Extreme fasting didn’t suit rats but my diet’s good for us
COULD some fasting diets increase the risk of type 2 diabetes? That was the question posed by scientists last week, after researchers unveiled evidence that seemed to suggest they might.
For obvious reasons, I was concerned – mainly because it flies in the face of everything research into fasting diet has proven over the years.
And having looked at the new data, I’d like to give you the facts.
As you no doubt know, I have been writing about intermittent fasting for years now, most recently with my New 5:2, part of my Life Plan, exclusively in The Mail on Sunday.
In my 2013 book The Fast Diet, I suggested that people doing the 5:2 should cut their calories on their two ‘fasting’ days to about 600. Today I recommend a more generous 800 calories a day as well as eating a healthy Mediterranean-style diet, whether or not you are fasting.
Over the past five years there have been numerous studies showing its safety and effectiveness, which I will go into in a moment. But first, let’s look at the new research presented at the European Congress of Endocrinology in Spain this week. In this particular study rats were put on an absolute fast – nothing to eat at all – every other day for three months.
The rats lost weight but, worryingly, they put on fat, particularly around the abdomen.
The researchers note that their stomachs ‘greatly increased in size’. As a result of this swelling girth, the rats’ pancreas became increasingly full of fat and their blood sugar control got worse. This is a surprising finding because it contradicts so many other animal and human studies of intermittent fasting. I wasn’t given detail about what the rats ate on non-fast days, but if they were allowed to gorge, that would undoubtedly skew any result.
So that was a rat study, using an extreme version of intermittent fasting. I would not, anyway, recommend an absolute fast every other day as you need adequate levels of protein to maintain muscle mass.
What about human studies using more sensible approaches to intermittent fasting, such as 5:2? Well, there have been a number of studies in recent years and they have been consistently positive.
There was a 2013 trial in which 115 women were given either a two-days-a-week calorie- or carbrestriction diet, or told to stick to a standard steady weight-loss approach. The two-day dieters lost nearly twice as much weight over the first three months as steady dieters and an average of 17 lb after six months.
Most of the weight loss was fat and they saw big improvements in their insulin sensitivity – a measure of diabetes risk.
In a more recent study from the University of Surrey, published in the British Journal Of Nutrition this March, researchers randomly allocated a group of 41 overweight volunteers to either the 5:2 or a standard calorie-restricted diet. Women ate 1,400 calories a day, men 1,900.
The 5:2 dieters not only hit their weight-loss targets faster, they saw big improvements in blood pressure and blood fats. No significant negative effects were reported in either group.
More anecdotally, I have received thousands of messages over the years from people who have done the 5:2. Many have reported fantastic results, others have struggled. None has reported significant side effects beyond the usual things you encounter when dieting, such as hunger, irritability or headaches.
Finally, I would point to a really important randomised controlled trial of 298 type 2 diabetics published a few months ago in The Lancet. Those allocated to an 800-calorie diet every day for 12 weeks not only lost large amounts of abdominal fat but nearly half were able to come off all diabetes medication.
Scans of the pancreas and liver showed they were far healthier than at the start of the trial.
I hope you find this encouraging. I do.
MANY OF YOU HAVE REPORTED GREAT PROGRESS DOING THE 5:2