Your egg cell feels what you eat

UAntwerp study shows that high-fat and high-sugar diets lower egg cell quality

For some time, fertility centres have been reporting that obese women have a harder time getting pregnant. Research at UAntwerp now shows that the composition of the ovarian or follicular fluid is strongly influenced by what the mother eats. ‘A diet rich in fat and sugar significantly reduces the quality of the egg cells. Normalising the diet and losing weight improves egg cell quality again, but not entirely.’

Earlier studies have shown that those who eat very fatty and sugary foods change the environment of their egg cells or oocytes. The follicular fluid in the oocytes of obese women has been found to be abnormal. For further research, scientists at the University of Antwerp examined the oocytes of cows in test tubes.

‘Cow oocytes are very similar to human oocytes and in the test tube we mimic the obese environment’, as Professor Jo Leroy, chair of the European Society of Human Reproduction and Embryology, explains about the research. ‘Oocytes are real opportunists. They absorb all types of nutrients from their environment. For example, if we provide more fats in the test tube, the oocytes will absorb the fat. This leads to cell damage and serious problems. The largest cell in the female body shows signs of stress and is much harder to fertilise.’

The study also showed that the embryo formed is of poorer quality, has genetic defects and therefore often dies early.

Fatty oocytes

To see whether this is the case not only in test tubes but also in living beings, the researchers conducted tests on mice. Conducting this research on humans would be both ethically and practically unfeasible. For several weeks, the mice were exposed to fast food rations, which closely mimic a human diet rich in fat and sugar. The mice became fat and developed health problems, as humans would. For example, their blood sugar was too high and they had more inflammation.

And yes, the mice’s oocytes also accumulated up to twice as much fat and their quality deteriorated. The fat mice became pregnant only with great difficulty. ‘The synthesis was correct’, says PhD student Anouk Smits. ‘Reduced oocyte quality due to a diet excessively rich in calories and fat plays an important role in fertility struggles. So this may help explain the observations in fertility centres concerning obese patients.’

Irrevocably affected?

But how can we help these women? That was the topic of Smits’ PhD research. For four years, she researched whether it was possible to improve oocyte quality again by adjusting the mother's diet. Overweight mice on fast food rations were given the opportunity to diet for several weeks before conception: they were given normal rations with less fat or even subjected to a crash diet.

The animals were monitored in detail for several weeks. The fact that their metabolic disorders disappeared quickly was very encouraging. Most animals became much healthier and returned to a healthy weight. The ‘preconception care’ that the researchers had provided proved to work well. The oocyte quality improved significantly and the animals became pregnant again more easily.

But that recovery was not 100%. Certain oocyte parameters remained abnormal compared to the healthy control group. Even after several weeks of improved health in the mice, their oocytes still showed abnormalities, on average half as much as the mice in the control group. This possibly shows that even the still immature, resting oocytes are irreversibly affected by an unhealthy Western diet. Further research should confirm this.

Healthy eating before conception

It turned out that easily getting pregnant was not enough either, because the quality of the oocyte also appears to have a big influence on the offspring’s health. ‘An earlier study showed that the offspring of mother mice slimmed down to a healthy weight nevertheless showed important early signs of diabetes. So the oft-heard “you are what you eat” can certainly be transferred to “your oocyte is what you eat” and even “your child will be what your oocyte eats”. Working on a healthy pregnancy, but also on the health of the next generation, therefore begins before conception’, Leroy says.

The study appeared in the scientific journal Reproductive Biology and Endocrinology: