Junkfood Science: Fat, healthy moms

December 06, 2006

Fat, healthy moms

This week, “skinny or underweight women” were being frightened by headlines that they’re at heightened risk of miscarriage. Except, the study being reported couldn’t reliably conclude that. A more accurate statement of the study’s findings also happens to be a much more positive and reassuring one:

Being fat does not increase risk for miscarriages

This is information millions of women need to know. Women wanting children have been threatened and terrorized about their fatness for years. Public health officials have been telling them that their “extra body weight” poses serious and life-threatening complications and that they are putting themselves and their unborn babies at risk. Among the popularly believed scares are that “obese women are far more prone to complications such as miscarriage.” Never reported, however, is that the quality evidence — or more precisely, the lack thereof — doesn’t support the greatly exaggerated scares.

Tomorrow, we’ll see an example and look at the study behind the most recent admonition that “women must lose their pregnancy weight because weighing even a few pounds more jeopardizes their second pregnancy.” It made all the news.

Today’s heartening study was published in the International Journal of Obstetrics and Gynaecology. Researchers at the London School of Hygiene & Tropical Medicine looked for associations between biological and lifestyle factors and the odds of miscarriage. The researchers took care to try and ensure they were looking at a sample of women representative of the general population. They gathered data collected on surveys from about 6,700 British women, which asked the women about their reproductive histories, considering each pregnancy in turn. They were also asked to complete a lifestyle survey and a food frequency recall questionnaire surrounding their most recent pregnancy. About 600 first trimester miscarriages were reported; but to increase the information on miscarriage risks, women whose latest pregnancy was not a miscarriage were given another questionnaire about their most recent miscarriage. The researchers applied statistical modeling of the data to look for correlations among factors they thought might be important (such as smoking and caffeine) and determine the odds ratios.

This type of study design is called “case-controlled” and is retrospective because it looks backwards through histories trying to explain an adverse outcome among a certain group. There are several caveats to these types of studies. Researchers look for things they think may be related to a health problem and could miss more important ones. The data relies on people’s memories and is subject to recall bias, where people are more apt to remember things they believe related to their illness. It’s the — “Oh, it must have been those burgers I ate” — guilt phenomenon. And, of course, they are looking for correlations, hoping to find ones that are statistically significant, but which can never prove cause.

They found three correlations that could be considered viable for these types of observational studies (relative risks two to three times higher than baseline): Higher maternal age (over 40 years) had 5 times the risk for miscarriage; stress, depression or traumatic events was associated with 3 times higher risks; and women who drank alcohol every day had 2 times the risk. The body of research supports a higher risk among older women, and some studies have suggested links between stress and pregnancy-related problems, including premature births and low birthweight babies. Researchers with the March of Dimes Birth Defects Foundation believe these are the most significant factors in the increases seen since 1981 in pregnancies not carried to term (9.4% to 11.9%) and today’s highest rates of preterm births ever in the U.S.

But when it comes to the lifestye and other dietary factors, the odds ratios found were not tenable — they were too small to be considered valid for these types of studies. In other words, none of them proved to be a concern. The numbers were so trivial they could be due to chance, statistical bias or errors in the computer model, or to things not even considered in the study design. Trying to make sense of these small untenable percentages is impossible because they aren't sensible. So using nonfindings to make any conclusions or recommendations is unsound. Remember, finding a solid correlation is the first step towards narrowing down a cause that will need confirmation with other types of studies; and if researchers can’t even find a credible correlation, then we can relax and move on.

Yet the political correctness in the reporting of this study’s findings were unmistakable. The media and researchers were quick to promote the idea that eating more fruits and vegetables and having a “healthy diet” and taking vitamins “may lower risks for miscarriage by 50%.” The study didn’t actually show a cause and effect at all, merely associations, so it’s an unsupportable leap to make such a suggestion. I’ll show you why in a minute.

Here are a few examples of how foods and behaviors are oftentimes more likely to be markers for something else. Their results found eating fruits and vegetables each day was associated with a 50% lower risk for miscarriage. (That is 50% of a 12% actual incidence.) It’s not that eating fruits and vegetables are bad, because good nutrition is important during pregnancy; but whether fruits and vegetables are the answers to reducing miscarriages or have any effect at all simply wasn’t shown in these weak correlations, nor has it been shown in the available research to date. Some may scoff at this concern thinking it’s not harmful to believe it anyway, but it is important because increasingly people suffering from health problems are being wrongly blamed for “bad” behavior or eating “incorrectly,” and made to feel guilty that a health problem is their own fault. More likely, if this correlation is ever able to be replicated, it’s indicative of women of better social class, economic means and with better access to health care.

In fact, those 50% lower risks were identical to those of women in the study who said they had planned for their pregnancies — meaning the women were less likely to be poor, young, unwed mothers and more likely to have stable homes and economic situations, and better prenatal care.

And even more interesting, those risks were identical to those of women who had flown in the past 3 months — with those flying the greatest number of hours having even greater reductions in risk (60% lower). Clearly, this is measuring either business travel from higher-level employment or vacation travel from greater disposable income. In other words, all of these lifestyle factors are more likely markers for wealth and advantage.

“Women, rack up those frequent flyer miles to lower your risk for miscarriage!”

Saying that sounds illogical, but it reflects just how faulty it is to apply these types of associations.

In addition to promoting fruits and vegetables, we heard that eating daily chocolate reduced risks. If that is ever replicated in clinical studies, it might actually prove to not be the chocolate at all, but perhaps a marker for women who are more relaxed, happily enjoying their foods, eating well and not dieting. Looking at the study, chocolate was associated with a mere statistical 15% reduced risk. On the other hand, eating white meat was associated with an 18% lower risk. And red meat, eggs, 1 or less drinks a week, and caffeine had no effect.

But the value of this study can probably be most appreciated for what it didn’t show to be a concern, besides all of those negligible dietary factors. Negative findings - when they can't even find a correlation - are every bit as important as positive ones. And anything that can lessen needless concerns and stress for expectant mothers might also prove to help ensure even better outcomes.

Being fat did not affect the risks for miscarriage at all, despite beliefs that it does. In fact, the “obese” women had even slightly lower risks than the “overweight” women. And that is news women can use.

Bookmark and Share