I think they're crap. I don't get the point of putting yourself on a fad diet that cannot be sustained long-term. I've lost over 70lbs by being gluten free (I have an intolerance, wheat caused major weight gain and vitamin deficiencies for me) but making sure I have a BALANCED diet is the key to staying fit and healthy despite being gluten free. Every nutritionist I've been to has talked about eating balanced (I've been to like 3). The point is having a protein and carb at every meal along with non-starchy veggies to fill yourself up so you don't over eat at the next meal (or you can substitute with some fruit at breakfast). Carbs aren't just breads, pasta, rice, etc. They are yogurt, starchy veggies (avocados, beets, etc), legumes, quinoa, peas, corn, etc. Fats and dairy is even important too and should be added if possible. Proteins are mainly derived from animals (lean grass fed meat is great) but it can be peanut butter, legumes, quinoa, poultry, eggs, etc. So it's 25% carbs, 25% protein, and 50% non-starchy veggies.
The point is to have 3 meals a day like this so you're feeling full and satiated throughout the day and don't get into the overeating/undereating cycle. Also, you're getting nutrients from all the core food groups so your energy is sustained throughout the day as well. So you're not on a high protein diet and missing carbs that you need for energy.... you're getting it ALL and it's lasting you throughout the day until your next balanced meal. Since I'm gluten free, my carbs can be gluten free items but I mainly stick to starchy veggies, rice, and corn since it's less processed. I make healthy substitutions.
An example of this for dinner would be: A cut of grilled salmon over 1/2 cup of brown rice with grilled broccoli, yellow peppers, and onions. Then sprinkle some colby cheese on top and maybe cut up a few olives for additional fat. Have a glass of water... and voila, you have a balanced dinner meal.
What do I eat for breakfast? Well, I'll have Greek yogurt (about 1/2 cup or a bit more) with blueberries, strawberries, and sometimes some peaches. Then I take gf granola or even gf chex cereal and sprinkle some all over. Yogurt is one of those weird things that are a carb AND a protein so it's great for energy. Then the fruits give me the vitamins and minerals I need.
I've eaten this way for the past year and a half and have never paleatu'd or felt the need to overindulge. I do have a lot of self-control though. I also don't work out every week like I used to (I was a barefoot runner). I run around NYC mostly and thats my exercise but it's very true when they say 80% is what you eat and 20% is working out.