Intermittent fasting (IF) keeps popping up with increasing regularity in the media and on the internet. The idea is that short-term caloric restriction interspersed with “normal eating” has a variety of health benefits.
There are several different types of IF:
- Alternate Day Fasting: eating <600 calories every other day
- The 5:2 diet: eating 500-600 calories two days a week
- Daily Intermittent Fasting: eating within a set time “window” each day (and effectively fasting the rest of the time)
The good thing about IF is that it allows for individual adjustment. None of the rules are set in stone and adherents are expected to fast in a way that suits their needs and lifestyle. It also isn’t a short term “diet” – rather, the aim is to switch to IF as a lifestyle change and then maintain it permanently.
It also isn’t being touted as a weight loss strategy – yes, it can be expected as a welcome “side effect”, but the intention is to improve physical and mental well-being in general. Some research suggests that IF lowers blood pressure and increases heart and brain cell resistance to stress. This effect can improve the functioning of the nervous system and could potentially delay the onset of age-related neurodegenerative diseases like Alzheimer’s. Potentially. Most of this research has been carried out in mice, so we just don’t know yet.
Trying out IF with the sole intention of weight loss probably isn’t entirely advisable either. In Rena Wing’s study, obese patients on IF diets did lose more weight than those simply on low calorie diets (14 vs. 10.5kg over 50 weeks) – but the caveat is that the IF diet was more “fasting intermittent with a low-calorie diet”. In the end, the differences just weren’t that impressive.
Some practitioners have also made the argument that switching to IF will only be beneficial alongside other positive eating and lifestyle changes; fasting will not be of much use if it is interspersed with overeating and a poor diet.
I was somewhat sceptical about the reality of IF. First of all, it can’t be very practical. Second, I would have expected surviving on a measly 500 calories to be, at the very least, unpleasant – and at worst, debilitating. By contrast, it doesn’t seem that IF particularly affects cognitive function: attention, memory and reaction times seem to be unaffected by up to 24 hours of fasting. Studies in people observing the Ramadan (which requires abstinence from food and drink during daylight) suggest that IF can actually increase vigilance but increases feelings of fatigue. Having said that, Michael Mosley tried out the 5:2 variant of IF for BBC’s Horizon and said he found it “surprisingly easy“. So it seems that the psychological effects of IF are negligible.
A word of warning: one study conducted in mice found that caloric restriction led to decreased sexual arousal and made the male mice less attractive to female mice. Just saying.
So, it seems that the jury is out on the benefits of IF. The science is not as wild about the benefits as some of the blogs I’ve seen – but it doesn’t appear to be harmful. Personally, I’d like to see more research on the emotional consequences of IF, and its impact on quality of life and interpersonal relationships.
If you’re thinking about trying out intermittent fasting, see the 5:2 NHS page for some comprehensive advice and a review of the evidence.
Have you tried intermittent fasting? What was your experience?