The study appears online in the American Journal of Physiology -- Regulatory, Integrative, and Comparative Physiology, published by the American Physiological Society.
Methodology
The researchers used data from a study in obese people comparing gastric bypass to vertical-banded gastroplasty. At 1 and 6 years after surgery, these patients were asked to fill out questionnaires that included a series of questions to determine whether they avoided certain foods.
The researchers also performed either Roux-en-Y gastric bypass or sham operations on rats. At time points ranging from 10 to 200 days after surgery, these animals were subjected to various food preference experiments.
In one experiment, the rats were offered either high- or low-fat chow, with the researchers comparing the animals' intake of both foods before and after surgery. Similarly, the rats were presented with bottles containing either water or various concentrations of a fat emulsions, with the researchers recording intake of each liquid. To determine whether taste could be responsible for preference, the researchers recorded how many licks the animals took at each bottle when it was offered for only a brief amount of time.
To determine whether digestive effects instead might be responsible for aversions, rather than taste, the researchers offered the rats water flavored with saccharine, which they typically prefer to unflavored water. They then placed a feeding tube directly into the stomachs of the animals and infused some with corn oil and others with saline solution. Other animals received an injection that causes unpleasant sensations. Previous studies have shown that animals can be conditioned to avoid foods they associate with illness -- for example, by avoiding saccharine-flavored water after becoming ill from lithium chloride. Consequently, the researchers reasoned that if corn oil caused unpleasant digestive effects, the rats fed this liquid might also avoid the saccharine-flavored water. Additionally, the researchers tested the levels of GLP-1 and PYY, hormones previously linked with food avoidance, in both the Roux-en-Y and sham-operated animals.
Results
Questionnaires from human patients revealed that those who had gastric bypass were significantly more likely to report a reduction in dietary fat intake compared to those who had gastroplasty instead.
The researchers found that rats who underwent Roux-en-Y surgery consumed significantly lower proportions of high-fat chow and higher proportions of low-fat chow compared to the sham-operated animals. Additionally, those animals who underwent the bypass surgery showed a lower preference for high concentrations of the fat emulsions compared to those who received the sham operation. The Roux-en-Y animals had about the same preference for all concentrations of the fat emulsion when exposed to these liquids for only brief amounts of time. However, those that had a small amount of corn oil infused into their stomach were more likely to avoid the saccharine-flavored water than those infused with saline, much like those given the lithium chloride injections. Levels of GLP-1 were significantly higher in the Roux-en-Y rats compared to the non-bypass animals.
Importance of the Findings
The results suggest that people and animals who undergo Roux-en-Y gastric bypass decrease their consumption of both solid and liquid dietary fat, possibly helping people stick to a healthier diet. This avoidance does not appear to be triggered by taste alone, but can be influenced by the effects after ingestion. The hormone GLP-1 might be partly responsible for these effects.
"These findings suggest that changes in fat preference may contribute to long-term maintained weight loss after gastric bypass," the authors wrote. "By elucidating the mechanisms by which obesity surgery reduces the consumption of high fat foods, new surgical and non-surgical therapies could be developed that mimic these mechanisms to offer safe and effective weight loss."
Study Team
The study team was composed of Carel le Roux, Marco Bueter, Torsten Olbers, Hutan Ashrafian, Thanos Athanasious and Stephen Bloom, all of Imperial Weight Centre, Imperial College London, UK; Nadine Theis, Christian Löwenstein, and Thomas A. Lutz, the Institute of Veterinary Physiology Zurich, Switzerland; Malin Werling, Goteborg University, Goteborg, Sweden; Alan Spector, Department of Psychology, Florida State University, Tallahassee.
Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by American Physiological Society.
Journal Reference:
Carel W. Le Roux, Marco Bueter, Nadine Theis, Malin Werling, Hutan Ashrafian, Christian Löwenstein, Thanos Athanasiou, Stephen R. Bloom, Alan C. Spector, Torsten Olbers, Thomas Alexander Lutz. Gastric bypass reduces fat intake and preference. American Journal of Physiology -- Regulatory, Integrative, and Comparative Physiology, 2011; DOI: 10.1152/ajpregu.00139.2011Note: If no author is given, the source is cited instead.
Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.
