Theory is it will dilute all the mineral, after 2 hour your body will absorb better.
This theory come from KOREA.
Morning, wake up can not drink water.
REASON why no water during meals:
Water During Meals
1. Avoid drinking water with your meals. Drinking water with your meals dilutes the gastric juice and slows down the process of digestion in the stomach and intestines. Even if you need to drink water just sip water kept at room temperature. Ideally, Ayurvedic texts recommend sipping minimal amount of plain warm water during meals.
2. Cold water during the meals reduces the digestive fire. Digestive enzymes become inactive, digestive process is hampered and leads to accumulation of toxic waste in the body. Hence drinking of iced water, soft drinks, sodas, tea or coffee or alcohol is strictly prohibited.
3. Chew your food properly and it will easily pass down to your stomach. Do not drink water to swallow food in a hurry. If required drink water after swallowing food.
Source: http://www.yoga-for-beginners-a-practical-guide.com/drinking-water-during-meals.html
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