Weight Fluctuations after Bariatric Surgery
Weight Loss
4 Causes of Weight Fluctuations After Bariatric Surgery

Weight fluctuations after bariatric surgery are more common than many patients are led to initially believe. Weight loss surgery can help patients lose a significant amount of weight; however, it does not come without changing lifestyle habits, including diet and exercise. 

Weight fluctuating between +/- 5 to 10 pounds is completely normal and happens to most patients. In many cases, when a patient experiences weight fluctuations after bariatric surgery, especially within the first two years, it is due to a change in their lifestyle – whether that be a change in eating habits or stress levels. However, it could also be due to other underlying conditions. In this blog, we will discuss the various reasons a patient may experience weight fluctuations after bariatric surgery and what they can do about it. 

Reasons for Weight Fluctuations after Bariatric Surgery

Vegan diet food quality over quantity1. Change in eating habits

One of the most common reasons patients will see their weight go up (or down) is their eating behaviors. Typically, we see patients regaining weight after a year post-op because they fall into old eating habits. 

Two behaviors that are almost always the culprit for weight regain post-op are frequent snacking and the overconsumption of carbohydrates.

Snacking between meals can lead to significant weight gain after weight loss surgery due to the quality and quantity of food consumed. Most often, snack foods are full of carbohydrates and sugar. They are considered “low density” food items due to the lack of nutrition.

When you don’t sit down for planned meals, it is easy to overeat or eat foods that are not on your nutrition plan. Although we suggest bariatric patients eat five small meals daily, we also suggest they plan accordingly.

The second reason you may experience weight fluctuations after bariatric surgery is the overconsumption of carbohydrates. Although the body needs a certain amount of carbohydrates to fuel itself, you will gain weight if you do not burn more than you consume. Therefore, we recommend bariatric patients avoid high-carb foods such as fruit, starchy vegetables, and grains (including pasta and bread). Your body will receive enough carbs from the other foods on your nutrition plan to function correctly and still help you lose weight.

2. Change in exercise habits

Another reason a patient may experience weight fluctuations after bariatric surgery is a change in their physical activity. Weight loss is a result of burning more calories than you consume. If you have recently started or ended a workout routine, your weight may adjust to reflect the change in calorie burn, especially if you are not changing your calorie consumption. 

Similarly, if you have recently started a workout routine focused on strength training and notice your weight increasing (especially after it has plateaued for a while), don’t be alarmed. Strength training increases your muscle mass, thus increasing your weight since muscle weighs more than fat.

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3. Change in stress levels

Stress is known to cause weight fluctuations — both up and down. After bariatric surgery, there will be times when you experience high levels of stress, whether that be because of the loss of a family member or the day-to-day with your work.

When we are physically and emotionally stressed, our body produces a hormone called cortisol. Cortisol helps your body make glucose from proteins. Therefore, if you have elevated cortisol levels, this could lead to glucose dysregulation-aka weight gain. Similarly, when our cortisol levels are off-balance, our metabolism is lowered, and our thyroid function is impaired, causing weight gain. Also, high cortisol levels are often linked to depression, food addictions, and sugar cravings.

On the contrary, some people deal with stress by not taking care of themselves at all, including not eating. Therefore, you might experience stress-related weight loss after bariatric surgery. 

4. Change in the anatomy of the surgical site

Anatomical changes are the final and least common reason a patient may experience weight fluctuations after bariatric surgery. Over time, patients can train their pouch to accommodate a higher volume of food without “complaining” as much. This can lead to weight gain if you are not careful since you will not have the original feeling of fullness you once had. 

Another anatomical reason for weight gain postoperatively for gastric bypass patients could be a gastro-gastric fistula caused by a staple line leak or “a technical complication derived from the incomplete division of the stomach during the creation of the pouch.” A fistula is categorized as food entering the bypassed stomach and traveling the pre-op intestinal anatomy. When a fistula occurs, the weight loss effects of the gastric bypass become ineffective. Luckily, a fistula occurs in less than 6% of patients and can be managed by revising the bypass to a duodenal switch. 

Other anatomical reasons for weight fluctuations after bariatric surgery are strictures and ulcers. Strictures occur when the opening between the new gastric bypass pouch and the small intestine narrows. This can lead to feelings of fullness, which can result in eating less food. Similarly, if a patient develops an ulcer, they may feel nauseous therefore eating less. 


There are several reasons why a patient may experience weight fluctuations after bariatric surgery. It is normal to have your weight fluctuate over time and even to hit a weight loss plateau. However, if you notice a significant increase or decrease in your weight, more than 5 to 10 pounds, we recommend you make an appointment with your bariatric care team to rule out any anatomical concerns. 

Patients who constantly communicate with their care team postoperatively are also more likely to experience long-term success. When weight gain becomes an issue, we can address it early on before it becomes a more significant concern. 

This article was originally published on the Bariatric Centers of America website

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