If you're eating one meal a day, you're fasting for roughly 23 hours at a stretch — and what you drink during those hours determines whether you feel sharp or spend the afternoon foggy, headachy, and counting minutes until dinner.
Here's the short answer: during an OMAD fast, stick to water, black coffee, unsweetened tea, and a zero-calorie, zero-sweetener electrolyte drink. Electrolytes are the piece most people miss, and they're usually the difference between a hard fast and an easy one.
Below is the full breakdown of what to drink, when, and why.
Why OMAD depletes electrolytes faster than shorter fasts
When you fast, your insulin levels drop. Lower insulin signals your kidneys to flush sodium — and water follows sodium out. Over a 16-hour fast, most people barely notice. Over a 23-hour OMAD window, repeated daily, the losses add up: sodium, potassium, and magnesium all trend downward, and you're only getting one meal a day to replace them.
That depletion is behind most of the classic fasting complaints:
- Headaches — often low sodium, not low calories
- Brain fog and trouble focusing — your brain is sensitive to sodium and hydration status
- Fatigue and lightheadedness, especially when standing up
- Muscle cramps — typically magnesium and potassium
- Hunger that's actually thirst or salt craving in disguise
Plain water alone can make this worse, not better. Drinking liters of water without electrolytes dilutes what sodium you have left. If you've ever felt worse on a fast despite drinking plenty of water, this is likely why.
What to drink during an OMAD fast
Water
Your baseline. Aim for roughly 2–3 liters across the day, adjusted for body size, climate, and activity. Sparkling water counts and can help blunt hunger.
Fasting electrolytes
A zero-calorie electrolyte drink is the single highest-leverage addition to an OMAD routine. Look for one with meaningful sodium (fasting-specific formulas typically contain 500–1,000 mg per serving — far more than sports drinks, which are built for people who are also eating), plus potassium and magnesium, and zero sugar and zero sweeteners so there's no insulin response and nothing to break your fast.
This is exactly what FASTRX was formulated for: fasting-specific electrolyte ratios with nothing that interrupts the fasted state. One can mid-morning and one mid-afternoon covers most people through a 23-hour window.
Black coffee
Fine during a fast, and the caffeine may modestly support fat oxidation and appetite control. Keep it black — no milk, cream, sugar, or flavored syrups. Note that caffeine is mildly diuretic, so coffee slightly increases your electrolyte needs.
Unsweetened tea
Green, black, herbal, oolong — all fair game as long as nothing is added. Green tea in particular is a popular appetite-management tool during long fasting windows.
What breaks an OMAD fast
Anything with calories breaks a fast in the strict sense. The common gray areas:
- Diet soda and artificial sweeteners: technically zero-calorie, but some people find sweet taste triggers cravings, and the research on sweeteners and insulin response is mixed. If your goal is a clean fast, skip them.
- Bone broth: contains calories and protein — it breaks a fast, though some people use it intentionally on harder days.
- MCT oil or butter in coffee: calories. Breaks the fast, even if it keeps you in ketosis.
- "A splash" of milk or cream: breaks a strict fast. Whether it matters depends on your goals — for autophagy-focused fasters, keep coffee black.
- Zero-calorie electrolytes without sweeteners: do not break a fast. This is why unsweetened formulas exist.
The key principle: front-load electrolytes before symptoms appear. By the time a fasting headache hits, you're already behind.
FAQ: fasting electrolytes and OMAD
Do electrolytes break a fast? No — as long as the drink contains zero calories and zero sugar. Sodium, potassium, and magnesium don't raise insulin or trigger a metabolic response that ends the fasted state.
How much sodium do I need on OMAD? Needs vary, but many experienced fasters target an additional 1,000–2,000 mg of sodium during a 23-hour fast, more if they're active or in hot weather. Start on the lower end and adjust based on how you feel.
Can I just add salt to water? You can, and it helps with sodium — but it doesn't cover potassium or magnesium, and most people find plain salt water hard to drink consistently. A formulated fasting electrolyte drink solves both problems.
Why do I get headaches on OMAD? The most common cause is sodium loss from lowered insulin, compounded by drinking plain water all day. Caffeine withdrawal (if you changed your coffee timing) is the runner-up.
Is OMAD safe for everyone? No. OMAD is an aggressive protocol. It's not appropriate for people who are pregnant, have a history of disordered eating, have diabetes or take blood-sugar or blood-pressure medication, or have other medical conditions — and anyone starting an extended fasting practice should talk with their doctor first.
The bottom line
OMAD success mostly comes down to what happens in the 23 hours you're not eating. Water keeps you hydrated, coffee and tea keep you functional, and fasting electrolytes keep you sharp — replacing the sodium, potassium, and magnesium a long daily fast steadily drains. Get the hydration right, and the one meal takes care of itself.
FASTRX is a zero-sugar, zero-sweetener electrolyte drink formulated for fasting. Nothing in this article is medical advice — talk to your healthcare provider before starting OMAD or any extended fasting protocol.
