Researchers from the USA have found that a diet containing 25% protein disrupted the normal genetic imprinting pattern in mice embryos at a very early stage in their development. The diet also adversely affected subsequent embryo implantation in the womb and foetal development.
The research was carried out by a team led by Dr David Gardner, Scientific Director of the Colorado Center for Reproductive Medicine, Englewood, USA,
Dr Gardner said: "Although our investigations were conducted in mice, our data may have implications for diet and reproduction in humans."
Previous research has shown that the amount of protein in the diet affects the levels of ammonium within the female reproductive tract in cows and mice. It is known that ammonium adversely affects mouse embryos developed in culture in the laboratory, inducing altered imprinting of the H19 gene and retarding foetal development. The H19 gene, found on chromosome 7, is an important gene involved in growth.
Normally, genes act in the same way, whether they are transmitted by the mother or the father. But, a few genes break this genetic rule. Whether they are switched on (expressed) or off depends on whether they are inherited from the mother or the father. The process of inheriting specifically from the mother or the father is called imprinting.
Dr Gardner set out to discover the effect of a moderately high protein diet on imprinting and the viability of mouse blastocysts (early embryos) during reproduction in the living animal.
He fed mice on a diet containing either 25% protein (moderately high) or 14% protein (as the control group) for four weeks. The mice were mated and 42 of the resulting blastocysts were examined to discover the imprinting status of the H19 gene; 174 blastocysts from mice on both diets were transferred to mice eating a normal diet in order to discover the effects of the maternal diet during the preimplantation stages on subsequent foetal development.
"We found that only 36% of blastocysts developed in mothers on the 25% protein diet showed a normal imprinting pattern, compared to 70% in the control group," said Dr Gardner. "Furthermore, only 65% of the embryos in the high protein group developed into foetuses once they had been transferred, compared to 81% in the control group. Not only did fewer embryos develop into foetuses when transferred from the high protein group, but of all the embryos that implanted, only 84% developed further, whereas in the control group 99% of the embryos that implanted continued to develop.
"Analysis of foetal development on the fifteenth day of gestation showed that foetuses from the high protein group were a third of a day behind the control group in their development, and one foetus had a neural tube defect.
"These data show that eating a moderately high protein diet, which results in elevated ammonium levels in the female reproductive tract, adversely affects the preimplantation embryo in the living animal. Blastocysts from mothers on a 25% protein diet exhibited abnormal imprinting of the H19 gene and retarded foetal development after transfer. Furthermore, there was significantly higher foetal loss rate at the preimplantation stage in the 25% protein group. Our observations are consistent with data on embryos developed in the laboratory in the presence of ammonium.
"These findings, together with similar work carried out in cows, mean that it would be prudent to advise couples who are trying to conceive, either naturally or via ART, to ensure that the woman's protein intake is less than 20% of their total energy consumption. The available data certainly indicate that a high protein diet is not advisable while trying to conceive."
Abstract no: O-076 (Monday 15.15 hrs CET Hall 7)
According to the American Heart Association, the average diet in the US consists of 14% protein - the same amount as was used in Dr Gardner's control group.