The latest trend in coffee may boost your energy and help you lose weight. Or maybe you’ll just throw up.

Go ahead, put some butter in your joe.

Well, not just any butter, and not just any coffee.  The butter has to be unsalted and grass-fed, and the coffee beans have to be low-toxin – not the ones you find at the supermarket or Starbucks.

Let Dave Asprey, creator of Bulletproof Coffee, explain.

The caffeine in normal coffee, Asprey says, gives you an initial buzz, but in a while you’ll eventually crash. His low-toxin Bulletproof Coffee, on the other hand, contains MCT oil – a blend of coconut and palm oil – and has healthy fats that keep you going for hours.

"It’s about how you feel two hours later," Asprey said.  "With normal coffee, you get a food craving and get tired two hours later.   [Bulletproof coffee] doesn’t cause a 10:30 crash we’re used to.  It gives you a huge boost over normal coffee."

Asprey says MCT oil is digested faster than other fats, so it boosts energy and promotes weight loss. He says he adds it to his coffee to provide "laser focus."

"When you blend low-toxin coffee with butter and octane oil (MCT oil), the butter turns off some of your food cravings and provides things the brain needs, including micronutrients," he said. "It turns off inflammation in the brain."

Asprey insists on grass-fed, unsalted butter because "there are a lot of inflammatory ingredients in normal butter." The same applies to much of the coffee sold in the U.S., which he says is filled with fungal toxins. 

The practice of putting a pat of butter in your morning drink isn't new. For generations, Tibetans have made yak butter tea. In fact, Asprey came up with the idea of putting butter in his coffee after trying yak butter tea during a visit to Tibet three years ago. A health and fitness fanatic who had given up coffee, he’d found the perfect solution.

"I wanted to drink coffee, and some days it didn’t make me feel good. I would get groggy," he said.

As for the taste, Asprey says "It’s like the creamiest latte you’ve ever had."

So I tried it. And I agree –- it tastes like a latte. But I wasn’t a huge fan of the butter. I felt full and satisfied, but also a little sick.

Asprey says his butter-coffee devotees have grown to 3 million and they swear by it. Many follow a paleo diet, which is high in animal fats and protein.

But is this stuff all it’s cracked up to be?

"There’s no scientific evidence to support the idea that adding butter to coffee provides an extra energy boost or that it may help you lose weight," said registered dietitian Tanya Zuckerbrot. "However, these claims may have some merit based on what we know about fat and digestion."

Zuckerbrot said people need some fat in their diets, in part because it helps the body absorb nutrients in the foods they eat.

"We also know that fat slows down digestion," she said. "Therefore, in theory, butter could slow the absorption of caffeine into the bloodstream. This would result in a prolonged energy boost rather than the peak and crash you might experience if you drank your coffee without the fat."

Zuckerbrot, author of "Miracle Carb Diet: Make Calories and Fat Disappear – with Fiber," said she knows people who add butter to their coffee and swear by the results.

But butter is very high in saturated fat, and some health experts caution that it can increase your risk of heart disease and stroke.  And while this elixir will make you feel full, it’s worth noting that adding the recommended 2 tablespoons of butter to your coffee will also add about 200 calories.

Want to try it?  Here’s how to make your coffee Bulletproof-style:

Recipe: Bulletproof Coffee