I found this article from the Daily Express interesting. Women over 50 seem to be ok though.
CAVEMAN FASTING DIET MAY LEAVE WOMEN DIABETIC
The 5:2 diet can have a detrimental effect on your health
Sunday January 27,2013
By Jane Symons
THE 5:2 weight-loss fad has been heralded as a miracle plan that boosts brain cells while reducing your risk of cancer and dementia but, as JANE SYMONS discovers, regular fasting has worrying health implications for women.
You probably know someone who is on the 5:2 fasting diet, you may even have tried it yourself.
Its promise to melt away pounds with minimal pain is seductive and, unlike so many fad diets, comes with promises of extraordinary health benefits. Just like the Atkins, cabbage soup and blood group diets before it, however, the latest flavour of the month weight loss regime could leave a bad taste in the mouth.
The few studies which confirm its benefits also reveal a potentially dangerous divide.
Intermittent fasting is very effective for men but potentially dangerous for many women.
There is increasing evidence that women are less likely to lose weight and more prone to unpleasant side effects such as insomnia, impaired fertility and increased stress hormones.
According to Michael Moseley, the doctor turned-television presenter who popularised this new approach to weight loss, the proof is in the pudding (which remains on the menu for five out of seven days). After trying the feast-and-famine regime for five weeks for the BBC documentary Eat, Fast and Live Longer, he lost almost a stone and reduced his body fat, cholesterol and blood sugar.
He also halved his levels of IGF-1, an insulin-like growth factor, which increases the risk of cancer. However Dr Catherine Collins, Chief Dietician at London's St George's Hospital, warns that basic differences in biology make it effective for men, but unsuitable for many women.
For starters, men have a higher percentage of muscle, which gives them a faster metabolism, so if a man and woman of comparable size restrict their intake to 800 calories a day the man will lose more weight.
Their greater muscle mass also protects men from some of the downsides of the diet. Dr Collins explains: “The average adult turns over 300grams of protein a day.
Eighty per cent of that is recycled, broken down and reused; a bit like Lego bricks, but after a certain period of time these proteins become worn out and are lost to the body.
“What we cannot salvage, we need to replace and once you start skipping meals you will compromise your intake.
“Protein is non-negotiable, and unlike other micronutrients you need it every day, but men have a higher reserve of muscle they can call on for protein during fasting days.â€
The simplicity of 5:2 dieting is undeniable.
You eat normally for five days a week and cut calories to 500 (for women) and 600 (for men) a day for the other two, using diet shakes or the low carbohydrate “paleo†diet of our caveman ancestors.
Advocates argue that it is easy to stick to, prolongs life and reduces the risk of cancer, heart disease, diabetes and dementia.
However, Dr Susan Jebb, head of diet and population health at the Medical Research Council cautions: “As with every new diet that comes along there are always more claims made for it than are supported by the science.â€
Large population studies which appear to confirm the benefits of fasting are not always as clear cut as they seem. For instance, one which analysed the health records of 4,629
Americans reported that intermittent fasting reduced the risk of heart disease by 39 per cent, but the fasting group was made up almost entirely of Mormons, who also shun alcohol, tobacco, coffee and other unhealthy habits as part of their faith.
Even those who promote fasting admit the evidence is patchy. After reviewing all the published trials, Professor Krista Varady who featured in the BBC documentary admitted: “The human studies are limited, they all lacked control groups and used short trial lengths.â€
Closer examination of the handful of smaller, well-controlled studies on fasting reveal that women may actually miss out on the much-touted improvements in glucose tolerance and insulin responses and could actually increase their risk of developing diabetes.
The danger was identified in a 2005 study published in Obesity Research which tracked eight men and eight women as they tried intermittent fasting for three weeks. All were a healthy weight or carrying only a few extra pounds, with BMIs between 20 and 30.
At the end of the trial there was no insulin improvements in the women and their glucose response got worse, while the men had no glucose changes and their insulin response improved.
American scientist, author and blogger Stefani Ruper, who was one of the first to question the safety of the 5:2 regime, warns: “The IF regime was not just neutral for women, but was downright harmful.â€
In part, this may be due to differences in the way we store fat. Women are most likely to be pear-shaped and pile extra pounds on to their hips while men become apple-shaped and gain weight around their middle, which is much more dangerous and increases the odds of developing diabetes and heart disease.
Dr Collins says: “You would expect men to benefit more because the natural distribution of their body fat predisposes them to metabolic syndrome [a precursor to diabetes]. Losing weight around the middle will increase insulin sensitivity, and reduce their risk.â€
This dangerous apple-shape becomes more common in women after menopause, which suggests there may be some benefits to the 5:2 regime for those over 50. However, for younger women there are serious concerns about fasting and fertility.
Studies at the American National Institute on Ageing found that when rats are put on a restricted diet the females stop ovulating and their ovaries shrink.
They also become increasingly alert and active, which may account for the fact women are also more susceptible to insomnia on the 5:2 regime.
Lead researcher Bronwen Martin says these changes may explain why women are more vulnerable to anorexia and that also worries Dr Collins.
Eating disorders are rooted in psychological problems, but she says fasting encourages “disordered eating†and that could tip at-risk dieters into a full-blown eating disorder. “Fasting creates a feeling of euphoria because blood sugar is running quite moderately and that can be addictive. It is very important that you don't do more than two days a week,†she says.
We have to get away from this idea that the 5:2 diet is a panacea, an optimum diet. It isn't.
Dr Collins
The warning is borne out by research at Columbia University which found changes in female brain chemistry are directly related to food intake; the greater the hunger, the bigger the impact.
In female rats, even a modest cut in calories triggers a sharp increase in corticosterone levels and encourages the body to lay down fat stores, according to studies at the National Institute of Ageing.
In males, intake had to be slashed by 40 per cent before there was any change in the diet-busting hormone.
Dr Collins says, “We have to get away from this idea that the 5:2 diet is a panacea, an optimum diet. It isn't.â€
All the evidence suggests it undoubtedly works for men and it may work for overweight or obese women, but those who don't need to shed a lot of weight may have a lot more to lose than a few pounds"
Taz x
