Why It Seems Like Diet Advice Flip-Flops All the Time An R.D. explains how to make sense of the ever-changing nutrition recommendations.
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First, you were supposed to drink skim milk. Then, research came out saying whole-fat dairy was the way to go to slim down. Chocolate used to be considered the ultimate indulgence, but now it’s been elevated to super food status. And don’t even get me started on whether it’s better to eat egg whites versus whole eggs. If it’s hard for you to keep up with constantly conflicting nutrition advice, you’re not alone. But why is it that food-related findings seem to change all the time?
Truth be told, all research is full of mixed messages. That’s the infuriating beauty of how the scientific process works: One study leads us to conclusions down one road, and more studies build from there, possibly taking a turn down another road. We're constantly learning new things and disproving incorrect beliefs—but here's why nutrition research can seem particularly confusing:
1. Nutrition is a younger field than many others: While people have been using herbs and foods for medicinal purposes since before history was recorded, scientific studies only date back to the end of the 19th century. Roughly 160 years of study is not a lot of time to figure out that much about how foods affect us. We need many, many studies with similar results over time to get reliable conclusions—and we just haven’t been doing it long enough to be at that point.

 A photo posted by @healthy_lifeways on Apr 7, 2015 at 9:10am PDT

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2. It’s really hard to design a good nutrition study: It's impossible to only change one thing about someone's diet when you're conducting a study—and so many things besides food influence weight, metabolism, and wellness. All of which is to say that you can think the results in one study might be attributable to one factor (or food), and there might be something else at play. That's why the distinction between correlation (which just means there's an association between a factor and an outcome) and causation (which means a factor actually causes an outcome) is so key.
3. Many headlines sensationalize or over-simplify studies: Not all media outlets are guilty of this (Women's Health, for instance, always try to present info in a balanced way), but many publications gloss over the nuances of research (like correlation versus causation)—and they can also overlook that we each have different medical conditions, genetics, and food histories. Translation: Nutrition claims aren't one-size-fits all, no matter how much we may want that to be the case.
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4. Good research is expensive, and the people funding the studies often have something to gain: Sports drink companies may fund some research that finds their products are good for you, but keep in mind: They're interested in selling sports drinks. Even the greatest research loses credibility if the person fronting the operation has something to gain from the findings.
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Does this mean that you should ignore nutrition research? Definitely not—but here’s what you should be looking at when new studies hit the scene.
●    Who funded the study: Per the point above, you should look for research that comes from third parties that don't stand to gain from the results: universities, government institutions (think NIH and USDA), and not-for-profit sources (e.g., the American Heart Association and National Cancer Institute) are your best bets.
●    Whether the results are in line with findings from previous research: Good research builds on the research of others—so ideally, there should be more than one study that supports the conclusions.
●    The source: Look for .org, .gov, .edu and sources that are public interest-minded. Steer clear of research and headlines that seem over-simplified—or that are promoting messages that seem too good to be true.



And you should always ask yourself one big question: Does this make sense for my lifestyle? While a lot of people want there to be one new magic super food (or one food they should ban) to lose weight and improve their health, the truth is that a healthy diet is about eating a variety of nutritious foods—and unless you have a medical or personal reason to avoid certain items, you can incorporate almost anything into your diet in a healthy way. Which is why the nutrition advice you should take is the advice that makes the most sense in your life. If you know you can’t stick to one ounce of chocolate and you always end up overindulging, then you don’t need to add chocolate to your diet just because a study came out touting its antioxidants—you can get your fill from berries or a glass of wine instead. And if you genuinely prefer the taste of egg whites to whole eggs, keep eating them.