The practice also recommends avoiding cold water, on the basis that it causes fats and oils from food to harden in the digestive tract, slowing digestion and raising disease risk. Meals are to be consumed within strict time windows for designated periods depending on the condition being treated.
The effectiveness of Japanese water therapy in treating complex conditions such as type 2 diabetes and cancer is not supported by scientific evidence. Some benefits — better hydration, potential support for weight management through calorie restriction, and reduced risk of constipation, headaches, or kidney stones — are plausible as consequences of increased water intake generally, not of the therapy’s specific protocol.
There are also documented risks. Consuming large amounts of water in a short period can cause water intoxication, particularly in people with certain health conditions or those engaged in intense physical activity. The strict meal timing may also trigger rebound weight gain and heightened hunger over time.
How much water per day? The 8×8 rule is a starting point, not a prescription
The widely cited “8×8” rule — eight 8-ounce glasses of water per day — is a common reference point, but individual hydration needs vary considerably. Age, gender, activity level, climate, and underlying health conditions all influence how much water a person actually requires.
A more useful approach involves paying attention to personal factors rather than applying a single number universally. Healthcare professionals can provide personalized guidance, particularly for people with conditions that affect fluid balance.
On the question of weight loss, the evidence is similarly measured. High water consumption can increase feelings of fullness and may reduce calorie intake, and water-induced thermogenesis has been shown to modestly boost metabolism. However, scientific research on the direct impact of water intake on weight loss remains inconclusive, and the timing of consumption does not appear to significantly alter these effects.
