The FastDay Forum

I guess if I am losing weight then my TDEE is correct and if I am not then I am eating too much......simples.

Maybe that is the only way. The study that Caro cites which finds that individuals with BMI 35 may vary from the average by plus or minus about 600kcals a day - that is a huge variation! It dwarfs any differences from using one formula or another.

I only use the sedentary value for TDEE figuring that any exertions above that point represents calories burned to my advantage.

Since actual TDEE is difficult to ascertain, and would vary all over anyway depending on exertion, a relativistic (but still unknown) personal TDEE can be had by watching trend-based weight. As you've shown with numerous graphs in the past a gain says the chosen TDEE estimate (consumption) was too high where as losing weight says the TDEE was too low. Far more likely though: conformance to that recommended 25% TDEE fast day limit just isn't happening.

So given that 1.375 * BMR value, we're all naturally inclined to optimistically predict that we will go out and do the 7 additional miles (11k) necessary to burn those calories. But past experience says that we are very unlikely to actually do it.

Optimistic TDEE's add fat; pessimistic ones don't.

I found a nice review article summarizing the metabolic changes that take place upon weight loss: http://www.jissn.com/content/pdf/1550-2783-11-7.pdf

I'm in maintenance tho' I've had some BMR/TDEE estimations based on previous scans/breath analysis.

The Scooby's Workshop calculator is an amalgam of several formulae and is very popular as it seems to deliver fairly good estimates of TDEE, particularly if people follow the suggested tailoring (tho' few do).

I projected from my last Dxa scan body composition results to modify the calculations for my present weight (assuming no loss of lean body mass: Dxa reports also use Miffin-St Jeor).

BMR is now <900kcals because of my low levels of muscle mass.

Projected TDEE is approx. 1000kcals on a sedentary day and 1275kcals on an active day (such as one when I kayak).

This is why I stick to 4:3 in maintenance: I find it easier to cope with 3 FD and have what seems like a reasonable amount of food on non-fast days. Assuming that it's true that we need to reduce our intake by 10% per decade as we grow older, by the time I'm in my 70s/80s it will feel more like I'm eating once a week.

[carorees]

Thanks for this @MaryAnn

I particularly like figure 1 on page 2 of the pdf. It very clearly shows why exercise has so little effect on weight loss...only 5% of one's TDEE is down to exercise, while 70% is due to BMR. The rest being non-exercise activity (NEAT) and the energy cost of digesting one's food (TEF).

TDEE components.jpg

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Unfortunately, the data about exercise derived from young athletes does not prove true for post-menopausal women. I have seen data suggesting that exercise does nothing significant to promote maintenance in us older ladies. And there is always the problem that exercise raises stress hormones that increase hunger. There are other very good reasons to exercise, most notably heart health and preserving mobility, but weight loss and maintenance are not among them.

Nor, if I'm correct (I don't have the reference handy) is there any proof that slow weight loss reduces the hormonal changes caused by significant weight loss.

But I have to say that 7 months into this diet, I am starting to think that 5:2 with over TDEE refeeds does prevent the drop in leptin that causes such a strong psychological drive to eat. Every time in the past I have gotten down to my current weight, I have found myself going through strange mental changes where it suddenly seems really important to gain back some weight. There's always some rational excuse, but there's an irrationality driving it along with increased physiological hunger.

When I tried increasing my fasts these past two weeks to prepare for my visit to my son (and his restaurant) I immediately noticed a huge rise in hunger and "what the heck" thoughts. So I am starting to think that for me, overeating on the feed days is an essential part of being able to lose and, eventually maintain. I decided it was probably better, long term to miss a fast than to depress my leptin levels through too much dieting. Attempting a window approach did not help. I was ravenously hungry much of the day. So back to good old 5:2 (when I get back next week.)

This discovery implies that I will have to keep fasting forever to maintain my current, not-quite-at-goal weight, of course, as there is no way I can eat over the TDEE at goal without regaining.

I'm also very curious to see if my body figures out the trick that I have been playing on it. If it doesn't, then we will have to rename this the "Fast/Refeed diet!"

[carorees]

My experiment of n=1 is that whenever I have periods of overeating, I lose weight faster afterwards. Even now I am in maintenance. This has been true throughout my journey both doing 5:2 and 16:8. Periods of over-eating do seem to be very useful as long as you can avoid turning the refeed into a new WOE!!

@carorees, Yes. You had suggested loosening up and eating a bit more to me a while back when I had seen my weight loss slow way down and had reacted by restricting calories more on my non-fast days. I followed your advice, and the outcome was that things got moving again. Gotta love that!

What is interesting to me is that some years ago I had seen some data that suggested that IF did not keep leptin levels from dropping. But it turns out that data came from a study using alternate day fasting. I suspect the 2 and 3 day refeeds with 5:2 may be long enough to keep those leptin levels up. I have been surprised at how hunger-freee I have been the past month. But as soon as I went to 3 fasts in one week, I found myself contending with severe hunger.

There is still so much to learn about this diet! Let's hope someone with access to a fancy lab gets interested in it enough to measure those leptin levels for us.