Experts agree this is beneficial. Studies show even mild dehydration (1-2% body weight loss) negatively affects mood, alertness, and cognitive performance. Rehydrating promptly can counteract this, improving focus and energy. One review noted that drinking water in the morning reduces thirst, anger, fatigue, and poor mood, with larger amounts (around 500ml) also enhancing working memory.
It’s also practical: Starting with water establishes a hydration habit, making it easier to meet daily needs (about 3.7 liters for men and 2.7 liters for women, including from food).
Now, for the bolder claims. Many sources tout a 25-30% metabolism boost from morning water on an empty stomach, aiding weight loss. This stems from studies showing cold water increases calorie burn slightly via thermogenesis (warming the body). However, the effect is temporary (30-40 minutes) and modest—not unique to mornings or empty stomachs. No strong evidence links it directly to significant weight loss; replacing sugary drinks with water helps more overall.