Which diet is best for losing weight? That is probably one of the most debated topics. The findings of the largest and most extensive study ever done on popular diets was just published in the New England Journal of Medicine. What did they find? The best diet for weight loss is any diet that is low in calories and saturated fats and high in whole grains, fruits and vegetables. This study says it doesn't matter which diet you choose. The bottom line is how many calories you consume. They found that cutting calories was the most important factor when losing weight.