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I was surprised to see, in this popular infographic, that there was evidently promising evidence that coconut oil could help with obesity. Well, if you pump the stomachs of rats with purified medium-chain fatty acids—one component of coconut oil—they end up eating less food. But, you don’t know if there’s any relevance to humans until you put it to the test.

Researchers compared breakfasts with the same amount of dairy fat, coconut-oil fat, or tallow (beef fat), and “no…effect…[on] hunger, fullness, satisfaction,” or how much they then went on to eat at lunchtime. So, where did this whole idea that coconut fat was somehow different come from? Well, six years ago, an “open-label pilot study” was published. They asked 20 men and women to eat two tablespoons of coconut oil a day for a month, and the men appeared to lose about an inch off their waist. Now, “open-label” means that the participants knew what they were eating; there wasn’t like some placebo control. In fact, there was no control group at all. So, you don’t know if the effects would have just happened anyway, without the coconut oil. There’s a well-recognized effect in dietary studies, where just being in a dietary study under observation tends to lead to a reduction in caloric intake—because you know they’re going to weigh you, and looking over your shoulder. But, there had never been a controlled study of coconut oil and waistlines in men and women until 2015.

About a hundred men and women were given about a tablespoon of coconut oil a day for three months, and lost nearly an inch off their waist after three months, compared to control. What did the control group get instead? Nothing. There was no placebo. And so, they were comparing doing something with doing nothing. And, when one does that, there’s often a placebo effect, regardless of the true efficacy of the treatment. And, they also suggested the coconut-oil group may want to take their dose with fruit. And, if they did end up eating more fruit, that, in and of itself, may help—as, despite its sugar content, fruit consumption tends to be associated with “anti-obesity effects.”

What we need to see, if coconut oil has some special effect, is to give people a spoonful of coconut oil versus some other oil, and see if there’s any difference. And, when you do that—two tablespoons of coconut oil a day, versus two tablespoons of soybean oil a day—no significant difference in waistlines. But, what did happen was a significant increase in insulin resistance in the coconut-oil group, which is what eventually causes type 2 diabetes—despite being told to increase fruits and vegetables, cut down on sugars and animal fat, and despite an exercise program of walking 50 minutes a day, four days a week.

The only other placebo-controlled study of coconut oil and waistlines was published in 2017, and no significant changes in weight or waist or hip measurements, total fat, belly fat, nor butt fat. No benefit to coconut oil for obesity over placebo shown in any study to date.

So, how can coconut oil proponents get away with saying otherwise? Well, they like to talk about studies like this, showing that Pacific islanders who ate more traditional coconut-based diets were slimmer than those eating more modern diets with fewer coconut products. But, guess what they were eating instead? “The modern[ized] dietary pattern [was] primarily characterized by high intake[s] of sausage [and] eggs and processed foods.”

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