Read enough health studies and you come to realize darn near every theory has one study proving one thing and another study proving the exact opposite. It's a cold, confusing world out there, and though science tries to make sense of it all, absolute truths and facts are hard to come by. That doesn't mean science is going to give up, though. 

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Consider the case of butter. For the past however many years, we've been drilled to think butter is bad. Butter is a saturated fat and heaps of research have found that saturated fats lead to heart disease. Plus, the molecules of saturated fats are packed closely together, meaning they store loads of energy. Translation: lots of calories, stay away. There isn't a set date when fat became the enemy, but some look to July of 1976 as a good starting point. Heart disease was becoming a problem and Senator George McGovern called a hearing that led to the first set of dietary guidelines for Americans. Fat became the enemy, carbs were good for you, and the food industry responded with countless fat-free offerings, from yogurt to muffins to pretzels and everything in between. The problem was, the fats had to be replaced with something, and refined carbohydrates and sugar stepped in to fill the void. By trying to cut down on fats and prevent heart disease, we loaded fat-free and nearly fat-free foods with carbs and sugar, people gobbled them up thinking they were healthy, and people got fatter, with spikes in diabetes and obesity following along for the ride. 

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Eventually, science began realizing the error of our ways. Studies started finding that unsaturated fats, especially polyunsaturated fatty acids found in foods like nuts, raised the "good" HDL cholesterol and lowered the "bad" LDL cholesterol. Saturated fats were found to raise both the "good" and "bad" cholesterol, making them not as healthy as polyunsaturated fats from nuts and vegetables but not as bad as trans-fats, which lowered "good" cholesterol and raised "bad" cholesterol. Unfortunately, the public and the U.S. dietary guidelines lagged behind science. The message was complicated, members of the media aren't scientists, and explaining all of the ins and outs was difficult, especially for people who didn't fully understand it all themselves. Fat was still the enemy. People kept gobbling up foods high in sugar and refined carbs but low in fat, and our waistlines got larger. 

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Then, last year, an Annals of Internal Medicine study came out and created a huge commotion. Using metadata analysis (a statistically powerful technique for revealing overarching trends from many individual studies), researchers explored more than 70 studies and investigated the comparative impact saturated fats (butter, cheese, meat) and unsaturated fats (fish, nuts, vegetable oils) had on heart disease. The conclusion was unconventional—and direct: "Current evidence does not clearly support guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of total saturated fats. "The media rushed to cover it, people read it, and butter was back, baby! 

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But, the study was flawed. Researchers mixed up the results of certain studies, for instance claiming a study showed omega-3 fats, an unsaturated fat, had no significant effects in reducing heart disease when in fact, the study showed it did. Researchers also whiffed on two important studies of omega-6 fatty acids. Scientists understood this, but by the time all the flaws and problems were revealed, the media's message was out, and there was no going back.

So where does that leave butter?

The answer was never going to be cut and dry. First, let's get this out of the way: Polyunsaturated fats are widely accepted in the science community as reducing the risk of heart disease. Second, replacing saturated fats with refined carbohydrates and sugar will not reduce your risk of heart disease. Third, vegetable oils like olive oil and soybean oil are considered good for you. So are nuts. Lastly, omega-3 and omega-6 fatty acids are extremely important (from building healthy cells to helping brain and nerve functions) and fish, nuts, seeds, and vegetable oils will help you get enough of these fatty acids.

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Back to butter. Dariush Mozaffarian, dean of the Friedman School of Nutrition at Tufts University and a coauthor of the 2014 metadata-analysis study, believes that eating less fat, and saturated fat in particular, is less important than what you replace the fats with.

"Although saturated fat content is unhelpful for judging foods, people should prioritize those foods that we know improve health, and butter is not one of them."

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Walter Willett, chair of the Harvard School of Public Health, agrees: "Butter is not back. Long-term health will be better with olive and other oils."

In the end, scientists and nutritionists seems to agree on this: Eating less fat, and saturated fat in particular, isn't as important as how you're replacing these fats. In addition, changing our understanding of diets from a nutrient-based approach to a food-based approach may be the best option going forward. So, butter doesn't seem to be back, but don't be afraid of it, either. The question may be black and white, but the answer is somewhere in between. A shade of gray, we guess, but definitely not 50 shades. Definitely. Not.

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