Caloric restriction doesn't work for several reasons.
First, it isn't sustainable. The individual is essentially starving themselves and the constant hunger, constant restriction of calories is only a temporary fix. the individual will return to this as soon as the diet is over.
Second, restricting calories without changing the composition of these calories will actually serve to leave the individual with less energy without as much weight loss. Allow me to explain.
If insulin is spiked because of the types of calories consumed, then insulin is determining where those sugars and fatty acids are going. There is a marker called LPL (Lipoprotein Lipase) that is attached to fat cells or muscle cells and it is this marker that determines where fatty acids and sugars (in the form of glycerol) go once they are in the bloodstream.
Think of this gauge as a metric for judging insulin levels. I just picked a random image.
View attachment 241465
When insulin levels are high, fat and sugars are diverted to the fat cells for storage. Once inside, the fat cells use two fat molecules and one glycerin to create a Triglyceride. These are stored and cannot be removed from the fat cells without first being broken down.
When insulin levels are low, these fats and sugars go to muscle cells (via the LPL marker) for energy. You burn them.
If someone simply cuts calories but keeps the same amount of carbs and sugars, all that means is the muscle cells are getting less energy from the already small partition of fats and sugars they got before. The patient gets more sedentary. Weight loss is extremely challenging.
Instead, understand how to keep the insulin level low by changing the calories you put in your body and then the fats and (hopefully minimal) sugars are used for energy in muscle cells. Remove sugars and refined flours and bad carbs from the diet completely and for long enough and the body has to tap into fat cells and break down triglycerides for use. This makes the individual leaner, lowers triglycerides and is overly beneficial to the patient.
I've skipped a lot of the technical stuff to try to keep it simple.
You do not lose weight without some type of calorie restriction.