The drink, made from mixing butter and medium-chain triglyceride (MCT) oil with coffee, is touted by popularizer Dave Asprey as a "biohack" that can give consumers the "clarity and energy to rip it up for hours."

Asprey, a Silicon Valley veteran who aspires to live until he is nearly 200, sells a variety of brain-stimulating products through his Bulletproof Nutrition website and accompanying Bulletproof Coffee store in Santa Monica. He's one of many diet gurus currently promoting a high-fat, low-starch diet, and butter coffee is at the center of his program.

Like other so-called superfoods, butter coffee has inspired a cult of true believers who attribute all kinds of miraculous effects to consumption of the beverage.

"It's rocket fuel," said Jerrod Epps, a CrossFit enthusiast from Maryland. "You are beyond awake when you consume this stuff, you spring awake, and you aren't hungry for hours."