In his recent book, "Always Hungry" Dr. Ludwig reports on a study he conducted with 21 young adults with high BMIs and brought their weight down by 10-15% for a start.
"Energy expenditure (metabolism/calorie burning) plummeted on the low fat diet. On the low carb (high fat) diet, energy expenditure - metabolic rate - didn't drop at all. Despite the weight loss, a low carb diet had completely abolished the negative effects of weight loss. Meta-training diet was in the middle."
Read more: http://www.joe.ie/fitness-health/study-shows-which-diet-keeps-your-metabolism-burning-calories-the-fastest-2/544766
I believe that a low carb diet, especially one where people just eat real food, is most effective because it's most natural for our body. There are no drastic fluctuations in blood sugar, and with sufficient balance of protein, fat and nutrients from fruits and veggies people don't experience spikes typical to sugar burners (from carbs).