The FastDay Forum

[carorees]

As Michael and Mimi point out in their book, there are lots of scientific research studies about the effects of intermittent fasting on humans underway at the moment.

I am keeping an eye on what is being published and will attempt to report to the group about any interesting new information that emerges. Please feel free to join in the Science watch if you spot any new info!

[carorees]

So, the first recent science report that attracted my attention investigated whether people who fast before exercising injure their muscles more or less than people who don't.

The study (http://www.ncbi.nlm.nih.gov/pubmed/23266375) evaluated indicators of exercise-induced muscle damage in 29 volunteers (average age 22yrs) who either fasted for 8 hours water-only or ate a controlled diet in the 8 hours before exercising in the laboratory. Muscle pain, resting elbow extension, upper arm girth, isometric strength, myoglobin, total nitric oxide, interleukin 1beta, and tumour necrosis factor alpha were measured before and after arm exercises (elbow flexors) on five separate sessions. Overall, the measurements showed no major differences between the two groups. However, some of the biochemical markers were significantly different in the fasting group than the non-fasted group.

I think this is interesting because I have come across people who say that exercising in the fasted state will be damaging to the muscles. This study seems to support the statements Michael makes in the book about exercise during fasting being OK.

[carorees]

Here's another interesting article published last month. It looks at inflammation in people fasting because of Ramadan and compared the indicators of inflammation with those before and after the Ramadan period (http://www.ncbi.nlm.nih.gov/pubmed/23244540).

Fifty (21 men and 29 women) healthy volunteers who practiced Ramadan fasting (i.e., no food or water during daylight hours during the month of Ramadan) had their levels of various factors that are known to be increased in inflammatory conditions, and also had their weight, body fat and blood pressure measured. The measurements were made 1 week before Ramadan fasting, at the end of the third week of Ramadan, and 1 month after the cessation of Ramadan month. The researchers found that inflammatory factors in the blood, immune cells, diastolic blood pressure, body weight and body fat percentage were all significantly lower during Ramadan compared with before or after Ramadan.

This is interesting because, although Ramadan involves fasting every day, it backs up other studies showing that fasting can reduce inflammation and also shows that stopping fasting means that everything goes back to how it was before!

[carorees]

Here is a paper from 2011 (http://eje-online.org/content/165/1/45.long) that, although I don't understand all of it, found that obese people respond differently from normal weight people to fasting. The study looked at how a 36-hour fast affects production of the hormone, ghrelin, from the stomach and how this in turn influences growth hormone release. Growth hormone is a key player in getting fat mobilised to be used as fuel during fasting. The researchers found that in obese people, ghrelin is low both when fasted and fed and so is the production of growth hormone.

They also found that the obese group tended to have a lower amount of fatty acids in the blood during the fast and had significantly lower ketones. This suggests that fat mobilisation during fasting is poorer in this group.

These results could perhaps be interpreted in two ways that are interesting to our group. One is that the obesity causes the difficulty in mobilising fat stores making it hard for obese people to lose weight. The other is that people with a low growth hormone response might be more likely to become obese in the first place. For us 5:2 fasters it may explain why some people are losing lots of weight and others are struggling and also why some people feel washed out while others are full of energy with fasting.

Another point to speculate about is that as we generally seem to find fasting easier with practice is that perhaps the more we do it the better our growth hormone response becomes to the fast so mobilizing the fat stores easier and therefore giving us more energy and better weight loss! This study only looked at a one off fast...it would be very interesting to know what the findings might be in a group of people used to fasting and also to compare people before and after weight loss.

The whole ghrelin story is very interesting. I am doing a bit more research and will report back shortly (if anyone is interested?).

Although not an actual study the following article (originally posted by BreadandWine on mumsnet) gives a good balanced view and helps to explain some of the science behing the benefits:
http://www.scientificamerican.com/artic ... thier-life

[carorees]

Thanks skippyscuffleton! It's a shame the article did not post links to the research because I am interested in the rats whose heart muscle was affected. I will try to track down the study...

I agree Caroline, I think someone made mention of the Brazilian study on MM's twitter recently and I meant too follow up on it. Was a little disappointed to see it was a rat study though, am v keen to see more human studies.

[carorees]

I've just come across an interesting paper published last year about the famed metabolic slow down with dieting.

The study (http://www.ncbi.nlm.nih.gov/pubmed/22535969) looked at the effect of diet and exercise on fat free mass (i.e. muscle, bone, organs, water etc. but for the purposes of this study, muscle) and on resting metabolic rate (how much energy the body uses to maintain itself when at rest) in severely obese people (BMI approx 50; body fat about 50%). Their metabolic rate was measured before and after 30 weeks of diet and exercise. By 30 weeks they had lost over a third of their body weight (83% was fat and 17% fat free mass). Their resting metabolic rate decreased dramatically and the decrease was out of proportion to the amount of weight lost. Despite the fact that the exercise stopped too much fat free mass being lost it did not prevent dramatic slowing of resting metabolism out of proportion to weight loss. The authors concluded "This metabolic adaptation may persist during weight maintenance and predispose to weight regain unless high levels of physical activity or caloric restriction are maintained."

I don't know whether the same applies to people who are less overweight than in this study but it would help explain how dieting usually leads to weight gain in the long run! It is depressing reading on one hand, but on the other, the 5:2 approach means that we should be able to maintain the calorie restriction.

Of course it would be really interesting to know whether losing weight by intermittent fasting (which also helps to preserve fat free mass) might not result in a metabolic slow down because of the days of normal eating. We can only hope that this will be the case!

[carorees]

Although not an actual study the following article (originally posted by BreadandWine on mumsnet) gives a good balanced view and helps to explain some of the science behing the benefits:
http://www.scientificamerican.com/artic ... thier-life

Thanks skippyscuffleton! It's a shame the article did not post links to the research because I am interested in the rats whose heart muscle was affected. I will try to track down the study...

Well, I finally tracked the article about the damage to rats' hearts by long-term alternate day fasting (ADF): http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2953475/

The authors are not able to explain why this effect occurred but say that other studies have not found this in rats. They caution that widespread use of ADF should not be adopted until more studies are done.

My take on this study is that ADF represents a much bigger calorie restriction and stress on the body than twice a week fasting. Also as a rat has a much shorter lifespan than a human, perhaps each day's fast in a rat could be the equivalent of a much longer fast in a human. As we know that the weight loss etc we are getting brings substantial benefits then I think it likely that the benefits of long-term twice a week fasting are likely to outweigh the potential risks. Whether the same can be said of long-term ADF or even 4:3 we don't know.

Note: I am not medically qualified and the above opinions are my own. Please form your own view on whether you should/should not participate in fasting.

Caroline - Many thanks for tracking that paper down. It is certainly interesting reading. I wonder how, if at all, that study impacts Prof Varady's research on ADF. Would also be interesting to see if there are any long term (>6mths)case studies in human practitioners of ADF.

Not that I disagree with what you wrote above but I think it's also copying/pasting exactly what the researchers quoted regarding their warning:

Only 4 human studies have been published to date on the effects of ADF (31–34). A decrease in body weight and fat mass, an increase in insulin sensitivity, an increase in plasma HDL cholesterol concentration (women), a decrease in plasma triglyceride concentration (men), and decreases in markers of oxidative stress and inflammation have been observed. While these results are promising, the dietary intervention lasted for a relatively short time periods (1–3 months), involved small sample sizes, and baseline (pre-ADF) measurements were used as control values. The present findings of deleterious effects of ADF on cardiac function in experiment on rodents provide a cautionary note to the adoption of long-term ADF regimens in humans.

I've just come across an interesting paper published last year about the famed metabolic slow down with dieting.

The study (http://www.ncbi.nlm.nih.gov/pubmed/22535969)

I think this is a study of "Biggest Loser" participants. The measured RMR of the 11 completers fell from 2614 at baseline to 2258 at week 6 and 1763 at week 30.

Expressed per kg of fat free mass these averages become 35.5, 31.9 and 28.2 which does look like a sharp drop.

Katch-Mcardle BMR Formula:
BMR = 370 + (21.6 x Lean Body Mass(kg) ) would predict RMR of 1960, 1900 and 1720 respecively, which suggests that the slimmed down metabolic rate is what Katch & McArdle would expect but the fatter versions of the same people had a higher metabolic rate than expected because K-M don't consider fat as metabolically active.

The Mifflin-St.Jeor equation is said to be better for obese subjects, I had to make soem guesses about age and assume they were all male but this equation predicts BMR of 2380, 2330 and 1800 respectively. Again the slimmed down post-diet people have the metabolic rate the equation predicts, within 3%.

So it looks to be more like a case that these folks were "off the scale" of the prediction equations and came back onto the forecast line when the excess was shed - bear in mind they were borderline obese even at the end (BMI = 29)

The image below shows the change in adjusted metabolic rate for each participant, and the prediction based on FFM :


Nobody's RMR is below 1500 at the end so they don't appear to have dropped to an unusually slow metabolic rate.

[carorees]

Ah thanks for that...I only read the abstract = lazy! Reassuring analysis, Phil!

[carorees]

I just spotted this fascinating paper (not too recent but so interesting) about weight #setpoint. It runs through different theories about how and why our bodies seem to try to avoid losing weight. It is quite hard to understand the theories but the authors suggest that we may have an upper and lower limit body weight which our bodies try to avoid going over. They think that the lower limit represents the point at which our bodies think we are starving and so try to prevent this by lowering our energy requirements. They think that the upper limit varies enormously from person to person and that this explains why some people seem to put on weight easily while others can eat what they like and not gain weight.

They also pointed out that the amount of weight lost before our bodies try to prevent more loss seems to be around 10%.

I have seen a few mentions of this 10% figure as being a point at which weight plateaus. I'm now on a hunt to find out if there are any scientific studies that indicate how we can persuade our bodies that losing more than 10% will be fine!

[carorees]

I found another fascinating review paper (here)! In it the author debunks lots of theories about how the body defends a certain weight #setpoint and how the energy balance (i.e., calories going vs calories burnt) affects weight gain. Really interesting. Most interesting, though, is the conclusion that by snacking on carbohydrate rich foods/drinks we keep topping up our glycogen stores (the first port of call for energy when we are not eating) and this prevents the body from ever needing to call on the fat stores. It also means that in times of energy excess it all gets converted to fat. He reckons that if we can lower the amount of energy stored as glycogen it will increase fat burning. Leaving long gaps between food and not eating too much carbohydrate will help with this.

I am wondering if this idea might be partly behind the mention in Dr Mosley's of avoiding high GI foods? And, of course, to the idea that we need to have long periods of not eating for maximum benefit. (BTW I have seen Dr M tweet to people asking about weight loss stalling that they need to keep their sugary food and drink down on feed days as well as fast days.)

Interesting stuff, eh?

Thanks for posting these Caroline, there's a lot of info there to take in and mull over. One piece of info that caught my eye whilst skim reading the above link was that fat metabolism decreases when glycogen levels are high. I hadn't realised this just like I was unaware till recently that insulin causes us to store fat. Therefore fasting and exercise really do help when it comes fighting, if that's the right word, fat.