Basically, it means going an extended period without eating. Sounds technical AF, right? (Unlike plain ol' healthy eating and regular movement, which is clearly not sexy enough to attract the attention of the masses!)
IF is fancy-sounding enough to get the attention of those who want the next magic bullet that will help them lose weight and/or get healthier.
So, nearly everyone.
But especially those who already have issues with weight concern, body image, disordered eating or eating disorders - the folks I see the most often.
In actuality, almost all of us intermittently fast. Every night. When we are asleep. Not so sexy, I know. So let's talk a bit about the sexier, newer, more restrictive version.
Holes in the science
For the variations of IF with the tightest feeding windows, OMAD or One Meal A Day has recently risen in popularity.
Based on the limited amount of research that has been done on IF, the purported benefits include:
- life extension
- reduced blood lipids
- reduced appetite
- reduced blood pressure
- reduced markers of inflammation
- increased fat burning
- improved blood sugar control, and of course
- short term weight loss.
However, there are a number of problems with simply reading a list like this (without further investigation as to how the list was compiled), and deciding that from now on you're going to push breakfast out to 11am - or ditch it completely.
1. Poor experimental control groups
It seems that these benefits are attractive enough to outweigh the fact that most of these reported benefits have been gleaned from very limited research, a lot of it from animal studies.
Human experiments using IF are extremely limited, short lived, and often use poor experimental control groups. Sample sizes are small and studies have only been conducted on highly specific groups - clinically obese patients, athletic men, or mice.
Such specific results are not that easy to directly translate to the general population. This is the problem with a lot of studies. However, once the media gets a whiff of anything remotely weight loss-y, any fragments of science will get twisted in all kinds of devious ways (see no.4).
2. No studies done on women
From a clinical perspective, I have found that women who practice intermittent fasting generally do not do well on it. I mean, women's bodies work pretty differently compared to those of athletic men (or mice), the only control groups that have been used in IF research thus far.
Female bodies have a far more sensitive hormonal set up than men's bodies. Because women doing IF often use it as a way to restrict calories (they simply skip breakfast instead of eating it later in the day), it is technically becomes a semi-starvation diet.
Female bodies do not like being starved because female bodies are in charge of making babies, which requires some serious nutritional inputs. An extended fast (say, 16 hours instead of 12), tends to send "famine" signals to the female brain. In the long run, this can lead to metabolic, digestive, hormonal and mood dysregulation as the body adapts to the perceived famine. I explain this process in my article The Wellness Diet Cycle.
3. The purple smoke reaction
People (i.e. the media) see things that work in clinical populations and think, "Woohoo, we can use this to lose weight... AND get healthier!," without looking at the implications. This all takes place on a cultural stage that is obsessed with weight loss and weight control.
Inconclusive science +
Diet culture +
So we've got three highly volatile substances here that when combined, create quite the show. It's like that time your Grade 10 chemistry teacher added a few drops of water to a mix of iodine and aluminium powder and the whole thing lit up in a gobsmackingly impressive (yet kinda toxic) display of violet smoke.
Combine a few drops of inconclusive science with copious volumes of media buzz in a container of diet culture, and you've suddenly created the next diet fad sensation. This sells magazines, newspapers, books, and oh yes, DIETS.
As with other dietary fads, it's only once the diet is out there being used by everyone from recreational athletes to pregnant women that the science starts to catch up and shows that there are many implications that don’t get discussed.
4. Results twisted by the media
To top it all off, like most fad diets with a sliver of scientific research behind them, results (however slippery) are not only immediately grabbed by the media with hungry hands, but are also presented by said media in a way that sounds deceptively, well, scientific.
It's all well and good to hear something like, "intermittent fasting reduces insulin-like growth factor 1 (IGF-1), which is a scientific-sounding thing that increases your risk of diabetes. So reducing IGF-1 is good."
Everyone is scared of diabetes and associates it with 'obesity', so claiming that IF reduces this thing that may reduce diabetes risk sounds pretty sexy.
But without an understanding of the complex physiology of human metabolism, and without knowing that there are literally dozens of hormones, enzymes, vitamins, minerals and factors that influence blood sugar and insulin levels in both the short and long term, the context and relevance of such an isolated finding are usually lost amidst the sciencey-sounding rhetoric in a weight loss-obsessed culture ("Science AND weight loss? I'm SOLD!")
It's like saying "surgically scrubbing your hands for 20 minutes with our fancy new soap significantly reduces your risk of food poisoning. So you need our soap (and our soap only) and a bunch of effort to not get sick."
A quick hand wash before meals with some ordinary soap is probably enough to help you avoid food poisoning. Likewise, imposing additional strict requirements to attain some level of health may be overkill. Especially when that same level of health could be attained by eating a varied, balanced, nutritious meals at regular times according to appetite and schedule, i.e. normal eating.
The fact is that any restrictive diet where calories are reduced will temporarily seem to improve blood markers. I mean, you're eating less - of course your blood sugar and blood lipid levels are going to drop temporarily.
Then there's the effect of stress hormones.
Intermittent fasting is a stressor
That means, IF is primarily used as a diet, i.e. a way of restricting calories for the purpose of weight loss or control.
Any time you restrict food (be it calories, carbohydrates, fats etc), you are placing a stressor on the body. With intermittent fasting, a calorie deficit is usually created by skipping meals and/or using the time restricted feeding windows. This is certainly the case with 5:2 and often the case with 16:8.
When you begin any form of diet (i.e. calorie restriction), there is an initial surge of the stress hormones adrenaline and cortisol. The effects of these stress hormones may well explain all of the perceived benefits of IF. I explain this phenomenon, coined The Honeymoon Period, here.
Once you read this, you'll understand why the finding that intermittent fasting reduces IGF-1, blood sugar and appetite is just as (if not more) attributable to the effect of the stress response, as it is to the claims that IF truly is health generating in and of itself.
These isolated findings from short term, poorly designed studies are not really enough information to extrapolate that IF is going to have significant, long-lasting, positive impacts on your health.
It is enough information to show us, yet again, that calorie restriction pushes the body into a stressed state.
Just Another Restrictive Diet
If intermittent fasting is simply another way to restrict calories (in this case by skipping meals, rather than avoiding certain foods or food groups as many other diets like to do) then it’s JARD - Just Another Restrictive Diet. And we all know diets don’t work by now (don’t we?)
By “diets don’t work”, I mean that in the long run (within 2-5 years) 98% of dieters regain all the weight they may have lost, usually plus some. And the remaining small percentage who keep the weight off have usually developed some form of disordered eating / ED.
So the options are: weight loss followed by weight regain, weight loss followed by even more weight regain, or an eating disorder. Fun.
DISORDERED EATING & Intermittent fasting
I’m talking to the people who use IF as a tool to hide their disordered eating habits. And going by what I see in the wellness world, that’s a lot of people.
Many of the clients that I work with have used intermittent fasting as a way to justify what they were already doing. They were already skipping breakfast, and/or restricting all day, often followed by night time bingeing (because, y'know, they were starving.) With the rise of IF to fame they could now simply say, “Oh, I just intermittently fast. Science says it's good for me.” Sigh.
Here are the common arguments I hear from folks who are adamant about doing IF, despite having a screwy history around food and eating:
- But... I’m NOT HUNGRY in the morning! Some people just don’t feel like eating as soon as they wake up. That is fine. Brunch is a beautiful thing. I’m not speaking to brunchers. I’m speaking to people who use IF as a reason to regularly skip breakfast as a way to restrict their overall calories. If you have a history of restrictive dieting or disordered eating, chances are your hunger and fullness cues have become seriously dulled. To the point where you don’t notice you’re hungry until you’re absolutely starving. You can’t trust your hunger and fullness cues if you’re coming off the back of this kind of thing. “I’m not hungry” may be an incorrect interpretation of long term deprivation-altered body cues.
- But... SCIENCE! As noted above, the research on IF in humans is often twisted by the media. The science itself in its infancy and rapidly changing. The latest research is now moving from a 16:8 fasting:eating timeframe, towards a 12:12 window. It’s showing us that we can get the same "benefits" (and I say that with hesitation, again as explained above) from a shorter fasting window. A 12:12 schedule could mean dinner at 7pm and breakfast at 7am. In other words, it's not significantly different from normal eating patterns (as noted above). So... why not just eat normally?
- But... FASTED CARDIO! DETOXIFICATION! FAT ADAPTATION! Ah, so many fancy dress costumes from disordered eating land. So little time.
Basically, if you have any history of disordered eating, then this is not an appropriate approach. Absolutely not. It’s just another way of masking excessive energy restriction. It does not foster a positive relationship with food. It could well - and from what I've seen in clinic, too often does - damage your relationship with food even further.
But I don't have an eating disorder - could IF be for me?
Are you meeting your nutrient requirements in that 8 hour block? (in the case of 16:8) If not, you are creating a calorie deficit i.e. you are dieting. If this isn't something you can happily, comfortably and healthily sustain for the rest of your life (clue: it's not), then why on earth would you even go there?
Does it impair your relationship with food? For example, do you feel guilty if you break the allotted feeding windows? If it does, hello disordered eating.
Does it mess up your ability to eat out with friends? Again, hello disordered eating.
The bottom line: IF is a stressor on the body. Any form of calorie deprivation is a stressor on the body. If you don’t have any other life stressors, and you have no history of disordered eating, and you REALLY want to try it... then I'd say a tentative "maybe".
If the purported benefits are the primary motivating factor for you, I would make sure that you've already covered your fundamentals before trying something as complicated and potentially restrictive as IF.
In other words, do you eat a balanced, varied diet of mostly whole, nutrient dense foods? Do you exercise regularly? Do you manage your stress levels? Do you get ample sleep and rest time? Chances are if you do these things, you’ll get many, if not all, of the benefits that IF claims.