Dec. 11, 2009 -- It is another study with broad appeal but not a lot of science behind it yet. It says -- at least in headline form -- that drinking beer may help men ward off prostate cancer.
There are some studies people just want to believe. Even if they're disproven by later ones.
Beer is hardly the first popular food to get headlines because of a study that suggests it may be good for you. At the same Houston conference as the beer study, other researchers presented a small study suggesting that pistachio nuts may help prevent lung cancer.
Coffee is also a popular subject for studies that draw headlines, although its potential benefits have been better studied. But in recent years, any number of foods have gotten headlines for possible health benefits, whether it be boosting the immune system or preventing cancer.
(The cynical might note that we are learning about all these presumed superfoods at a time when we know people are eating more of everything -- including things that are good for you.)
"Small studies are better than no studies at all, but usually small studies require more studies, and I wouldn't recommend someone change their decisions or change their diet based on a small study," said Keith-Thomas Ayoob, director of the nutrition clinic at the Albert Einstein College of Medicine.
Neither the beer study nor the pistachio study quite say there are long-term benefits in humans. The beer study showed an ingredient in hops that might be beneficial, while the pistachio study showed that people absorbed vitamin E when they ate them. The authors noted that vitamin E has been shown to help prevent lung cancer. Of course, with a finding from a small study, other findings can easily knock them down.
"Basically, we've got a series of weak links here," said Dr. David L. Katz, director of the Yale Prevention Research Center. "Interventional studies (studies where vitamins are given to subjects) of vitamin E have shown an increased cancer risk."
He noted that the increased cancer risk was a variant of the form looked at by researchers in the current study, but the bottom line, he said, is that people cannot smoke and expect a pistachio-heavy diet to protect them.
"Do not make this your insurance policy against lung cancer," said Katz.
The Value of the Small Study
Studies are costly, Ayoob said, so sometimes a good study is small simply because the researchers didn't have the funds to test their conclusions on more people.
"Sometimes a small study may be all you can get," he said of nutrition studies. "They're extremely costly to do. I wouldn't say it's not worthy. It just means you need more of them."
"It depends upon the scientific method, it also depends upon the outcome," said Katz.
A larger sample size, he explained, is "to help us know if [findings are] a fluke or if [they're] real."
A trial where patients were kept in a clinic and given a set diet might help draw stronger conclusions, but putting those restrictions on a study subject would make the study even more expensive.
While larger trials reduce the possibility that an outcome arrives by chance, there are cases in which cause and effect are clear, and a large trial isn't necessary.
"If we had 36 people and we randomly assigned 18 to take a bullet to the chest…the difference in health outcomes between the two would be emphatically real and reliable," Katz said, adding that such a "study" would obviously be "deplorable."
But cause and effect is less clear when it comes to nutrition, and so most studies can merely show associations, rather than causes.
"Associations are a weak form of science; they help us ask questions but they rarely give us definitive answers," Katz said. For instance, he said, few people with television sets get tuberculosis, although the two have nothing to do with each other.
Small studies may help scientists design future, larger studies, like a study of whether pistachios can help prevent lung cancer, but they typically do not stand on their own.
"This study is an invitation to scientists to start asking questions. This is not a finding that's ready for prime time," said Katz.
Why You Can Avoid Food You Hate, No Matter What Studies Say
Even if pistachios don't prevent lung cancer, they do have other benefits.
"I think we already know from multiple lines of research that nuts are nutritious foods," said Katz. "I wouldn't put pistachios quite at the top of that list," he added, saying he would put walnuts first, followed by almonds.
And people shouldn't jump to eat the latest superfood in excess -- or even at all if they don't like it.
"We don't want to hang our hat on any single food as the answer in disease prevention," said Connie Diekman, the director of university nutrition at Washington University in St. Louis. "Single studies should not give the consumer a message that says, 'I must do.'"
But that can change as more studies confirm possible benefits from a food. One example making headlines recently is coffee, which is being shown to have benefits, but by multiple studies over many years.
In the end, though, Diekman said, individual food studies should show a consumer an overall message of a balanced and varied diet rather than one of choosing superfoods.
"The food we eat does play a role in our overall health. How and what that role is and what it looks like is less clear, but the food choices you make are going to make a difference to your health," she said. "I hope what they hear in that message is think as you make food choices, as opposed to doing whatever's the easiest, the fastest."