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Understanding the Normal Digestive Process

[Extracted from]

Normally, as food moves along the digestive tract (see figure 1), appropriate digestive juices and enzymes arrive at the right place, at the right time to digest and absorb calories and nutrients. After we chew and swallow our food, it moves down the esophagus to the stomach, where a strong acid continues the digestive process. 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 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.

Diagram of the body's digestive organs

How Does Surgery Promote Weight Loss?

The concept of gastric surgery to control obesity grew out of the weight-loss results of cancer and ulcer surgeries that removed large portions of the stomach or small intestine. Patients undergoing these procedures tended to lose weight after surgery, some physicians began to use such operations to treat severe obesity.

The first operation that was widely used for severe obesity was the intestinal-bypass. This operation first used 40-years ago, produces weight-loss by causing malabsorption. The idea was that patients could eat large amounts of food, but the food would be poorly digested or passed along too fast for the body to absorb many calories. This surgery became associated with severe long-term problems and its side effects were unpredictable and sometimes fatal. The original form of the intestinal-bypass operation is no longer used.

Surgeons now use techniques that produce weight-loss primarily by limiting how much the stomach can hold. These so-called restrictive procedures are often combined with modified gastric- bypass procedures that somewhat limit calorie and nutrient absorption and may lead to altered food choices.

2 ways surgical procedures promote weight-loss:

1. Decrease food intake (restriction). Gastric- banding, gastric-bypass, and vertical-banded gastroplasty are surgeries that limit the amount of food the stomach can hold by closing off or removing parts of the stomach. These operations also delay emptying of the stomach (gastric pouch).

2. Cause malabsorption (food is poorly digested and cannot be absorbed). In the gastric-bypass procedures, a surgeon makes a direct connection from the stomach to a lower segment of the small intestine, bypassing the duodenum, and some of the jejunum, thereby decreasing absorption.Although results of operations using these procedures are more predictable and manageable than the original intestinal bypass operation, side effects persist for some patients.

Body Mass Index. Find your weight on the bottom of the graph. Go straight up from that point until you come to the line that matches your height. Then look to find your weight group.

2 ways surgical procedures promote weight-loss:

Although results of operations using these procedures are more predictable and manageable than the original intestinal bypass operation, side effects persist for some patients.

Restriction Operations

Restriction procedures are the surgeries most often used for producing weight-loss. These operations serve only to restrict food intake. They do not interfere with the normal digestive process.

These procedures restrict food intake by creating a small pouch at the top of the stomach where the food enters from the esophagus. The pouch initially holds about 1-ounce of food [20cc], an amount that expands to 2-3-ounces with time. The pouch's lower outlet usually has a diameter of about 1/4 inch. The small outlet delays the emptying of food from the pouch and causes a feeling of fullness.

After an operation, the patient usually can eat only 1/2 to 1-cup of food without discomfort or nausea. Also, food has to be well chewed. For most patients, the ability to eat a large amount of food at one time is lost. Ideally, patients will progress to eating modest amounts of food without feeling hungry.

2 Types of Restriction Procedures:

Gastric Banding and Vertical Banded Gastroplasty

1. Gastric banding or laparoscopic placement of a LapBand^TM. In this procedure, a band made of special material is placed [usually with laparoscopy] around the stomach near its upper end, creating a small pouch and a narrow passage into the larger remainder of the stomach (figure 2). This band is usually placed via a laparoscope, a fiber-optic tube (and light source) through which some surgical instruments may be passed. The Food and Drug Administration approved laparoscopic gastric banding a few years ago.

Illustration of a stomach with an adjustable gastric band

2. Vertical banded gastroplasty (VGB) or laparoscopic V band. This procedure was, at one time, the most frequently used restrictive operation for weight control. It is now rarely used. As figure 3 illustrates, both a band and staples are used to create a small stomach pouch.

Common problems of restrictive procedures:

Vomiting: if food is not well chewed, the small stomach is overly stretched which leads to vomiting.
Erosion of the band.
Breakdown of the staple line.
Leakage of stomach juices into abdomen: requires emergency surgery.
Death rate: less than 1%.

Restrictive procedures lead to weight-loss in almost all patients. About 30% of persons undergoing vertical banded gastroplasty achieve normal weight, and about 80% achieve some degree of weight-loss. However, some patients are unable to adjust their eating habits and fail to lose the desired weight. Some patients experience a regaining of weight. On a long-term basis [greater than 5- years] this procedure has a significant failure rate. In all weight-loss operations, successful results depend on the patient’s motivation and behaviors.

Gastric Bypass Operations

These operations combine the creation of a small stomach pouch to restrict food intake with the construction of a bypass, of the duodenum and other segments of the small intestine, to cause malabsorption.

· Roux-en-Y gastric-bypass (RGB)[Open or Laparoscopic]. This operation (figure 4) is the most common gastric-bypass and bariatric procedure performed in the United States. First, a small stomach pouch is created by stapling or by vertical banding. This causes restriction of food intake. Next, a Y-shaped section of the small intestine is attached to the pouch to allow food to bypass the duodenum (the first segment of the small intestine) as well as the first portion of the jejunum (the second segment of the small intestine). This results in reduced calorie and nutrient absorption.

Illustration of the Roux-en-Y gastric bypass (RGB)

· Extensive gastric-bypass (bilio-pancreatic diversion). In this more complicated gastric bypass operation (figure 5), portions of the stomach are removed. The small pouch that remains is connected directly to the final segment of the small intestine, thus completely bypassing both the duodenum and jejunum. Although this procedure successfully promotes weight-loss, it is not widely used because of the high risk of nutritional deficiencies.

Gastric-bypass operations (figures 4 and 5) that cause malabsorption and restrict food intake produce more weight-loss than restriction operations (figures 2 and 3) that only decrease food intake. Patients who have bypass operations generally lose two-thirds or more of their excess weight within 2-years.

The risks of pouch stretching, band erosion, breakdown of staple lines, and leakage of stomach contents into the abdomen are about the same for gastric-bypass as for vertical banded gastroplasty. However, because gastric-bypass operations cause food to skip the duodenum, where most iron and calcium are absorbed, the risk of some nutritional deficiency is higher in these procedures. In menstruating women, anemia may result from malabsorption of vitamin B₁₂ and iron. Decreased absorption of calcium may cause osteoporosis and metabolic bone disease. Patients are required to take nutritional supplements that usually prevent these deficiencies.

Gastric-bypass operations also may cause "dumping syndrome," whereby stomach contents move too rapidly through the small intestine. Symptoms include nausea, weakness, sweating, faintness, and, occasionally, diarrhea, all of which occur after eating. Some patients experience weakness and excessive perspiration after eating sweets. The patient must lie down until symptoms pass.

The more extensive the bypass operation [the longer the length of the bypassed small intestine], the greater is the risk of complications and nutritional deficiencies. Patients with extensive bypasses of the normal digestive process require not only close monitoring, but also life-long use of special foods and medications.

Illustration of Biliopancreatic diversion (BPD)