I wanted to point out to confused newbies that the rules some commenters here are following are not the same as Dr Mosley outlines in his book. As I understand it, the Fast 800 diet means 800 calories per day, eating fresh healthy food – nothing processed, no sugar, no “low fat” products. Meat, vegetables, and pulses. Some fruit. Healthy low-GI carbohydrates are fine, and only calories are measured. Full fat products like milk and cheese, healthy fats from nuts and olive oil, but the diet is not high fat. Processed meat like bacon only a few times a week.
Some commenters here are having great success with staying under 50g of carbohydrate, lots of fat to put you in ketosis, not necessarily counting calories. There is nothing wrong with that if it’s working for you, but it doesn’t seem to be that close to Dr Mosley’s plan. More like Atkins maybe? I just wanted to mention it because a lot of people are reading the book then coming here and getting confused that they are told to eat under a certain level of carbs or over a certain percentage of fat when it doesn’t say that anywhere in the book.