I saw a PBS program by Dr Michael Mosely that documented this diet. It’s also called Alternate Day Fasting (ADF) and is very simple. One day you eat whatever you want. The next day, you fast. And Dr Mosley tried it both ways: eating and fasting every other day, and eating for five days and fasting for two. After a brief period, Dr Mosely thought the ADF a little too much like hard work and found that it played havoc with his social life, so he went to the 5:2 diet; and he lost weight on it; but beyond that, by implementing the diet, he made changes in his body chemistry that improved his general health and increased his predicted longevity, changes which included lower LDL cholesterol (bad cholesterol) levels, lower glucose levels, blood pressure decreases, and ‘metabolic reprogramming’.
With the 5:2 diet, you get to eat something every day. For 5 days of the week, any 5 days you choose, you can eat whatever you want up to a 2,000 calorie intake maximum for women and a 2,600 maximum for men; for two days of the week, you restrict yourself to 500 calories for women, 600 calories for men. On the 600-calorie days, you are still free to eat whatever you want but eating your 600 calories in one bite first thing in the morning might make for a long day. For most people, it is more workable to munch on low-calorie foods throughout the day just to make the diet less of a grind. It might be better to do a split: a ‘fasting-day’ breakfast of 300 calories that might consist of two scrambled eggs with ham, water, green tea or black coffee; and a 300-calorie lunch or dinner of grilled fish or meat with vegetables. Dr Mosely went for the split.
One of the links between fasting, weight loss, and longevity is a hormone called Insulin-like Growth Factor 1, or IGF-1 for short. This hormone, generally speaking, keeps our body cells revved. Adequate levels of IGF-1 are necessary for growth when we are growing, but later in life the same levels that made us grow actually accelerate ageing and promote some of the problems that accompany aging. Fasting lowers levels of IGF-1 and activates a number of repair genes: this is because, when we run out of food, our bodies switch from ‘growth mode’ to ‘repair mode’.
In a Nutshell:
• With the 5:2 diet, you eat whatever you like five days a week — the ‘feeding days’. On the two ‘fasting days’ you limit to 500 calories if you are a woman, 600 calories if you are a man.
• It doesn’t matter which days are ‘feeding’ and which 'fasting', as long as the ‘fasting days’ are non-consecutive and you maintain the 5:2 ratio.
• On ‘fasting days’, you can consume your calories in one meal or spread them through the day — there has been no research made into whether filling up at one sitting or snacking throughout the day is more effective.
• On 'feeding days' you can eat whatever you like. Most dieters, rather than feeling a need to gorge, find that they are satisfied to consume around 2,000 calories for women and 2,600 for men, and that they did not crave high-fat foods.
• A caveat: according to current medical opinion, the benefits of fasting are ‘unproven’ by accepted research protocol. Fasting is not recommended for pregnant women or diabetics on medication. Anyone considering a diet that involves fasting is advised to consult their GP first, and carry out their fast under medical supervision.
I’ve included this link for anyone interested in more information: "The-52 diet can it help you lose weight and live longer"