Randomised trial · Nutrients · 2016Conflicts declared

Barley and oat flour phytochemicals in a muffin trial

Sawicki CM, McKay DL, McKeown NM, Dallal G, Chen C-, Blumberg JB · Free full text

In 13 overweight adults, muffins made with whole barley or oat flour did not raise blood levels of grain phytochemicals or change markers of blood sugar, inflammation or antioxidant activity over 24 hours, compared with refined wheat muffins.

The authors say the dose and the glucose drink given at the same time may explain the lack of effect.

What they found

Studies in people

Phytochemical levels

Blood levels of tocopherols, phenolic acids and alkylresorcinols tended to rise from baseline, but there were no significant differences between the barley, oat and refined wheat muffins. The authors suggest the amount of phytochemicals in the muffins may have been too low to raise blood levels.

Blood sugar and insulin

The barley and oat muffins did not change the blood sugar or insulin response after the glucose drink compared with the refined wheat muffin. The authors note that a previous study found at least 10 g of barley beta-glucan was needed to see a benefit on blood sugar in obese women, while the muffins here provided 2.4 to 3.2 g of soluble fibre.

Inflammation and blood vessels

Markers of inflammation such as hsCRP, IL-6, IL-8 and TNF-alpha, and a marker of blood vessel remodelling called MMP-9, did not differ between the three muffins over 24 hours.

Antioxidant activity

Measures of antioxidant capacity, including FRAP, total thiols and the resistance of LDL cholesterol to oxidation, were unchanged after all three muffins. The authors say this matches most other studies comparing whole grains with refined grains.

What the authors conclude

“In conclusion, we found no statistically significant differences in the bioavailability or postprandial metabolic effects of whole oat and whole barley compared to a refined wheat control when administered in muffins together with a glucose bolus challenge.”

Sawicki CM, McKay DL, McKeown NM, Dallal G, Chen C-, Blumberg JB, 2016

Also in their conclusions

They conclude that they found no statistically significant differences in the bioavailability or postprandial metabolic effects of whole oat and whole barley compared to a refined wheat control when administered in muffins together with a glucose bolus challenge.
They advise that future studies should consider using whole grain varieties with minimal processing that deliver the highest possible intake of bioaccessible phytochemicals in the context of whole or functional foods.

How it was done

The authors wanted to find out whether phytochemicals in the outer bran layer of whole grains, not just fibre, could help explain the health benefits linked to whole grains. They also wanted to test whether these compounds affect markers of type 2 diabetes and heart disease risk.

They ran a randomised, three-way crossover trial in 13 healthy overweight or mildly obese adults aged 40 to 70. Each person ate muffins made with 48 g whole oat flour, whole barley flour, or refined wheat flour plus cellulose, with a glucose drink, and had blood tests over 24 hours. There was a one-week washout between each muffin.

What it can’t tell you

The study was small, with only 13 people, and all were overweight or mildly obese adults, so the results may not apply to other groups.
The muffins were eaten with a large glucose drink, which may have overwhelmed any small effect of the grains on blood sugar.
The phytochemical content of the muffins was not measured, so it is not known exactly how much was eaten.

Who paid

Conflicts: The authors declare no conflict of interest. N.M.M. has received funding from ILSI North America and the General Mills Bell Institute of Health and Nutrition; serves as an unpaid science advisor for the Whole Grains Council. J.B.B. is a member of the Scientific Advisory Board at the Center of Excellence in The Quaker Oats Company.
Authors work at: Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, USA

The paper

Title: Phytochemical Pharmacokinetics and Bioactivity of Oat and Barley Flour: A Randomized Crossover Trial
Type: Randomised controlled trial
Evidence: Studies in people
Summarised from: Full text
Cite: Sawicki CM, McKay DL, McKeown NM, Dallal G, Chen C-, Blumberg JB (2016). Phytochemical Pharmacokinetics and Bioactivity of Oat and Barley Flour: A Randomized Crossover Trial. Nutrients. doi:10.3390/nu8120813Free full text PubMed 27983687 DOI

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