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Tuesday, October 04, 2005

Fat Absorption, Fat Substitutes After WLS

Our friend Kabuki Dancer recently asked about fat absorption after gastric bypass weight loss surgery. She also asked about fat substitutes and how they work in our bodies. Here’s what I learned:

Fat Absorption:
In a gastric bypass the stomach size is reduced to about a cup and most of the small intestine is bypassed. The stomach outlet is attached to the jejunum (middle section) of the small intestine. Most food absorption occurs in this section. The specialized cells of the jejunum contain digestive enzymes, carrier proteins and other secretions. However, because the digestive tract has been significantly reduced in the bypass there is less time for foods to be absorbed. In the case of gastric bypass the body will absorb fats in limited amounts.

Incidentally, most gastric bypass patients do not tolerate fats in the form of fried food. Eating fried foods can cause vomiting, diarrhea and weight gain. Monounsaturated good fats found in olives, nuts, avocados, olive oil and canola oil should be consumed sparingly. Polyunsaturated fats, the Omega-6 fats found in nuts, seeds, grains, leafy vegetables, soybeans, dairy products, corn oil, safflower oil and soybean oil, should also be consumed in limited quantity. Saturated (animal and dairy fat) and trans fats (hydrogenated oils) should be avoided.

In a lap-banding procedure the small intestine is not shortened or disrupted so the opportunity for full-fat absorption exists as it did before the lap-band was installed. Most lap-band patients do not report the nausea associated with fat intake that a gastric bypass patient reports.

Fat Substitutes:
As you know, I turn to Dr David Katz often for general health information. In his book “The Way To Eat” page 219 he talks about fat substitutes. His final conclusion states “For now, limited use of products that use fat substitutes seems quite reasonable, but reliance on fat substitutes as a primary strategy to reduce fat or calorie intake cannot be recommended.” Applying his conclusion to the WLS lifestyle we must again use the word, moderation.

Here is what he says about fat substitutes:

- The principal reason for fat substitution is to reduce total fat and calorie intake

- The available evidence suggests that fat substitutes are generally effective at reducing fat intake, but not necessarily at reducing calorie intake, because people often make up for the removed fat calories by eating more calories from other sources.

- There are three basic categories of fat replacers: fat mimetics, fat substitutes, and low-calorie fats. Fat mimetics are nonfat food items that replace fats; mimic in the properties fats confer including effects on flavor and palatability, creaminess and mouth feel; and add fewer calories than the fats they replace. Examples include starches, cellulose, pectin, proteins, dextrins, polydextrose, and other products.

- Fat mimetics are often useful in desserts and spreads, and are generally of less use in foods that require frying or other high-temperature preparation. Fat mimetics range from 0 to 4 kcal (kilocalorie) per gram.

- Low-calorie fats are fat molecules (triglycerides) modified to deliver less than the 9 kcal per gram of most naturally occurring fats. Commercially produced low-calorie fats are poorly absorbed due to the attachment of fatty acids of varying chain lengths to glycerol; the calorie content of such products as Caprenin (Proctor & Gamble) and Salatrim (Nabisco) is approximately 5 kcal per gram.

- Soluble fibers used as fat substitutes confer health benefits independent of fat replacement, such as cholesterol reduction and reduced insulin release. For some individuals, processed, fat-reduced foods could become a significant source of soluble fiber.

- The most studied fat substitute to date is a sucrose polyester, Olestra, developed by Proctor & Gamble and marketed as Olean. Because it is essentially indigestible, Olestra passes through the gastrointestinal tract carrying fat-soluble micronutrients with it. Approved by the FDA for use in snack foods, Olestra is controversial because of the potential for both gastrointestinal upset and the leaching of these fat-soluble nutrients.

Olestra decreases absorption of vitamins A, D, E and K, but this effect is at least partially compensated by the fortification of Olestra-containing foods with fat-soluble vitamins. Most evidence suggests that Olestra-containing snack foods, consumed under ordinary circumstances, do not produce any more gastrointestinal symptoms than standard products.

- A variety of products derived from alteraions of fat molecules are under development.

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