What breaks a fast and what doesn’t

Lets have a look at what breaks a fast and what doesn’t. What I really hope you get out of this post is that fasting can be a lot more flexible than people think!

There is a lot more that can be consumed on a fast that will still allow people to still achieve their weight loss goals, and make fasting a little bit more sustainable. 

Table of Contents

Different Types of Fasting

Dry Fasting

This is the strictest form of fasting. Consume nothing at all – no food, not even water. This is the form of fasting done by Muslims from dusk till dawn during the month of Ramadan.
what breaks a fast

Water Fasting

Water Fasting is where you don’t eat anything but can consume water freely.

And if you’re a purist like all the people who commented on my ‘Can you drink coffee when fasting video’ then you’ll probably leave it at that and say that anything else breaks a fast.

I totally respect your viewpoint, and this is a completely valid way of looking at things.

Others will say if it has any calories in it then it will cause a metabolic response and will disrupt fasting. This is also a very valid way of thinking about things and for losing weight this is probably the optimum way of doing things. But it’s not the only way of doing things.

At the other end of the spectrum we have something that purists would probably say isn’t fasting at all, but can still be really effective!

The 5:2 diet

This has been really popular over the last few years. If you haven’t heard of it it basically works like this:

5 Days a week you eat exactly what you would normally eat.

The other two days a week you restrict yourself to eating just 500 calories for women and 600 calories for men throughout the whole day.

Now the only reason that there is any food allowed on the fast days at all is that Dr Michael Moseley didn’t think that people would accept a complete fast for 2 days a week.

But what is really important here is not whether this is truly fasting in the purest sense, but is it helping people achieve their weight loss goals, and the answer is a resounding yes.

So if you can still achieve your goals and eat 5-600 calories on a fast day then surely there must be a grey area.

The Metabolic Function of a Fast

Personally I like to think about fasting in a different way, not necessarily in terms of putting names on it, but in terms of how it supports your weight loss goals.

In order to work out whether something breaks a fast or not, we need to think about the metabolic function of a fast.

The goal is to get into and maintain a fasted state in your body, and in order to get the best results out of fasting, it’s good to STAY in this state as much as possible.

The Fasted State

The fasted state is characterised by

  1. Low Insulin Levels
  2. Raised Glucagon levels (insulins opposite number)
  3. Normal blood glucose levels (in non-diabetics)
  4. Increased fat burning and ketone production

Key Point – In the fasted state, you’re burning your own body fat for energy and of course, that’s what you want for weight loss.

So in order to work out whether something really breaks a fast, we need to know what impact it has on that fasting state.

Macronutrient Impact

All macronutrients (that is carbohydrates, proteins and fats) have an impact on insulin levels but to a greater or lesser degree.

Take a look at this graph.

We have time running across the bottom, and insulin levels up the side.

We can see that carbohydrates have a big impact on insulin levels.

Protein also has an impact on insulin levels, but much less than carbohydrates.

Fat on the other hand has a minimal impact on insulin levels, but interestingly not none.

Consuming any of these things will increase insulin levels to varying degrees.

They will also supply your body with energy which it will use preferentially rather than burning it’s own stored body fat.

But when we’re thinking about fasting for weight loss we need to consider the time it’s going to take for your body to deal with what you’ve just eaten, in order to get back to that same state of fat burning that you were in before.

And don’t worry if you’re not 100% clear on what I mean, I’m going to take you through some examples.

Do these food and drinks break a fast?

Green Tea

Now we’re talking. This is the jackpot. Green Tea is Amazing. This is something you really should consider drinking when fasting for weight loss.
It’s good for you on so many levels but importantly it’s got some good evidence that it increases the metabolic rate and increases fat burning.

Black Tea

Much the same as the first two, but who drinks black tea? It’s certainly not how we do things here in England. It needs some milk in it, and we’ll talk about milk shortly!

Herbal Teas

what breaks a fast

You used to know where you stood with herbal teas. They are pretty much free of any metabolic effect on the body. But herbal teas are getting a bit strange. People are trying to get clever and are putting all sorts of bits and bobs in there.

If it’s plain old herbal tea, you should be fine. If it looks a bit strange, check the label, but realistically it’s unlikely there will be anything in there that will significantly disrupt your fast.

Black Coffee

No fat, protein, no carbs. All good to go for fasting!

Artificial sweeteners

We are talking about…

  • Saccharin – Sweet’N Low
  • Sucralose – Splenda
  • Aspartame – which is the sweetener in most diet drinks
  • Stevia
  • Sugar Alcohols – e.g. Xylitol & Erythritol

I don’t want this to turn into a post about whether sweeteners are good for you or not. Personally I’m not a big fan of artificial sweeteners as whilst they don’t have the same effect on you as sugar, most of them are synthetic chemicals and I wouldn’t classify them as ‘real food’, which is one the core principles at Carb Dodging.

But this is about whether they break a fast or not

Do they increase blood glucose?

No, they don’t. Using these in your coffee, tea or drinking diet beverages won’t increase your blood glucose. What is less clear is what is the long term effect of consuming these sweeteners on blood glucose levels.

There are some studies that have found negative effects of sweetener consumption on gut bacteria, which appears in turn to have a negative impact on blood glucose control. However, most of these studies have been done in animals and we’re not sure if this translates to humans or not.

Do they affect insulin levels?

Generally not, but Sucralose (Splenda) and Saccharin (Sweet’N Low) show mixed results with some studies saying they do. Limited studies are available.

So do sweeteners break a fast?

In a word… No…

What about Coffee with Cream?

A small amount of cream is going to provide your body with a small amount of fat and a very, very small amount of carbohydrate.

That fat in the cream fat will raise your blood insulin a tiny amount as will the small amount of carbohydrate but the effect on your fast is going to be minimal and you’ll quickly get back where you started.

Pumpkin Spice Bullet Proof Coffee

The 50 calories from 1 tablespoon of cream is 50 calories your body doesn’t have to find from your own fat stores, so it will slow down your weight loss very slightly.

So yes, cream technically breaks a fast, but in practical terms, it’s unlikely to cause you much of a problem if you’re only having a small amount. However if you have 4 teaspoons of cream in every cup of coffee and 5 cups of coffee during the day you might find your results are a little less pleasing.

Bulletproof Coffee

So what is in bulletproof coffee? Well there are lots of different recipes but the classic version contains

  • Coffee
  • Butter / Ghee
  • Medium Chain Triglyceride Oil

There are about 9x more calories in a mug of bulletproof coffee than there is in a coffee with a tablespoon of cream in it but it’s pretty much all fat, and the carbohydrate content is negligible. The effect on your insulin levels and glucose levels will be minimal and you’re staying very close to that fasted state.

I want to give you 2 scenarios as examples of where bulletproof coffee might be used when fasting, with varying impact on the overall fast.


If you’re doing 16:8 fasting or 1 meal a day fasting, and you have a bulletproof coffee in the morning, metabolically you’re still going to remain in the fasted state for the most part, but your body has an extra 500 calories of fat on board that it can use for energy that it didn’t have before.

Whilst I’m not trying to reduce everything down to a simple formula of calories in vs calories out (it’s not that simple I’m afraid), clearly this isn’t going to be as good for your weight loss as skipping that meal altogether.

But if just getting started with a ketogenic diet, this can be a useful tool to transition to 16:8 or one meal a day fasting.

This is exactly how I started out on my weight loss journey back in 2016 and I was still able to lose loads of weight even with almost daily bulletproof coffees in those first few months.

Longer Fasting

Now think about if you’re doing alternate day fasting, and on your fast day, you decide to have a bulletproof coffee as a pick me up.

The MCT oil is readily turned into ketones in your liver. This can have an energy-boosting effect and can be really handy to have before a workout for example. But it is still energy your body will use before burning its own fat.

You’re still only consuming 500 calories in the whole day, with a minimal effect on the hormone levels needed to maintain that fasted state.

Yes, technically to the letter of the law you’re ‘breaking your fast’ but you’re still getting almost all of the benefits of that longer fast!

Using pretty much pure fat in this way is commonly called fat fasting. People also use fat bombs, which are snacks which are pretty much pure fat, with a similar effect.

If you’re trying to do longer fasts for the first time and you’re struggling a bit, rather than breaking your fast early with a full meal, it’s an option to try fat fasting.

Tea & Coffee with milk

Milk is kinda at the other end of the dairy scale to cream and butter.

It’s got a lot more of the milk sugar lactose in it and not so much fat.

Lactose is two sugar molecules stuck together. Glucose & Galactose

When you drink milk the lactose is broken down in the body and the galactose is turned into glucose so I always find it helps to think of the sugar in milk as just glucose.

So milk is definitely going to raise your blood glucose levels which will cause your insulin levels to rise and distribute the fasting state much more than the same number of calories of cream or butter would.

But what if you only have just a small amount?

Yes, the quantity of milk here is really important. If you’re having just a splash of milk in your tea or coffee then you’re ingesting only a very small amount of glucose which will cause a minimal blip which your body will quickly deal with and in theory you should be back to the fasted state in no time at all!

Compare that to a Latte, which is made almost entirely from milk. Just using a grande (medium) latte from Starbucks as a reference… It has about the same carbohydrate content as 4-5 teaspoons of sugar.

That’s clearly going to have a pretty significant impact on your fasting state for some time to come.

What about Lactose-Free Milk?

So I had a few people comment on my video about coffee, if lactose is the problem in milk then surely I can just drink lactose-free milk?

I like your thinking here people! I like your thinking!

They make lactose free milk for people who can’t break down the lactose themselves. Basically, they add an enzyme that breaks it down so you don’t have to do it yourself.

This simple bit of biochemical trickery solves the problem for people who can’t digest lactose itself, however, it doesn’t actually change the carbohydrate content of the milk in a meaningful way! In fact, it actually makes the sugars in the milk slightly simpler, and it is noticeably sweeter than normal milk.

So sorry, lactose free milk latte’s are not the solution.

Plant-Based Milks such as Almond Milk

Who knew you could milk an almond eh?

Yes, there are some options here which in terms of carbohydrate content are better than milk, if you enjoy the flavour of these.

These figures are the amount of carbohydrate in a regular-sized 8oz / 225ml glass.

Whole Milk 12 grams

Almond milk 1 gram

Coconut Milk 2g

Soy Milk 4g

Rice Milk 22 g

Always be sure to avoid the sweetened versions of these plant-based milks else those figures will be VERY different!

Drinks with sugar or honey

or any of the hundreds of things that sugar can be called will break your fast.

Refined carbohydrate

Will rapidly raise your blood sugar levels and insulin levels which will

  • Stop fat burning
  • Start rebuilding glycogen stores

Depending on the amount and how well your body is able to process sugars it could take hours to get back into the fasted state.

Definitely avoid sugar in all its many forms and that includes fruit juice.

Apple Cider Vinegar

Is pretty in vogue at the moment, and with good reason. Technically, it has a few calories in it so it technically breaks a fast, but it has such a wonderful effect on the body in terms of improving insulin sensitivity it is absolutely fine to consume it when fasting for weight loss.

Bone broth

Is another very popular health drink because it is full of micronutrients which will have little or no impact on a true fast, however it also contains collagen which is a protein so technically it breaks your fast.

Having a single mug of good quality bone broth to support you through a longer fast is unlikely to have any significant impact on the weight loss impacts of a fast however.


Protein Shakes

There is so much protein here, I’d generally think of it as a liquid meal and therefore it really does break a fast. Whey protein has a significant impact on insulin levels and protein powders tend to be mixed with all sorts of other stuff. Definitely one to avoid when fasting.
Best Protein Sources


BCAA stands for Branched Chain Amino Acids. They’re like a stripped-down version of protein shakes, which only contain the stuff that is needed for building muscles. So it’s a lot ‘cleaner’ than a protein shake in that respect.

However one of the amino acids Leucine is one of the amino acids in there which is well known to provoke an insulin response. So yes, technically BCAA breaks a fast.

Nevertheless, lots of people take BCAA’s during exercise whilst on fasting protocols as it may support the healing of your muscle tissues after exercise.

Exogenous Ketones

Clearly, these are metabolically active and have an impact on your own ketone production, so yes they technically break a fast.

I think of them as similar to MCT oil in the effect they have. Really useful on occasions as an energy boost, particularly before a workout but it’s energy your body isn’t going to be finding from its own fat stores.


Creatine is another really popular supplement which has absolutely no effect on fasting so is absolutely fine to take.

Omega 3 Fish Oil

Fish oil… yes it would technically be like any fat. It’s likely the dose you’ll be taking is so small as to not have any particular lasting impact on your fasting. You might not want to take it on an empty stomach however!

That goes for other supplements too. Magnesium makes me vomit really badly.

I can’t think of any other supplements that would break a fast. Besides, the doses that you’re taking them in are so small that it’s unlikely any of them will do anything that will significantly disrupt your weight loss efforts.

Other Considerations


This might seem like a crazy question but a lot of vaping oils are sweet, so it is a question I get asked from time to time.

As far as I can tell none of that should get into your bloodstream in a form that could raise your blood glucose or provoke an insulin response. Neither does nicotine.


If you’re smoking, and concerned about the effects that it might have on your fasting, you strongly need to reconsider your priorities. I can’t say for sure the impact that smoking has on fasting as there are so many chemicals in there, it’s difficult to know. It doesn’t appear to make any meaningful difference to ketone levels.

Speaking as someone who used to smoke, I get it! Giving up is difficult but it’s not impossible, but it’s the single biggest change you need to make for the sake of your health if you are a smoker!


I think that’s about all the common questions I get asked about what breaks a fast.

I hope this has given you a bit more of an idea about how flexible you can be with fasting.

So yes, you’re probably going to get the best results if you take a purist approach to fasting, but when it comes to living your life and integrating fasting to achieve your goals, it’s ok to experiment a little bit without massively decreasing your results.