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Does intermittent fasting lead to muscle breakdown and protein deficiency?

I recently read a comment in a newspaper by obesity researcher Professor Lau from the University of Calgary. He made the point that “muscle protein breakdown occurs in the first 24 hours of starvation,” and expressed concern that people who fast may be losing crucial muscle mass.

My response to this is that he is really talking about long term fasting, ie fasting for days or weeks at a time. With intermittent fasting you are not fasting for 24 hours or longer. In the version that I practice, I never go more than 12 hours without eating. If your protein intake is adequate, and we actually recommend an increased protein intake on fasting days, then you are not going to get “muscle protein breakdown”. In fact the evidence from human studies clearly point towards intermittent fasting being better than standard diets when it comes to muscle preservation.

Dr Krista Varady of the University of Illinois at Chicago has done a number of human trials using intermittent fasting. Her most recent paper was in, Metabolism, Volume 62, Issue 1, Pages 137-143, January 2013. In this study thirty-two overweight volunteers, average age 42, were put on an ADF (alternate day) intermittent fast for 8 weeks. At the end of 8 weeks the volunteers had lost an average of 4kg and seen significant improvements in biomarkers related to the risks of diabetes and coronary heart disease.  Interestingly, the weight loss was all fat, not muscle. As she points out “A similar preservation of lean mass was noted in a previous ADF study conducted by our group.” This retention of lean mass, ie muscle, is not seen with standard calorie restricted diets. “The reason why ADF may assist with the preservation of lean mass is not known at present, but will undoubtedly be of interest in future studies in this field”

In another study of intermittent fasting (Int J Obes . 2011 May;35(5):714-27), 107 young overweight women were randomly allocated to either a standard low calorie diet or a diet where for two days a week they ate 650 calories a day. At the end of 6 months the intermittent fasting group had lost an average of 6 kg of fat and 3 inches from their waists compared to 4.9 kg of fat and 2 inches from waist for the normal dieters.

Doing the diet, I have now lost just over 22lbs and my body fat is down from 28% to under 20%. I walk everywhere and do 30 press ups each morning. Keeping muscle mass is important, not just because it looks better but also because muscle is more metabolically active than fat; it burns calories even when you are asleep. Rest assured, the diet will keep you healthy as well as help you lose weight.

Archive for the ‘science in the news’ Category:

Does intermittent fasting lead to muscle breakdown and protein deficiency?

28th April 2013

I’ve written about the 2 Day Diet  before (see below) and I promised to write a review; somewhat belatedly, here it is.

I think Michelle and Tony Howell have done a great job. There are lots of  books out there based on some variation of intermittent fasting, but this is one of the few that is actually written by two people who genuinely know what they are talking about. The book is based on research they have been carrying out for many years at the Genesis Breast Cancer Prevention project based in Manchester. As the name implies the emphasis is on intermittent energy restriction for 2 days, while encouraging people to eat a healthy Mediterranean diet for the other 5 days.  They suggest that the two days should be back to back, for a variety of reasons.

Firstly they think that if people do them back to back they are more likely to actually do them.

Secondly “it may have additional health benefits”. The reasoning is that if you do your fast days back to back you are spending more time in a better metabolic state. As they point out, “levels of insulin and leptin fall quickly (within 24 hours) when we eat less, so cells can put more effort into staying in top condition”.

I suspect that many people find it easier to split the fast days; that is certainly what most people who contact me say. I would be very interested to see a trial comparing back to back with split days eg Mondays and Thursdays. I have had a lot of contact from people whose blood glucose and cholesterol levels have improved markedly using the split day method.

In addition to the science, “how to do it” and recipes, there is lots of sensible advice on exercise. I think it is well worth a read and I wish their research all the best






An interesting variant on intermittent fasting is something called the 2 Day Diet, based on research by Dr Michelle Harvie and Professor Tony Howell. You will be hearing a lot more about this as they have a book out soon and the book is being serialised next week in the Daily Mail. It is also given a lot of support in today’s Daily Mail by Jenni Murray

Dr Harvie is a leading research dietician and Tony Howell is professor of medical oncology at the University of Manchester; he is also research director of Genesis Breast Cancer Prevention based in Manchester.

Their primary motivation is finding ways to reduce the risk of breast cancer and I have written about their research in The Fast Diet.

Their most recent study was a randomised trial at the beginning of last year, the results of which have been sent off for publication to a nutrition journal. In it they did a three way randomisation of 115 women comparing a daily energy restricted Mediterranean style diet (ie a standard diet) to two different versions of the 5:2 diet.

The first version of the 5:2 diet involved eating 650 calories a day for two days; on those days the women had to cut out pasta, bread, potatoes and all fatty foods. The diet consists mainly of milk and vegetables. For the other five days a week they could eat as much as they liked, although encouraged to eat healthy foods.

Women on the second version of the 5:2 diet were banned from eating carbohydrates for two days of the week but they did not have a specific calorie limit. A sort-of modified Atkins approach.

The third group followed a standard weight-loss diet, sticking to about 1,500 calories a day and avoiding high-fat foods and alcohol.

The striking finding was that after three months the women on either of the 5:2 diets had lost an average of nine pounds (four kilos) – nearly twice as much as those on the standard diet, who lost just five pounds (2.4 kilos). They were also almost twice as likely to have stuck to their diet.

As I mentioned above, they have a book out called The 2 Day Diet which I look forward to reading. It provides considerable further support to research showing that intermittent fasting offers benefits over and above standard dietary advice.

I’ve been in email chat with Dr Harvie, who generously praised my “excellent” Horizon. “The fact that you did it and showed it worked was, to us, very powerful television. We see intermittent dieting as another approach that people may wish to use but it clearly does not suit everyone. However it could have considerable public health importance and that is why we wrote our book, the proceeds of which will go to the charity Genesis who support our work.”

I will write a review when they send me a copy.  I will also keep you up to date with further developments. Exciting times…..

Archive for the ‘science in the news’ Category:

Does intermittent fasting lead to muscle breakdown and protein deficiency?

A review article in the Journal of the American Medical Association which was published on the 2nd January caused a lot of excitement in the press/

The excitement came because the scientists involved claimed to have found evidence, based on 97 studies involving nearly 2.9 million people, that people with a Body Mass Index (BMI) of between 25 and 30 (which officially makes them overweight) are 6% less likely to die than people considered to have a healthy BMI ie 18.5 to 25.

So is “Being overweight OK”, as some headlines claimed? I’m not convinced, and nor were most obesity experts. The criticisms were vigorous and in some cases vitriolic

Professor John Wass, vice-president of the Royal College of Physicians, said: “Have you ever seen a 100-year-old human being who is overweight? The answer is you probably haven’t”, while Dr Walter Willett, from the Harvard School of Public Health said: “This is an even greater pile of rubbish” than a study conducted by the same group in 2005.

The main criticisms were:

  1. Confounding factors. The people regarded as “normal weight” may have previously been overweight, then lost weight through ill health
  2. Mortality is not everything (though it is, of course, pretty important). What this study didn’t reveal was whether the overweight lived that extra 6% longer in good health or in hospital with drips in them. Living longer is not the same as living better. We know obesity is a strong predictor of diabetes and diabetes can lead to serious and unpleasant health problems
  3. BMI is probably not the best measure that can be used to measure obesity. A tape measure may be a better predictor of future health. Gut fat is extremely unhealthy, but it is not clear that fat on your bottom or thighs is quite as bad. It is all about distribution, not quantity.

I certainly am not going to allow the pounds to creep back up in the hope this will allow me to live 6% longer. I like being slimmer, feel much better on it and all the tests I’ve done to date suggest that I have extended my healthy life, not shortened it.

Archive for the ‘science in the news’ Category:

Does intermittent fasting lead to muscle breakdown and protein deficiency?

This is one of those questions that I get asked a lot and the short answer is, “yes, it seems to be fine to combine the two and may indeed be beneficial”. The long answer is a lot more complicated. I am just working my way through the academic literature on this, some of which is in the book, but the headlines are:

  • Make sure you are well hydrated. We get a lot of fluid from food (some of it added during the manufacturing process to add weight, bulk and therefore value), so if you cut your calories to a ¼ during your fasting day you will be consuming less water. I recommend drinking lots of calorie free fluid during the day, whether you are exercising or not. This can be black tea, black coffee (the idea that coffee makes you dehydrate is a myth), water from the tap, herbal teas, whatever. I am not a fan of diet drinks for reasons i will write about later.
  • I have had tweets saying things like, “i have a dry mouth” or “my mouth sometimes tastes funny on a fasting day” and this is almost certainly a sign of dehydration.
  • Men seem to not only tolerate but respond better to exercise on fasting days. For women the picture is more complicated. I welcome feedback on this

One of the key benefits of exercise and fasting is they both increase insulin sensitivity, and insulin sensitivity is an independent predictor of future mortality. But they work in different, complementary ways. Exercise for example, particularly short burst of HIT (High intensity training) depletes the glycogen stores in the muscles, while Intermittent Fasting (IF) depletes the glycogen stores in the liver.

On a more general note I had a look at the government guidelines for the BBC R4 series, You and Yours, on exercise, 5 a day and alcohol. I attach links to features I wrote about them for the BBC

BBC features:

‘Confusion’ over how active we should be

Five-a-day campaign: A partial success

Alcohol message ‘is confused’

Archive for the ‘science in the news’ Category:

Does intermittent fasting lead to muscle breakdown and protein deficiency?

My features on drinking triggered a lot of media interest, some of which seems to have misunderstood what I was trying to say. I am not, for example, telling people they should not drink but rather trying to give them the evidence so they can make their own judgements. The science researchers I spoke to were keen to emphasise the value of having two alcohol free days a week, something which fits in neatly with the Fast Diet.

The Public Health Minister Anna Soubry came on Radio 4 after my series had gone out and said:

“That was a brilliant report if I may say…I thought the 2:2 was a cute message. Good, simple and accurate as well. Certainly I’ll talk to the CMO (Chief Medical Officer) about that.”

I have listed the media response to the guidelines below if you would like to see what others are saying.

BBC Breakfast TV interview

I was on the sofa up in Manchester on Tuesday 2nd January talking about the Fast Diet but also about a new series for You and Yours looking at government guidelines in relation to exercise, booze and “5 a day”. If you want to watch the BBC Breakfast interview the link is here. As an added bonus you get to see a Christmas present from my wife, a new shirt that is not pink.

The media response to drinking guidelines

UK press:

Alcohol guidelines ‘too high’ say doctors

The new Puritans don’t understand the joy of drinking

So it’s OK to be a little plump, then. Raise a glass (or three) with me to another blow against the health fascists

Julian Baggini: Confused about health? Drink more

Even a tipple a day is one too many – warning from doctors

Foreign press:

A daily tipple may be the death of you

Anti-Alcohol Guidelines ‘Ineffective’

Archive for the ‘science in the news’ Category:

Does intermittent fasting lead to muscle breakdown and protein deficiency?

From twitter: @DrMichaelMosley My partner’s dodgy knee has improved since diet; not sure if cos less weight on it or inflammation down.

My reply:

One of the things that I am particularly interested in is the anti-inflammatory effects of intermittent fasting (IF). A number of studies, in humans and in mice, have shown that IF reduces inflammatory markers (unlike high protein diets which seem to increase them). In a review paper for The Journal of Nutritional Biochemistry, March 2005, Dr Mark Mattson (whose work I cite frequently in my book as he is one the great researchers in this field) writes:

 “Intermittent fasting and caloric restriction (CR) extend lifespan and increase resistance to age-related diseases in rodents and monkeys and improve the health of overweight humans. Both IF and CR enhance cardiovascular and brain functions and improve several risk factors for coronary artery disease and stroke including a reduction in blood pressure and increased insulin sensitivity…The beneficial effects of IF and CR result from at least two mechanisms — reduced oxidative damage and increased cellular stress resistance.”

I will go into the mechanisms around oxidative damage and what he means by cellular stress resistance at a later date if anyone out there is interested.