The FastDay Forum

[carorees]

For those searching for information on how long to go without any calories on 5:2 fast days (or if doing 16:8 or similar), I found this study: http://www.ncbi.nlm.nih.gov/pubmed/2202174 which, although not really aimed at investigating fasting for health, had some interesting observations.

The looked at people with (7 subjects) and without diabetes (9 subjects). In those without diabetes, blood glucose concentration was 7% lower after 18 hours fasting than 12 hours. At the same time, plasma insulin concentrations fell and fatty acid concentrations rose (compared with a 12-hour fast). More importantly, it was clear that the subjects were using more fat and less glucose as their energy source with an increase in fatty acid oxidation (fat burning) of 55-76% and a drop in glucose oxidation of 37% in the non-diabetics.

This study, therefore, shows that extending the fasting time from 12-hours to 18 hours does dramatically increase the amount of fat being used for fuel...which is what we are all trying to do. Unfortunately, it is only a tiny study and the researchers did not investigate how metabolism changed hour-by-hour up to their 18-hour mark or beyond, but it does indicate that the longer you can avoid taking on board any calories, the more your body will be using fat as a fuel.

This also ties in with our findings from the questionnaire that those who lost weight most rapidly tended to be those who fasted for longer on fast days.

For those of us with thyroid issues who eat a little protein, an egg or a few nuts say, after 12 hours, so as not to exacerbate thyroid issues, is this advantage completely lost?

[carorees]

My guess would be that as long as carbs are low your body will stay in fat-burning mode.

[carieoates]

That's the part I find difficult, cutting the carbs. Did unbelievably well on dukan and that other horrible low carb one. But am now in a different place with regards to food, being that I like to eat wholesome, local sourced and homemade food. But with both of those it involved too many additives, artificial flavours and generall to many nasties for my liking. I'd never manage 18hrs unless ill or ordered nil by mouth by a surgeon. Lol. I have to eat at about 5.30 as my daughter drives me mad otherwise, and the hubs eats when he gets home much later. I've just got to cut out nibbles etc on the night before then don't I.

The one thing that concerns me about this WOE whereas before I was massively enthusiastic (and it is slightly connected to this post) is that I keep reading about IF not having great implications for glucose tolerance in women (and I know there aren't many studies) but I have read that in some of the studies done glucose tolerance in women DECREASED (contrary to what it is supposed to do re insulin sensitivity etc) and I find that worrying because that is becoming my own experience. I don't have diabetes but a family history of it and one of the reasons I was so attracted to this WOE was the purported (and apparently true for men) decreased glucose levels and diabetes risks. Of course if I or anyone stays obese then that's going to increase one's risk but I do find that slightly concerning so I'm going to try and modify the length of time I fast to see what that does. Would be grateful for any suggestions or points of view! I am eating fairly low carb and GI etc. Also please don't think I am rubbishing this WOE - it's the only one where I've managed to lose weight and appetite - so I only wish there wasn't this (apparent) side effect for me.

Thanks

Liz

[carorees]

I found this paper by (among others) Mark Mattson (he is one of the experts Dr M interviewed for the Horizon programme), comparing the effects of eating one meal per day during a 4-hour eating window (so a 20:4 regimen) with a normal three-meals per day regimen. http://www.ncbi.nlm.nih.gov/pmc/article ... rt=classic

This study in normal weight men and women had the subjects change from eating three meals a day to one meal a day but keeping the calories the same. The researchers found that heart rate, body temperature and blood chemicals, were unaffected by meal frequency; however, when on one meal/day, subjects lost fat mass, and had significant increases in levels of total and LDL and HDL cholesterol. Further, on the 1 meal per day regimen, insulin response to an oral glucose tolerance test worsened. This is in line with other work on fasting which has been used to suggest that fasting may not be healthy in the long term. The authors discuss reasons for their findings, including an artefact arising due to the timing of the meals and the drawing of blood for testing. They also point out that, had the study not insisted that the subjects ate the same amount in their one meal than the three meals so as to ensure the only difference was the number of meals/timing of meals, then they surely would not have eaten so much in their one meal.

What springs to mind for me is that the diet the subjects were eating was the standard 50% of cals from carbs, 35% from fat, 15% from protein, which for a 'standard woman' needing 2000 cal per day means a daily carb intake of 250g. I would be fascinated to know what the results of the same study with a diet on 30% carb, 55% fat and 15% protein would be (i.e., 150g carbs based on 2000 cal per day).

And, what would be the effect of eating 2 meals a day?

And, what would be the effect of, instead of eating 3-meals worth of calories in 1 meal, the subjects ate whatever a comfortable 1-meal per day calories might be in 3 meals?

Not quite sure what to make of these two studies. I suspect that there is a degree of lag on the part of the body activating the appropriate metabolic pathways. By this I mean that when fasting the body takes a while to switch to fat burning (hence the increase in fat burning with a longer overnight fast) but then when food (specifically carbohydrate) is available again the body is slow to release insulin and change to burning glucose.

In practice, I think it suggests that longer fasts are better for burning fat but one needs to be careful about how one breaks the fast...high GI/GL foods would be a bad idea, but if the carb content of the meal is fairly low then the slow insulin response after fasting would be unimportant.

What do you think?

That's a really interesting article. I (and I know this is not just about me!)am not a scientist and so sometimes find the real science stuff baffling, but as an experiment 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). Really helpful though, so thanks Caroline.

[carorees]

That's noble of you @loversghost to risk a slow down of weightloss in the cause of science! Are you going to split your meals up on both fast days and non-fast days or just fast days? (Not sure what you are doing at the moment).

Interesting. I found that 5:2 messed my blood glucose up a lot. It was my main reason for trying 16:8. That did bring them down but not to the level I had achieved doing straight low carb. This last week or so has been manic and stressful due to family problems so I haven't been managing to stick to my usual 16:8 routine. I have been eating my usual low carb/high fat but my eating window has been much larger. I have tried to stay off any between meal snacks though as I don't want to get back into a habit of grazing. I noticed this morning when I downloaded my monthly BG figures from my meter that my BG has dropped quite a lot over this last week since I started eating more frequently. With all the stress I would have expected it to go up but its much nearer to my target than it has been since I started experimenting with fasting.

We have a funeral Friday after which things should start to even up so I shall see how I do then when I go back to proper 16:8.

Oh I'm very noble, me! I have been up to now eating just one meal in the evening on a fast day and then not feeling very hungry the day after so often not eating until lunchtime (which sort of makes it around a 40 hour fast which made me feel oh so virtuous) but I am going to try and split the fast day calories up (hopefully without massively increasing the hunger) and eat a bit more regularly on non fast days (but low carb)and see what that does. Interesting to see what miffy49 says too about eating more regularly and her blood glucose being lower. I have so much conflicting advice online about fast/don't fast blah blah and I think as others have said on here, sometimes you've just got to experiment a bit to see what works for you. Might give 16:8 a go too. Interesting that the article Caroline referred to says the blood glucose pattern is reversible. Phew!

I do think this forum is a great help though and I LOVE the Progress Tracker - it's the highlight of my week (so maybe I should get out more).

[carorees]

I've been thinking that one major problem with all these studies is that they take people who've been eating at least three times a day, on a high carb diet most likely, then they make a dramatic change to their eating habits for just a short period and make the assumption that carrying on with the new style of eating will continue to give the same results.

However, there are studies that show there are hormonal changes (in insulin, ghrelin and leptin) that occur at mealtimes even in the absence of meals, showing that the body "predicts" the arrival of food. Plus, we know that it takes a while to adapt to fasting or low carbing. So, really we need to look for studies done on folk who are already adapted.

There must be a lot more experiments being done now, surely, with the growing popularity of fasting. I am looking forward to lots of new, useful data being published. Wouldn't it be great if the NHS dietary advice would promote a form of IF, even if it's just to point out the benefits of giving the digestive system a daily 12 hours of rest and put decent amounts of funding into research. Their current advice, which imo promotes frequent "sensible" snacking (grazing) not only doesn't work, but actively encourages hunger stimulation and overeating.

In the Eat Stop Eat book, this subject was touched briefly (page 50 if you're looking ). According to a research, the author wrote : "After only 24 hours of fasting, the amount of fat being released from people’s fat stores (lipolysis) and the amount being burnt for fuel (oxidation) had been significantly increased by over 50%."

Following this paragraph, a graph was showed, and in this graph he highlited that the biggest change in fat release occurs between 18 to 24 hours fasting. (Am I allowed to attach screenshot of the pdf here?). It's in line with the research Carorees mentioned.

So many interesting yet inconclusive research out there . Thought I'd throw that one in the mix

[Betsysgr8]

@Deewidiastuti Screenshots and links are all fine to add. It's always good to have more information.

I do more of a 20:4, 3 times a week... because I only eat dinner now on my fast days.

I break two of my fasts with a small meal with my family, usually with carbs, protein and veggies. The third fast I break with a larger meal where I don't count calories.

It feels like I'm losing fat.