A study recently published in the American Journal of Clinical Nutrition set out to determine whether changes in diet after bariatric surgery could predict weight change 10 years post-procedure. Greater weight loss was achieved by patients who adapted soon after the surgery to a diet that consisted of both a lower caloric intake and reduced fat consumption.
Bariatric surgery refers to a variety of procedures, most commonly a sleeve gastrectomy or gastric bypass, performed to help those struggling with obesity to lose weight. Since bariatric surgery results in sustained weight loss and reduced risk of related diseases, it is widely viewed as the most effective treatment for morbid obesity. However, some patients rely solely on the surgery itself instead of making the necessary behavioural changes to lose their excess weight. In fact, approximately 20-30% of bariatric surgery patients do not achieve adequate weight loss, with some even experiencing a net weight gain. Not only that, researchers estimate that about 20-25% of weight lost after bariatric surgery can be regained within a 10-year period. Prior short-term studies have accordingly hinted at the important role of dietary adherence within the first post-surgical year in achieving and maintaining the required weight loss. However, a recent study published by the American Society for Nutrition aimed to conduct research over a much longer timespan—10 years, to be exact.
The results presented in the paper were generated from participants recruited from the Swedish Obese Subjects (SOS) study—a prospective, non-randomized, surgical intervention trial. Of the 6095 eligible patients for the SOS study, 2010 were in the surgical group and thus, included in the current study. Physical examinations and questionnaires were completed prior to surgery, as well as 6 months, 1, 2, 3, 4, 6, 8, and 10 years after surgery. The questionnaire included 49 questions to gauge patients’ habitual dietary intake over the previous 3 months.
From the recorded frequencies of food and drink consumption, daily caloric and nutrient intakes were calculated and compared to each patient’s unique basal metabolic rate—an estimation of their body’s daily energy requirements at rest.
Following statistical analysis, the researchers observed a correlation between the self-reported reduction in energy intake six months post-bariatric surgery and greater weight loss over the 10-year period. In addition, the earlier adaptation to a macronutrient composition with a reduced relative proportion of energy from fat in favor of either carbohydrates or protein was associated with greater weight loss; between the two, however, favoring protein over carbohydrates proved to be more beneficial. The reasoning behind this may be that protein helps people feel full both longer and faster, thus leading to weight loss. One limitation of the study may stem from the self-reporting of the dietary intake data; it has been speculated that obese individuals and, in general, women are more prone to misreporting food consumption. However, the dietary questionnaire used in the SOS study was validated against laboratory measurements for energy and macronutrient consumption.
Bariatric surgery forces patients suffering from obesity to decrease the quantity—and hopefully, increase the quality— of the foods eaten. Thus, much of the change in dietary habits and weight post-procedure are due to the surgery itself. This study highlights the importance of complementing the surgery with conscious dietary habit changes—most prominently, daily caloric restriction—in order to ensure not only an adequate amount of weight loss, but its maintenance as well. As macronutrient ratios were also observed to have an effect on weight loss, the researchers generally recommend a low-fat diet for bariatric surgery patients. However, randomized interventional studies still need to be conducted in order to confirm the casual effect of dietary changes on long-term weight loss. In the meantime, patients should not rely on the procedure alone for weight loss, but instead adopt healthy behaviours—namely, a calorie-conscious, low-fat diet combined with physical exercise—in order to maximize the effects of bariatric surgery.
Written By: Rebecca Yu