The proportion of Australians who are overweight or obese is at an all-time high. We know excess weight is linked to many adverse health consequences. There is now growing understanding that it also affects fertility.
Being overweight affects female fertility
A fine hormonal balance regulates the menstrual cycle. Overweight and obese women have higher levels of a hormone called leptin, which is produced in fatty tissue. This disrupts the hormone balance and can lead to reduced fertility.
The quantity and distribution of body fat also will affect the menstrual cycle. The more weight in particular; more abdominal fat, the greater the risk of fertility issues.
Excess weight, particularly excess abdominal fat, is linked to insulin resistance. Insulin resistance causes the body has to produce more insulin to keep blood sugar levels normal. Carrying extra weight also decreased levels of sex hormone-binding globulin (SHBG). This is a protein that is involved in the regulation of the sex-hormones androgen and oestrogen.
This increases the risk of irregular menstrual cycles which reduces fertility. One study found women who were obese were much less likely to conceive within one year of stopping contraception than women in the normal weight range (66.4% of obese women conceive within 12 months, compared with 81.4% of women of normal weight).
Changes in the fine-tuned hormonal balance that regulates the menstrual cycle triggered by excess weight and obesity also increase the risk of anovulation (when no egg is released by the ovaries).
The quality of the eggs produced is also reduced. The evidence for this is that among women who ovulate, each unit of BMI above 29 reduces the chance of falling pregnant within 12 months by about 4%.
This means a woman with a BMI of 35, is 26% less likely to fall pregnant in 12 months. Woman with a BMI of 40 it is 43% less likely when compared with women with a BMI between 21 and 29.
Excess weight affects male fertility
In men, obesity and being overweight is also associated with lower fertility. This is likely due to;
- hormone problems,
- sexual dysfunction
- other health conditions linked to obesity such as type 2 diabetes and sleep apnoea (which are both associated with lowered testosterone levels and erectile problems)
It’s estimated carrying an extra 10 kilos reduces male fertility by 10%.
Obesity not only reduces sperm quality, it also changes the physical and molecular structure of sperm cells.
The good news
While the facts about obesity and fertility can seem daunting, there is some good news too. Weight-loss that includes both diet and exercise, can help regular the menstrual cycle and improve the chance of pregnancy. In obese women who don’t ovulate, if they lose 5-10% of their weight this will improve fertility and the chance of conceiving.
Lastly, men and women are twice as likely to make positive health change if their partner does. So becoming pregnant will be more likely if you diet and exercise together.
Originally published in The Conversation, written by