Does Bariatric Surgery Work By Changing Gut Bugs?

As readers are well aware, bariatric surgery is currently the most effective treatment for severe obesity. Yet, we are still not quite sure how exactly surgery works. For one, we know that simplistic notions of surgery “mechanically” inhibiting food intake are simply wrong – were that the case, simply having your jaws wired shut would be as effective. Nor does caloric malabsorption account for much of the weight loss (except perhaps with biliopancreatic diversion) – there is indeed good evidence that with contemporary bypass procedures, the remaining gut has no problem extracting all the calories it needs from the diet. One of the reasons bariatric surgery works in the long term is because it changes gut hormones (e.g. ghrelin, GLP-1, PYY) and thus counteracts the homeostatic mechanisms that counteract weight loss. But recent observations that bariatric surgery also prevents much of the decrease in metabolic rate normally associated with weight loss suggests that there is more going on than meets the eye. Now, a study by Ling-Chun Kong and colleagues from Paris, France, in a paper published in the American Journal of Clinical Nutrition supports the notion that bariatric surgery may have additional effects on energy homeostasis by affecting the gut microbiome. The researchers profiled the gut microbiota from fecal samples and adipose tissue samples in severely obese individuals, before as well as three and six months after roux-en-Y gastric bypass surgery. In these patients, surgery resulted in a remarkable increase in richness of gut microbiota (previous studies have shown that gut microbiota phylogenetic richness is lower in obese than in lean subjects), whereby almost 40% of the increase in gut bacteria belonged to the phylum Proteobacteria. Most of these changes occurred early, with no further differences noted between the three and six month samples. The researchers also found significant associations between gut microbiota composition and adipose tissue gene expression (including numerous genes related to metabolism and inflammation) as well as clinical phenotype – as substantial proportion of which were independent of any changes in caloric intake. As to the cause or clinical implications of these changes, the authors can only speculate. As they point out, some of these changes may be due to alterations in diet composition, eating behaviour (e.g. increased chewing), or biological changes that include differences in pH and other aspects of intestinal milieu. Although such “correlational” studies cannot prove cause and effect, this study does document… Read More »

Obesity & Energetic Offerings, May 31, 2013

For several months now, my colleagues at the University of Alabama have been compiling a weekly list of selected obesity related articles in a list they call Obesity and Energetic Offerings. The list is compiled by David B. Allison, Michelle Bohan-Brown, Emily Dhurandhar, Kathryn Kaiser, and Andrew Brown. The following is a selection of articles from this week’s list that caught my attention –  – the link headings are theirs, not mine: Featured Donna Arnett “Transforming cardiovascular health through genes and environment: presidential address at the American Heart Association 2012.” Civility and fidelity called for in scientific communications – even if complex. Self-report–based estimates of energy intake offer an inadequate basis for scientific conclusions. Headlines versus Studies Headline: Drinking 5 cups of coffee everyday may lead to obesity: study. Headline: Wrong amount of coffee could kill you Study: A study of mice, involving a substance found in coffee, but no coffee, showing no significant weight gain, and reporting no deaths. Findings Contrary to Hypotheses or Popular Ideas Controlled trial to prevent childhood obesity in maternity and child health care clinics improved maternal glucose tolerance test results, but did not affect maternal weight gain, newborn anthropometry or infant weight gain. RCT: A pedometer-based physical activity intervention with telephone support produces no effect on health outcomes among type 2 diabetes patients. RCT: No effect of whey protein supplementation vs isoenergetic control on resistance exercise-induced changes in lean mass, muscle strength, and physical function in mobility-limited older adults. Overweight and obesity are not associated with dental caries among 12-year-old South Brazilian schoolchildren. Genetically obese mice do not show increased gut permeability or faecal bile acid hydrophobicity. RCT: No differential effect of experimental low-glycemic-load or conventional low-fat diet for 6 months in Treatment of Fatty Liver in Obese Children. RCT: The addition of a protein supplement to the diet of overweight and obese young adults, with dietary counseling incorporated, did not improve diet quality or suppress fasting appetite. Could the Net Health Effects of Food Stamps Be Negative? Meta-analysis shows no association between consumption of soft-drinks and the risk of cancer. CT: No effect of a program of lifestyle changes to promote weight reduction, a randomized controlled trial in primary health care. RCT: The relative carbohydrate and protein content of the diet, when combined with intensive CBT, does not significantly affect attrition rate, weight loss and psychosocial outcome in patients with severe obesity. The obesity paradox in… Read More »

Best of 2012: October

Here’s a review of my favourite posts for 2012 or those that piqued the most interest from my readers (not always the same): Is Obesity the Worst “Choice” a Person Can Make? Lady Gaga Found This First: ‘Fat’ Poem Chewing Gum For Weight Loss? Why Comments on What Christina Aguilera Did Not Say Still Matter Does Short-Term Overeating Make You Hungrier? Very much appreciate your thoughts on these topics. AMS Edmonton, AB

Weekend Roundup, October 12, 2012

As not everyone may have a chance during the week to read every post, here’s a roundup of last week’s posts: A Light-Hearted Look at Obesity Social Networks Do Not Explain Physical Activity Levels and Obesity in Younger Adults Chewing Gum For Weight Loss? Happy (Canadian) Thanksgiving Everyone! Have a great Sunday! (or what is left of it) AMS Cincinnati, OH

Smells Like I Am Full

An important aspect of enjoying food, in addition to the actual taste and mouth feel, is the complex sensory stimulation of the olfaction system. After the food enters the oral cavity, aroma molecules find their way to the sensitive olfactory nerve endings in the nose by making their way up the back of the throat into the nasal cavity (apparently the nose has a clever way of telling whether this aroma is coming from the food on your plate or from the food in your mouth). This activation of specific brain areas by a retronasally sensed food odor is not only associated with the perception of the aroma of the food that is consumed but is also hypothesized to directly contribute to its satiating effect (sensory-related satiation). A paper by Rianne Ruijschop and colleagues from The Netherlands, published in the Journal of Agricultural and Food Chemistry, provides a splendid overview of this fascinating area of research. In this paper, Ruijschop and colleagues describe a series of experiments that examine a wide range of factors that can affect retronasal olfaction-related satiation. Not surprisingly, solid and semisolid foods that required a greater amount of chewing and swallowing elicited a stronger and longer-lasting retronasal aroma release pattern than the rather short-lived spiked pattern observed with liquid foods. A higher extent of retronasal aroma release may therefore be one of the explanations why solid foods appear to be more satiating than liquid foods. Indeed, the researchers did observe a negative trend between the extent of retronasal aroma release and the amount of ad libitum food intake. Subjects who had a higher extent of retronasal aroma release tended to consume less. However, retronasal aroma release intensity and profile morphology appeared to be subject specific, which may support the hypothesis that subject differences in the extent of retronasal aroma release are linked to subject differences in sensory satiation and food intake behavior. In further studies, the researchers found that certain aromas were better at eliciting a satiation response than others. Thus, aromas that suggest fat content (i.e., lactones) were less effective in creating a satiation response than aromas suggesting carbohydrate content (i.e., maltol) or the breakdown of protein (i.e., “animalic”). In a separate experiment, custard products with the addition of maltol or animalic at sensory detection threshold were able to increase subjects’ feeling of fullness significantly. These results are in line with the observation that macronutrients… Read More »