August 01, 2011
Gastric Bypass Surgery Causes Aversion To Dietary Fat

Does cutting the size of the stomach thru bariatric surgery cause weight loss by cutting the appeal of fatty foods?

Bethesda, Md. (July 27, 2011)—Roux-en-Y gastric bypass, the most common type of bariatric surgery in the United States, is currently considered the most effective therapy for morbid obesity. Patients who undergo this procedure, in which the stomach is reduced to a small pouch and connected to the middle of the small intestine, often lose massive amounts of weight. However, the reasons behind this surgery’s success have been unclear. Shedding more light on why this procedure prompts such dramatic weight loss, a team of researchers has found, in a study using both humans and rats, that Roux-en-Y appears to lead patients to significantly reduce their intake of dietary fat. This effect, which was present for both solid and liquid dietary fat, lingered for up to 200 days after surgery in the animals. Further experiments suggest that this fat avoidance is triggered through digestive consequences, rather than just altered taste, and may be the result of an excess of hormones previously linked to food avoidance.

Unpleasant gastrointestinal sensations as a consequence of fat consumption might play a role in causing an aversion to fat after gastric bypass surgery.

What mechanism causes this aversion to fat? One hormone linked with reduced appetite, glucagon-like peptide-1 (GLP-1), was found to be higher in those who have undergone gastric bypass surgery. Perhaps injections of GLP-1 and/or other appetite-suppressing hormones could some day emulate at least some of the effects of gastric bypass surgery. Or perhaps a messenger RNA drug or a gene therapy could adjust the stomach to secrete more GLP-1 or Peptide YY in response to a meal. Turn up the body's sensitivity to food to more quickly and intensely suppress appetite when food hits the stomach or intestines.

Share |      Randall Parker, 2011 August 01 10:23 PM  Brain Appetite

pierre said at August 2, 2011 11:36 AM:

Oddly enough many folks are losing weight by eating most of the calories from fat...

Louis said at August 2, 2011 12:18 PM:

My wife had a Rue-en-Y 3 years ago and I had a Deudonal Switch with Bileopancreatic Diversion 5 years ago. Between the two procedures, the Rue-en-Y is less sensitive to fat consumption and more sensitive to sugar consumption. The DS is VERY sesnsitive to fat consumption and not as sensitive to sugar consumption. Both of our experiences re-enforce that when something makes you sick after you eat it, you tend to avoid it. This is actually a result of our evolutinary biology. I think this is the driving force behind the long term dietary changes.

In either case, it works. Finally having control over food is terrific.

Shannon Love said at August 2, 2011 2:31 PM:

IIRC, the Roux-en-Y gastric bypass also bypasses the gaul bladder making fat digestion more difficult. I'm not surprised that people who have that procedure begin to avoid fat.

Of course, one reason people might not seek out fats is that as they begin to lose weight, they are saturated in fat released by their own body tissues. That is after all how people lose weight. There metabolisms may have all the fat they can burn and their appetite mechanisms switch to searching for proteins and critical micronutrients. Protein seeking is a well known behavior of starving people and people with a gastric bypass are starving as far as their bodies internal sensors can tell.

Loosing 50 pounds of fat requires that the body transport and process fat just as it would if the individual had eaten 50 pounds of lard over the same period. It has the same effect on the appetite and cardiovascular system. Fat is fat. All biochemical, hormonal and behavioral effects related to weight loss should be evaluated with that in mind.

PacRim Jim said at August 2, 2011 5:19 PM:

Works the other way, too.
I eat fat and notice I have an unaccountable aversion to gastric bypass surgery.

DensityDuck said at August 3, 2011 8:44 AM:

I'd like to see the actual questions (I don't have a subscription to the journal, so I can't read them.)

The only gastric-bypass patient in my experience (a co-worker) pretty much lived on Slim-Fast shakes, because that's all his reduced stomach could handle. I have to ask whether the apparent "preference" for non-fatty foods is entirely incidental to the dietary restrictions that come from bariatric surgery.

Phillep Harding said at August 3, 2011 2:14 PM:

Cross check: How many people with gall bladders removed lose weight and have an aversion to fatty foods?

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