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Depending on when you read or watch the news meat will either kill you or it won’t. Alcohol is both good for you and bad for you. And low carb is the best thing ever except when it lowers your life span.

Welcome to the wonderful world of nutritional studies, and the sensationalism that surrounds them.

It’s no wonder people are confused about what to eat and what’s good or bad with all the misinformation and sensationalism out there.

Here’s what you need to know about nutritional studies. There are two main types of nutritional study: epidemiological and double-blind placebo controlled, and both have major limitations.

Epidemiological studies are generally conducted on thousands of people, over long periods of time, and involve food surveys. There are so many problems with this type of study it’s comical. These studies do have some use, but it’s very limited.

-First, this type of study can never prove that one thing causes another. It can only show that two things are correlated. For example, increased ice cream consumption and shark attacks are highly correlated, but one does not cause the other. The thing they have in common is the summer months. So, when a study says meat will kill you ask yourself if meat is causing the adverse outcomes or is it correlated with negative outcomes. There’s a gigantic difference.

-These studies rely on people remembering what they ate anywhere from 6 months ago to the past 5 years. Do you remember what you ate a month ago? Exactly. These surveys are notoriously prone to error because of the difficulty of food recall.

-Healthy and unhealthy user basis. People who are healthy tend to say that why engage in more healthy activities on their survey, whether they do or not. Unhealthy people tend to say that they engage in more unhealthy activities, whether they do or not. This clouds the results.

Any time you see a study that says it involved more than a 1000 people that’s generally a dead ringer for an epidemiological study, and the best that study can show is that two things are correlated not that they cause each other. Always be skeptical of the claims of these studies. Again, all they can show is that two things are correlated not that one caused the other.

The other type of study, namely the randomized-controlled double blind placebo study is the gold standard of research. However, it’s really hard to do when it comes to food (as opposed to pills) because most people don’t want live in a metabolic ward for 6 months and eat the same thing. These studies tend to have way fewer people like 50-200 and they’re generally shorter because it takes a lot of money and time to run them. These studies can establish causation, but they’re very hard to do in terms of recruiting people, funding them, and doing them over the proper length of time.

Does this mean we can’t learn anything from nutritional studies? No. But we need to be crystal clear on what these things can show and what they can’t show and we need to avoid falling for the sensationalistic media hype that blows the results of studies completely out of proportion.

So, the next time you hear that beef will kill you or eggs are the devil, please view those claims with the appropriate level of skepticism and see what the data is to back up those claims.