I do believe we are designed to fast CLKD! Human beings have evolved over thousands of years as hunter gatherers, and often would go through 'lean times with little or no food for long periods. Then we would 'feast' if we killed an animal, or found plentiful berries etc. I think our fear of hunger (and low blood sugar) is deep rooted, and a belief I used to hold. Now I know differently - I have been on the 5:2 way of life (I hate the word diet) since last September not long after the Horizon programme, and I have lost 1 stone 9 pounds. Yes I feel hungry at times, but it never builds and builds to anything terrible, just a background feeling. I think that the days I ever had a headaches were when I didn't drink enough. Because a lot of the food we eat contains moisture, cutting the calories and food intake is bound to decrease body fluid levels. I drink lots of hot water on fast days, and this helps with keeping headaches at bay, as well as constipation (which can always be a problem for me if Im not careful). It really is a fantastic way of getting unwanted weight off, reclaiming a lean body that is our birthright, and just generally getting oneself back in order after years of feeling quite frankly - shite! I still have chronic pain and fatigue, low moods at times, and menopausal symptoms, but at least I am doing something positive for my body. And - it's only 2 days a week!! Good luck everyone, you can do it if I can.