I’m not sure how this fits in with the scientific theory and was wondering if anybody can explain how I lost 2 3/4 lb overnight. I weighed myself 3 times before going to bed and all readings were the same and this morning I weighed myself 3 times and all readings were the same. The scales were in the same position. I had a wee in the night which I weighed at 1/4 lb.

This is the third week of dieting and I have lost 7lb and 4lb. I only weighed myself on the Monday of each week.

I’m 54 years old male and weighed 15 stone 11 lb before starting. I’m 5′ 10″ and I would describe myself as lightly active. I sit in front of a computer all day and play 2 rounds of golf a week.

I fast on Tuesdays & Thursdays so yesterday was the second fast day of the week and I weighed 14 stone 7 1/4 lb this morning.

If my understanding of the science is correct, water is lost in the first couple of weeks as glycogen is used up because of the calorie deficit. You then lose fat or muscle.

1 lb of fat is supposed to be about 3500 calories. I think muscle is about 1700.

According to the web sites calculator my BMR is 1800 calories. So sleeping for 8 hours should burn 600 calories.

Can anybody explain what is going on?

Thanks. That’s interesting about the weight in the evening & morning being different.

In regard to the glycogen store. Wouldn’t it remain depleted as long as you don’t have a period where calorie intake exceeds the energy used? So in simple terms, once the glycogen store is used up, then as long as you don’t eat more calories in a day than the TDEE, you will be burning fat or muscle every day on the diet.

Yes, any surplus energy from carbohydrates converts to glycogen but if you start the day with no glycogen store and your TDEE is greater than your total energy intake then you start the next day with no glycogen store as that is supposed to be the first energy source that gets used up.

So for a person who has been putting on weight as fat they will most likely start the diet with a full glycogen store then the first fast day will clear it out and from then on every day will be started with an empty glycogen store provided the TDEE is not exceeded during any 24 hour period.

So this morning I would have had no glycogen after fasting for 1 day & 2 nights. My TDEE is approximately 2400 calories and I have consumed about 2000 (not all carbohydrate though) so at some point before tomorrow morning any glycogen that has been added will have been burnt off and at least 400 calories will have to come from fat/muscle.

Then on the next fast day you will be starting the day with no glycogen stored. Only 600 calories will be ingested with not all that being carbohydrate so fat and muscle will be burnt off to a calorific value of at least 1800 calories.

Does that sound right?

Thanks.

I’ve done a lot of diets (different types) in my time and I must admit that what I’ve read and what I’ve experienced differs to what you are saying. I’m actually quite good at losing weight, it’s just I lapse into bad habits when I’ve reached my target weight.

Whenever I start a diet I always see 7lb or 8lb loss in the first week. I’ve read and been told that most of this is water when the glycogen gets burned up and releases the water that it binds to. Then weight loss tends to average about 1lb or 2lb a week until I stop dieting when there’s a big increase (say 5lb) which I’ve been told is the glycogen reserves (+water) filling back up.

I don’t really see the 5:2 diet being any different to a low calorie diet, except the calories are reduced by about 1700 on 2 days rather than by a smaller amount each day. The 3400 reduction equates to about 1lb of fat. I don’t think there’s anything magic about fasting or the 5:2 diet, it’s just about net calories over the long term. However some people probably find it easier to be disciplined for 2 days rather than 7. There may be some other benefits to health from fasting and this may or may not apply to the 5:2 diet.

Can you point me to any studies which back up what you are saying about glycogen levels and fat v muscle loss? I have seen studies that claim to show that low deficit diets lose more fat as a percentage of weight lost than high deficit diets. I’m not sure whether there any fat v muscle studies relating to the 5:2 diet though.

Thanks. I have been reading up on human physiology. That is why I am concerned. I’ve also done searches on the subject of IF and can only find one study by Gabriel J. Wilson which was conducted on rats. Results would indicate you could be losing muscle.

Your link shows I am right to be concerned. You’ve got one expert saying not to fast for more than 24 hours and Michael Mosley claiming he doesn’t. Keeping up protein intake is recommended. The study by Dr Krista Varady claims no muscle loss in an 8 week period but is a test on 16 humans and limits fasting to 24 hours. The summary makes no reference to protein consumption.

In regard to glycogen levels. Everything I read says that glycogen is used first when blood levels of glucose are insufficient to meet the bodies fuel requirements. This would mean that somebody eating less than their TDEE once these levels are depleted after a fast day will not start the day with a glycogen store (I note your point about glycogen stored in the muscles and therefore refer to liver stored glycogen).

Re. glycogen store, let me explain with a simplified example. Let us assume that TDEE for a person is 2400 calories and that use is linear @ 100 calories an hour. Let us assume they eat 500 calories for breakfast @ 0800, 500 calories for lunch @ 1300 and 1000 calories for dinner at 1900.

For the 24 hour period starting at 0600 we see:

0600 glycogen store = 0 burning fat
0700 glycogen store = 0 burning fat
0800 breakfast, glycogen store = 500, burning glycogen
0900 glycogen store = 400, burning glycogen
1000 glycogen store = 300, burning glycogen
1100 glycogen store = 200, burning glycogen
1200 glycogen store = 100, burning glycogen
1300 lunch, glycogen store = 500, burning glycogen
1400 glycogen store = 400, burning glycogen
1500 glycogen store = 300, burning glycogen
1600 glycogen store = 200, burning glycogen
1700 glycogen store = 100, burning glycogen
1800 glycogen store = 0, burning fat
1900 dinner, glycogen store = 1000, burning glycogen
2000, glycogen store = 900, burning glycogen
…
0500, glycogen store = 0, burning fat

So in the 24 hour period we burn 400 calories of fat and the glycogen store is empty when we get up. No marathon, just 2400 calories of energy used in a 24 hour period.