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Eating for Fertility

Let’s start at the beginning & address weight

One of the most important factors affecting fertility is weight. Conceiving is more difficult if you’re underweight or overweight. It’s believed that weight issues cause 12% of infertility.

Body fat is beneficial for pregnancy to occur and be carried to term. Fat cells make oestrogen, having too many or too few fat cells affects the amount of oestrogen in the body, which then affects fertility[1].

It’s best to get close to your ideal weight before you seek help with fertility treatments since this simple change often can result in normal ovulation and pregnancy. It also can reduce the risk of pregnancy complications and of having a baby who’s too large or too small at birth.

Underweight A certain amount of body fat is needed for regular ovulation and menstrual cycles because some oestrogen is produced in women’s fat stores. In fact, body weight changes of just 10% to 15% below normal can disrupt menstrual cycles.

If you’re seeking medical help for infertility, first check you’re not underweight (BMI less than 20). Research shows that being underweight increases your chances of having a low birth weight infant or a baby who’s born preterm [2].

A maternal body weight closer to your ideal weight is best for conceiving and carrying a healthy baby to a healthy weight at term.

Overweight For women, excess body fat can affect the amount and types of circulating hormones, which influence fertility. It’s estimated that 25% of ovulatory infertility can be attributed to being overweight [3]. Overweight is linked to polycystic ovary syndrome (PCOS), a cause of infertility. Insulin resistance, which can result from having PCOS or being overweight, also is related to infertility [4].

The good news is that studies show that overweight women have great success in conceiving once they’re closer to their ideal body weight. In fact, losing just 5% to 10% of total body weight can dramatically improve ovulation and pregnancy rates. In one small study, losing 6kg drastically improved women’s ovulation and pregnancy rates [5].

An expanding waistline also can affect a man’s fertility. In fact, it can be harder to get pregnant if both partners are overweight because it increases the likelihood that it will take more than a year to get pregnant [6]

Overweight men tend to have lower testosterone and increased oestrogen levels, and decreased ejaculate volume. Men with a BMI greater than 35 are more likely to have a lower sperm count and higher numbers of sperm with DNA damage compared with normal-weight men[7]. Sleep apnea, which is more common in men who are obese, also can cause a decrease in testosterone levels. Excess fat in the inner thighs and pubic region also may cause warmer temperatures in the pubic area, which is enough to alter sperm production.

Clearly, nutrition and lifestyle play a critical role in fertility. Before going through the expense and emotional roller coaster of fertility treatments, it’s wise for a woman who’s trying to conceive to work on improving her diet and that of her partner first. Dietitians are the perfect source of information for this highly motivated population.


[1] Weight. American Society for Reproductive Medicine website. http://www.reproductivefacts.org/topics/detail.aspx?id=1763.

[2] Beyene J, Han Z, Liao G, Mulla S, McDonald SD; Knowledge Synthesis Group. Maternal underweight and the risk of preterm birth and low birth weight: a systematic review and meta-analyses. Int J Epidemiol. 2011;40(1):65-101.

[3] Nohr EA, Vaeth M, Rasmussen S, Ramlau-Hansen CH, Olsen J. Waiting time to pregnancy according to maternal birthweight and prepregnancy BMI. Hum Reprod. 2009;24(1):226-232.

[4] American Dietetic Association; American Society for Nutrition, Siega-Riz AM, King JC. Position of the American Dietetic Association and American Society for Nutrition: obesity, reproduction, and pregnancy outcomes. J Am Diet Assoc. 2009;109(5):918-927.

[5] Clark AM, Ledger W, Galletly C, et al. Weight loss results in significant improvement in pregnancy and ovulation rates in anovulatory obese women. Hum Reprod. 1995;10(10):2705-2712.

[6] Ramlau-Hansen CH, Thulstrup AM, Nohr EA, Bonde JP, Sørensen TI, Olsen J. Subfecundity in overweight and obese couples. Hum Reprod. 2007;22(6):1634-1637.

[7] Chavarro JE, Toth TL, Wright DL, Meeker JD, Hauser R. Body mass index in relation to semen quality, sperm DNA integrity, and serum reproductive hormone levels among men attending an infertility clinic. Fertil Steril. 2010;93(7):2222-2231.

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