Fasting: 5 questions answered

I posted recently about intermittent fasting for karate practitioners. If you don't want to read it, I'll summarize: I believe fasting (going for periods from 16 hours and up without eating anything, though probably no more than 72 hours at a time) is a great way to control bodyfat, insulin sensitivity, and might provide some other intriguing health benefits with very few risks. It might also improve sports performance (by facilitating fat adaption) and muscle mass and strength (which is counterintuitive).

I'm on a few fasting related message boards and a few things come up repeatedly as people ask about IF. Here's a summary of answers:

1. Can I fast if I'm diabetic?
MAYBE but NOT UNSUPERVISED. I can't stress this enough.
If your'e on diabetes medications you can't just suddenly decide to skip meals or entire days of meals without changing your meds. Diabetes medications are designed to reduce blood sugar. The dose you're on should be well calibrated to your current body and diet. If you suddenly change your diet, those meds might not work anymore. You can't expect your blood sugar to end up in a good place if you suddenly stop eating any more than you'd expect it to stay low if you suddenly started eating a sheet cake with every meal.
The real danger is that if you started eating an entire sheet cake with every meal your sugar would go UP, and that's less acutely dangerous (i.e. having very high blood sugar this very minute won't kill you this very minute, even if it's doing long term damage). Having very low blood sugar actually can make you pass out or die.
So fasting might be a great and healthy thing to do if you're diabetic, BUT you have to carefully monitor your blood glucose and adjust your medications to match as you do it. DO NOT try this alone.

2. Will consuming break the fast?
I see this question constantly - "I like to have a hard boiled egg in the morning, does that break the fast?" "Will coffee with cream break the fast?" And so on.
The answer to this is a little layered.
First of all, it isn't completely proven that fasting provides benefits beyond the caloric restriction that comes with it. It's not conclusive that a 20/4 eating plan that gives you 2000 kCal/day is better in any way than a spread out plan where you consume the exact same quantity of food over the whole day.
But I strongly suspect that the 20/4 is better. If you disagree, then you shouldn't care about breaking the fast because you don't think the fast is doing anything useful.
We still don't know exactly what it is about fasting that provides these additional benefits. So we can't say with real certainty what 'breaks the fast' because we don't know exactly what 'the fast' means from a physiological perspective.
Water probably doesn't 'break the fast' because nobody really thinks that dehydration has anything to do with the benefits of fasting. So plain water definitely doesn't break the fast.
Non-caloric, no-taste nutrients probably don't break the fast. I mean things like caffeine pills, vitamins and minerals, and electrolytes. I have never seen an idea for 'how fasts work' that would be broken by taking some electrolytes or Vitamin D, for example.
Small or large amounts of dietary fat by itself almost definitely doesn't break the fast. So you can add cream to your black coffee. Why am I so sure of this? Because while fasting your body can dump tons of fat into your blood, from your own bodyfat, anytime. And it does. If having fat in your blood 'broke the fast' nobody would ever be able to fast, at least not while alive.

Non-caloric non-sweetener flavorings probably don't break the fast. Think flavored water type beverages that aren't sweet, or black coffee, or unsweetened tea. These things might impact insulin, which might 'break' the fast's benefits, but I doubt it. Future science might prove this wrong.

Non-caloric sweeteners are a really tough call. They might increase insulin, which might 'break the fast' in terms of halting the benefits of fasting. But if you take them regularly, that effect might go away, and in real terms it's terribly unclear how much insulin you'd need to release to have an important physiological effect. So... I'm not sure. If you are absolutely committed to fasting, play it safe and skip the diet sodas. If you just can't manage without them... I sympathize, but I honestly can't tell you how bad it is (and nobody else can, either).
Protein or carbohydrates in small amounts either don't break the fast or only set it back a little. What do I mean by 'small amount?' Imagine eating a single peanut. It's possible that could knock you out of a fasting state, but for how long? A few minutes?
The problem comes when people extend this logic to encompass larger portions of protein and carbohydrate foods. What if you ate a peanut every 2 minutes all day long? I bet that would negate the fast. Or the hard boiled egg I mentioned above (that was taken from a real question on a fasting support forum). Nobody can really answer how detrimental a single egg can be - does it negate an hours worth of fasting? Half an hour? Two hours? Nobody knows.
Foods with lots of protein and/or carbohydrates will definitely break the fast. That's literally what breakfast is.

3. I'm having . Is it okay to skip my fast or break it early?
Good grief, yes.

4. What about fasting and detoxification?
OMG please stop with the detox.
"Detox" as it's used in popular diet talk is meaningless. If anybody talks about a 'detox diet,' ask them to specify what toxins are being removed from your body and by what biological process.
If they answer (they won't), post it to comments and we can look into whether skipping a few meals can interfere with that process.
Any kind of caloric restriction can reduce inflammation, which can help with a whole host of chronic conditions. That doesn't mean you're 'removing toxins from your body.'

5. Can I exercise while fasting?
Yes, you can do any exercise while fasting that you could do while fed. Your performance will probably suffer, though, especially if you're combining fasting with a low carbohydrate approach (which is popular but not what I personally recommend). You will, in my experience, find that the more you exercise while fasted the easier it gets. Either way, it's not dangerous or harmful to try.


I'm not a fasting evangelist. I'm not an anything-evangelist. My goal is never to tell you the absolute best way to do anything, because I am never certain that I know the best way to do anything. I do try to honestly give you the best advice I can, distilled from the best advice popularly available today, based on the best scientific evidence and reasoning that we have available. New studies could turn up tomorrow that force us to rethink some of these ideas, and when I find out about them, I'll post it here.
Osu.