The FastDay Forum

Didn't get around to post the screen shot of the book yesterday, but here it is:

[carorees]

Thanks for posting that...I've been able to find the abstract of the original study here: http://www.ncbi.nlm.nih.gov/m/pubmed/8238506

Following the related articles link from the above PubMed page revealed another article comparing the effect of fasting on men vs women: http://www.ncbi.nlm.nih.gov/m/pubmed/11701450 and the full paper here: http://ajpendo.physiology.org/content/281/6/E1333
This study found that the increase in fat burning with longer fasting (from 14 to 22 hours) was less in women than men.

So it seems that the optimal length of fast differs between men and women.

I am going to try splitting the meals (but still staying within the guidelines and TDEE) a bit more so I eat more regularly and just as a self experiment see what it does - because what it seemed to be saying in that paper reflects what I have been finding. I'll be curious to see if it alters (ie slows down) weight loss - from the usual pound or so a week).

Hmm.., , if you eat more, and more frequently during fasts, especially carbs, wouldn't it be very surprising if your weight loss didn't slow down?

Perfectly fine if you feel it's more sustainable of course, but what else do you want to achieve with such an experiment?

If it's getting the blood glucose under control, it seems to me like the problems with blood glucose and fasting has something to do with the potential fact that it perhaps is difficult for the body to handle a very sudden switch to intense glucose burning after having adapted to fat burning for more than 18 hours. I wouldn't be surprised if it's better to ease into it, let the body adapt.

Thanks for posting that...I've been able to find the abstract of the original study here: http://www.ncbi.nlm.nih.gov/m/pubmed/8238506

Following the related articles link from the above PubMed page revealed another article comparing the effect of fasting on men vs women: http://www.ncbi.nlm.nih.gov/m/pubmed/11701450 and the full paper here: http://ajpendo.physiology.org/content/281/6/E1333
This study found that the increase in fat burning with longer fasting (from 14 to 22 hours) was less in women than men.

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So it seems that the optimal length of fast differs between men and women.

I don't know what to make of this. They compared fat men with lean women, none of them "fat adapted" (if the term actually has any scientific value).

Would this study suggest obese men wanting to lose body fat benefit more from long fasts than women in the same situation? Would it mean women can just as well fast 24 hours instead of 36 or 40, and men should benefit more from hanging in there?

[carorees]

The abstract states that the men and women were matched for adiposity...where are you seeing a comparison between fat men and lean women? What am I missing?

Also they were looking at the difference between 14 hours fasting and 22 hours, not longer. As it is the rate of lipolysis that was being measured, you still get more fat burned the longer you fast but men need to fast longer to reach the same rate as women. It probably reflects the larger glycogen stores in men.

I completely concur that there seems to be a kind of metabolic inertia in which the body resists changing from one fuel to another and so you are right that it's best not to break one's fast with a high carb meal as it's likely to cause high blood sugar...which is what has been found experimentally. But as you say, none of these experiments have involved fat adapted participants!

Let's see, perhaps I'm misinterpreting, but in http://ajpendo.physiology.org/content/281/6/E1333

To match men and women on percent body fat, we recruited female subjects who were lean [body mass index (BMI) = 21 kg/m2 and 24% body wt as fat] and male subjects who were slightly overweight (BMI = 26 kg/m2 and 23% body wt as fat),

If you want to compare, well.., men and women of equal physical status regarding how "fat" or "healthy regarding weight" they are it seems odd to to pick such lean women and these slightly overweight men, they must have very different life styles. Such lean women should reasonably be more efficient in their fat burning than their chubby counterparts. Fitness fanatics vs couch potatoes.

A healthy woman from what I understand is supposed to have a lot more body fat than a healthy man.

But, one indication from the study would be that men have to fast longer to get some serious fat burning started? If it's because of the larger muscle mass and glycogen stores, it seems to me like exercise during fasts would be a very good thing. I really should pull myself together and get to the gym.

Let's see, perhaps I'm misinterpreting, but in http://ajpendo.physiology.org/content/281/6/E1333

To match men and women on percent body fat, we recruited female subjects who were lean [body mass index (BMI) = 21 kg/m2 and 24% body wt as fat] and male subjects who were slightly overweight (BMI = 26 kg/m2 and 23% body wt as fat),

Their body weight as fat % is pretty similar. Is this why they've chosen these two types of participants?

[carorees]

Ah, yes, I see what you mean...Karen is right that they decided to match the men and women by body fat %. I suppose in an attempt to match the lean:fat ratio. Whether that's the right thing to do is hard to know. No wonder.so many studies are done in rats...humans are too complicated!!

Does this help shed any light?

Whole-body and adipose tissue glucose metabolism in response to short-term fasting in lean and obese women

http://ajcn.nutrition.org/content/73/3/517.full.pdf

[carorees]

Not sure if it sheds light FatDog, but it is an interesting paper nonetheless. The women in the study comparing men and women were not obese so they should have had a good response, the men were not really overweight at a BMI of 26 so I think the difference between men and women of the same adiposity is a real difference and not due to insulin resistance caused by obesity.

However, I guess you could conclude from all the above papers that men who are slightly overweight or heavier and women who are obese or more need to fast for longer than normal weight women in order to get the fat burning really going. What do others think?

The paper you highlight, FatDog, also shows once again how obesity (in particular abdominal obesity) causes problems due to the high insulin levels so that not only is fat accumulation easy but also losing the fat is hard unless one fasts and/or lowers carbohydrate intake.

I find this all really interesting, especially since I've been a bit sceptical of the possible correlation between length of fast and amount of weight loss.

The papers talk about fat burning though as opposed to weight loss. I was a bit confused by the Mark Mattson paper, that showed one meal per day significantly reduced fat mass compared to three meals per day of the same calorific value - because it also said that all the subjects maintained their weight within 2kg over the 6 month period. So does that mean that the subjects increased muscle mass - is this possible?

I know we should be focusing on fat loss rather than obsessing over weight loss but I'd still like to understand better what is going on.

Possibly I've misinterpreted something and I admit that I haven't read all the papers in great detail but this was just one point that jumped out to me.

I completely concur that there seems to be a kind of metabolic inertia in which the body resists changing from one fuel to another and so you are right that it's best not to break one's fast with a high carb meal as it's likely to cause high blood sugar...which is what has been found experimentally.

I'm wondering now if one might be able to extend the effective duration of a fast by timing when you eat your first carbs of the day.

For example, if someone can easily manage a 14 or 16 hour fast (skip breakfast, maybe a late-ish lunch) and then break the fast with zero-carb (or near zero-carb) foods, keeping their appetites in check for the next 4-6 hours by eating as much zero-carb foods as they might want, and their first carbs of the day are eaten at hour 18-22 leaving a 2-6 hour window where you lift the carb restriction, could you see the same fat-burning benefits as an 18-22 hour fast?

It would be sort of like gaming this "metabolic inertia" you speak of, fasting for a portion of the day, low-carb for a portion of the day, then a narrow window of "eat whatever you want" where of course you wouldn't go crazy but you would also stop avoiding certain foods.

Decided I would bump this up as it is interesting for those of us whose weight loss has slowed, thought it might inform

Food for thought ... wonder if your idea would work Bruce?

Yes. I'm trying what Bruce is pondering. Blended Coffee, butter and coconut oil the following morning. Can extend until lunch very easily.