生男秘诀：多吃高热量食品

Women on low-calorie diets or who skip breakfast at the time of conception are more likely to give birth to girls than boys, British scientists said on Wednesday.

New research by the universities of Exeter and Oxford provides the first evidence that a child's sex is associated with the mother's diet, and higher energy intake is linked to males.

"This research may help to explain why in developed countries, where many young women choose to have low-calorie diets, the proportion of boys born is falling," said Fiona Mathews of the University of Exeter.

There has been a small but consistent decline, of about one per 1,000 births annually, in the proportion of boys being born in industrialized countries over the past 40 years.

In humans, going without breakfast may be interpreted by the body as signaling low food availability, since it depresses levels of blood sugar.

Although sex is genetically determined by fathers, it is known that high levels of glucose encourage the growth and development of male embryos while inhibiting female ones, although the exact mechanism is unclear.

Mathews and colleagues studied 740 first-time pregnant mothers in Britain and found 56 percent of those in the group with the highest energy intake at conception had sons, compared with 45 percent in the lowest group.

In evolutionary terms, this correlation may make sense.

Males' breeding potential is strongly influenced by fitness, while females breed more consistently.

"If a mother has plentiful resources then it can make sense to invest in producing a son because he is likely to produce more grandchildren than would a daughter. However, in leaner times having a daughter is a safer bet," Mathews said.

Some researchers have been sounding alarms for years over the change in sex ratios in developed countries and have in the past blamed pollutants and synthetic chemicals such as those found in some pesticides which disrupt human hormones.

The latest findings were published in the journal Proceedings of the Royal Society B: Biological Sciences.

英国科学家于上周三称，在受孕期间饮食摄入热量较低或不吃早餐的女性生女孩的可能性更大。

英国埃克塞特大学和牛津大学联合开展的一项最新研究首次证明，孩子的性别与母亲的饮食有关，在受孕期间摄入高能量食物的女性生男孩的可能性更大。

埃克塞特大学的菲昂纳马修说：“这一研究也许可以解释为什么发达国家的男孩出生率持续下降，这可能与很多年轻女性选择低热量饮食有关。”

在过去40年中，发达国家的男孩出生率一直以每年约千分之一的比率小幅下降。

人在不吃早餐的情况下，血糖会降低，身体则会发出食物量不足的信号。

虽然从基因上来说，孩子的性别是由父亲决定的，但大家知道，人体内葡萄糖含量较高能够促进男性胚胎的生长发育、同时会抑制女性胚胎的生长发育，但其中的具体原理目前还不清楚。

马修及其同事共对英国740名生了第一胎的妈妈进行研究。研究结果显示，在受孕期间饮食摄入热量最高的那组妈妈中，有56%的人生了男孩；而摄入热量最少的那组只有45%的人生了男孩。

从进化论角度看，这种说法也是有道理的。

男性的生育能力受健康状况的影响较大，而女性的生育能力则更为稳定。

马修说：“由于男孩能够‘传宗接代’，所以在生活富足的情况下，女性为了生男孩而不惜大量投入确实可行，但在物质匮乏时期，还是生女儿更保险。”

近年来，一些研究人员一直在就发达国家的性别比率问题发出警告，并将这一问题归咎于各种污染物以及一些杀虫剂中所含的化学合成物，这些物质会损害人类的荷尔蒙。

这项最新研究结果在《英国皇家学会会报B：生物科学》上发表。