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Hi I am Clare writing as part of the 121 Dietitian team. Below is my own assessment of Michael Mosley’s fasting diet.

Why I did 5:2 fasting diet

I’m soon to graduate as a Dietitian and I have a keen interest in weight management and awareness of food content. When I heard about this diet, I knew that I would be asked about it and decided the best way to be able to give my view/understand what people were dealing with, would be to try it out myself.

“Dietitians should take into account what people actually do rather than what we would like them to do” – Dr Krista Varady

Note: I didn’t do the fast diet with the aim to lose weight; simply to see how it would feel and the effect it would have on my health and lifestyle.

In the UK, nearly 2 in 3 adults, and 1 in 2 children, are overweight or obese. (2012)

Having a BMI above 25kg/m2 puts you at higher risk of many other diet-related diseases including Type 2 Diabetes, Heart Disease and Cancer. this is something to be taken seriously and probably one of the biggest reasons for our world’s growing obsession with diets.

* To work out your BMI: divide your weight (kg) by your height squared (m)2 

e.g. if you are 57kg and 1.62m, it would be 57/2.62 = 21.8kg/m2

Dieting is no new thing; a quick search in google brings up some odd historical diets ranging from the self explanatory ‘chew and spit diet’ to eating tapeworm eggs…

 So what about this 5:2 fasting diet from Michael Mosley?

Fasting is no new concept either. it is an important practice in a number of religions (consider lent, Yom Kippur, Ramadan) carried out to fulfill a number of purposes that include practicing self-control and purifying oneself. In the early Christian church, Wednesdays and Fridays were traditionally fast days, and those partaking would abstain from meat, fish, eggs and butter. ‘i fast twice a week’ – Luke 18:12.

“gluttony makes a man gloomy and fearful, but fasting makes him joyful and courageous” – Saint Nikolai of Zicha

I have a nagging suspicion that there’s some wonderful underlying truth about improved health with fasting just waiting to be discovered.

Does the 5:2 fasting diet work?

Start – 4.3.13 –  weight 127lbs; BMI 21.8 kg/m2; serum cholesterol 3.8mmol/l

Finish – 12.4.13 – weight 127lbs; BMI 21.8kg/m2

This is interesting. My weight stayed stable. Admittedly, on a couple of occasions I cheated, going a little bit over the 500kcal allowance or being sneaky and ‘fasting’ from 2pm one day to 2pm the next day and still allowing myself 500kcal in between (and having a takeaway pizza for lunch at 1.30pm just before i started).

Also, this period in my life has been one of celebration and freedom from structure and responsibility. Therefore I have been eating out, throwing dinner parties and having coffee dates much more frequently than usual.

So what I have found is that this diet has allowed me to do is to maintain a happy weight whilst eating in a ridiculously undisciplined fashion 5 days a week. It has also shown me that I am disciplined enough to work around food all day (in a cafe on my days off) and not give in to temptation 2 days a week. It required effort in planning and calorie counting and commitment but it brought a sense of achievement and self-control when mastered.

I am aware that lowered cholesterol and blood sugars are supposed to be the other health benefits in the fast diet. Prior to starting, and in the name of science I visited my GP to measure my blood sugar and cholesterol levels, but it turned out they only measured my cholesterol (as seen above). Because of this I did not return post fast period because my cholesterol was at a healthy level on starting and I had nothing to compare my sugars to! Not very scientific after all. For anyone else wanting to try out this diet, please make sure to get your bloods checked before and after!

Did I over-compensate for my fast days?

Yes. Definitely. However, I think that had I started the fast diet with a genuine desire to lose weight, I would easily have been able to refrain from over-compensating. in Mike Mosleys book, Dr Krista Varady carried out a study which showed people generally did not compensate for their fast days by having 175% on a feed day.

personally, because I wanted to push boundaries with this diet, I think I have proven that to see all the results you need have a motivation and be very, very strict.

What are the benefits of 5:2 fasting diet?

Bearing in mind that there have been no long term studies carried out in humans, here is a list of some of the believed benefits of fasting:

  • · longevity (in mice: lowered IGF-1*)
  • · weight loss (i have spoken with a number of people who have lost between 8lbs and 21lbs)
  • · improves learning and memory in mice (possibility of reduced risk of Alzheimer’s?*)
  • · improves nutritional awareness (constantly reading labels)
  • · reduced risk of cancer (due to weight loss and decreased % body fat*)
  • · lowered blood sugar and cholesterol levels
  • · choose your days/ make it suit you
  • · improved self discipline

*The science bits.

1) this is a quote from Mike Mosley’s book.

“The IGF-1 hormone (insulin-like growth factor) is one of the drivers which keep our bodies in go-go mode, with cells driven to reproduce. This is fine when you are growing, but not so good later in life.

There is now evidence suggesting that IGF-1 levels can be lowered by what you eat. Studies on calorie restrictors suggest that eating less helps, but it is not enough. As well as cutting calories you have to cut your protein intake. Not entirely – that would be a very bad idea. It’s about sticking to recommended guidelines, something most of us fail to do. The reason seems to be that when our bodies no longer have access to food they switch from “growth mode” to “repair mode”. As levels of the IGF-1 hormone drop, a number of repair genes appear to get switched on.

– according to ongoing research by Professor Valter Longo of the University of Southern California.”

So Mosley states (but gives no proof) that protein directly affects IGF-1 levels and that low levels of IGF-1 = increased immunity to diabetes and cancer because DNA damage is more likely to be repaired.

2) Another experiment mentioned in Mosley’s book suggests that mice on ‘feed and fast’ days lived without obvious signs of Alzheimers for 6 months to a year longer than they would otherwise have done.

3) There are 2 ways to look at the effect of fasting on fat.

  • · If glycogen is available, the body will use this for energy. if it isn’t, the body draws on fat stores for energy.
  • · Depriving yourself of necessary daily calories puts you in physical “starvation mode.” Your body will think that there isn’t enough food available and that you’re starving. When you go off your diet, your body will store even more fat in reserve against future lean periods. You’ll also be more likely to overeat during this period. Note: eating 500kcal on 2 days a week is not ‘starvation’.

What are limitations of the 5:2 fasting diet?

  •  hunger/ compensation
  •  lack of energy (however, Mosley would disagree!)
  •  hunger/ compensation
  •  lack of energy (however, Mosley would disagree!)
  •  organisation/ planning ahead required
  •  not a balanced diet
  •  ?sustainable
  •  food obsession – ‘we humans are always looking for things to do between meals’ – Leonard Cohen
  •  unhealthy attitudes to food (on your non fast days)

If I was doing the 5:2 fasting diet again what would I do?

  •  keep a diary of progress
  •  weigh once a week on the same day at the same time and record it
  •  measure % body fat before and after
  •  have bloods – sugars, cholesterol – checked before and after
  •  waist circumference
  •  measure my neck size (apparently excess fat around your neck causes some people to snore)
  •  food diary
  •  picture of self before and after
  •  eat low GI and high protein foods on fast days

How to do the 5:2 fasting diet

I tried several different methods: 1) brunch and dinner 2) breakfast and dinner 3) breakfast and lunch 4) 2pm to 2pm (the one i consider a cheat unless you completely fast).

Obviously i found option 4 the easiest.  The other one that worked best for me was brunch and dinner.

I would have a poached egg on plain Ryvita or plain toast and maybe an apple = ~ 200kcal and then a small portion of salmon, baby boil potatoes and green veg for dinner and drinking water throughout the day.

I found myself craving something sweet, a little dessert, a cup of tea. so instead of finishing my meal i might actually have a cup of tea and a square of chocolate = ~ 50kcal.

I would suggest you do your fasting on busy days. I found it easiest when my work shift was from 12-6pm and I ate just before it and when I came home and the day felt almost normal!

Is fasting healthy? What about general healthy eating?

This is the question I am particularly interested in.

From my personal experience, I cannot say that I found the fast diet a particularly healthy one. I found that on fast days, yes, I chose lower GI foods and ate less sugary and fatty foods (i.e. more unlikely to consume empty calories on fasting days i.e. eat less; eat better), but I also did not achieve my 5 a day due to the surprising calorific value of fruit. My diet was not balanced on non fast days either because as I mentioned earlier, I compensated for only eating a quarter of my usual intake the previous day by tucking into takeaways and cake because I felt that i deserved it.

I do feel that if I had been doing this diet with a personal motivation to lose weight/ improve my bloods, it would have been easier to eat a healthy balanced diet on non fast days and to be strictly disciplined and organised in my fasting twice a week.

Quote from Mosley: “I stuck to this diet for 5 weeks, during which time I lost nearly a stone and my blood markers, like IGF-1, glucose and cholesterol, improved. If I can sustain that, it will greatly reduce my risk of contracting age-related diseases like cancer and diabetes.”

Who shouldn’t fast?

Since the evidence for fasting is still unfolding, it is recommended that anyone who is pregnant, Type 1 Diabetic, has an eating disorder, is a child or is already very lean, should not begin fasting.

Conclusions on the 5:2 fast diet

In conclusion, I think we should calorie restrict and intermittently fast. For years we have hypothesised and accepted that.

‘calorie restriction without malnutrition delays the onset of aging and extends the lifespan in diverse animal models. the mechanism underlying this phenomenon is still unknown. we have hypothesised that a reprogramming of energy metabolism is a key event in the mechanism of calorie restriction.’ – Anderson and Weindruch 2007

I feel that it is most important to be constantly disciplined in how and what we consume, that is, constantly being aware of the choices we are making and always eating a healthy balanced diet within a calorie allowance for a healthy BMI. however, I feel that there are so many benefits to fasting (both mentally and physically) that it is something that should always be an option in our weeks, a way to reset ourselves after a big weekend or a holiday and a way to remind ourselves how yummy healthy food can be if we allow ourselves to become hungry more often.

Clare x

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Information checked & correct on 16th May 2018 and Jan 2021.

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