People with diabetes who take soluble fibre supplements have slightly lower blood sugar than diabetics who do not add this type of fibre to their diets, a research review that was published this month finds.
Researchers focused on supplements containing viscous fibre, a type of soluble fibre that forms a thick gel when mixed with water. Foods like legumes, asparagus, oats, and flax contain viscous fibre; supplements with this type of fibre include guar gum, psyllium and pectin.
To examine the connection between viscous fibre supplements and blood sugar, researchers examined data from 28 clinical trials with a total of 1,394 participants with diabetes. People were randomly chosen to take viscous fibre supplements or to use other types of supplements without viscous fibre or no supplements at all.
Among the people taking viscous fibre supplements, half consumed doses above 13g daily, for periods ranging from three weeks to a year. Compared to participants who did not take viscous fibre, those who did had better blood sugar control. They had lower levels of haemoglobin (Hb) A1c, which reflects average blood sugar over about three months. They also had lower blood sugar levels on an empty stomach, known as fasting glucose levels.
These results "suggest that intake of around one tablespoon of concentrated viscous fibres such as konjac, guar, pectin or psyllium would result in reductions in A1c and other diabetes risk factors," said senior study author Dr Vladimir Vuksan of St Michael's Hospital and the University of Toronto in Canada.
People with diabetes have long been advised to consume more fibre as one way to help lower their blood sugar. But many, particularly those who follow a typical Western diet with lots of meat and potatoes, do not get anywhere near enough fibre to make a meaningful difference in diabetes, the study authors note in Diabetes Care.
Supplements have become an increasingly common way for these patients to get more fibre. While the reason viscous fibre seems to lower blood sugar is not clear, scientists think that it might work in a variety of ways, including improving microbial health in the gut.
Most trials in the study focused on HbA1c levels. Readings above 6.5 per cent signal diabetes. Fibre supplements were associated with average A1c reductions of 0.58 per cent, which is greater than the minimum 0.3 per cent reduction the US Food and Drug Administration looks for in evaluating new diabetes drugs, the study authors note.
In addition to HbA1c, other markers of diabetes including fasting glucose and insulin sensitivity were also improved.
One limitation of the analysis is that some studies were too small and brief to draw broad conclusions about the long-term impact of fibre supplements on all patients with diabetes.
It is also possible that so-called publication bias, or the disclosure of only positive trial results, may have made fibre supplements appear more effective than they really are, the study authors note.
"These results suggest that viscous fibre supplements could be considered in the management of type 2 diabetes," said Nour Makarem, a researcher at Columbia University Irving Medical Center in New York City who was not involved in the study.
"However, additional studies are needed to further examine the effects of different types of fibre on blood glucose regulation and to comprehensively study the health effects and the optimization of incorporating viscous fibre supplements into a healthful diet pattern," Marakem said by email.