Well, I finally tried it. Coffee with Kerrygold butter and coconut oil (I didn't buy the branded coffee beans and MCT oil, so I guess it's just bullet-resistant coffee) and hey, it's kind of delicious. But will it improve my mental clarity? Fight cravings and lead to effortless weight loss? Let's take a look at the science behind the claims.

Putting butter in coffee is not so different from putting cream in coffee, after all; both of those are mainly milkfat. (Butter has 99 percent of calories from fat; cream is 94 percent.) There is a Tibetan tradition of salted yak butter tea, which Dave Asprey says was his inspiration for a butter-containing coffee as a keystone of his Bulletproof(TM) diet.

It makes sense that a high fat, low carbohydrate breakfast would avoid the blood-sugar roller coaster that some of us feel affects our energy and mental focus throughout the day. That much is supported by science; your blood sugar will stay more stable. If you focus better that way, a high fat breakfast is a good way to go.

The amounts called for in the Bulletproof coffee recipe are two tablespoons of grass-fed butter and one tablespoon of medium-chain triglyceride oil, blended into a large cup of coffee. (The recipe recommends starting with smaller amounts and building up, and the quantity of coffee is different on various parts of the Bulletproof website, so it's hard to pin down exactly.) Those three tablespoons of oil add up to 360 calories (140 from butter and 120 or so from the oil), mostly from saturated fat which most of us would agree is reasonably healthy. Fatty coffee doesn't make a very balanced breakfast, but can be a good tool to extend a period of fasting until you're ready to eat your real food for the day.

What's questionable is whether butter coffee is any better than other low-carb breakfast options, and whether the Bulletproof-branded version of butter coffee is worth the extra money and trouble.

Is Bulletproof(TM) coffee something special?

Dave Asprey makes a lot of scientific-sounding claims on his website and in the Bulletproof coffee video. We'll take a look at the main ones.

First, he insists that you start with his brand of coffee beans, claiming that "toxins in cheap coffee [steal] your mental edge and actually [make] you weak, but clean coffee is actually healthy, and gives you important antioxidants."

Coffee has both good and bad effects on health, It does have antioxidants, but whether and how they help your body isn't well understood. Coffee is one of the most commonly consumed antioxidant sources for Americans, but it's unclear what exactly it does to our bodies and how. Making specific health claims (say about weight loss) would be premature without waiting for a lot more science to roll in.

What about those toxins in coffee? It's true that coffee can contain trace amounts of mycotoxins from mold that grows on the beans during processing. Asprey claims that his company uses a low-mold process and tests the beans for toxins.

These toxins exist in coffee, but at very low levels. If you are concerned about these toxins, it's possible to buy low-mold coffees. That said, there's no evidence that they have specific health effects like what Asprey claims. He says they are why coffee can make you jittery, but there's no science behind that idea. Ochratoxin toxicity has never been reported in humans.

He also claims that butter from grass-fed cows is better for you than "cheap butter." It's true that grass-fed butter has more omega-3 fatty acids and less omega-6, but once again there's no scientific reason to believe that a shift in a small amount of the fat content of your diet would have dramatic effects on weight loss, mental focus, or the vague qualities Asprey lumps into words like "performance." The same goes for his branded "Brain Octane" oil. To say it's different from regular MCT oil, or even from coconut oil, is really splitting hairs. There's no reason to believe you'd notice any real life differences. Don't forget, any fat you work into your morning coffee is a small contribution to your total fat intake of the day.

At the end of the day, Bulletproof coffee is just a gimmick from a gimmicky diet, and certainly not a guaranteed way to drop 75 pounds in 75 days, or achieve some kind of clarity you can't get with careful attention to a regular diet of real foods. If you like it, drink it. But don't think it's anything magic.