It isn't so much the diet as it is the will of the person to change their behavior. They need to get their mind focused on a goal and decide to not live the way that they did in the past. I used to be over 300 pounds and tried a few things over the years that didn't help very much. I'd get on a big project and gain the weight back again because I was eating crap food and was always at my desk. I had some heart rhythm problems one day and to help diagnose the problem, my doctor had me wear a heart monitor for a week. After hearing about this, my mom and my older sister drove 1000 miles (some of it through a blizzard) to take care of me. After that, I swore that I'd never put my mom through that again and I wasn't going to be the lardass carted off to the hospital in an ambulance ever again. Monitoring my food intake via smartphone apps has been a huge help in addition to making what I eat at home instead of going out or eating pre-packaged stuff. I'm nearly 100 pounds down from my max weight and would be doing better if I could just stop doing stupid things that limit my ability to exercise (hell, I didn't know that shoes could be considered "worn out" before all the tread was off the bottom and that you can mess up your legs trying to run with them - but I do now.
So if your friend wants a doctor to prove to him that a particular diet plan to work, then it doesn't sound to me like he's had a "I have change, or I'm going to fucking die" moment. I hope he comes to that realization before he has any serious problems and can get to a healthy weight.
I see no reason why a pill couldn't be made to inhibit the intake, or facilitate the evacuation of, an unhealthy level of fats and carbs in the same way we can with sugars.
That already exists: http://www.webmd.com/diet/alli... If the first time you take it and then eat a really greasy meal (fried chicken, pizza, ribs, onion rings, etc), the next trip to the toilet will be a surprise. It will look like the Exxon Valdez ran around in the toilet bowl, but with globs of orange fat floating in the water instead. Also, when one feels and hears a rumble deep in your guts, it is time to find a bathroom as quickly as possible, because as Jim Lahey would say "the express shit train is all greased up and ready to leave the station".
In the real world we save our best seed and livestock year to year using that to grow the next generation.
The part about saving seed hasn't been that common place in western countries for several decades. Registered seed growers could do that, but then again, their harvest goes to a seed company, not the general market.
The potential liability and government oversight is simply not worth it
The only reason for this is because of politics.
"Conversion, fastidious Goddess, loves blood better than brick, and feasts most subtly on the human will." -- Virginia Woolf, "Mrs. Dalloway"