Gastric bypass, gastric banding and other surgical approaches to weight loss are considered to be among the most successful ways for obese people to lose weight. However, nutrient deficiencies are common after surgery, and it is estimated that 10 to 20 percent of those treated with bariatric surgery regain most or all of the weight they lost from the surgery.

QUESTION: How does bariatric surgery cause weight loss?

ANSWER: A variety of surgical procedures are currently used that are designed to restrict the amount of food that can be consumed (usually by greatly reducing stomach size) and/or cause reduced absorption of the calorie-containing components of foods.

Among the most common procedures, the irreversible Roux-en Y gastric bypass operation combines both restriction and malabsorption by reducing the stomach volume to about 15 milliliters (one tablespoon) and bypassing the upper portion of the small intestine.

A reversible procedure called laparoscopic adjustable gastric banding is designed only to restrict how much food can be consumed in a meal. An adjustable band is placed around the upper portion of the stomach to form a pouch that is 15 to 20 milliliters in volume. This technique has a greater failure rate than the gastric bypass. The band requires periodic readjustment to maintain the restriction. If this is not accomplished, weight regain is the obvious result. In addition, the stomach pouch often enlarges and can require surgery to reposition or remove the band.

Q: How does bariatric surgery cause nutrient deficiencies?

A: Whenever food intake is restricted, the overall diet must meet nutrient needs with less food. Consequently, the quality of the diet must be high — plenty of nutrients for each calorie. Add malabsorption to this low-calorie diet and it becomes virtually impossible to meet essential nutrient needs without dietary supplementation.

Q: What are the most common nutrient deficiencies?

A: One of the most common problems is inadequate protein intake. This leads to a loss of lean muscle tissue, which can slow fat loss and promote fat regain. Low protein intake often is accompanied by deficient intake of iron, zinc, and vitamin B12. Other nutrient deficiencies are common, with copper deficiency becoming increasingly recognized as being a problem with gastric bypass surgery.

Multivitamin/mineral supplements are part of the follow-up therapy of bariatric surgery, but one study reported that only 33 percent of patients adhered to the recommended supplement regimen when studied over a 10-year follow-up. Clearly, permanent surgical changes to the gastrointestinal tract require lifelong supplementation with vitamins and minerals along with attention to meeting protein needs.

Q: What causes weight regain after bariatric surgery?

A: After surgery, lifestyle adjustments are necessary to maintain weight loss. Too many calories can be consumed with frequent small meals of calorie-rich foods, sometimes called grazing. Add to this physical inactivity, and weight regain is very likely. To further complicate things, some people don’t experience the usual positive hormonal changes and have a greater hunger drive than others. Quoting Canadian obesity expert Dr. Arya Sharma, "The surgeons operate on your gut, not your brain."

———

Alan Titchenal, Ph.D., C.N.S., and Joannie Dobbs, Ph.D., C.N.S., are nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii-Manoa. Dobbs also works with University Health Services.