A while back I asked readers to submit ideas for questions you’d like to see answered on the blog. One reader responded with this, which I have heard variations on for as long as I’ve been writing about health:
[What is] the truth behind cancer causing foods and chemicals in food. I feel like there is a study every even year “sugar causes cancer” and then every odd year “sugar prevents cancer” or something to that effect. Help us see through the shock value!
The first part of that question is too big to answer in a blog post. Right now, research seems to indicate that a natural (read: unprocessed), plant-based diet is your best bet for preventing cancer, as well as a whole host of other diseases. But once you start looking at individual foods and chemicals, it gets tricky. There’s a mound of conflicting evidence because studies are conducted so differently—and foods and chemicals don’t affect everyone the same way. They also interact with other elements of your environment (whether you smoke or are exposed to secondhand smoke or another toxin, whether you exercise or get enough sleep, whether you have problems with anger or anxiety) in ways that are extremely difficult to separate out and control for in the context of a study.
News outlets rely on shock value to get your attention, so don’t expect them to tone it down or become more responsible any time soon. What you can do, and what I’ll try to outline here, is learn how to read past a headline and put a given study in its proper context. You can also check out reputable news sources that are less breathless about the latest research. Some of my favorites are listed in the Helpful Resources toolbar on the right.
Here is what I look for when I’m reviewing a study:
1) Is it published in a peer-reviewed journal?
This is a helpful first step in gauging whether a study is trustworthy. In order to be accepted into one of these journals, the study undergoes review by other experts in the field. Some of the best-known journals are The Lancet, the Journal of the American Medical Association (JAMA), and the New England Journal of Medicine, but there are hundreds of them. If you’re not sure whether the publication a study appears in is peer-reviewed, you can search for it on PubMed (see the Helpful Resources toolbar), which features a continually updated, searchable database of all studies published in peer-reviewed journals.
2) How big of a study was it?
In general, the more subjects a study uses, the more reliable its results. For example, the result of a study that only uses 12 people is more difficult to translate to the general population since there are so many factors that small sample size can’t account for. This doesn’t mean you should rule out small studies entirely, but keep this principle in mind.
3) What kind of a study was it?
The gold standard is a double-blind placebo-controlled study, which means that one set of subjects is given a placebo (the control group) and another is given the treatment being studied, and neither the subjects nor the researchers know which group is which. This helps prevent bias in the results and neutralizes some of the “placebo effect.” Another common type is an epidemiological, or population-based study, where researchers simply observe groups of people and their behaviors and try to draw conclusions based on data they collect from those people. These studies are considered less reliable since they are more open to bias and human error. They also cannot prove cause and effect because there are so many variables that the researchers can’t control or account for when they interpret their data. That’s why you’ll see so many studies that say “A is linkedto B”— the researchers can’t say for sure that A causes B, but they have observed that A and B are somehow related.
4) Is there other research to back it up?
Certainly, new studies with new results come out every day, but if you see something that contradicts what you’ve heard or read before, do a little digging. Check PubMed to see if there are other studies that have had similar results. Look at some of those reputable news sites I mentioned to see if there’s a general consensus among the research community (WebMD in particular is good about interviewing other experts in the field and getting their take on a new study). And take it with a grain of salt. Some debates will likely never be settled definitively (the health effects of artificial sweeteners comes to mind).
5) Check to see if the study authors have any paid affiliations with industry or other organizations that might sway their results.
Again, this isn’t a reason to automatically disregard a study, but if you read that red meat prevents cancer and see that the study author has ties to the National Cattleman’s Beef Association, well, keep that in mind.
6) Look for specifics.
Some study results only apply to certain populations, like people who have already had a heart attack, or who have never had a migraine. If you don’t fall within that population, the study results may not apply to you.
I hope you find this helpful! If you still have questions, don’t hesitate to ask in the comments!