A study has shown that the speed you eat has a big impact on the amount you eat, and how quickly you feel full. Eating slowly means you "feel" full quicker than if you shovel food into your mouth like someone is about to come and steal your plate from underneath you. So the idea behind the HAPIfork is to remind you when you're eating too quickly, and nudge you to slow down.
Hapilabs tells us that it takes about 20 minutes before you start to feel you're full - remember when your parents used to say, "Wait 20 minutes before moaning you're hungry", well they were right. So, logically, the fewer mouthfuls you take in those 20 minutes, the fewer calories and fat you'll consume in that time.
The hardware seems simple enough. The fork is able to sense when it's in your mouth because the metal part is sensitive to touch. It monitors the number of times it hits your lips, and when things get too fast and furious, it starts to vibrate.
This vibration is the main way the fork has of changing your behaviour, and because it happens in real time, it should have more of an impact than entering your meal choices into an online diet system after the fact, and learning that you've eaten too much. Another study has shown that humans respond far more proactively to things that are happening now, than what will happen in the future. So you're more likely to pay attention to a live prompter, than one you are aware of, but is not badgering you right there and then.
The fork does give you some feedback later though. It's able to track how many mouthfuls you took and over what period. This way, it's able to show how you're doing, and over time you should see the number of mouthfuls decrease. If you listen to your fork. There is an online dashboard to help with this, and apps for smartphones too.
The idea here is certainly solid, but there are obvious issues. No one eats a pizza with a fork, and we can stuff a massive one of those into our pieholes in mere minutes. Plus, the "fast" foods are often eaten with your hands, so unless you're going to break out the fork for a burger in McDonalds, this sort of thing is going to go unmonitored. And, of course, the fork doesn't know how much is on it, so if you stack it high, you'll be eating more food per forkful than is strictly necessary.
All in all, it's a neat idea, and something a bit different for weight loss. The science seems to back it all up, but it requires users to play by the "rules" to get the most from it. So people keen to lose weight should find it useful, those who aren't committed will struggle. But then that's true of any weight loss regimen.