Obesity leads to female infertility

27 August, 2007:

Another unhealthy aspect of being obese has been established: researchers have confirmed the empirical link between obesity and infertility by showing the ‘fat eggs’ of overweight women do not develop into healthy embryos.

The eggs were damaged by high levels of fat and cholesterol, which made diet a key factor in infertility, according to Cadence Minge, researcher at the Adelaide University Research Centre for Reproductive Health, Australia.

The eggs of female mice, which were fed a high-fat diet that made them insulin-resistant and pre-diabetic, were harvested and grown in-vitro but were unable to develop into healthy embryos.

They were much slower to divide and grow, and the way that the cells developed was also disturbed, Cadence Minge said.

She said scientists were yet to understand exactly why the ‘fat eggs’ were infertile and how they were damaged.

But her research had established that a protein in cells that surrounded and nourished the egg was linked to the induced fertility and its effect could be reversed by using an anti-diabetic drug such as rosiglitazone, marketed as Avandia.

The drug activated the protein that helped the egg to mature before its release so that normal embryo development function was restored.

However, the drug has side effects and is not advocated as a ‘quick fix’ for infertile women, according to Cadence Minge.

Consuming a diet of high fat causes damage to eggs stored in female ovaries. As a result, when fertilized, these eggs are not able to undergo normal, healthy development into embryos.

A protein called peroxisome proliferator-activated receptor gamma found in the cells that nourish the egg was the main reason for diet-induced infertility. The behavior of this protein helps to determine the way in which the ovaries sense and respond to fats, Minge said. Being able to control this protein will be very important in the quest to reverse infertility caused by poor diets.

Weight loss, Minge stressed, was by far the most effective way to restore fertility and even shedding five to 10 kilograms was enough to trigger ovulation in obese women who had ceased to ovulate.

Australia is on a par with ‘heavyweight’ nations such as the United States and the United Kingdom, with approximately 60% of Australian adults now overweight or obese.

A strong connection had been known to exist between body weight and infertility but this was the first time a scientific link had been identified, the researcher noted.

The next step was to understand better the damage done to the eggs. Micro-array techniques were being used in the laboratory to scan for differences in gene expression that would identify genes that were targeted by diet.

Researchers are now collecting and studying the cells of women undergoing IVF treatment.