“I’m doing Intermittent Fasting. What can I eat and drink during my fast?”
This is a question we hear, literally, every single day.
Well, either that or, maybe a little more commonly, “Can I eat/drink [insert food/drink] during my fast?”
Unfortunately, the answer isn’t “yes” or “no”, since it’s a little more complicated than that. Like with most things, the answer is “it depends”.
“Why does everything have to be so complicated, dammit?!”
Well, because life sucks and things are almost never black or white.
By the way, this is going to be a preachy-ranty kind of post, so keep that in mind.
What is Intermittent Fasting?
Before we talk about what you can eat during a fast, let’s first briefly explain what intermittent fasting is.
Simply put, intermittent fasting is, essentially, an eating pattern which involves alternating periods of fasting and periods of feeding.
So, for example, you may set your fasting period to be from 10 pm on one day until 4 pm on the following day. This gives you 18 hours of fasting and an eating window of 6 hours (from 4 pm until 10 pm every day).
This is known as the 18:6 protocol among those practicing intermittent fasting.
Other protocols are 14:10 (fasting for 14 hours), 16:8 (fasting for 16 hours), 20:4 (fasting for 20 hours) and so on.
There are also variations like 5:2, where you would fast for only 2 days per week and eat normally on the other 5 days, or Alternate Day Fasting (ADF) where you would fast on one day, eat on the next day, fast again on the 3rd day, eat on the 4th day and so on. For these two variations, you would usually eat a little (around 500 calories) on the fasting days rather than fast completely.
Which leads us to our next question.
What exactly is fasting?
According to the Merriam-Webster Dictionary, to fast can mean one of two things:
- to abstain from food
- to eat sparingly or abstain from some foods
As you can understand, since fasting can, technically, mean both completely abstaining from food AND eating a little/not eating some foods, we’re in a bit of a pickle.
Remember when we said at the start of this article that things are almost never black or white and that the answer is, usually, “it depends”? Well, this is partly why.
Hold your horses, though, because this is going to get a little more complicated.
Why would someone fast in the first place?
The motives behind why people fast are also something important to consider when trying to decide what you can eat and drink during a fast.
So why do people fast?
Well, different people fast for different reasons, the most common ones being:
- to lose weight
- to improve their health
- for religious reasons
- to test their “mental toughness”
What you can eat and drink during a fast
Okay, so let’s consider the reasons we listed above for why people fast and try to figure what you can eat and drink during your fast for each of these.
1. Fasting for weight loss
Unfortunately, many supposed “experts” make extraordinary claims about how intermittent fasting works for weight loss which are not supported by scientific evidence.
The claims made are usually about how fasting lowers insulin and/or increases ketogenesis, which results in increased fat burning and, consequently, weight loss.
With the above in mind, it would make sense that eating or drinking anything which raises insulin or disrupts ketogenesis is, inherently, not allowed. It also means that having dietary fat is not a problem, since fat neither raises insulin nor does it disrupt ketogenesis.
In short, this is flawed thinking, as the carbohydrate insulin model of obesity has been debunked several times in scientific research, such as in this metabolic ward study, in this metabolic ward study and in this meta analysis.
This is, of course, why low carbohydrate diets and ketogenic diets don’t seem to work better for fat loss when caloric intake and protein intake are controlled for.
As we’ve talked about before, fat loss is the result of a sustained imbalance between energy intake and output. Simply put, to lose fat we have to take in fewer calories than we expend consistently over time.
This is indisputable and supported by every well-controlled study in the history of ever.
And this is, essentially, how intermittent fasting (and every other diet approach) works – by helping you eat less, overall.
So where does this leave us with regards to what you can eat and drink during your fast?
Well, in reality, you can technically eat and drink anything you want at any time of the day, provided that you are maintaining a caloric deficit. Eating throughout the day, of course, means that you won’t be doing intermittent fasting. And, yes, this means that you don’t HAVE TO do intermittent fasting if it isn’t practical for you and if it doesn’t help you adhere to your diet.
Remember that intermittent fasting is merely a meal timing tool which is supposed to help you control your caloric intake.
Take home point:
If your primary goal is to lose weight, the answer to the question “Can I eat/drink [whatever] during my fast?” is “You can, technically, do whatever you want, as long as you are maintaining a caloric deficit consistently over time. However, if you are consuming foods/drinks with calories you wouldn’t be fasting”.
2. Fasting for better health
Next on our list is fasting for better health.
“Okay, so I don’t, technically, have to fast to lose weight, but doesn’t fasting have health benefits?”
Well, kind of but not really – at least not that we know of yet.
You see, although it has been claimed multiple times that fasting can improve health and increase longevity, the research showing these benefits is limited to:
- animal studies (which 99.9% of the time don’t translate to humans in drug/nutrition/supplementation research)
- in vitro studies (i.e. in a test tube)
- mechanistic studies (i.e. studies discussing how one thing might affect another, but not actually trying it and seeing it happen in real life)
- studies that don’t control for caloric intake (caloric restriction and weight loss have been shown to have a multitude of health benefits in countless of studies)
In short, what we currently know from human research is that there MAY be health and longevity benefits to fasting without caloric restriction, but that there is, currently, no strong evidence to support this.
“But x researcher/doctor disagrees with you”.
Well, power to them for being able to sleep at night knowing full well that their professional opinion is counteracted by mountains of scientific evidence.
“But this article/study says that fasting has health benefits”.
Okay, before you rush to any conclusions, investigate further!
Don’t just accept what the news website reports or what the abstract of a study says as facts just because they tell you what you want to hear. More often than not, claims are, at best, exaggerated by news websites, while study abstracts usually don’t tell the full story.
Remember to check the four points above and that the study referenced is not in animals, is not in vitro, is not mechanistic in nature, and that it controls for energy intake.
If you find a study that ticks the four points above and that reports health benefits in humans, please share it in the comments section below or email it to us. We are ALWAYS open to new research and willing to change our professional opinion in the light of new scientific evidence.
Take home point:
Fasting MAY have some health benefits, but there is no strong scientific evidence to support this yet, so don’t stress about x food/drink breaking your fast or not. If you want to improve your health, make sure that, above all, you are:
- maintaining a healthy weight
- eating a diet that is based on plants, lean proteins and healthy fats
- exercising regularly
- not smoking
- not drinking excessively
- not stressing
- maintaining healthy social relationships
3 & 4. Fasting for religious reasons and to test mental toughness
Fasting for these reasons is more of a personal matter and beyond the scope of this article.
If your religion says that you have to completely abstain from foods for so many hours or from some foods for so many days, it’s entirely up to you to decide whether you want to do it or not.
The same applies to fasting for mental toughness. If you want to test your limits and see how long you can fast for, it’s your decision to make.
Just bear in mind that prolonged fasts can be dangerous and should, preferably, be done under the close supervision of a licenced health professional.
Conclusions and recommendations
So what can we conclude from the above?
Well, based on the weight of the scientific evidence, unless you are fasting for religious reasons or for other personal reasons, it doesn’t really matter if you even fast at all in the first place.
This makes the questions of “What can I have during my fast?” and “Can I have [x food/drink] during my fast?” pretty much pointless to begin with.
Honestly, our best recommendation is to just not worry about it.
If you instist on wanting a specific recommendation, here’s one: avoid foods and drinks that contain calories during your fast.
Your response will, of course, be: “But I heard that it’s OK to have under x number of calories during my fast”.
Well, whatever. It depends on your definition of what a fast actually is in the first place.
Again, it’s best to just not worry about it.
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