Popular summary below followed by the journal abstract and comment
Fats hidden in thousands of foods can harm a woman’s chance of having a baby, scientists say. A study by scientists from Harvard University’s School of Public Health says the fats can increase the risk of fertility problems by 70 per cent or more. And eating as little as one doughnut or a portion of chips a day can have a damaging effect. The scientists behind the study have advised women who want to have a baby to avoid the fats, known as trans fats. They are used in thousands of processed foods, from chocolate to pies, as well as takeaway meals. They have no nutritional value [Really?? A selective definition of nutrition, I fear], but are included simply to extend the shelf life of food.
It is very difficult to know the precise amount of trans fats in any food because it does not have to be put on the label. The fats are found naturally in some red meat and dairy products, but most are produced artificially in a high-temperature process called hydrogenation, which turns oil into solid fat.
Nutritionist Rosemary Stanton said the study was more evidence labelling should be compulsory. “If you compel manufacturers to label products, evidence shows they will want to say their products have ‘no trans fats’. And this will stop them using these bad fats,” Ms Stanton said. Other studies showed that trans fats were bad for pregnant women because they stopped the benefits of omega-3 fatty acids reaching an unborn child’s brain, she said. Women should be wary of processed canola oil used in many Australian foods such as crisps, pastries and crackers, she said.
The US study’s lead researcher, Dr Jorge Chavarro, said the findings suggested that women wanting to conceive should watch their trans fat consumption, as well as give up smoking and maintain a healthy weight.
Dietary fatty acid intakes and the risk of ovulatory infertility
By Chavarro J.E. et al.
BACKGROUND: Pharmacologic activation of the peroxisome proliferator-activated receptor gamma (PPAR-gamma) improves ovulatory function in women with polycystic ovary syndrome, and specific dietary fatty acids can affect PPAR-gamma activity.
OBJECTIVE: The objective of the study was to assess whether the intakes of total fat, cholesterol, and major types of fatty acids affect the risk of ovulatory infertility.
DESIGN: We conducted a prospective cohort study of 18 555 married, premenopausal women without a history of infertility who attempted a pregnancy or became pregnant between 1991 and 1999. Diet was assessed twice during follow-up by using a food-frequency questionnaire.
RESULTS: During follow-up, 438 incidents of ovulatory infertility were reported. In logistic regression analyses, intakes of total fat, cholesterol, and most types of fatty acids were not related to ovulatory infertility. Each 2% increase in the intake of energy from trans unsaturated fats, as opposed to that from carbohydrates, was associated with a 73% greater risk of ovulatory infertility after adjustment for known and suspected risk factors for this condition [relative risk (RR) = 1.73; 95% CI: 1.09, 2.73]. Obtaining 2% of energy intake from trans fats rather than from n-6 polyunsaturated fats was associated with a similar increase in the risk of ovulatory infertility (RR = 1.79; 95% CI: 1.11, 2.89). In addition, obtaining 2% of energy from trans fats rather than from monounsaturated fats was associated with a more than doubled risk of ovulatory infertility (RR = 2.31; 95% CI: 1.09, 4.87).
CONCLUSION: trans Unsaturated fats may increase the risk of ovulatory infertility when consumed instead of carbohydrates or unsaturated fats commonly found in nonhydrogenated vegetable oils.
This is a long way from a double-blind control-group study. It is a cheap and nasty study based on a self-report questionnaire — with all the limitations that implies. The major deficit would appear to be a failure to allow for social class. Poor people probably both eat more fast food and are more ready to acknowledge it — thus being rated as big trans-fat consumers. And poor people tend to have more health problems. Surveys such as this do have the potential benefit of making meaningful sampling easier but there is no mention of sampling — which makes the results of unknowable generalizability
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