Low carb diets: ketogenic versus non-ketogenic

There is quite convincing evidence that low carbohydrate diets result in faster weight loss and better diabetic control (improved insulin sensitivity) in the short term than higher carbohydrate/low fat diets. But how "low" should one go when it comes to carbohydrate? If you go very low do you lose more weight than if you have a moderate but restricted intake? Do you need to go in to "ketosis" to lose weight faster?

A study by Johnston et al (American Journal of Clinical Nutrition, Vol. 83, No. 5, 1055-1061) investigated whether a
low carbohydrate (<50g) diet (which resulted in ketosis) compared with a moderate carbohydrate (>100g) (did not result in ketosis) was more effective at inducing weight loss. After 6 weeks on the diets, both groups lost similar amounts of weight (6kg) and both groups had improvements in insulin action/sensitivity. However the ketogenic diet resulted in adverse metabolic effects(increased inflammatory risk). The authors conclude that the use of ketogenic diets for weight loss is not warranted.