Fasting After Bariatric Surgery

Fasting After Bariatric Surgery: The Pros and Cons

February 5, 2018

I'm regularly asked by many long-term post-op patients if fasting after bariatric surgery a good addition to their WLS journey? There can be pros and cons to fasting after bariatric surgery. While some think this is a great way to shed a few extra pounds, there may not be as many benefits as you may think. While fasting can calm the spirit and reconnect with what’s important, there are also physical ramifications.

If someone’s primary reason to fast is to lose weight and they’ve had bariatric surgery, it may be a red flag that they have reverted to their old lifestyle and not using their surgical tool most effectively. This could also be a sign of deeper issues.

There is a reason you had weight loss surgery. For most people, that reason is to lose the weight and keep it off. Fasting for religious purposes is one thing, and fasting for weight loss after bariatric surgery is another. Even research studies show that people who fast for religious reasons can struggle after weight loss surgery because the surgery already puts them at a nutritional deficit. Fasting can create more of a deficit.

Fasting Can Mimic That Old Diet Mentality

Also, fasting can mimic the diet mentality. For many people attempting to get off the diet rollercoaster, this can be problematic because it brings back memories of starvation, feeling unfulfilled, and can recreate issues with food.

For many people who have emotional issues with food, there can also be negative side effects if they are continually feeling deprived due to a self-imposed fast. In addition, this may also impact their self-confidence, self-worth, and self-esteem. Someone may feel ‘not good enough’ if they struggle with maintaining the fast. Cheating or breaking the fast could also lead to other emotional issues, such as feeling like a failure. Furthermore, there can be issues with discipline and our old friend ‘willpower’ which may be relied upon to sustain the fast.

From a behavioral perspective, there seem to be a lot more cons than pros. However, the positives may consist of helping people to feel more in control if they aren’t complaining all day about how hungry they are or if they are not focusing on the deprivation. Instead, they are focused on the positives they will gain by doing a fast.

It is also important for people to recognize WHY they want to do a fast and check with their daily consistent or inconsistent behaviors because this will impact what will happen after the fast ends.

On a more positive note, fasting may also add a layer of feeling in control over your weight depending on the timing of the fasts and the way fasts are used as a weight loss intervention. You must have all the facts about fasting so that if you do decide to fast, that you choose the best method for you and have all the information on how it might impact you. It’s also essential that you run your ideas by a doctor or physician before considering any of the following fasts for your health and safety.

Types of Fasting After Bariatric Surgery

1. Intermittent Fasting or Time-Restricted Fasting or the 16/8 Method

This method is used by choosing an 8-10-hour window to eat (typically 8 am-6 pm) and then fasting for the next 14-16 hours. Why it is called the 16/8 fast if the hours are changeable, I am not sure. However, this fast is a very popular fast that people do to avoid eating too late in the evening and keep their meals between a very small window of time.

This type of fasting may have more of a beneficial impact because it still would allow weight loss surgery patients to get in three meals per day and to gain their water intake. Also, the ‘fast’ is limited to food only so that water intake would continue into the late evening, it is just the food that would be limited to the 8-10-hour window.

From a psychological perspective, this may help people who are chronically night snackers or night eaters in terms of giving them control on overnight eating and start them on a behavioral pattern of restricting food intake in the evening hours to keep them on track.

2. Weekly Fasting Using the 5/2 Method

This method suggests that you normally eat for five days and then restrict your caloric intake to 500 calories per day on two days of the week. Bariatric post-ops are typically getting anywhere from 800-1400 calories on an average day, so reducing it to 500 calories for two days per week may not seem so bad.

However, again looking at it from a psychological perspective, there could be some feelings of deprivation. Also, because weight loss surgery puts people in a state of a nutritional deficit, this may impact the type of nutrition a person is getting, and this would not be recommended for a new post-op.

3. Protein Fasts

Protein fasts are most likely what we call in the bariatric community “pouch resets” because the focus is on the protein. Protein fasts and pouch resets are very popular for those who struggle with a long-term stall, regain, or if they feel they have ‘stretched’ their pouch. However, these are a short-term fix for a long-term problem which is overeating, grazing, emotional eating, binge eating, and/or out of control eating.

Protein fasts can help people get back on track in the short-term; however, they have the potential for causing people to use them.

4. Water Fasts

Water fasts are known as fasts where there is no food intake, just water for a period of hours, days, or even weeks. These are potentially very dangerous because of the extreme nutritional deficit that can occur over time, and depending on the length of the fast, it could impact the metabolism. As this type of fast can mimic starvation, there could be other behavioral or psychological consequences that occur, such as negative affective and cognitive changes, which include decreased mood, increased anxiety or irritability, and more reduced concentration.

While there is a drastic weight loss with water fast, your body will go into conservation mode and burn calories more slowly as well. Also, the initial weight loss is mostly fluid, not fat.

5. Religious Fasts

Fasting is popular in Christianity, Judaism, and Islam, as well as in other faiths. These fasts typically have a beginning and end time. Some fasts can be difficult, especially if they last all day, like in Judaism and Islam.

There are typically high-holidays when fasting is most common, and so planning for these days can occur in advance. Jews typically fast on Rosh Hashanah, the Jewish New Year, and over Yom Kippur, which is the Day of Atonement. Muslims typically fast during the month of Ramadan for 30 days from sunrise to sunset. They fast from all food and water only to eat and drink from sunset to sunrise. Following weight loss surgery, it is important first and foremost that individuals are not overeating during the off-time of the fast and that they are getting in enough water and fluids, so they are not dehydrated.

In Christianity, there are many different ways to fast, and depending on the denomination followed (Baptist, Catholic, Church of Latter-Day Saints, etc.). There are various methodologies and different ways to fast that include a daily fast or a water fast. It’s important that if you plan a religious Christian fast, that you reach out to your pastor, priest, or church leader to discuss the proper ways to fast for your faith.

6. Long-Term or Open-Ended Fasts

Long-term or open-ended fasts are used typically to achieve a goal. These can be dangerous because if someone is focused on weight loss as their goal, then this could have both physical and mental/emotional consequences for the individual fasting. There are issues with cognitive functioning that impacts mood and the ability to focus, not to mention overall, causing overall lethargy. It’s essential that health is the primary concern when fasting for this reason. There is no reason that someone put their life or health in danger and if it is due to regain. You and your health come first.

Before choosing a long-term or open-ended fast, it is more appropriate to reach out to your bariatrician, primary care physician, surgeon, nutritionist or a psychologist/counselor to discuss your options or to help you get back on track if your weight gain has gotten out of control to the point that drastic measures are considered.

7. Short-Term Fasts

While short-term fasting has been linked with positive results in healthy women, there are variances for the bariatric community due to issues with malnourishment. Already at a nutritional deficit, there are pros and cons. Short-term fasting can lead to a sense of accomplishment and healthy controls, which lead to positive psychological experiences. However, they also have the same negative consequences, which include increased irritability, anxiety, frustration, and lower mood while fasting.


When deciding whether or not to fast, it’s important that each individual make an educated decision, and it’s essential to reach out to your surgeon, physician, nutritionist/dietician, to see if it’s the best fit for you. Furthermore, if you are looking for drastic measures to reduce your weight and have fallen back into old habits, it might be beneficial to reach out to a bariatric therapist, psychologist or behavioral health professional to assist you in getting back on track with your behaviors and to focus on long-term lifestyle change rather than short-term solutions.

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Kristin Lloyd, PhD is a licensed psychotherapist, mindset mentor, certified clinical hypnotherapist, and energy psychology practitioner guiding individuals to embrace healthy habits and fuller lives after WLS. A WLS patient herself, Kristin understands the challenges of WLS patients. She is the founder of Bariatric Mindset and author of the two bestselling books: Bariatric Mindset Success and Release Your Regain; both available on Amazon.
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