Does black coffee break a fast?

Plain black coffee and tea contain negligible calories and are generally considered fine during a fast by most intermittent fasting practitioners, though they do have mild physiological effects.

Which fasting protocol is best for beginners?

16:8 is generally the easiest starting point, since it usually just means skipping breakfast, which most people adjust to within a week or two.

Will intermittent fasting slow my metabolism?

Short-term fasting windows of 16-24 hours don't meaningfully slow metabolism for most people. Prolonged, severe calorie restriction over weeks is a different matter.

Can I exercise while fasting?

Many people train fasted without issue, especially for lower-to-moderate intensity work, though very high-intensity or long-duration training may feel harder without fuel for some individuals.

Intermittent Fasting Timer — 16:8, 18:6, OMAD

Fasting Timer

Choose your protocol

Select a fasting schedule and when you started (or plan to start) fasting.

Fasting protocol

Fasting start time

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until eating window opens

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Eating window starts

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Eating window ends

Fast start Eating window

Fasting protocols

Which protocol should you choose?

16:8

Most sustainable for beginners

This is the most researched and widely practised protocol, typically achieved just by skipping breakfast and having your first meal around midday. It requires the least lifestyle disruption of the common protocols, which is likely why it has the best long-term adherence in practice.

18:6 / 20:4

For experienced fasters

These longer windows are typically adopted after a few weeks of comfort with 16:8, once appetite and hunger cues have adjusted. The shorter eating window makes it harder to hit higher calorie or protein targets, which is worth considering for anyone trying to build muscle rather than just lose fat.

OMAD

One meal a day — the extreme end

Eating all daily calories in a single sitting is the most restrictive common protocol. It can make hitting adequate protein and micronutrient targets genuinely difficult for some people, and isn't necessarily more effective for fat loss than more moderate windows — the main driver of results is still total calorie intake, not the specific fasting length.

What the research says

Benefits, limits, and who should be cautious

Research on intermittent fasting shows it can be an effective tool for weight management, largely because restricting the eating window often leads people to naturally eat fewer total calories, not because fasting has some unique metabolic magic. Studies comparing intermittent fasting to standard calorie restriction at matched calorie intake generally find similar weight loss outcomes — the main advantage of IF for many people is behavioural (simpler decision-making, fewer meals to plan) rather than a distinct physiological mechanism.

Intermittent fasting isn't appropriate for everyone. It's generally not recommended for pregnant or breastfeeding women, people with a history of disordered eating (the structured restriction can sometimes reinforce unhealthy patterns), people with diabetes on insulin or blood-sugar-lowering medication (fasting can cause dangerous blood sugar drops without medical supervision), and growing children and teenagers. If you have any underlying health condition, check with a doctor before starting an extended fasting protocol.

FAQ

Frequently asked questions about intermittent fasting

Plain black coffee and tea contain negligible calories (under 5 kcal) and are generally considered acceptable during a fast by most intermittent fasting practitioners and researchers. They do have mild physiological effects (caffeine can suppress appetite and affect insulin sensitivity slightly), but they don't meaningfully break a fast in the way eating food does. Adding milk, cream, or sugar does introduce real calories, though.

16:8 is generally the easiest starting point, since it usually just means skipping breakfast and eating your first meal around noon — most people adjust to this within one to two weeks. Jumping straight to OMAD or 20:4 without building up gradually tends to be harder to sustain and increases the risk of overeating during the shorter eating window.

Short-term fasting windows of 16-24 hours don't meaningfully slow metabolism for most people — some research even suggests brief fasting can slightly increase norepinephrine and metabolic rate short-term. Prolonged, severe calorie restriction sustained over many weeks is a different matter and can lead to metabolic adaptation, but that's a function of the calorie deficit itself, not the fasting window specifically.

Many people train fasted without issue, especially for lower-to-moderate intensity work like walking, yoga, or light cardio. Very high-intensity or long-duration training may feel noticeably harder without fuel for some individuals, particularly early on before the body adapts. If performance suffers, scheduling harder sessions closer to or within your eating window is a reasonable adjustment.

Intermittent Fasting Timer

Choose your protocol

Which protocol should you choose?

Most sustainable for beginners

For experienced fasters

One meal a day — the extreme end

Benefits, limits, and who should be cautious

Frequently asked questions about intermittent fasting

Related tools

Calorie & Macro Calculator

Weight Loss Timeline Calculator

Intermittent Fasting Guide

Diet Comparison Guide