The FastDay Forum

Ok, so I have been doing this fast for about 4 weeks now and keep my calories on my two fast days to between 500-600. On feast days I don't count calories and eat whatever I want. However, I have not lost any more weight and my body fat percentage is staying stubbornly the same. I chose this diet precisely because it is only 2 days a week that you have to limit yourself and I don't want to count calories the rest of the time.

What I am wondering is whether the diet only works because there is supposedly a calorific deficit for two days of the week but even then I don't see how anyone can lose a pound a week since a pound is 3500 calories. In my case, my TDEE is approx 1500 calories per day, so even with a calorific deficit of at the very most 2000 per week, there is no way I would lose a pound a week. Also, if you have more calories on your feast days to make up what you lost on your fast days then you won't lose. So presumably you don't lose weight because of a calorific deficit but because fasting does something to your metabolism? Can someone please confirm because I just don't get it.

Weight loss is primarily due to the calorie deficit.

A lack of carbohydrate intake does shift some things in your metabolism, for example you have to start making glucose to maintain your blood sugar level and this means you draw down your glycogen reserves and release the associated water.

Personally I do not believe that you could eat double your TDEE 5 days a week and eat 500 for two days and lose weight overall.

The pound a week thing arises from higher TDEEs than yours :-

Weekly deficit = 3500
Calorie intake for week = 2 * 500 + 5 * TDEE = 7 * TDEE - 3500

From which 2 * TDEE = 4500 and TDEE = 2250

So for women eating 500 on fast days a TDEE of 2250 or higher is required to create the 3500 cals/week deficit, for men eating 600 on fast days a TDEE of 2350 or greater is required.

Or in general, TDEE needs to be (3500 + 2 * fast day cals)/2 which simplifies to 1750 + feed day calories in order to have a 3500 cals a week deficit. With hindsight this is the bleeding obvious conclusion that you need two days with a 1750 restriction to get a 3500 weekly restriction

[Moogie]

It's a common misunderstanding you have there my dear. Eat whatever you like means no foods are of limit, as in you can eat anything you like. It doesn't mean 'eat as much as you like' as in pig out every day! The idea is to eat normally on your feed days, normal being around your total daily energy needs.

You can theoretically eat whatever you want but if whatever you want is a pizza, two cheeseburgers and one tub of ice cream just for lunch then you won't lose weight.
Either eat within your TDEE or eat sensibly (perhaps you want to spy on your thin friends and see what they eat).
If you enter your data in the forum tracker, you will see what your TDEE is and how many calories you can eat on your fast days in order to achieve weight loss.