Ask the Doctors

Dear Doctor: I always thought fiber was fiber, but it seems that the FDA is about to crack down on food manufacturers who add weird ingredients to bulk up processed foods. Does it really matter whether the fiber we're eating is added or is a natural part of our food?

Dear Reader: For anyone not familiar with this topic, 26 ingredients that food manufacturers add to their products in order to bump up the dietary fiber numbers on food labels are currently under review by the Food and Drug Administration. These include fibers that have been extracted from plant-based sources, as well as synthetic fibers cooked up in a lab.

For example, inulin, frequently seen on processed food labels, is a naturally occurring carbohydrate that resists digestion. (It's the "resists digestion" that makes it, or any carbohydrate, qualify as dietary fiber.) Found in more than 36,000 plant species, inulin is most often sourced from chicory when it is used in food production. Polydextrose, on the other hand, another common entry on food labels, is a synthetic fiber. It may sound familiar if you've read the food labels on products ranging from breakfast cereals and baked goods to ice cream, salad dressing and even certain beverages.

All of which leads to the point behind the FDA's move to reconsider what, specifically, can count as a dietary fiber on food labels. The argument isn't whether or not these substances qualify as fiber. They are carbohydrates that can't be fully digested -- so in the broadest sense, they do. However, their presence in foods that are otherwise nutritional black holes can, in truth, allow manufacturers to use language like "high in fiber." And that, according to those behind the push to bump certain types of fiber from food labels, can mislead consumers as to the nutritional value of certain foods.

The FDA's goal, as stated in a rule published in 2016, is that "only certain naturally occurring dietary fibers such as those found in fruits, vegetables and whole grains, and added isolated or synthetic fibers that FDA has determined have a physiological effect that is beneficial to human health, could be declared on the label under 'Dietary Fiber.'"

And the truth is, whether or not those oddball added fibers meet the "beneficial to human health" criteria is not yet known.

Research has proven the beneficial effects of naturally occurring dietary fiber for decades now. Soluble fiber, which dissolves in water, forms a gel-like substance during digestion and can help slow the absorption of simple sugars. Insoluble fiber, which does not dissolve, adds bulk to the materials passing through the digestive system and helps with elimination. Diets high in fiber are associated with improved bowel health, lower blood cholesterol levels and regulation of blood sugar levels. In the bigger picture, studies associate high-fiber diets with lower rates of cardiovascular disease and certain cancers.

At this time, the FDA has hit the "pause" button on the food label decision when it comes to fiber. Meanwhile, if that sugary carton of yogurt is claiming to be high in fiber, we think a glance at the small print on the food label could be educational.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

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