones that regulate your metabolism, while also affecting your egg development and the ability to ovulate.

It’s for this reason that having either a BMI less than 19kg/m2 or greater than 25kg/m2 can delay the time to conceive, can reduce pregnancy rates, and increase the rate of pregnancy loss (1,2).

Having a BMI greater than 24 significantly increases the risk of ovulatory infertility (3). But how does body fat do that? How does a soft belly cushion affect how the ovaries work?

It’s the hormones and enzymes that adipose cells contain. In particular, the amount of adipose tissue on your body influences the function and effect of insulin, leptin, and the conversion of testosterone into estrogen.

Obesity is usually a consequence of poor insulin regulation. Insulin has a job to do: when you eat carbohydrates or sugars, your body releases insulin from your pancreas so that it can go around and start opening the doors on your cells to allow glucose sugar in. After all, you don’t want sugars milling about in your bloodstream in high amounts or for long periods of time. That’s what causes diabetes. But, when you continue to eat high carbohydrate diets, or excessive amounts of simple sugars and processed (fibre-lacking) grains, your body has to pump out insulin to compensate.

After a while, your insulin levels stay jacked up and your body, having seen insulin so often and in great amounts, doesn’t want to listen to it anymore.

We call this insulin resistance.

This creates a problem. That extra insulin in your bloodstream can act directly on the ovaries which have tons of insulin receptors and signals the ovarian follicle cells to make lots of testosterone. This interferes with normal egg development and the timing of ovulation. It’s also why those with PCOS (polycystic ovarian syndrome), a disorder that usually involves high testosterone and/or insulin, often have long or irregular cycles and struggle with infertility.

On top of this, high insulin concentrations tell your body to keep putting on more adipose tissue around your abdomen, keeping you in the cycle of having excess insulin and adipose tissue.

Leptin is another hormone that’s found in adipose tissue. When there’s too much of it around, it suppresses estrogen in the ovaries, preventing those eggs from growing correctly (4). High leptin can also decrease your natural progesterone levels, which isn’t good for your uterine lining and implantation.

Adipose tissue has something else in common with the ovaries: they both contain an enzyme called aromatase. This converts testosterone into estrogen, so uncontrolled conversions can really mess up the balance of these two hormones.

Meanwhile, if you have testicles, excess body adipose tissue leads to the same high aromatase activity. That means all that testosterone needed to make sperm get turned into estrogen!

Can you get pregnant if you have a high BMI?

Yes, but the risk of not actually ovulating is three times higher than someone with a BMI of 20-24.9.5

It’s also important to remember that obesity is associated with chronic inflammation and oxidative stress in the body. This can damage sperm, eggs and their DNA. If you get pregnant with a high body fat percentage, there’s an increased risk of developing gestational diabetes and high blood pressure (2).

So the concerns about going through advanced reproductive technologies like IVF with a high BMI are valid. In one study, having a BMI greater than 30 (compared to those with a BMI <30) decreased the odds of a live birth by up to 68% (6).

Although it might not always feel like it, your doctors are on your side. They want you to have the best possible chance at success, and they want you to experience a healthy pregnancy. At Conceive Health, we are here to help you achieve your goals. The journey isn’t easy, but spending three to six months on preconception to take care of your health and better balance your hormones is a great investment before having to undergo major fertility and hormonal treatments.

The best way to get a handle on insulin and adipose management is with diet and lifestyle factors, including regular exercise. If you have genetic factors or other disorders that affect your ability to lose weight in a healthy manner, we can help with that too! There are also many supplements that increase insulin sensitivity to help improve your ovarian function and health.

Get started with a complimentary 15-minute discovery call with a fertility naturopath. Book online today. 


  1. Gu L, Liu H, Boots C, et al. (2015). Metabolic control of oocyte development: linking maternal nutrition and reproductive outcomes. Cell Mol Life Sci. 72(2): 251-71
  2. Silvestris E, Lovero D, Palmirotta R. (2019). Nutrition and Female Fertility: An Interdependent Correlation. Front Endocrinol (Lausanne). 10:346
  3. Rich-Edwards JW, Goldman MB, Willett WC, et al. (1994). Adolescent body mass index and infertility caused by ovulatory disorder. Am J Obstet Gynecol. 171(1):171-7
  4. Moschos S, Chan JL, Mantzoros CS. (2002). Leptin and reproduction: a review. Fertil Steril. 77(3): 433-44
  5. Grodstein F, Goldman MB, Cramer DW. (1994). Body mass index and ovulatory infertility. Epidemiology. 5(2):247-50
  6. Moragianni VA, Jones SM, Ryley DA. (2012). The effect of body mass index on the outcomes of first assisted reproductive technology cycles. Fertil Steril. 98(1):102-8
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