Fiber: The New Face of Weight Management

Americans are in the midst of an obesity epidemic. According to recent National Health and Nutrition Examination Survey (NHANES) data, two out of every three people—127 million Americans—are carrying too much weight, with a body mass index (BMI) of at least 25. Of those, half are obese, with a BMI of 30 or greater, while those with a 25 to 30 BMI are “merely” overweight. Unfortunately, statistics show an increasing propensity for putting on pounds. Since 1976, obesity numbers have more than doubled, and people classified as overweight jumped 36%.

To combat our growing waistlines, new 2005 Dietary Guidelines for Americans emphasize calorie control and promote low-calorie, high-fiber foods, like fruits, vegetables, legumes and whole grains.

High-fiber diets are well known for their ability to control weight. Several large scientific studies show people who eat high-fiber diets weigh less and have lower BMIs than those who don’t eat high-fiber foods. People on high-fiber, low-fat diets will lose more weight and keep it off longer, compared to those just on low-fat diets. One study from Tufts University, Medford, MA, found the simple addition of 14 grams of fiber a day produced a 5-lb. weight loss in four months, regardless of caloric intake.

“With studies involving 40 to 80 grams of fiber, you’ll see an even greater weight loss,” says Glenn Gaesser, Ph.D., professor and director, Kinesiology Program, University of Virginia, Charlottesville; he also works with The Wheat Foods Council, Parker, CO. “The more fiber you eat, the more pounds you’ll lose.”

In light of these health benefits and with new interest in making fiber label claims, many manufacturers are adding fiber to a variety of food products.

How much do we need?

Current fiber intake levels leave much to be desired. The average American consumes roughly 13 or 14 grams a day. This is less than half of the 25 to 38 grams of fiber recommended for healthy adults in the Institute of Medicine’s (IOM) Dietary Reference Intakes for Fiber published in 2002, and the 20 to 35 gram level other health organizations, like the Chicago-based American Dietetic Association, advise.

Although the typical American diet is generally low in fiber, many food sources are available. In nature, whole-grain cereal fibers and legumes possess the highest concentrations, which can range from 4 to 10 grams per serving. Fruits and vegetables, while healthy options, generally average only 2 to 3 grams per serving. Therefore, they aren’t as efficient for significantly upping fiber intakes.

All fiber is not created equal

The nutrition community generally defines dietary fiber as the part of a plant that human enzymes in the stomach or the small intestine do not digest. It is then divided into two broad groups, soluble and insoluble, based on its physiological effects and chemical breakdown.

Soluble fibers dissolve easily in water and include pectins, gums, mucilages, beta-glucans, polyfructoses and oligosaccharides. They occur naturally in oatmeal, oat bran, psyllium, flaxseed, rice bran, barley, peas, beans, lentils and various fruits. During digestion, soluble fiber absorbs water, forming a gel that binds bile, which produces a cholesterol-lowering effect, slows down absorption and produces a sense of fullness. Then, soluble fiber travels to the colon, where beneficial bacteria, also known as probiotics, ferment it. When humans ingest large amounts of certain types of soluble fibers, their rapid fermentation causes bloating and gas. This issue often limits the amount of soluble fiber food manufacturers add to their products.

Because a portion of soluble fiber is actually digested after fermentation, some energy is released. According to Jit Ang, executive vice president, International Fiber Corporation (IFC), North Tonawanda, NY: “Although most dietary fibers are listed as 0 calories on the label, they may provide a small amount of energy, ranging from 0 to just under 4 kcals per gram. This would depend on their soluble-fiber content and fermentability. Normal carbohydrate yields 4 kcals per gram, so it’s still less than that.”

Viscosity is another beneficial characteristic of soluble fiber. “Viscosity is critical to slowing stomach emptying and regulating the uptake of energy from a meal,” says Coni Francis, Ph.D., R.D., scientific affairs manager, GTC Nutrition, Golden, CO. “This effect is important to controlling glycemic response and blunting the after-meal insulin surge, which is thought to have positive effects for healthy weight management.”

Like soluble fiber, insoluble fiber is fermented by bacteria in the gut. However, rather than being broken down in the upper colon, insoluble fiber is generally broken down in the lower colon. This difference produces a different set of health benefits, including increasing fecal bulk size and supporting laxation.

Fiber influences weight loss and satiety in several ways. First, foods naturally high in insoluble fiber usually require more chewing, giving the body more time to digest them and causing people to eat slower. Second, high-fiber foods in general tend to have a large volume, producing a greater mass in the stomach and greater likelihood of feeling full faster. Finally, their low energy density means high-fiber foods provide a large amount of food with little calories. Significant food sources of insoluble fiber in the American diet are wheat bran, barley, brown rice, beets, carrots and celery.

Lately, however, the distinctions between soluble and insoluble fiber have become blurred. Recently, food scientists discovered that not all soluble fiber is viscous and has hypocholesterolemic effects, and insoluble fiber’s association with laxation is also inconsistent. Thus, some traits thought to be characteristic of soluble fibers are popping up in insoluble fibers, and vice versa.

Joanne Slavin, Ph.D., professor of food science, University of Minnesota, St. Paul, says that in order to address these issues, as well as the fact that research shows the effect of fiber found in food is generally greater than the effect of isolated fiber fractions, new definitions and recommendations were developed by IOM in 2001. Published as Dietary Reference Intakes (DRIs) the next year, these guidelines state that “dietary fiber consists of nondigestible carbohydrates and lignins that are intrinsic and intact in plants and functional fiber (also known as added fiber) consists of isolated nondigestible carbohydrates that have beneficial physiological effects in humans.”

IOM’s fiber definition, however, has not been well received among industry, and much controversy surrounds this issue. Consequently, other definitions focusing on the physiological effects of fiber in the body, or the analytical methods used to test for fiber, are also being used.

What about resistant starch?

Resistant starch is not easily categorized. It can function as a naturally occurring fiber and is found in corn, green bananas, and cooked, cooled potatoes. It’s called resistant starch because it “resists” digestion in the small intestine. There are four different types, some soluble, others insoluble.

According to Rhonda Witwer, business development manager for nutrition, National Starch Food Innovation, Bridgewater, NJ, the company’s Hi-maize® resistant starch acts like an insoluble fiber in the body. “Like insoluble fiber, this resistant starch has a laxative effect. Like some soluble fibers, it is fermented in the large intestine, which keeps colon cells healthy,” she says. However, it is unique, she continues, because “unlike soluble, it is fermented deep in the distal—lower—colon and produces a compound called butyrate when fermented by probiotic bacteria. A newly published study in Obesity, in April 2006, found that Hi-maize and butyrate stimulate the expression of two satiety hormones, PYY (peptide YY) and GLP-1 (glucagon-like peptide 1) in the distal colon. This points out the importance of the fermentation location and the importance of nutrientgene interactions in weight management.”

Witwer notes that other studies have shown resistant starch increases insulin sensitivity and lowers glycemic response of food, which also may impact weight management. “A clinical study published by Janine Higgins, Ph.D., from the University of Colorado, just last year, suggests that eating a meal high in high-amylose corn RS2 increases the body’s fat-burning ability by 23%,” she says.

Since it is partly a starch, it does contain some calories (approximately 2.2 to 2.8 kcal per gram), notes Witwer, but less than carbohydrate or flour.

Fiber for all

Consumers consider fiber a hot topic. A study by HealthFocus International, St. Petersburg, FL, commissioned by National Starch Food Innovation, found that 38% of consumers state that they always or usually maintain a high-fiber diet. Another 31% said they are increasing their fiber intake.

New whole-grain recommendations have helped, as well. USDA Dietary Guidelines advise half of all our grain servings (approximately 3 oz.) come from whole grains. However, what constitutes a whole grain remains unclear.

Nevertheless, consumers are clamoring for more whole-grain products, and food manufacturers are only too willing to comply. In 2004 alone, nearly 100 new wholegrain products were introduced. Breads, cereals and bakery products reformulated with whole grains and extra fiber are particularly proliferous. Now, manufacturers are adding fiber to traditionally low-fiber foods like chocolate milk, cookies and cakes.

“Beverages, dairy products, like ice cream and yogurt, and nutritional bars are very big areas for us,” says Sally Romano, vice president of sales and marketing, Sensus America LLC, Monmouth Junction, NJ, makers of several inulin and fructo-oliogosaccharide (FOS) products. Inulin is a prebiotic soluble fiber extracted from the chicory root, and FOS is partially hydrolyzed inulin. “Because our new liquid inulin, Sweet Liquid Fiber, is 45% as sweet as sugar, it can replace 20% to 30% of these (carbohydrate nutritive) sweeteners, depending on the product,” she says. As the sweetener contributes only 1.7 kcal per gram, this saves considerable calories. The ingredient also can mask any aftertaste from high-intensity sweeteners while adding fiber.

In order to make a fiber claim, manufacturers must adhere to specific requirements. These include: “High fiber”—must contain 5 grams or more per serving; “Good source of fiber”—2.5 grams to 4.9 grams per serving; and “More fiber” or “Added fiber”—at least 2.5 grams more per serving than the reference food.

Resistant starch is another option for adding fiber to products without changing taste and texture. “Because resistant starch performs just like flour—it has a clean flavor, soft texture and tight structure—we recommend a direct 25% flour substitution for consumers and dietitians. In healthcare operations, foodservice operations can mix it into mashed potatoes or applesauce to up the fiber,” says Witwer. “For specific products, each one is formulated individually, based on the end result.”

Where is the future of fiber and foods heading? When it comes to weight management, more and more companies are looking at glycemic index and its affect on blood sugar levels, appetite and weight management. “Blood sugar level is something you can feel,” remarks Witwer. “This is where the science is heading.”

Diane A. Welland, R.D., is a registered dietitian and holds a Masters of Science from New York University and dual Bachelor degrees in Communications and Human Nutrition from Rutgers University. For the last 12 years, she has been a freelance food and nutrition writer and communications consultant specializing in culinary and nutrition foodservice. She can be reached at [email protected].