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Is Intermittent Fasting Bariatric Surgery Friendly?

July 6, 2020

Intermittent fasting is a diet that has become very popular in the media and has been talked about more and more. There are many different types of intermittent fasting being trialed, but they can be difficult dieting plans to stick with. Some studies show evidence of weight loss and improvement to some medical conditions, while other studies do not support this evidence. But is intermittent fasting safe for all populations of people?

What is Intermittent Fasting?

Intermittent fasting, or IF, is when you go for a planned, extended period without consuming food or beverage. The weight loss claim behind IF is that it can increase your body's responsiveness to insulin.

Insulin is a hormone that is released when we eat food, signaling our body to store glucose, or sugar, for energy. When you go a period of time without eating, which we refer to as fasting, your blood glucose levels drop due to lack of carbohydrate or energy intake. When this drop occurs, your insulin secretion decreases as well. This is when your body will start using that stored glucose for energy. When we fast longer than 12 hours, our body runs out of stored glucose and will start burning stored fat instead.

Types of Intermittent Fasting

Per the Cleveland Clinic, there are 4 types of intermittent fasting; the "twice a week" method or 5:2, alternative day fasting, time restricted eating, and 24 hour fasting. The 5:2 method recommends consuming only 500 calories 2 days per week, while focusing on protein and fiber, and then eat a normal, although still generally healthy, diet the other 5 days of the week. You are able to choose which days to fast, but there has to be a non-fasting day in between your two fasting days.

Alternate day fasting recommends limiting calories to 500 or less every other day and then, again, eating a normal, healthy diet on the days in between. The time restricted method recommends having set fasting and eating time frames, for instance, 16/8 would imply fasting for 16 hours of the day and consuming normal healthy meals for 8 hours of the day. 14/10 is another common time restricted method. This is an "easier" method to fit your schedule if you're an active person, or maybe trying IF for the first time. Lastly, 24 hour fasting, or the "eat, stop, eat" method recommends fasting for a full 24 hours. This is done 1-2 times per week.

Benefits and Downfalls of Intermittent Fasting

Intermittent fasting reports offering many benefits such as weight loss, decreased cholesterol levels, improved fat burning, and improved blood sugar levels in people with diabetes. The difficulty with intermittent fasting is that there isn't much evidence from human studies that have supported the claims.

There are multiple studies that show that these reports are true in animals, but these results may not always translate exactly the same into humans. Many humans have seen success with IF and there is evidence of short-term weight loss benefits. Some studies show very similar weight loss percentages in people following an IF diet versus people following a calorie restricted diet.

Unfortunately, there just aren't enough completed studies with scientific evidence for researchers to say that IF is a solution for long term weight loss.

People who trial IF have reported unpleasant symptoms such as headache, drowsiness, and irritability during their fasting periods. Have you heard of being "hangry" before? This implies someone that is so hungry that they're angry. The symptoms listed above are very common symptoms of being overly hungry. You are also at higher risk for binge eating on your non-fasting days when you let yourself get to this overly hungry stage.

Is IF Right If You’ve Had Bariatric Surgery?

Evidence points to no. For people who have undergone bariatric surgery, the main focus should be general healthy eating and balanced meals. The main reason why IF isn't supported in the bariatric surgery population is that intake of food is already limited as this population should be eating much smaller portion sizes compared to the general population.

Most individuals who have undergone bariatric surgery are recommended to consume 4-6 meals per day at 1-1.5 cups per meal long-term while focusing on protein intake as their main nutrient. To implement intermittent fasting, you would be decreasing the amount of time you have to consume nutrients and it is difficult enough to fit in 6 meals per day during normal waking hours.

While weight loss is the goal, it is still important for bariatric surgery patients to make sure they're consuming enough calories to maintain a "happy medium." If we intake too little calories for extended periods of time, weeks or months, our body will actually be more likely to store calories vs. shedding pounds as it sends our bodies into a type of starvation mode.

The bariatric surgery population is also at increased risk for vitamin deficiencies due to lack of absorption and decreased food intake, so limiting the time you have to eat meals would put you at an even higher risk of vitamin deficiency.

As previously stated, there also isn't enough current evidence to say that weight loss related to IF can be maintained long term. The bariatric surgery population should expect to follow the general healthy eating guidelines long term to continue to see weight loss and/or maintenance of a healthy weight.

While intermittent fasting may be beneficial in some populations, the bariatric surgery population is not currently one of them. With further studies being done in this area, we may see different recommendations in the future, but for the time being it is recommended for the bariatric surgery population to continue general healthy eating and balanced meals for overall health and weight loss.


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Amanda Daniels


Mandi Daniels is a registered and licensed dietitian in the state of Ohio working with Mount Carmel Health Systems Bariatric Surgery Program. She specializes in bariatric surgery nutrition and has a clinical nutrition background as well. She graduated from The Ohio State University with a Bachelor's of Science in medical dietetics and completed her internship through the university. She is passionate about the bariatric surgery community & enjoys providing the most up-to-date info to her patients.