There’s Something About Yogurt
作者 OLGA KHAZAN | 编者 Hugo TANG
Atlantic May 25, 2018 总字数 1,289 words 估计阅读时间 8 min
英文全文 + 中文翻译
A couple years ago, I was taking a swim with my very pregnant friend when I asked her if it was hard to keep straight all of the doctors’ health recommendations for expectant mothers.
Not really. For practically every symptom, she said, their recommendations were roughly the same: “Take a walk, eat a yogurt.”
It was another example of the Cult of Yogurt. Even though some varieties have more sugar than a Twinkie, perhaps no other man-made food is so often recommended by medical professionals—and to treat such a wide variety of ailments.
Whenever I’ve been prescribed antibiotics, I’ve always been told to eat a yogurt so that the antibiotics don’t eat up all the “good” bacteria in my system and leave me with a yeast infection. (Recently, I interviewed a doctor who suggested this is bogus; there’s no way for the yogurt cultures to make it all the way down there.)
Breath bad? According to a 2005 study, you should eat six ounces of yogurt a day. If you, like “87 percent of Americans, suffer from digestive issues like irregularity,” have some yogurt and you’ll soon be like Jamie Lee Curtis, spritely and unclogged with the help of Activia. (As a later FTC complaint showed, this was not quite true either.)
But now, a pair of new studies suggest there might be something about yogurt after all. In the female subjects, at least, it appears to help with markers of inflammation—and that, in turn, can keep other types of diseases at bay.
Inflammation, the body’s immune response to invaders, can be a good thing—it’s how our wounds heal, for example. But a steady, low-level simmer of inflammation in the body is associated with diseases like asthma and arthritis, as well as obesity, metabolic syndrome, and heart disease.
“People who are obese have chronic inflammation, which is why there are diseases associated with obesity, like cardiac disease,” says Caroline Childs, a lecturer in nutrition at the University of Southampton. “So if you can reduce the inflammation, you might have less associated diseases.”
Bradley Bolling, a food-science professor at the University of Wisconsin-Madison, decided to put some women on a yogurt-heavy diet. He and his colleagues had 60 women, half of whom were obese, eat 12 ounces of low-fat yogurt every day for nine weeks. A control group ate a non-dairy pudding during that same time. Then, they measured the levels of proteins excreted by immune cells to determine how much inflammation was in these women’s bodies.
In a study released late last year in the British Journal of Nutrition, Bolling and his colleagues found that the yogurt-eating group saw improvements in some markers of inflammation. (And, for some of the biomarkers, only the obese group improved.)
Meanwhile, for an article in the Journal of Nutrition, which was published last week, his team gave the women an “eating challenge,” feeding them a high-fat meal of Jimmy Dean sausage-and-egg sandwiches and hash browns. The point was to see how much inflammation their bodies showed in the immediate aftermath. Typically, our bodies get slightly inflamed after a meal as our immune systems try to sort out whether what we ate was just poison, or not.
The group that ate the yogurt before the fatty meal showed less inflammation over the next few hours. In the obese participants, there also appeared to be a faster return to normal blood-sugar levels after the meal, if they’d eaten a yogurt first.
It’s not really clear how the yogurt was reducing the inflammation. Its “live and active cultures” might have been strengthening the lining of the gut, thus preventing pro-inflammatory molecules inside the gut from leaking out. (Once they’re out, they can start signaling cells and increasing inflammation throughout the body.) Or, they might have been preventing the immune cells from releasing the inflammatory signals in the first place.
Past research doesn’t offer us much of a clue how, or if, this works. A couple of small studies from recent years have found probiotic yogurt did lead to slight anti-inflammatory effects, but a Chinese meta-analysis last year found that probiotics were pretty limited in their ability to help rheumatoid-arthritis patients.
The yogurts used in Bolling’s study contained the bacteria strains Streptococcus thermophilus, Lactobacillus bulgaricus, and Lactobacillus acidophilus. The lactose-intolerant or otherwise yogurt-averse could simply take those as probiotic pills, but Bolling says it could be that there’s something about the dairy itself that could be beneficial, above and beyond the benefit of the active cultures. A review paper found that dairy products themselves could be anti-inflammatory—in subjects who weren’t allergic to cow milk, of course.
The calcium might help you absorb less fat, Childs says. Because yogurt is protein-rich, it makes you feel more full. And if you’re trying to eat two yogurts a day, like the women in the study did, you might wind up eating fewer unhealthy snacks. You probably wouldn’t do that if you were just taking probiotic pills.
There are still reasons why all the excitement about yogurt could, uh, curdle. (Sorry.) Childs told me it’s not really clear how often people have to eat yogurt or probiotics to see benefits from them. “It seems likely that you have to eat it consistently,” she said. “The food industry would be very happy to have us eat it every day.”
And lo, Bolling’s study was funded by the National Dairy Council, a non-profit that’s supported by the U.S. Department of Agriculture.
Bolling defended the funding stream, saying, “Whether or not we had the study funded through NIH, or Dairy Council, or USDA, or some other funding agency, we’d come to the same conclusions.”
Also, because they were eating so much yogurt and pudding, the obese women gained about a kilogram of weight during the nine-week study.
“The [health] benefits may not be apparent in women who are not obese,” said James Versalovic, a professor of immunology at the Baylor College of Medicine in Texas. “The results were mixed and not uniformly positive, and the elevated sugar content in yogurt may have clouded possible benefits.” Plus, he added, if the “eating challenge” the women were given had been a healthier meal, instead of the sausage sandwiches, they might not have seen as significant of an anti-inflammatory benefit from the yogurt.
So, maybe, if you have an otherwise healthy diet, yogurt and its healthy microbes could nudge you toward even better health by reducing inflammation. But Versalovic says that by itself, it’s probably not enough to prevent inflammation-related diseases.
Childs agreed, saying, “we’re not quite there yet with the research” to show that yogurt can prevent things like asthma and arthritis. But there’s little risk attached to eating yogurt anyway.
And so we come to the most common reasons why certain foods are deemed “healthy”: It looks like they might benefit us, they don’t appear to cause harm, and they’re rather tasty, so why the heck not. In the messy world of nutrition research, that’s sometimes as close as we can get. When you add marketers to the mix, a health craze is born.
Objectively, I know it’s still premature to rely on yogurt to treat anything in particular. But when I was working on this piece, I nevertheless couldn’t resist emailing my mom, who suffers from painful arthritis, “Have you considered eating a yogurt every day?”
I figure it can’t hurt.