Japanese water therapy is the practice of drinking several glasses of room-temperature water first thing in the morning.

It also encourages strict eating windows of 15 minutes, with long breaks between meals and snacks.

While some people report that this habit has improved certain aspects of their health, many wonder whether it’s an effective tool for weight loss.

This article explains whether Japanese water therapy works for weight loss.

Water therapy for weight loss

Few scientific studies have been conducted on Japanese water therapy specifically, and the weight loss evidence for similar patterns of water consumption is mixed.

That said, the hydration component of water therapy may aid weight loss.

Keep in mind that many other factors are at play, such as your overall diet quality and exercise levels.

Hydration may support weight loss

Drinking more water may have a filling effect, as water takes up space in your stomach. In turn, it may prevent cravings and overeating that may otherwise contribute to unwanted weight gain (1).

One study found that adults with excess weight or obesity who drank 2.1 cups (500 mL) of water 30 minutes before a meal ate 13% less food than adults who didn’t drink fluids before eating (2).

Another study in moderate-weight men produced similar results (3).

What’s more, one review found that drinking water significantly increases resting energy expenditure (REE) in adults. REE refers to the base number of calories your body burns while at rest (4).

Additionally, research shows that replacing sugar-sweetened beverages with water can reduce calorie intake that may otherwise promote weight gain (5, 6).

Lastly, its 15-minute eating windows and breaks between meals and snacks may further reduce calorie intake.

Study results are mixed

Yet, some studies have observed that hydration has no weight loss effects (7).

Some studies suggest that water therapy’s 15-minute eating windows may impair long-term weight loss because your gut doesn’t have time to signal your brain that it’s full. As a result, you may eat too much, too quickly (8).

One study found that children who ate rapidly were three times likelier to develop excess weight than those who didn’t (9).

Conversely, eating slowly is associated with a lower risk of excess weight (10).

Research further reveals that calorie restriction may result in initial weight loss but tends to increase levels of the hunger hormone ghrelin. This may be one reason why only 20% of people who lose weight keep it off long term (11, 12).

SUMMARY

While adequate hydration may boost fullness and prevent overeating, research is lacking about the specific effects of Japanese water therapy on weight loss.

How does water therapy work?

While water therapy originated in Japan, it has become popular around the world largely thanks to word of mouth.

There are two main components to how Japanese water therapy works.

First, proponents of water therapy drink four to five 6-ounce (180-mL) glasses of room-temperature water on an empty stomach every morning, 45 minutes before any food or drink. (At the beginning, consider starting with only 1–2 glasses and gradually increasing the amount.)

Then, you drink water throughout the day as you normally would, paying attention to your thirst cues.

Additionally, most advocates recommend only eating meals for 15 minutes at a time, with a break of at least 2 hours before you eat or drink anything else.

Although no restrictions limit what or how much you eat on water therapy, sustainable weight loss requires healthy eating choices — not just hydration.

While you aren’t meant to follow water therapy for a set period, some people report benefits within a few weeks to months and continue to practice it as long as they experience results.

What does the research say?

Supporters assert that water therapy helps clear your digestive system, improves gut health, prevents constipation, and lowers your risk of conditions like type 2 diabetes, cancer, and high blood pressure. However, no scientific evidence supports such claims.

Still, drinking enough water keeps you hydrated, which may promote optimal brain function, energy levels, and blood pressure, as well as prevent headaches, constipation, and kidney stones (13, 14, 15, 16).

Keep in mind that basic water needs vary by individual. While 8 cups (1.9 liters) per day is a common recommendation, scientific evidence behind this amount is lacking (17).

Still, water therapy may account for approximately half of your daily water needs if you follow these recommendations.

SUMMARY

Japanese water therapy involves drinking room-temperature water in the morning and following a restricted eating timetable. No research backs its health claims, but proper hydration is beneficial.

Potential risks

While adequate hydration is beneficial for overall health, it’s possible to drink too much water.

Overhydration, also called water intoxication, occurs when you drink a large amount of water in a short period.

This can severely lower the sodium concentration in your bloodstream and lead to a dangerous condition called hyponatremia. In turn, this may cause nausea, vomiting, seizures, coma, and even death if untreated (18, 19).

While hyponatremia is rare among healthy people with normally functioning kidneys, it’s best to avoid drinking more than the maximum amount of water that healthy kidneys can filter — about 4 cups (945 mL) per hour (20).

Although drinking the recommended 4–5 glasses of water in the morning is likely safe for most adults, it may be too much water for some people to comfortably and safely consume. Listen to your body and stop drinking water if you begin to feel uncomfortable.

SUMMARY

If you drink more water than Japanese water therapy recommends over a short period, you run the risk of overhydration.

The bottom line

Japanese water therapy has been touted for its weight loss benefits, but there’s inadequate scientific evidence to support this effect.

Still, adequate hydration may lead to positive effects on weight loss by helping you feel full and preventing overeating.

However, hydration is only one part of the weight loss puzzle, and Japanese water therapy may overly restrictive calorie intake — which could lead to rapid food intake and weight gain.