What Breaks a Fast? And What I Actually Drink

By Brian Hupp · October 11, 2026

The short answer is anything with calories. Water doesn't break a fast. Black coffee and plain tea are usually counted as fine. Pop with sugar in it does, and I drink it anyway.

I went from 520 pounds to 200 by changing when I ate (the whole story is in How I Lost 300 Pounds With Intermittent Fasting). I'm not a doctor and this isn't medical advice.

The rule most people use

Dr. Krista Varady is a nutrition professor who runs fasting studies. In an NIDDK interview she describes the fasting hours this way: "you fast with water or calorie-free beverages, like black coffee or tea."

So the only thing to ask about a drink is whether it has calories.

What doesn't break a fast

• Water, plain or sparkling
• Black coffee, with nothing in it
• Plain tea, with nothing in it

What does

• Pop with sugar, juice, sweet tea, and sports or energy drinks with sugar
• Coffee or tea once you add milk, cream, or sugar
• Protein shakes and smoothies
• Food, including a small snack

A splash of cream has fewer calories than a can of pop. It still has some, so by the rule the fast is over.

Diet pop and zero-calorie sweeteners

By the calorie rule these don't break a fast, because there are no calories in them. People argue about whether the sweet taste makes you hungrier or does something else, and I can't settle that for you. I don't like diet pop, so I can't tell you from my own experience either. If you drink one and the next few hours get harder, pay attention to that.

Medication comes first

Some medication has to be taken with food. Don't move it or skip it to protect a fasting window. Ask your doctor or pharmacist first. In the same interview, Dr. Varady says people with type 2 diabetes "must work closely with their doctors to adjust medications" before they fast.

What I actually drink

When I get up I drink a glass of water. Most days after that it's just water and Mountain Dew. I'll drink any flavor of pop, but that's the one I pick. There's no limit and no pattern to it. I drink it when I want it.

I don't like coffee. I like tea. A few mornings a week I have a protein shake or a smoothie, nothing special.

Then I have one good-sized meal, somewhere between 5 and 10 at night. Other than the shake, the pop is the only thing I have outside my eating window.

Check that against the lists above. The shake breaks a fast, and so does the pop. By the strict definition, most of my days are not a clean fast.

Why I think it worked anyway

I can't prove why, but I can tell you what changed. I ate a lot less often, and over time my meals got smaller without me planning it.

That lines up with what Dr. Varady says about people who eat inside a 6 to 8 hour window: "they naturally reduce their energy intake." I was eating less, with or without the pop.

That doesn't make the pop okay. The CDC says frequently drinking sugary drinks is associated with weight gain and type 2 diabetes, among other things. It's the only habit I still have from when I was obese. It's bad, I still need to quit, and I'd lose even more if I did.

If you already broke it today

Then your fast ended early today, and nothing else happened. The days before it still count. Start again at your next one.

I have been breaking this rule the entire time, and one can of pop doesn't mean you failed.

Before you change anything

Fasting isn't right for everyone, and I don't want to push it on anybody. If you have a health condition, take medication, are pregnant, or have a history of disordered eating, talk to your doctor before you change how you eat. Before You Try Intermittent Fasting has questions worth bringing to that appointment.

If you want to try

The free Fasting Tracker runs in your browser and keeps your log on your own device. If you don't know which hours to start with, 12:12, 14:10, and 16:8: What Do Fasting Windows Actually Mean? explains the numbers, and the free Fasting Readiness Quiz is an educational tool that helps you think about where to begin. It can't tell you whether fasting is safe for you.

If you want more than that, Finding Your Window is my $9.99 PDF guide. It covers five fasting windows, including drinks during the fasting hours, and has tracking logs.

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