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Multi-Day Water Fasting. Appropriate for Bariatric Patients?

Woman pouring water into glass from sink tap

It seems you can’t turn anywhere on the Internet without seeing information about newfangled diets and biohacking tactics. These have become discussion topics among podcasts and social media influencers within and outside the medical community. With all this information swirling on the Internet and reports of some people spending millions each year to stay “young” and healthy, what do we know works, and what is simply clickbait and a money-making tactic?

Intermittent Fasting and Water Diets

A significant body of evidence offers support for intermittent fasting. For one, intermittent fasting is relatively easy on the body when performed correctly and according to established schedules. Intermittent fasting comes in many forms and flavors, including eating for only eight or 10 hours during the day while fasting for the rest of the 24 hours. Other fasting options can include eating nothing for an entire day once a week, for example. Speaking to your doctor and nutrition expert can help you determine the best choice.

The Water Diet

Some patients and medical practitioners have investigated water-only diets for longer-term fasting – 3 to 7 days. Some data shows that this can be very helpful in fat loss and cell turnover. For example, a recent study1 showed that after seven days of water fasting, many patients had lost a significant amount of weight, which consisted of both muscle mass loss and fat loss. However, when they started eating again, muscle mass returned quickly while fat regain was stunted. Interestingly, while the study followed a seven-day plan, results were also seen after three days. This phenomenon, however, could not be replicated in a water fast of under three days.

Some studies have shown no difference between intermittent fasting and continuous eating.2

On the other hand, water fasts have been associated with potentially problematic outcomes, including increased cardiovascular issues and a greater risk of all-cause mortality.3

Does a Water Fast Make Sense?

A water diet may be problematic and even dangerous for those in generally poor health or with significant comorbidities. As such, every diet must be started only with the advice and oversight of a doctor or qualified nutritionist. Further, a water diet has essential considerations, including how to start eating food again. Going straight back to a regular diet after an extended water-only diet can be dangerous and even fatal, causing a condition called Refeeding Syndrome. Food must be introduced very slowly.

Water fasts also require drinking enough, you guessed it, water. You don’t have the benefit of added food, which also introduces water and electrolytes to the body. So, speak to your nutritionist or doctor about the need for electrolyte supplementation; water alone may dilute essential salts in the blood and cause problems.

Lastly, you may find that a water diet makes you feel fantastic early on, after a headache or two, and as your body adjusts. However, you may lose some sharpness in acuity because your brain does not have the glucose it needs to function at its highest level.

Does this work for you as a bariatric patient? Maybe…or maybe not.

The Bottom Line

Water fasts seem to have positive implications for appropriate patients, yet it comes with some serious considerations that all patients must be aware of. Only start this and other diets with the oversight and advice of a qualified professional. Further, be mindful that your body has undergone some significant changes after bariatric surgery. Adding a water diet to the already limited caloric and nutritional intake you experience from the surgery can be a problem. Any water diet should only be considered once your doctor has cleared you or you are at least two years from your bariatric procedure.

1Pietzner M, Uluvar B, Kolnes KJ, Jeppesen PB, Frivold SV, Skattebo Ø, Johansen EI, Skålhegg BS, Wojtaszewski JFP, Kolnes AJ, Yeo GSH, O’Rahilly S, Jensen J, Langenberg C. Systemic proteome adaptions to 7-day complete caloric restriction in humans. Nat Metab. 2024 Mar 1. doi: 10.1038/s42255-024-01008-9. Epub ahead of print. PMID: 38429390.

2Lowe DA, Wu N, Rohdin-Bibby L, et al. Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical Trial. JAMA Intern Med. 2020;180(11):1491–1499. doi:10.1001/jamainternmed.2020.4153

3Sun Y, Rong S, Liu B, Du Y, Wu Y, Chen L, Xiao Q, Snetselaar L, Wallace R, Bao W. Meal Skipping and Shorter Meal Intervals Are Associated with Increased Risk of All-Cause and Cardiovascular Disease Mortality among US Adults. J Acad Nutr Diet. 2023 Mar;123(3):417-426.e3. doi: 10.1016/j.jand.2022.08.119. Epub 2022 Aug 11. PMID: 35964910.