Nutritional changes after bariatric surgery


This blog provides free general information for anyone who is seeking to understand more about some of the nutritional changes after bariatric surgery, not intended as a medical consult. Please seek appropriate medical and dietician advice for individual assessment and management.



Energy intake

For a normal/average sized adult living in our Western society the recommended energy intake is 8700 kilo joules (2078 Calories) a day.

To achieve significant weight loss the aim is approximately 1000 to 1500 Calories (or kilo calorie) a day. Hence sustained long-term weight loss is often only possible with bariatric surgery, without a return to food addictions and eating disorders combined with a lifestyle change and regular physical exercises.

Gradual increase in energy intake with time is consistently seen after all types of bariatric surgery. This accounts for some of the weight regain 1 or 2 years after surgery. This is expected and may be part of the body physiology changes and re-adjustment. Hence the emphasis for all patients is that they should be not be relying solely on surgery to maintain weight loss but to have a complete change in diet habits, relationship with food as well as having a regular set of exercises.

The essential message is:

  • Good food portion
  • Good food choices
  • Good eating habits
  • Adequate micronutrients
  • Regular physical activities
  • Good mental health and cognitive adaptation



Bariatric surgery

The purpose of any bariatric operation is to assist patients and positively affect eating habits (behavior modifications) and a complete lifestyle change. Surgery alone has limited results unless there is a change in eating habits/behavior accompanied by adequate amount of exercise daily, mainly aerobic type physical activity. Long-term maintenance of weight loss shouldn’t depend on restriction (dysphagia, vomiting) or malabsorption (diarrhea or dumping) but instead should be relying on an improved diet and lifestyle.

This blog focuses on the post-surgical dietary and nutritional changes to help patients understand the changes with food intake, why certain food groups are discouraged and to ensure adequate dietary nutrient. This section mainly concentrates on the effect after a gastric bypass, sleeve gastrectomy and gastric band.

Please refer to the section on “bariatric food pyramid” for more information on the recommended food types that should be eaten to ensure adequate energy or macronutrient intake.





Gastric bypass

Roux-en-Y gastric bypass is a great bariatric operation, with proven success to achieve durable excess weight loss, resolution of obesity related medical co-morbidities, which precedes improvement in physical and social wellbeing. This is considered to be a combined restrictive and malabsorptive procedure with permanent anatomical and physiological changes to the gastrointestinal tract, which will alter food habits and eating patterns. Dietary counseling aimed at modifying eating behavior is crucial in order to achieve maximum weight loss results and reducing complications such as food intolerance, dumping and macro or micronutrient deficiencies.

Avoidance of high GI index foods (simple sugars or sweets) is necessary in order to avoid early dumping syndrome. Avoidance of complex carbohydrates or starch (white bread, potato, pasta, rice) in the early post op period may reduce late dumping or gas bloating side effects. Intolerance of other food types such as milk, red meats and cereals has been reported, this may be due to the bloating, abdominal discomfort, temporary dairy intolerance or other reasons.

Severe and prolonged food restriction after surgery results in an unbalanced diet, protein malnutrition and micronutrient deficiencies, leading to adverse health outcomes.





Recommended daily intake

In general it is observed that most obese patients (before and after bariatric surgery) have an imbalanced nutrient intake, which is inadequate protein and excessive carbohydrates and total fats with regards to the recommended daily intake.

It has been suggested that protein intake be increased during periods of weight loss to help glycemic control, prevent lean body mass loss and maintain basal metabolic rate. Achieving the higher protein diet can be troublesome following a gastric bypass due to food intolerances. Micronutrient deficiencies following a gastric bypass have been reported.

Multi vitamin and mineral supplements are prescribed to all post-op patients. The most frequently reported deficiencies are in vitamin B12, folic acid, vitamin D, vitamin A, vitamin C, B1 (thiamine), B2 (riboflavin), B3 (niacin), B6 (pyridoxine), zinc, calcium, copper and iron. Adherence to daily multivitamin supplements may be a problem for some patients for the duration.

As dietary intake is unlikely to provide the required level of these micronutrients, monitoring for vitamin and mineral deficiencies with a blood test at least twice a year is necessary for the long term.

It has been found that the intake of fresh vegetables, fruits, low fat dairy and whole grains were way below recommendations. The consumption of lean meat is often inadequate even after 1 year. The consumption of sweets and fats (especially from animal sources) is proportionally much higher than recommended.

Specific food groups (fresh fruits, vegetables and whole grains), which provide many phytochemicals and dietary fiber and are low in fat, should be encouraged.