Results found consumption of high-amylose maize resistant starch (HAM-RS2) correlated with improved insulin sensitivity in females with insulin resistance.
HAM-RS2, which is found in starch foods such as green bananas, potatoes, and high-amylose corn, has previously been investigated for its effects on gastrointestinal health.
Resistant starch is only partially digested by human pancreatic enzymes. As a result, the starch molecules are cleaved in the colon by bacterial enzymes and then used as fuel by the gut microbiota.
Study outline
One randomised, placebo-controlled, double-blind, cross-over study enrolled 40 non-diabetic women aged 22–67 years in the normal-weight to obese BMI range (20.6–47.4 kg/m2).
Two doses of HAM-RS2 were tested, 15 and 30 g per day, administered in the form of cookies.
Participants were randomised in when they received the experimental and placebo product. Each regimen was 4 weeks, with a 4-week wash-out period in between.
Insulin sensitivity was assessed at the end of each 4-week arm of product consumption via a glucose tolerance test.
Results found that on average, insulin sensitivity was approximately 16% higher in subjects who received a daily 30 g dose of the fibre when compared to the control group.
Women who completed all criteria of the study recorded insulin sensitivity values 23% higher than the control group.
“HAM has a subtle effect on insulin sensitivity, but has never been shown to affect diabetes risk, which is more complex,” explained lead author Dr Barbara Gower, from the Department of Nutrition Sciences, University of Alabama at Birmingham (UAB).
“In epidemiological studies, whole grain consumption has been associated with reduced risk for T2D.”
Starch breakdown
Starches are divided into three groups: rapidly digestible starch (RDS, digested within 20 minutes), slowly digestible starch (SDS, digested between 20 and 120 minutes), and resistant starch (RS). RS is not digested but is fermented in the large intestine and has 'prebiotic' properties.
Resistant starch can be further divided into five types – RS1, RS2, RS3, RS4, and RS5– based on the properties that render them indigestible.
RS5 is considered a relatively a new category. It is created through a process that involves heating and cooling starchy foods with a specific lipid (e.g., fats or waxes)
Resistant starch can be found naturally in cold cooked potatoes, pasta and rice as well as baked beans and lentils.
Poor fibre intake
A UK government report has flagged dietary fibre intake as a nutrient of concern and deficiency is common in the country. The report stated average fibre intakes among adults are consistently lower than the recommended 30 g/day.
The delivery method of RS was a point of contention in the study as Dr Gower pointed out that subjects were unable to keep up with the regimen, expressing a dislike for the cookies and a preference for RS sachets.
“This was a demanding study, requiring women to commit to almost 6 months of involvement, with at least 12 weeks of product consumption, and three intravenous glucose tolerance tests.”
“In addition, some women tired of consuming two servings of cookies each day; a greater variety of snack choices may have increased adherence.”
Starch-infused bagels
Another recent study found that consumption of a HAM-RS2 bagel reduced the amount of insulin needed to control post-meal glucose levels while improving fasting insulin sensitivity in adults at increased risk of T2D.
The study, which was supported by Canada Bread Limited, recorded lower fasting (22.1%), 2-hour (23.3%) and 3-hour (18.9%) insulin levels as well as a 23.1% lower fasting insulin resistance when compared to the control bagel treatment.
Source: Nutrition & Metabolism
Published online ahead of print, DOI: 10.1186/s12986-016-0062-5
“Baseline insulin sensitivity affects response to high-amylose maize resistant starch in women: a randomized, controlled trial.”
Authors: Barbara Gower et al.
Source: The Journal of Nutrition
Published online ahead of print, doi: 10.3945/jn.116.239418
“Resistant Starch Bagels Reduce Fasting and Postprandial Insulin in Adults at Risk of Type 2 Diabetes.”
Authors: Alison Duncan et al.