No or significantly reduced carb diets such as Atkins or South Beach work around the idea that dieters start the meal plan by eating no or low amounts of carbohydrates to lose weight quickly. First of all, this is dangerous! Protein, carbohydrates and fat are macronutrients that are very important to full body functioning and wellness. Carbohydrates especially should consist of between 40-60% of overall food intake.
No/low carb diets work because they quickly release water retention. Sure, this is great for about ten minutes, until you eat normally, and gain it all back!
Low fat diets are just as bad! Fat in the diet is NOT bad! It should consist of 15-20% of overall food intake. It regulates hormones and helps absorb nutrients. Without healthy fats in your diet your hair will be stringy, skin is unhealthy and your nails become brittle.
So what's the best diet? A balanced one! Personally, I aim to reduce carbs. It's not a bad thing to eat a meal a day that only consists of protein and vegetables. Vegetables are carbs too but there is not nearly as many grams per serving as bread and grains. Healthy fats such as seeds, nuts and flax/olive oil is good for you.
Dieting is simple. Don't diet! Just eat healthy!