Men's calorie allowance increased to 800 on fasting days?

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Men's calorie allowance increased to 800 on fasting days?

This topic contains 6 replies, has 4 voices, and was last updated by  TrajanGregory 6 years, 4 months ago.

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  • In March this year, there was a newspaper article in which Dr M. explained that difference between 800 and 600 cals. on men’s fasting days wasn’t important. But can’t find this discussed on this website. Of course, depends on the individual. Anyone got confirmation of this idea?

    See: ​

    Now the diet’s creator, Dr Michael Mosley, has loosened the rules. But he insists his new version of the “Fast Diet” – which increases the limit to 800 calories on fasting days, is just as effective.

    “You don’t need to stick to 600 calories. Cutting down to 800 calories a day seems to be almost as effective and for some people much more ‘doable’.”

    “It’s low calorie, without being superlow-calorie. And if you want to have lunch, you can slip those extra 200 calories in there.”

    Yes, I remember it happening and am sure there was a bit of discussion about it at the time. In the scheme of things it doesn’t matter, but it will of course slow you down a bit, as the calorie deficit becomes smaller.

    In a year of normal 5:2 it will be 52 * 2 * 200 kcal = 20,800 kcal. One kg of body fat is equivalent to 7,700 kcal, so 20,800 equates to 2.7kg of retained fat.

    That’s a useful formula for fat v cals – thanks. It ties in exactly with my first 5 weeks of 5:2, though I seem to have reached a definite plateau.

    It’s not appealing visualising 2.7kg of fat; maybe I’ll stick to 600 cals, and try 4:3 to get off the plateau, plus HIT exercise.

    For water, 1 kg = 1 liter. For fat, 0.9 kg = 1 liter. So 2.7kg = 3liters of fat.

    Don’t worry about the plateau – we all hit them. Your body is using the empty fat cells to store water. At some point the body will give up on that idea and you will experience the whoosh! This s when you suddenly get a sharp weight loss in a very short time period. VERY enjoyable!

    use these numbers very loosely but adipose tissue (fat cells) contain about 10% water. The liver and muscles contain glycogen (stored form of glucose) + water. About 25% glycogen and 75% water. So roughly 1 gram of glycogen and 3 grams of water. That’s why lots of people experience a rapid loss of weight when they initially start 5:2. They are in fact depleting their stored glycogen which means they are getting rid of lots of water at the same time. 1g glycogen + 3g water. Once this is depleted the loss slows down as you are now accessing stored fat and the water loss associated with that loss only accounts for 10% of the loss. 9g fat + 1g water.

    glycogen has 4cal/g, fat 9cal/g. So once you have depleted your glycogen stores and are into burning fat, you have to burn more than twice the number calories to get rid of 1 gram of weight. hence weight loss slows down from that initial rush.

    Hope that helps rather then confuses where the loss is coming from and why the initial loss slows down.

    That’s seriously useful…thanks. That steered me to this article: though probably a bit dated by now. The BMJ paper followed:

    I was also interested in initially changes of metabolism(?) when starting on 5:2. Changing one’s ‘normal’ diet to 5:2 certainly changed mine. Elimination of solids is going to decrease, but I was concerned about extremely regular peeing, almost to the extent of seeing my GP, over the first 2-3 weeks. This probably isn’t the place to ask, but is that an expected consequence of starting on the 5:2?

    If one pound equals approximately 3500 calories, then we can determine the weight difference between a 600 cal vs 800 cal day:

    200 ÷ 3500 = 0.057142857 (200 calories as a proportion of 3500 calories)

    0.057142857 x 16 oz = 0.914285714 oz (convert to ounces)

    In other words, if you choose to eat 800 calories instead of 600 calories, you would miss out on less than one ounce of weight loss, in a perfect world …

    When I did the math, I felt comfortable occasionally eating over 600 calories…. piece of mind is worth less than one ounce…

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