Coffee and Intermittent Fasting for Fast Caffeine Metabolizers

Coffee and Intermittent Fasting for Fast Caffeine Metabolizers

Intermittent fasting, for the uninitiated, is where you alternate between a period of fasting and a period of feeding. The feeding window is usually compressed in to 8 hours or less. Other variations include a full 24 hour fast once a week. Read the Ultimate Guide to Intermittent Fasting here.

I use intermittent fasting almost every day; in an unstructured way. I get up, head to the coffee shop and work for the first few hours of the day. I don’t follow any specific eating window, I just eat my first meal when I am hungry or my concentration starts to wane. During the fasting period I will drink coffee and water. My first meal is typically somewhere between 12 and 2pm. If I’m travelling most of the day or I’m hungover I might not eat my first meal until the evening.

That *may* be a pint of coffee

That *may* be a pint of coffee

Benefits of intermittent fasting

I believe that fasting has many benefits, I’m not going to talk about the somewhat contradictory research on the actual health benefits, but rather the practical benefits for someone who wants to be productive and in great shape.

For me personally, there are two main practical benefits.


Coffee and Intermittent Fasting


Focus, productivity & ease

I like to get up, drink a coffee and start working. Sometimes I will read first while having my coffee, sometime I will jump straight on the computer. Either way, I won’t be bothered about eating.

I’m naturally a night owl and generally do my best work from 6-10pm; this is when I feel most focused and in the zone. However, when I get up and just have coffee, I can get straight in to work and also get a highly productive 3-4 hours in the morning.

If I get up and eat first thing, I find that it distracts me. The longer I am up without starting to do something useful, the more I procrastinate. Once I go down that route, it can be a hard train to get off.

The way that I start the day – and I think this applies to most people – sets the tone for how it continues. Managing your morning routine and what you spend the first hour of the day doing is a huge productivity hack.

Beyond that, eating first thing tends to make me sluggish. I don’t remember if that was always the case, or something that has developed because my body is now not used to eating first thing. Digesting food is actually pretty taxing on the body and it requires significant energy. Energy that could otherwise be directed to the brain and achieving something.


Effortless calorie and food timing control

I like to eat big meals and when I have started eating, I tend to be hungry all of the time. Before I start eating though, I’m not really hungry and content with a cup of coffee for a good few hours.

This makes intermittent fasting a very easy way for me to either:

  • control total caloric intake without being hungry and miserable all the time
  • eat the majority of my calories around my workout

Depending on what my goals are, I may or may not eat before training, which I typically do around mid afternoon. This is when I feel my best – most with it mentally and physically for working out.

Intermittent fasting really is a practical choice for me. However there is something that I have noticed, when I fast, that is a definite consideration for those who want to give it a go…


Coffee and intermittent fasting for fast caffeine metabolizers

I’m a fast caffeine metabolizer. That means caffeine hits me quickly and then clears my system quickly.

You can do tests to see the efficiency of your caffeine metabolism*, which I did a few years ago, but you probably have a good idea anyway. Do you easily get buzzed? Can you drink caffeine late in the day and still sleep? You’re a fast metabolizer.

* Mine was part of my genetic profiling from 23 and Me.

caffeine metabolism

If coffee was going to give me a heart attack, I’d be long gone by now.


Here is my observation, and I haven’t seen anyone else talk about this:

As a fast caffeine metabolizer, if I have more than one coffee while fasting, I will get massively overstimulated. My mind will be all over the place and I will not be able to focus or sit still. I have to eat to bring my energy back to a sensible level.

Sometimes I will feel a bit sick. I’m not a high energy, bouncing around type of person – I’m the polar opposite of that. When I am over-caffeinated I really don’t have much of an outlet for it.

I have to eat to bring myself back to earth.

This doesn’t happen if I drink a lot of coffee after having had my first meal; and sometimes I drink A LOT of coffee.


How I avoid over-stimulation from caffeine when intermittent fasting

Something that I noticed when I was in London and would often drink Americano’s with pouring cream if I was at Starbucks/Costa/Cafe Nero, is that the cream seems to blunt the stimulatory effects.

This isn’t exactly a surprise, because technically I’m not fasting if I’m taking calories in through the cream in my coffee.

Interestingly though, having a coffee with milk, even a latte or something with a lot of milk, doesn’t have the same effect.

I don’t know whether it is the slow release of energy, or it blunts the speed of the caffeine response.

Drinking coffee with cream does allow me to drink multiple coffees and not have to eat – if I so desire.


Does this have any practical application?

I think it does. If you want to try intermittent fasting, but you’re a coffee addict like me, or feel that you need an energy boost.

Lean Gains; which is the predominant authority on intermittent fasting recommends drinking coffee as you fast and I agree – but if you metabolize caffeine quickly, you need to be careful to not over do it.

You can chill on the coffee and drink tea instead, but that wouldn’t satisfy me. I would rather take my coffee with heavy cream than drink tea at all.

If you find that you get overstimulated while fasting and drinking coffee, try adding heavy cream to your coffee.


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  • seanorama

    Phil – Great post.

    I’m a slow metabolizer but follow similar rules to you. If I have caffeine alone then I get jittery, lose focus, heart rate goes up and often get a bit of a sweat (no AC here in Europe).

    I still want the coffee for it’s other benefits or social reasons I’ll add L-Tyrosine which usually helps with the focus. Or to really chill out, I’ll use L-Theanine.

    Interestingly, I’m hearing more and more people saying they don’t do well or even recommend large amounts of caffeine while fasting (complete fasting, not with cream/fats). Heard it discussed by Robb Wolf and a few others.

  • Interesting Sean. I get hungry if I don’t have coffee. A complete fast feels like something I have to make concerted effort to do. Having coffee and no food is EASIER than eating

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