All diets designed to lose weight have one thing in common, all aimed at reducing calories. Some diets are stricter than others but that's how diets work.
We all know that to lose weight you need a calorie deficit. But just creating a deficit with a strict diet is not a good choice. And the faster you want to lose weight, the tighter your diet.
So at the start of your diet program, you can lose weight and you are truly happy. But as time goes by progress gets slower and finally stops.
So obviously the next step is to reduce your calories even more until you basically eat nothing and you reach hunger mode. Keto diet-approved foods is a very nutritious diet.
The human body for thousands of years has developed a mechanism for weight control. When food is available, the body stores it as fat for times, when food is not available.
And when times are hard and food is not available then your body tries to "protect" you by holding on to fat. Your body doesn't care if you want to lose weight to look better, very low calories means starving. This is called hunger mode.
That is why people can survive for days, weeks and even months without food. People can survive only with water for a very long time because the body's alarm bells ring to keep you alive. So the body slows down metabolism and makes fat loss almost impossible because fat is energy.
The less food you eat, the less energy your body has to deal with. It is impossible to spend more energy than is available. And this is the reason why diets to lose weight quickly don't work. The key is to burn fat and feed muscles.