What Else Can I Drink During Intermittent Fasting? (Complete Guide)

Water. Black coffee. Plain tea. Sparkling water. Those are your four safe options during a fasting window.

They have zero calories, they don't trigger insulin, and they won't pull your body out of fat-burning mode. A small squeeze of lemon, under 5 calories, is fine too. Anything with sugar, milk, cream, protein, or artificial sweeteners is off the table.

But knowing why certain drinks break your fast helps you make smarter calls when you're staring at a menu or reaching into the fridge at 7am. Here's everything you need to know.

Why Does It Matter What You Drink?

Intermittent fasting works because your body shifts from burning glucose to burning fat when it goes long enough without caloric input. Research confirms that the benefits, improved insulin sensitivity, better blood sugar control, reduced inflammation, and cellular repair, all depend on keeping insulin low during the fasting window.

Insulin is the key. When you eat or drink something that raises blood sugar, your pancreas releases insulin. Insulin signals your body to store energy, not burn it. That shuts down fat oxidation and pauses the cellular cleanup process called autophagy.

So the question isn't really "does this have calories?" It's "does this spike insulin?" Most of the time those are the same thing. But not always.

What Drinks Won't Break Intermittent Fasting?

These are safe during your fasting window:

• Still water. Zero calories, zero insulin response. Drink as much as you want.
• Sparkling water. Same as still water, as long as it has no added flavours, sweeteners, or juice. Plain carbonated water is fine.
• Black coffee. No milk, no sugar, no cream. Black coffee has roughly 2 calories per cup and doesn't meaningfully raise insulin. It also makes the fasting window easier by suppressing appetite.
• Plain green tea. Zero calories, and some evidence suggests it may support fat oxidation during fasting.
• Plain herbal tea. Chamomile, peppermint, ginger. No added honey, no sweeteners.
• Plain black tea. Same rules as coffee. No milk, no sugar.
• Electrolyte water. Only if it's genuinely zero calories and zero sweeteners. Many electrolyte products contain sugar or artificial sweeteners. Read the label.

Most people already drink one or two of these. The problem is the add-ons. A splash of oat milk in your morning coffee, a teaspoon of honey in your tea, those additions are enough to trigger an insulin response and technically end your fast.

What Breaks Your Fast?

Anything with calories breaks your fast. But a few specific things catch people off guard:

• Milk and cream in coffee. Even a small amount adds calories and protein, both of which stimulate insulin.
• Bulletproof coffee. Butter and MCT oil are calories. This breaks a strict fast, even though some people use it in modified fasting protocols.
• Fruit juice. High sugar, high insulin spike. Even "natural" juice breaks your fast immediately.
• Smoothies. Same issue. Blending fruit doesn't change its caloric content.
• Protein shakes. Protein is one of the strongest insulin triggers. Save these for your eating window.
• Diet sodas and artificially sweetened drinks. This one is debated. The evidence is mixed, but some research suggests artificial sweeteners can still provoke an insulin response in certain people. The safest approach is to avoid them during your fasting window.
• Flavoured sparkling water with sweeteners. Check the label. Many popular brands contain sweeteners that may affect insulin.
• Bone broth. Contains protein and calories. It breaks a strict fast, though some practitioners allow it in extended fasting protocols.

How to Lose 2kg in a Week With Intermittent Fasting

Losing 2kg in a week is possible, but most of it will be water weight and glycogen, not pure fat. That's not a bad thing, it's how the process starts, and it's real weight off the scale.

Research shows intermittent fasting produces spontaneous reductions in caloric intake of 20 to 30 percent, with weight loss typically ranging from 1 to 4 percent of body weight over several weeks. To push toward the higher end in a single week, stack a few things together:

1. Use a 16:8 or 18:6 protocol. Fast for 16 to 18 hours, eat within a 6 to 8 hour window. This is the most studied and most sustainable approach.
2. Stick strictly to zero-calorie drinks during your fast. Any caloric slip extends your eating window and reduces the metabolic benefit.
3. Eat whole foods in your eating window. Fasting doesn't give you a free pass to eat whatever you want. Lean protein, vegetables, and whole grains will keep you full and support fat loss.
4. Cut sodium and processed food. High sodium causes water retention. Dropping it for a week accelerates the initial weight drop.
5. Stay active. Even a 30-minute walk each day increases fat oxidation during the fasted state.

When I tried a strict 18:6 protocol with clean eating for a week, the first 2 to 3 days were the hardest. After that, hunger during the fasting window dropped significantly. Your body adapts faster than most people expect.

Is Intermittent Fasting Good If You Have High Cortisol?

This is where you need to be careful. Fasting is a physical stressor. It raises cortisol temporarily, that's part of how it triggers fat burning. For most people, that's fine. For people who already have chronically elevated cortisol, adding more stress can backfire.

High cortisol is associated with increased appetite, fat storage around the abdomen, poor sleep, and blood sugar dysregulation. If you're already dealing with those symptoms, aggressive fasting protocols can make them worse rather than better.

Clinical consensus suggests that people with high cortisol should approach intermittent fasting cautiously. A shorter fasting window (12 to 14 hours rather than 16 to 18) is a more appropriate starting point. Eating a protein-rich breakfast within an hour of waking is sometimes recommended for people with cortisol issues, as it helps stabilise the cortisol awakening response.

If you have diagnosed adrenal fatigue or HPA axis dysfunction, speak with a practitioner before starting any fasting protocol. The metabolic benefits of fasting are real, but they're not worth triggering a cortisol spiral that disrupts sleep and increases fat storage.

Does Intermittent Fasting Lower PSA Levels?

PSA (prostate-specific antigen) is a protein produced by the prostate gland. Elevated PSA can indicate prostate inflammation, benign prostatic hyperplasia, or prostate cancer. If fasting reduces inflammation, could it lower PSA?

The direct evidence is limited. There are no large randomised controlled trials specifically testing intermittent fasting's effect on PSA. What we do know is that intermittent fasting reduces systemic inflammation markers and improves metabolic health, and chronic inflammation is one driver of elevated PSA.

Some observational data and smaller studies suggest that caloric restriction and improved insulin sensitivity, both outcomes of consistent intermittent fasting, are associated with lower PSA levels and reduced prostate cancer risk. But this isn't the same as saying fasting directly lowers PSA.

If you're monitoring PSA levels, intermittent fasting is unlikely to hurt and may help as part of a broader anti-inflammatory lifestyle. It should not replace medical monitoring or treatment. Talk to your doctor about what's driving your PSA before making protocol decisions based on it.

Three Things Most Articles Get Wrong About Fasting Drinks

1. Artificial sweeteners are not a safe swap. Most fasting guides say diet drinks are fine because they have zero calories. The reality is more complicated. Some research suggests certain artificial sweeteners can trigger cephalic phase insulin release, your body anticipates sugar and releases insulin in response to the sweet taste alone. The effect varies between individuals, but if your fasting results have stalled, cutting artificial sweeteners is worth trying.

2. Electrolytes matter more than most people think. Extended fasting depletes sodium, potassium, and magnesium. That's what causes the headaches, fatigue, and brain fog that people blame on "detox." Plain water doesn't replace electrolytes. Adding a pinch of quality salt to your water, or using a zero-calorie electrolyte supplement, can make a significant difference in how you feel during a fast, especially in the first week.

3. Coffee timing affects cortisol. Most people drink coffee first thing in the morning. But cortisol naturally peaks within 30 to 45 minutes of waking. Drinking coffee during that window can amplify the cortisol spike and lead to an energy crash later. Waiting 90 minutes after waking before your first coffee, still black, still fasted, tends to produce more stable energy through the morning. When I tried this shift, the afternoon slump I'd been blaming on fasting mostly disappeared.

Frequently Asked Questions

Can I drink lemon water while fasting?

Yes, in small amounts. A squeeze of lemon in water adds roughly 2 to 5 calories and a minimal amount of natural sugar. That's unlikely to break your fast or trigger a meaningful insulin response. A full glass of lemon juice is a different story, that's enough sugar and calories to end your fast.

Does black coffee break a fast?

No. Black coffee has around 2 calories per cup and doesn't produce a significant insulin response. It's one of the most commonly used fasting-window drinks across clinical intermittent fasting protocols.

Can I drink green tea while fasting?

Yes. Plain green tea has negligible calories and doesn't break a fast. Some evidence suggests it may support fat oxidation, making it a useful addition to a fasting protocol.

What about apple cider vinegar?

A small amount of apple cider vinegar diluted in water, one to two teaspoons, is generally considered fasting-safe. It has minimal calories and some research suggests it may support blood sugar regulation. Avoid ACV drinks with added honey or juice.

Can I drink sparkling water while fasting?

Yes, as long as it's plain carbonated water with no added sweeteners, flavours, or juice. Check the label, many flavoured sparkling waters contain sweeteners that may affect your fast.

Will drinking more water help me lose weight faster during fasting?

Staying well hydrated supports every metabolic process, including fat oxidation. It also reduces hunger signals that are sometimes mistaken for thirst. Drinking adequate water during your fasting window won't directly accelerate fat loss, but dehydration will slow it down and make the fast harder to sustain. For personalized guidance on fasting protocols, Paramount Health offers evidence-based support.

Is it okay to add salt to water while fasting?

Yes. A small pinch of sodium in water helps maintain electrolyte balance during extended fasts. This is especially useful if you're doing fasts longer than 16 hours or if you're exercising while fasted.

What to Do Now

Start with this: audit what you're currently drinking during your fasting window. Write it down for one day. You may find a habit, a splash of milk, a flavoured sparkling water, a sweetened tea, that's been quietly ending your fast every morning without you realising it.

Then make one swap. Replace whatever is breaking your fast with plain black coffee, plain tea, or water. Give it two weeks before judging the results.

If you want support building a fasting protocol that fits your health goals, including managing cortisol, improving metabolic markers, or working around specific health conditions, the team at Paramount Health can help you build something that actually works for your body.

About the author

Armstrong Lazenby

BSc (Human Nutrition) registered nutritionist. Bachelor of Science (Exercise Science major) Master of Sports Medicine.

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