LCHF, short for Low Carb High Fat, is a ketogenic diet. I am not a nutrionist, but put simply, carbs are turned to glucose by the body, which brings ups and downs in the blood glucose level. Without carbs, blood glucose will remain constant, usually on a lower level than on a carb-diet. Glucose is also the easiest source of energy for the body to burn, so these will be consumed first. If carbs are reduced in the diet, like in LCHF or other low-carb diets, the body is forced to burn fat instead. The liver uses the fat to produce ketone bodies, which replace glucose as the main energy source.
Fat is essential in the LCHF-diet because it becomes the main energy source. In addition, it is argued that fat reduces hunger and makes you eat less. Some people even claim that eating much fat increases the metabolism, enabling you to eat more calories than on a low-calorie diet. I do not know if this is true and it has not been empirically proven. I lose weight with LCHF, but I usually eat less than 1500 kcal a day. In fact, I find it very difficult to eat more than that on this diet. Off course, the things that we usually overeat, like sweets and snacks all contain carbs and are not allowed. But in addition to that, I do not want to overeat! My cravings for sweets are gone because I eat real food that makes me full. On any other diet, I ate about as many calories as now, but I was always hungry after a salad lunch or low-fat dinner. Now I lose weight without being hungry while also enjoying good food. Win-win :)
Obviously, this diet is quite controversial as it contradicts with most current dietary advice. Especially the high levels of fat scare people off. Sometimes people tell me how unhealthy it is to eat as much fat as I do and that my arteries will be blocked by all the fat. In fact, there are no long-term studies proving this. LCHF-advocates talk about others being fat-scared, which is understandable after years of diet recommendations telling us to avoid fat. I was (and still am) very concerned about this, but I feel great and my body is healthy. Yet, I would not recommend anyone to eat this diet without regular health checks, especially not until there is more facts about the long-term effects of eating LCHF.