Increasing Soluble Fiber Leads to Lower HbA1c Levels in Type 2 Diabetes

More evidence that the higher the dietary fiber intake, the greater the health-promoting benefits, and soluble fiber alone may achieve reduce hemoglobin A1c levels substantially.

With Vladimir Vuksan, PhD, Frank Hu, MD, PhD, and Joanne Slavin, PhD, RD

The health benefits of dietary fiber continue to inform clinical recommendations. In a report by a team of Canadian researchers,1 individuals who regularly consumed soluble fiber were found to have lower hemoglobin A1c (HbA1c) levels, an important benchmark for people with diabetes.

In this meta-analysis, the researchers noticed that soluble fiber (or as they prefer, viscous fiber) at a median dose of at least 13 grams a day (half of the individuals had more, half had less)—the equivalent of one tablespoon of soluble fiber—reduced HbA1c levels by about .60%.1 That reduction was similar to that achieved by some antidiabetes medications, said Vladimir Vuksan, PhD, professor of clinical nutrition at St. Michael's Hospital in Toronto and a faculty member at the University of Toronto, Canada.

For instance, a patient with a typical HbA1c of 8% may see the HbA1c 7.5% simply by increasing the amount of soluble fiber to their daily diet, if these results held true for them. This has the potential to offer a simple treatment strategy for any patient with diabetes who would benefit from a reduced HbA1c target for anyone with diabetes.

Soluble Fiber May Be Effective in Driving HbA1c Down

To arrive at these recommendations, the researchers identified 28 clinical trials to review.  Most of the selected studies used the fiber in a concentrated form (ie, a dietary supplement) that was added to food and beverages; yet, six of the trials examined the soluble fiber content from foods.

Overall, consuming the viscous fiber at the median dose of one tablespoon daily decreased the HbA1c by the .58%, Dr. Vuksan said. "A reduction of -.58% in HbA1c seen in our study exceeds the clinically meaningful threshold proposed by the US Food and Drug Administration for the development of new drugs for diabetes (that is, higher than -0.3%).'' The reduction achieved with viscous fiber was similar to that from some diabetes drugs, he said

Adding soluble fiber be it oatmeal or a supplement is beneficial for those with T2D.People with type 2 diabetes looking to reduce their HbA1c can add a soluble fiber supplement or a bowl of oatmeal daily, according to the latest research.

"The take-home message is simple," Dr. Vuksan told EndocrineWeb. "This research gives us confidence to advise an increase in the amount of viscous fiber in the diet for all individuals with type 2 diabetes (T2D). The results of our study suggest that an intake of approximately one tablespoon of viscous fiber per day, either taken as a fiber concentrate in a form of a supplement added to regular food and beverages, such as psyllium, konjac or guar gums, or by consuming foods that are a rich source of viscous fiber (beta-glucan) such as oats, would result in a significant reduction in HbA1c and other diabetes control markers."

Zeroing In on Dietary Fiber Promises Significant Health-Promoting Benefits

Soluble, or viscous fiber, dissolves in water to form a gel-like material, which slows the absorption of glucose, and in turn, leads to lower blood sugar levels, the authors said. Besides oats, good sources of soluble fiber can be found in peas, beans (legumes), apples (from the peel), carrots, and barley, as well as from viscous fiber supplements.2

Individuals still benefit substantially from insoluble dietary fiber (ie, whole wheat and wheat bran, nuts and seeds, and vegetables), which has been reported to decrease all-cause mortality, incidence of cardiovascular disease and mortality, type 2 diabetes, as well as breast and colorectal cancers.3 In fact, data gathered in a systematic, meta-analysis of 185 prospective studies and 58 clinical trials, suggested a decrease of 15-30% in these adverse disease outcomes,3 which was published in Lancet.

Not surprisingly, the greatest risk reductions were seen in the groups consuming the highest intake of dietary fiber, and which was reinforced with evidence of a dose-response effect.3

Men who are 51 years and older should aim for 30 grams of dietary fiber a day, experts say, while younger men need about 28 grams daily; for women, those at 51 years or more are advised to aim for at least 21 grams, and younger women, at least 25 grams daily.2

Supplements May Fulfill Needs When Diet Changes Miss the Mark

While some critics worry that encouraging patients to take a soluble fiber supplement is the wrong message, and that the findings may give patients an easy out, Dr. Vuksan responded by saying the same concern might be expressed about diabetes drugs—that people who take metformin may have a tendency to lean on the drug and ignore their diet.

Most foods containing viscous fibers are already suggested in the dietary guidelines of major health organizations, he said, so it behooves clinicians to encouraged patients with T2D as well as prediabetes to increase their intake of viscous fiber—in foods and/or as a dietary supplement.2

“Taking a soluble fiber supplement alone will not give individuals the other beneficial components in fiber-rich foods,” said Frank Hu, MD, PhD, professor, and chair of nutrition, Harvard T.H. Chan School of Public Health who reviewed the findings but did not participate in the study.

The message is not ''pop a pill and forget the diet as overall, I think the evidence (about soluble fiber supplements) is modest in terms of the benefits," he told EndocrineWeb. "For people who have difficulty in terms of consuming a sufficient amount of fiber-rich foods or those with certain conditions, such as diabetes, I think fiber supplements can be considered as a kind of supplemental or complementary approach."

Nutrition Education, Lifestyle Remain Lynchpins in Diabetes Care

"Since all the trials lasted on average about only eight weeks, the amount of soluble fiber supplementation was not that high, on average 13 grams, and patients were still able to see a significant reduction in their HbA1c," Dr. Hu said.

The findings from the Valnuk study are important, said Joanne Slavin, PhD, RD, professor of food science and nutrition at the University of Minnesota in St. Paul, in reviewing the findings. "We are always trying to get consumers to eat more foods high in dietary fiber, yet we find that the usual intake is nearly always less than half of the amount recommended, so fiber supplements may be appropriate for those patients who do not or cannot consume adequate fiber."

Since diet remains the first line of defense in managing T2D, the idea that soluble fibers may help glucose control is a good strategy to know about, Dr. Slavin said. She encourages people to eat more whole grains, legumes, vegetables, nuts, and fruits, to boost their fiber intake for all reasons,''but fiber supplements offer another alternative with sufficient research support as to their effectiveness."

None of the doctors have any relevant financial disclosures.

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