It's crap.
That's my default stance on ANY new diet out there, and so far I've yet to see an exception.
Low carb diet, grapefruit diet, Atkins, natural diets, vegan diets, so far, all crap. At least, the reasons for them are crap. Some work, but the way they work has nothing to do with the "explanations" provided for them.
We're omnivores. We also have a wide range in our operating parameters, so to speak. The body can make up for a lot of what it's missing, so as long as you're pretty close to your nutritional needs you'll be fine. There are a few things to consider for a diet, that make it "good", regardless of other factors:
1. Variety. Any diet that pushes for a majority of a single food or group (grapefruit diet) or the complete removal of groups (low carb, Atkins) is automatically bogus. Avoid it. Some peopel with specific dietary needs may benefit from something along these lines (lactose intolerant, diabetics, etc), but a doctor should place them on it. Eat veggies, fruits, meats, breads, grains, dairy, etc. Get some of everything.
2. Moderation. Goes along with variety. To get a wide variety of food, you eat moderate amounts of any food type. Don't overload on fatty foods, or meats, or veggies. Don't eat signifigantly larger amounts of one group than another. Follow recommended serving sizes.
3. "Process" tree. Eat less of heavily processed foods, more of unprocessed foods. THis is a genenral rule of thumb. Basically, what I mean by processed is how much it resembles the starting state. Low processed foods: steaks and lean meats, fresh fruit and veggies, water. Medium processed foods: Ground meats, canned fruits or veggies, frozen meats (fish fillets and such), pre-packaged dinners. High processed foods: hot dogs and sausage, Twinkies (aka "Oblong Death Sponge"), Anything chopped and form or cloaked into unrecognizeability by sauces and gravies. Generally, more from the low end and fewer from the high end. Has nothing to do with the natural = better fad, but just the idea that the processing typically removes vitamins and minerals. Milk is an exception (fresh is good, but high fat and chance for disease), as some other foods. Use common sense.
4. Ye Olde Foode Pyramide. Think ease of acquisition. Eat more furits and veggies than meats. Eat fewest of sweets and such. Think about how easy it is to get those types of foods if alone on a primitive world. THe easiest are what you need more of. I think this idea has merit because it falls into the accepted food pyramid pretty well, and intuitively it matches with our evolution (we'd obviously evolve to make more use of available foods...meats had to be hunted, and were less common but useful, fruits and veggies could be gathered relatively easily, etc).
Everything else is a fad diet. To lose weight, eat smaller portions and less of them (lower calories) and/or increase your exercise. To gain weight, eat more of each group and exercise. To stay the same, eat the same and exercise

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That's about all I have to say on diets. If any new diet idea doesn't match up to my four principals, I pretty well dismiss it out of hand unless there is very strong evidence for it. So far, history has proven me right
