Fasting has become a popular tool for people looking to improve weight management and metabolic health. One of the most common questions is what you can safely drink while you’re not eating. The short answer is simple: choose low‑ or no‑calorie beverages.

Why Water and Zero‑Calorie Drinks Won’t Break Your Fast

Water does not contain calories, so it does not trigger the body’s nutrient‑sensing pathways that signal the end of a fast. During a fast, glycogen stores are depleted and the body excretes more sodium, which can lead to fluid loss, especially in the first 24‑48 hours. Replenishing fluids and electrolytes helps prevent dehydration, headaches, and fatigue.

Common Low‑Calorie Choices

• Plain water – the best and most essential drink.
• Unsweetened electrolyte water – useful on longer fasts when sodium loss is higher; just check the label for added sugars.
• Black coffee – typically under 5 calories per cup and rich in antioxidants; avoid creamers and flavored syrups.
• Plain tea – black, green, or herbal teas contain about 2 calories per cup and provide additional antioxidants.
• Sparkling water – carbonated water without sweeteners is a refreshing alternative.
• Zero‑calorie diet soda – sweetened with stevia or monk fruit; some research suggests artificial sweeteners may affect gut microbiota, but evidence in humans is mixed.

When Small Calories May Not Matter

Technically, any calories end a strict zero‑calorie fast. However, for most practical goals—such as modest weight loss or improved insulin sensitivity—tiny amounts of calories (a splash of cream, a few grams of collagen, or a low‑calorie broth) are unlikely to derail the overall benefits. The body’s response depends on the type and amount of calories consumed; carbohydrates raise insulin the most, while fat has the smallest effect.

What to Avoid If You Want a Strict Fast

Any beverage that contains measurable calories—such as regular soda, fruit juices, milk, or bone broth—will break a zero‑calorie fast because they activate nutrient‑sensing pathways and raise insulin. Protein‑rich drinks, especially those high in leucine or arginine, can also stimulate mTOR signaling, which shifts the body toward growth processes rather than the fasting state.

Practical Tips for Staying Hydrated

Listen to your body’s thirst signals and drink to satisfaction. There is no universal daily water target for fasting; needs vary based on activity level, climate, and individual physiology. If you’re fasting for more than a day, consider adding a pinch of salt or an electrolyte supplement to your water to replace the sodium lost through urine.

Bottom Line

If you want to maintain the metabolic benefits of fasting, stick to water, unsweetened tea, black coffee, sparkling water, and zero‑calorie electrolyte drinks. Small amounts of calories are unlikely to cause major setbacks, but for a strict fast, keep those calories out of your cup.

Original reporting: KRDO (Colorado Springs metro) — read the source article.