The FastDay Forum

Two guys I know that are at the same age, weight, height and who works out/train just the same - are gonna try out 5-2. They have asked me how much calories they ought to eat on fasting day. If I use the calculators I see online they should of course eat the same amount of calroies since their values are the same.

But one of the guys have a really high natural metabolism, he can never get fat, even if he eats LOTS of food. The other guy is the opposite with a slow metabolism. Even if he eats normally he is close to putting on wight.

So my question is: should they really eat the same amount of calories on a day of fasting? Or should their different metabolism in some way affect this?

How about one eats 600 calories per fast day as recommended by Dr MM, and the other a quarter of his TDEE (e.g TDEE at 2800 calories so fast day would be 700)?
A good opportunity to monitor what happens and report back after a month too :0)

@potlatch,

You raise an important point, and one that far too many nutritionists seem to ignore. All the figures generated by all the calculators come from formulas derived from the averages found in large groups of people who participated in studies. None take into account that natural variation.

In addition, there is some very good quality research that has found that people who have lost significant amounts of weight (50-100 lbs, eg) have slower metabolisms than people of the same weight who didn't get there by dieting. It isn't known whether this is because their weight loss depressed the metabolism or because their innately slower metabolisms caused them to pack on weight in the first place.

But whatever the explanation is, many people who struggle with weight DO have slower metabolisms and their caloric need is lower than that of luckier people.

Whenever you raise this point in many diet venues (usually those frequented by young, healthy, hyperactive males, some ideologue will chime in about the law of thermodynamics and claim this means that there is no such thing as a slow metabolism. But these are the same people who would tell you two cars weighing the same amount should burn the same amount of fuel to go the same distance. They won't because some engines are better engineered than others.

If you are really interested in this question and incline towards obsessive behavior, try logging everything you eat for a few months very carefully, noting portion sizes and track your daily, weekly, and monthly weight loss against your average daily calories. You will soon find out what your personal TDEE is.