Why You Should Drink Water on an Empty Stomach Immediately After Waking Up

Here’s a breakdown of the claimed benefits and what the science actually says:

Most Common Claims and the Science Behind Them

1. “Rehydrates the Body After a Night’s Sleep”

   • The Claim: You wake up in a dehydrated state because you haven’t had water for 6-8 hours.

   • The Science: This is largely true and beneficial. Mild dehydration is common upon waking. Drinking water first thing helps rehydrate your cells, kickstart circulation, and support basic bodily functions. It’s a simple and effective way to start the day hydrated.

2. “Boosts Metabolism”

   • The Claim: It increases your metabolic rate, helping with weight loss.

   • The Science: The evidence is moderate and temporary. Some studies show that drinking about 500ml (17 oz) of water can increase metabolic rate by 24-30% for about an hour (a phenomenon called water-induced thermogenesis). However, the total calorie burn is modest (about 20-30 calories), and the effect isn’t exclusive to an empty stomach—it happens anytime you drink a large glass of water.

3. “Flushes Toxins”

   • The Claim: It stimulates your kidneys and digestive system to “flush out toxins.”

   • The Science: This is overstated. Your liver and kidneys are your body’s 24/7 detoxification system, and they work best when you’re consistently hydrated throughout the day. Drinking water in the morning supports their natural, ongoing function; it doesn’t trigger a special “detox flush.” The increased urine output is simply a sign of proper hydration.

4. “Improves Digestion and Prevents Constipation”

   • The Claim: It stimulates peristalsis (gut contractions) and prepares the digestive tract for food.

   • The Science: This is plausible and helpful for some. For people prone to constipation, warm water on an empty stomach can stimulate a gastrocolic reflex, potentially encouraging a bowel movement. It also helps soften stool.

5. “Enhances Mental Alertness”

   • The Claim: Dehydration can cause brain fog, so rehydrating improves focus.

   • The Science: This is well-supported. Even mild dehydration (1-2% of body weight) can impair mood, concentration, and short-term memory. Drinking water upon waking can quickly reverse this morning dehydration.

Potential Downsides (For Some People)

• Feeling Too Full: For some, drinking a large volume of water right away can dampen morning appetite.

• GERD/Acid Reflux: Drinking a lot of water on a very empty stomach might temporarily dilute stomach acid, which could, for some individuals, affect early digestion or trigger reflux.

• Hyponatremia Risk: This is extremely rare from morning water alone but worth noting. It involves dangerously low sodium levels from consuming a massive amount of water in a very short time without electrolytes. A glass or two is perfectly safe.

Practical Recommendations

If you want to try this practice, here’s a sensible approach:

1. Start with 1-2 glasses (8-16 oz / 250-500 ml) of water at a comfortable temperature. Warm water is often recommended for digestion.

2. Wait 15-30 minutes before having breakfast to allow for rehydration.

3. Listen to your body. If it feels good and helps you establish a healthy hydration habit, it’s a great practice. If it makes you feel bloated or uncomfortable, simply focus on drinking consistently throughout the day.

The Bottom Line

Drinking water upon waking is a healthy habit that promotes general hydration, which is fundamental to nearly every bodily process. Many of the extraordinary claims (like dramatic detoxification or permanent metabolic boosts) are exaggerated. However, the core benefit—correcting overnight dehydration—is simple, scientifically sound, and a fantastic way to start your day.

Think of it less as a “miracle cure” and more as the first, most important step in maintaining good hydration from the moment you wake up.