How Bariatric Surgery Affects Digestion,
Food Intake & Calorie Absorption
Weight Loss Surgery - The Normal Digestive
Process
Normally, as food moves along the digestive
tract, digestive juices and enzymes digest and absorb calories and nutrients
(see figure 1, below). After we chew and swallow our food, it moves down
the esophagus to the stomach, where a strong acid continues the digestive
process.
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The
stomach can hold about 3 pints of food at one time. When the stomach
contents move to the duodenum, the first segment of the small intestine,
bile and pancreatic juice speed up digestion. Most of the iron and
calcium in the foods we eat is absorbed in the duodenum. The jejunum
and ileum, the remaining two segments of the nearly 20 feet of small
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intestine, complete the absorption of almost all calories and nutrients.
The food particles that cannot be digested in the small intestine are stored
in the large intestine until eliminated.
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How Does Surgery Promote Weight Loss?
Gastrointestinal surgery for obesity, also
called bariatric surgery, alters the digestive process. The operations
promote weight loss by closing off parts of the stomach to make it smaller.
Operations that only reduce stomach size are known as “restrictive
operations” because they restrict the amount of food the stomach
can hold.
Some operations combine stomach restriction
with a partial bypass of the small intestine. These procedures create
a direct connection from the stomach to the lower segment of the small
intestine, literally bypassing portions of the digestive tract that absorb
calories and nutrients. These are known as malabsorptive operations.
Weight Loss Surgery
Malabsorptive Operations vs.Restrictive Operations
Malabsorptive operations produce more weight
loss than restrictive operations, and are more effective in reversing
the health problems associated with severe obesity. Patients who have
malabsorptive operations generally lose two-thirds of their excess weight
within 2 years.
Nutritional Deficiencies of Malabsorptive
Operations
In addition to the risks of restrictive
surgeries, malabsorptive operations also carry greater risk for nutritional
deficiencies. This is because the procedure causes food to bypass the
duodenum and jejunum, where most iron and calcium are absorbed. Menstruating
women may develop anemia because not enough vitamin B12 and iron are absorbed.
Decreased absorption of calcium may also bring on osteoporosis and metabolic
bone disease. Patients are required to take nutritional supplements that
usually prevent these deficiencies. Patients who have the biliopancreatic
diversion surgery must also take fat-soluble (dissolved by fat) vitamins
A, D, E, and K supplements. |
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