I thought I’d summarise the evidence because anyone trying to lose weight (or help others lose weight) can benefit from the information.
Although the diets have been criticised, the truth is that there is some credible research behind them. Neverthless this is often misinterpreted by the media (we love sensation let’s not forget).
So, let’s kick off with intermittent fasting.
Intermittent Fasting – also known as 5:2, day on day off,2 day diet, ADF.
Intermittent fasting or intermittent energy restriction is a form of a dieting which involves alternating between spells of ‘normal eating’ with fast days, or days of severe calorie restriction, typically to 25% or less of normal intake – that’s around 600 calories for men and 500 for women. For over 100 years studies in animals show this type of calorie restriction prevent cancer and can ‘slow’ ageing. More recently there is interest in the benefit of intermittent fasting for weight loss.
Since 2005, Michelle Harvie (a research dietitian at the Genesis centre in Manchester) has been working with groups of overweight women at risk of breast cancer to find out whether two days of intermittent fasting or calorie restriction is easier to follow than being on a diet seven days a week. In addition they wanted to know whether this gets better results in terms of weight loss and other risk factors for diabetes, heart disease and cancer. We know that dieting is hard work and not many people stick with it, so anything that makes the process easier is win-win.
Meanwhile, over in the U.S. researchers (Kristen Varady and JB Johnson) have been busy investigating alternate day fasting in groups of overweight adults – that’s one day of ‘normal’ eating followed by one day of ‘fasting’, and so on.
So what have they found?
In the first study from Michelle’s group, the women followed either a ~1500 calorie / day Mediterranean diet or a healthy eating plan with two days of intermittent fasting (650 calories per day consisting of milk, fruit and veg). At the end of the study those in the ‘fasting’ group lost more body fat (6kg vs 4.9kg) and had better reductions in fasting insulin.
In a follow up study they confirmed that intermittent fasting was more beneficial than daily calorie restriction for both lowering body fat and insulin levels. They also found that 2 days of low carb eating per week was as effective as two days of ‘fasting’ in terms of results. And once they’d lost the weight? One day of low carb or fasting per week appeared to keep it off.
In the U.S. the study groups have been smaller, but with similar results. In one group of ten overweight adults, alternate day fasting lowered body weight by 8% in eight weeks, improved inflammatory markers and asthma symptoms. In a ten week trial, body weight reduced by almost 6kg during the diet phase with reductions in cholesterol and blood pressure. Importantly in all the studies, adherence is good if not better than what we see with the regular diets.
Didn’t this all start with the horizon programme?
Not really. The horizon programme ‘Eat, fast and live longer’ was aired in October 2012, and featured Michael Mosley, a medical journalist who set out to investigate the benefits of fasting for longevity. During the programme he met with Varady and other U.S. researchers researching fasting and came up with his own version which involved two days of fasting per week, with impressive results.
There’s no doubt the programme put fasting on the global map, but the research had already been going on long before the programme. Howevr since then the media has been unindated with variations of the fasting diet (DODO, 5;2, 3;4 etc), and as of January 2014 there are around 130 diet books on the subject -no kidding.
What is not always so clear is that many of the versions of the diet have been popularised, but with no evidence. There’s also varying advice on supplements, what you can eat on non fast days and how you should spend your calories.
So what do we actually know?
- Intermittent diets appear to be an effective alternative to being on a weight loss diet seven days a week
- Dieters don’t appear to ‘overeat’ or have disordered eating on non fast days (but this might not be true for everyone)
- intermittent calorie restriction appears to have additional benefits for insulin levels and other inflammatory markers than a standard weight loss diet
And what don’t we know?
- what happens in the long term (although from an evolutionary perspective, periods of intermittent fasting would be natural, and you could argue whether this is a ‘normal’ state)
- the ideal pattern of fasting for maximum health benefit – is it alternate day, 2 days a week, 12 hour windows etc
- how it applies in people with diabetes, morbid obesity
- effects on energy expenditure and muscle mass
- whether the benefits are relevant for people of a healthy weight
So is IF for you? If you’re looking to lose weight, it’s an option to consider. It’s not necessarily easy, but the results and research are promising and if you find a seven day diet impossible to stick to, it’s worth trying.
That said, it’s not an excuse to eat junk on non fast days, and if you find it’s creating unhealthy habits between fasts, you might want to reconsider.