Let's start with the base, the metabolic pathway of ketogenesis is an adaptation system of our human body, created by very low carbohydrate consumption, high fat consumption and moderate protein consumption. The reasons for this procedure were initially, in the early 1900s, to control severe epilepsy in children whose medications were ineffective. Today, this diet is popularly used to achieve weight loss. 

Let's take a closer look at the metabolism involved. By significantly reducing our sugar consumption, being the preferred and most used fuel by our body, especially by the brain, our body's glucose (sugar) reserves are depleted. The body must, therefore, find another way to generate energy. The liver will then use the fat by separating these molecules to create fatty acids and produce ketones that will be used as energy sources.

Without going into further details and remaining in the subject of wood loss here are the current data:

Being recently popular for its weight loss effects, we need more time to do long-term studies. Few of them are carried out for more than 12 months. The studies are inconclusive, and the results of these studies are highly variable. The negative energy balance represents the common point of the studies. This shows that, whether or not carbohydrates, consuming fewer calories than you spend generates weight loss.

This is a rather general summary, without opinion, of the current facts. Since nutrition is a very new science, we must be open-minded about possible changes. What was believed to be an absolute truth can be claimed by the results of conclusive studies even years later. One thing is certain, we essentially need time and more long-term studies on this subject to guide our recommendations.

Sources :

https://opdq.org/wp-content/uploads/2018/06/Position-Diabete-Diete-Cetogene.pdf

Sumithran P, Proietto J. Ketogenic diets for weight loss: A review of their principles, safety and efficacy. Obesity research & clinical practice. 2008;2(1):I-ii.