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【bio-news】饮食决定生男生女？
Issue: November 2006
Can eating the right foods help you have a baby? And can your diet determine the sex of your child?
After years spent avoiding pregnancy, I thought nature had to be kidding!' Today 36–year–old Lauren Holmes* can laugh at her '14 months of gaily abandoned but fruitless sex,' but two years ago it left this vibrant fashion agency head feeling frustrated and increasingly anxious. 'It wasn't part of my life plan, dammit–my own business by 26, marriage by 30, and baby by 32.'
Lauren's gynae could detect nothing wrong in spite of a 'teenage scare with an STI,' and recommended an appointment with a fertility specialist. 'I had a girlfriend who went that route successfully, but I didn't fancy hormone injections, mood swings–or a freaked–out husband. So Tom and I decided to give nature a really good go.'
Lauren's mother introduced them to the writings of British nutrition guru Patrick Holford, and they found a registered dietician and a yoga teacher and focused on 'eating really well', exercising, and controlling stress. In August this year, her mother toasted victory with them–a 3,4kg baby boy. 'I quickly lost my bit of baby flab, and Tom and I are in better shape than we've been in years.'
The best odds for conception and a healthy pregnancy, says Holford, are achieved when both partners prepare for pregnancy. It takes three months for sperm to mature, while the egg or ovum takes a month, he explains in his New Optimum Nutrition Bible (Piatkus Books, ISBN 0749925523). 'During these pre–conceptual months if each of you pursues optimum nutrition, minimises your intake of anti–nutrients–especially alcohol–and stays healthy, the chances of a healthy conception are high.'
Holford advocates that anyone consider–ing fertility treatment should first try this route. IVF has an average success rate of about 20 to 30%, he reasons, while research by pre–conceptual care organisation Fore–sight shows that a holistic approach, where both partners are given optimum nutrition and any underlying health problems are resolved, has a success rate of over 78%.
His recommendations range from balancing your hormones with sensible eating: very little animal fat, and organic produce where possible to reduce exposure to pesticides and hormones, to checking your levels of homocysteine, an amino acid found in blood. Holford hails homocysteine as 'a new health marker associated with infertility and pregnancy complications', and claims it can be 'correctly balanced' in three months with nutritional supplements.
But not everyone is convinced you can eat your way to a baby. 'There are simply too many factors involved in successful conception,' says Professor Jack Moodley, retired head of Gynaecology and Obstetrics at the University of KwaZulu–Natal Nelson R Mandela School of Medicine in Durban. 'As long as you have a reasonably balanced diet and aren't seriously mal–nourished, it shouldn't affect conception. Poor nutrition will influence the baby's growth in the uterus, but these babies catch up in childhood,' he says. The only supplement he considers necessary is folic acid, less for conception than 'because a lack of folic acid can produce tubal defects'.
Cape Town dietician Nadia Bowley concurs. 'Eating a healthy, varied diet to ensure you have sufficient vitamins and minerals should be started pre–conception to ensure the foetus has access to the right nutrition from the first day, even before you know you're pregnant, but I know of no clear scientific evidence that the vitamin and mineral intake of the mother affects her ability to conceive.'
Body–fat content, on the other hand, has an important influence on fertility, says Bowley, as 'at least 22% of your body' must comprise fat to maintain regular ovulation. 'Top athletes often have average or high body weights due to muscle mass, but their very low body fat content can interfere with their ovulation cycles and decrease their fertility.' If you have a low body weight from bulimia or anorexia nervosa, or are underweight with a body mass index (BMI) below 19, you can struggle to conceive, she says.
But obesity (BMI of over 30) also affects ovulation and fertility. 'Losing weight can correct this, but it's vital you avoid restricting your diet immediately before conception as this can limit the quantities of nutrients available to you or your baby,' says Bowley. 'If you need to shed weight, do it three or four months before attempting to conceive.'
Some dieticians do believe that much can be done to enhance the chance of get–ting pregnant naturally, and that scientific research is mounting in support of this idea. Karen Charlton, a dietician and research fellow at the Chronic Diseases of Lifestyle Unit of the Medical Research Council in Cape Town, says there's now evidence that a man's diet is important: 'Zinc is needed to produce healthy sperm, and recently there's been much interest in the type of dietary fat consumed and sperm health. Long–chain fatty acids, particularly DHA found in fish oil, appear to influence sperm motility (how fast it swims) as well as sperm concentration.' Trials are not yet available on whether dietary supplementation with DHA improves conception, she says, 'but it seems a good idea for both of you to consume fatty fish like salmon, mackerel, pilchards or herring at least twice a week.'
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作者:admin@医学,生命科学 2011-05-28 05:11
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