Speaking in Germany at the annual conference of the European Society of Human Reproduction and Embryology, researchers from the US reported that a diet containing 25 per cent of 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.
"Although our investigations were conducted in mice, our data may have implications for diet and reproduction in humans," said Dr David Gardner, scientific director of the US-based Colorado Center for Reproductive Medicine and who led the research.
If further studies confirm the Colorado research, the findings are likely to have an impact on food products specifically rolled out by food makers to target the burgeoning low carb market. A recent survey by Reuters Business Insight shows that 3.4 per cent of all new foods and beverages coming onto the US market in 2003 were designed to be marketed as low-carbohydrate products.
Analysts predict that in 2004 alone, low carb products and services sales will hit $25 billion, a massive $10 billion increase from a year ago.
But this latest study joins a growing body of criticisms against low carbohydrate diets such as Atkins. Observers have quoted the example of red meat, suggesting that eating red meat and saturated fat is less than beneficial for the body, linking the diet to liver failure and heart disease. But the confirmed following of the diet in the US has been big enough to not only affect domestic markets but also foreign ones as well. Reuters reported recently that Brazil's orange juice exports to the US are shrinking in part because of the popularity of low-carbohydrate diets in North America.
The diet, which requires limited consumption of carbohydrates, such as potatoes, rice, bread and some juices, and ample servings of proteins such as meats, eggs and fish, is also said to have boosted demand for US beef prior to the recent mad cow scare.
According to the scientists, 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 per cent protein (moderately high) or 14 per cent 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 per cent of blastocysts developed in mothers on the 25 per cent protein diet showed a normal imprinting pattern, compared to 70 per cent in the control group," said Dr Gardner. "Furthermore, only 65 per cent of the embryos in the high protein group developed into foetuses once they had been transferred, compared to 81 per cent 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 per cent developed further, whereas in the control group 99 per cent of the embryos that implanted continued to develop, the researchers added.
"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 animals," conclude the scientists. They advise couples who are trying to conceive, either naturally or through fertility treatment, to ensure that the woman's protein intake is less than 20 per cent of total energy consumption.