Yogurt, the fermented panacea?

Have the health benefits of yogurt been exaggerated? ‘Science-ish’ investigates.

by Julia Belluz

The Statement: “Fermented milk products such as yogurt and kefir contain friendly probiotic bacteria that may help guard against disease… Yogurt’s active bacterial cultures can help stimulate the immune system, reduce symptoms of antibiotic-associated diarrhea and improve the absorption of lactose in people with mild to moderate lactose intolerance.” (Leslie Beck, The Globe and Mail, 06/23/2011)

Yogurt has been starring in the news lately for its panacea-like ability to do everything from “stimulate the immune system,” as Beck writes, to help aid weight loss, according to reports about a new 20-year Harvard study. Of the latter, the Toronto Star recently stated, “Vegetables and fruits helped keep weight in check, but nuts and yogurt were the most effective. Most of the test subjects ate no-fat or low-fat yogurt.”

But before you go stocking up on the fermented miracle food, know this: research into the health benefits of yogurt and probiotics is patchy and inconsistent.

Let’s start with the question of weight loss. Dr. Brian Haynes, professor of clinical epidemiology and medicine at McMaster University, looked at the Toronto Star article and found the claim that certain foods, such as yogurt, were more effective at keeping weight off to be a “misdemeanor” of sorts. He said, “The study does not test whether one food item has a different effect than another. If you switched, say, yogurt and nuts for vegetables and fruit, you would likely gain weight—especially if you were heavy on the nuts, which have way more calories than low-fat yogurt.”

As with many nutrition studies, it’s important to note the great difficulty (near impossibility?) of drawing correlations between the consumption of a specific food item and a particular health outcome. For example, people who eat low-fat yogurt are likely to have healthy lifestyles or may be trying to control their weight, so their success at the scale may have more to do with a calorie-limiting approach than any special attributes of the dairy products they consume.

Also, Dr. Haynes pointed out that those who reported on the study may have missed this little caveat from the authors: “Yogurt consumption was also associated with less weight gain in all three cohorts. Potential mechanisms for these findings are unclear; intriguing evidence suggests that changes in colonic bacteria might influence weight gain.”

In other words, even the study’s authors can’t explain the association between yogurt and weight.

For Beck’s assertions that the “friendly probiotic bacteria” found in yogurt may “help guard against disease” and “stimulate the immune system,” we called Dr. Gregor Reid, director of the London, Ont.-based Canadian Research & Development Centre for Probiotics.

(Before we go any further, it’s worth defining what probiotics are. According to the WHO, they consist of “live microorganisms which when administered in adequate amounts confer a health benefit on the host.” They can include one or more species of bacteria, including Lactobacillus and Bifidobacterium—both part of normal human intestinal flora—or yeasts such as Saccharomyces.)

Dr. Reid noted that probiotics come in many different forms and have many different health effects—many of which haven’t been adequately studied. These effects are not all intrinsic to yogurt. “People have to be very careful when they generalize about yogurt,” said Dr. Reid, pointing out that few yogurts in Canada actually contain probiotics, despite the claims bandied about in the dairy aisle.

Of Beck’s statement that yogurt’s “active bacterial cultures can help stimulate the immune system,” Reid said, “Yogurt has active bacterial cultures but, in general, they don’t do anything to the immune system because they die in the stomach and bile.” In fact, the European Food Safety Authority (EFSA) reviewed the scientific evidence for health claims made by food companies, and it found that of the hundreds of probiotic strains of bacteria examined, none were shown to improve immunity or gut health.

After these negative rulings, yogurt-maker Danone withdrew its requests for the EFSA to approve claims about its Actimel and Activia yogurts’ immune-system boosting and digestion-aiding effects. On a similar note, in the US last year, the Federal Trade Commission found Danone went too far in promoting the healing power of its yogurt products. The company agreed to pay the government $21 million in a settlement and was prohibited from claiming any “yogurt, dairy drink or probiotic food or drink reduces the likelihood of getting a cold or the flu.”

In 2004, the esteemed Drug and Therapeutics Bulletin analyzed the scientific literature on probiotics and their relationship to gastrointestinal disorders. They found that the evidence about whether probiotics improve gut health was patchy, though there was strong evidence to suggest probiotics help children with acute infectious diarrhea. The authors also stated, however, that more studies were needed to find which strains and doses of probiotics are most effective and whether probiotics help adults with the same affliction.

Science-ish found another systematic review (the highest form of evidence) on the subject of probiotics and diarrhea, which concluded that they can shorten the duration of acute diarrhea and reduce the risk of a prolonged diarrhea episode. So while Beck could have been more specific about the effects of yogurt on diarrhea, there was some evidence to back this claim.

The probiotics question is just one example of the general dubiousness of diet-related health claims that flourish like bacteria in newspapers every day—an inspiration for this blog and something you’ll be reading more about. As one of the patron saints of Science-ish, Ben Goldacre of the Guardian newspaper, writes in his book Bad Science, “Diet has been studied very extensively, and there are some things that we know with a fair degree of certainty: there is reasonably convincing evidence that having a diet rich in fresh fruit and vegetables, with natural sources of dietary fiber, avoiding obesity, moderating one’s intake of alcohol, cutting out cigarettes, and taking physical exercise are protective against such things as cancer and heart disease.” Everything else is probably science-ish.

*Thanks to reader Mariam Morshedi from New York City for requesting a post on health claims about yogurt. “What’s with probiotics?” she asked.

Julia Belluz is the associate editor at The Medical Post. Got a tip? Seen something that’s Science-ish? Message her at julia.belluz@medicalpost.rogers.com or on Twitter @juliaoftoronto




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Yogurt, the fermented panacea?

  1. There’s a podcast of PRI’s Changing World radio series that covers yogurt. Sounds like it’s been a triumph of game-changing marketing (convincing people that some food is medicine) and high margins (a few cents’ milk and flavouring become a few dollars’ worth of yogurt).

    The podcast can be found here: http://www.podbean.com/podcast-detail?pid=18177 It’s one of the “Foods that make Billions” series at the top.

  2. “Diet has been studied very extensively, and there are some things that we know with a fair degree of certainty: there is reasonably convincing evidence that having a diet rich in fresh fruit and vegetables, with natural sources of dietary fiber, avoiding obesity, moderating one’s intake of alcohol, cutting out cigarettes, and taking physical exercise are protective against such things as cancer and heart disease.”

    Other than avoiding obesity – which is nonsense on stilts – lifestyle described above would benefit average person of moderate health. Common sense – no cigs and everything else in moderation is best way to live if you want maximum best health. 

    However, avoiding obesity is much easier said than done because there is plenty of evidence that appetite is controlled by genes. 

    “Height, weight, and body mass index (BMI) were assessed in a sample of 1974 monozygotic and 2097 dizygotic male twin pairs. Concordance rates for different degrees of overweight were twice as high for monozygotic twins as for dizygotic twins. Classic twin methods estimated a high heritability for height, weight, and BMI, both at age 20 years (.80,.78, and.77, respectively) and at a 25-year follow-up (.80,.81, and.84, respectively). 

    Height, weight, and BMI were highly correlated across time, and a path analysis suggested that the major part of that covariation was genetic. These results are similar to those of other twin studies of these measures and suggest that human fatness is under substantial genetic control.”

    http://jama.ama-assn.org/content/256/1/51.abstract

    McArdle: Over the last five years or so, I’ve noticed that public health efforts about obesity are not just amping up the volume, but exploring increasingly coercive methods to induce weight loss: taxes on junk food, lawsuits against fast food companies (which are basically a tax on junk food), and so forth. Does that match your analysis?

    Campos: It’s the classic pattern of moral panics. As public concern about the damage being done to the fabric of society by the folk devils increases, increasingly intense demands are made on public officials to “do something” about the crisis, usually by eliminating the folk devils. 

    That of course is the strategy for this crisis. If fat people are the problem, then the solution is to get rid of them, by making them thin people. The most amazing aspect of this whole thing, for me, has always been the imperviousness of policy makers, and even more so people who consider themselves serious academics and scientists, to the overwhelming evidence that there’s no way to do this. 

    I mean, there’s no better established empirical proposition in medical science that we don’t know how to make people thinner. But apparently this proposition is too disturbing to consider, even though it’s about as well established as that cigarettes cause lung cancer. So all these proposals about improving public health by making people thinner are completely crazy. They are as non-sensical as anything being proposed by public officials in our culture right now, which is saying something. 

    http://www.theatlantic.com/business/archive/2009/07/americas-moral-panic-over-obesity/22397/

    • I will agree with your statement.  But lets not over shadow high caloric intake (ie.high glucose corn syrup etc.), refined foods (GMO wheat), fast foods and lack of exercise as a major contributing factor to the obesity epidemic.  Especially in our young.

  3. “Most of the test subjects ate no-fat or low-fat yogurt.”

    As with many nutrition studies, it’s important to note the great difficulty (near impossibility?) of drawing correlations between the consumption of a specific food item and a particular health outcome. ”

    Excellent point. Experts and studies have to be viewed collectively, or as a whole, and society should not follow just one or two studies because our understanding of causation/correlation are terrible. 

    “Most people can count calories. Many have a clue about where fat lurks in their diets. However, fewer give carbohydrates much thought, or know why they should.

    But a growing number of top nutritional scientists blame excessive carbohydrates — not fat — for America’s ills. They say cutting carbohydrates is the key to reversing obesity, heart disease, Type 2 diabetes and hypertension.”

    http://articles.latimes.com/2010/dec/20/health/la-he-carbs-20101220

  4. At least reading this article kept me away from the fridge long enough.  I bet online media promotes weight loss…anything to keep me from diet and exercise.  Thanks for doing the research, Belluz! 

  5. You could probably devote the Science-ish blog entirely to questionable diet claims and still never run out of things to blog about.

    • This is true. Too much out there to tackle. One post at a time.
       

  6. It has to be right – it is natural. lol

  7. Umm, I just have to say that a thorough search of PubMed would reveal many, many studies that show probiotics have a beneficial effect on human health. And in fact, if something is called a probiotic, then it by definition is good for health.

    The problem is that these are two separate issues: health claims for probiotics in general, and health claims for yogurt. The yogurt claims are dubious, yes, since (1) companies sometimes generalize their claims, assuming that a certain strain of bacteria will have the same benefit for middle-aged men as for children, which isn’t always borne out by the studies, and (2) there’s no guarantee that the beneficial bacteria will survive the transportation process and be alive by the time they are consumed: the guarantees on the packages say “X amount of bacteria were present at the time of manufacture.”

    Bottom line: if you DO want the health benefits of probiotics, don’t rely on yogurt. There are other really great ways to get them. See intestinalgardener.blogspot.com

  8. I find it odd that an article that’s talking about weight loss and yogurt fails to mention added sugar. You can eat all the yogurt in the world, but if it’s got sugar (not including fruit), it’s likely going to have the opposite effect you are looking for. Especially since the effects of sugar are cumulative and it is now in nearly every processed food we eat.

  9. It’s important to note that grocery store yogurts do not contain what would be considered as a therapeutic amount of Culturing Unitss to have much health benefits to report.  As well, contain high amounts of sugar.  Bio-K is a probiotic yogurt that has done many studies for its use against C-Difficile in hospitals. 

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