Phytochemical pharmacokinetics and bioactivity of oat and barley flour: a randomized crossover trial

Authors: SAWICKI, CALEIGH - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; MCKAY, DIANE - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; MCKEOWN, NICOLA - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; DALLAL, GERARD - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; CHEN, CHUNG-YEN - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; BLUMBERG, JEFFREY - Jean Mayer Human Nutrition Research Center On Aging At Tufts University

Submitted to: Nutrients
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2016
Publication Date: 12/15/2016
Citation: Sawicki, C., McKay, D.L., McKeown, N.M., Dallal, G.E., Chen, C., Blumberg, J.B. 2016. Phytochemical pharmacokinetics and bioactivity of oat and barley flour: a randomized crossover trial. Nutrients. 8:813. doi: 10.3390/nu8120813.

Interpretive Summary: Higher consumption of whole-grain foods has been linked to a lower risk of type 2 diabetes mellitus, cardiovascular disease, and mortality. While dietary fiber is a predominant nutritional attribute of whole grains, there are phytochemicals present in whole-grains that might confer metabolic health benefits. These phytochemicals are located principally in the outer bran layer and include alkylresorcinols, flavonoids, lignans, phenolic acids, phytosterols, tocopherols, and tocotrienols. Once they are absorbed and metabolized, these phytochemicals can improve health via anti-inflammatory, antioxidant, and/or anti-proliferation effects. Thus, health benefits of whole grains may be the result of a synergistic effect of the fiber and constituent phytochemicals. The major bioactives in barley include phenolics, tocols, and folate, while those in oats include tocopherols and tocotrienols, phenolic acids, sterols, selenium, and avenanthramides. To date, no controlled metabolic studies have determined the acute bioavailability and pharmacokinetics of oats and barley flour or considered the post-prandial effect of these phytochemicals on markers of metabolic, inflammatory, and oxidative stress in response to an oral glucose tolerance test. Thus, we conducted a human study in which people were randomized to receive muffins made with either 48 g whole oat flour, whole barley flour, or refined wheat flour plus cellulose. At the same time, an oral glucose tolerance test was administered. In addition to plasma phytochemical concentrations, glucose and insulin responses, biomarkers of antioxidant activity, lipid peroxidation, inflammation, and vascular remodeling were determined over a 24-h period. We found no significant differences in the absorption or postprandial metabolic effects of whole oat and whole barley compared to a refined wheat control. These null results may be due, in part, to the inclusion criteria for the subjects, dose of the whole grains, and concurrent acute administration of the whole grains with the glucose bolus. Future studies should consider using whole grain varieties with minimal processing that deliver the highest possible intake of absorbable phytochemicals in the context of whole or functional foods.

Technical Abstract: While dietary fiber plays an important role in the health benefits associated with whole grain consumption, other ingredients concentrated in the outer bran layer, including alkylresorcinols, lignans, phenolic acids, phytosterols, and tocols, may also contribute to these outcomes. To determine the acute bioavailability and pharmacokinetics of the major phytochemicals found in barley and oats, we conducted a randomized, three-way crossover trial in 13 healthy subjects, aged 40-70 years with a body mass index (BMI) of 27-35.9 kg/m2. After a two-day run-in period following a diet low in phytochemicals, subjects were randomized to receive muffins made with either 48 g whole oat flour, whole barley flour, or refined wheat flour plus cellulose (control), with a one-week washout period between each intervention. At the same time, an oral glucose tolerance test was administered. In addition to plasma phytochemical concentrations, glucose and insulin responses, biomarkers of antioxidant activity, lipid peroxidation, inflammation, and vascular remodeling were determined over a 24-h period. There was no significant effect on acute bioavailability or pharmacokinetics of major phytochemicals. Administered concurrently with a glucose bolus, the source of whole grains did not attenuate the post-prandial response of markers of glucoregulation and insulin sensitivity, inflammation, nor vascular remodeling compared to the refined grain control. No significant differences were observed in the bioavailability or postprandial effects between whole-oat and whole-barley compared to a refined wheat control when administered with a glucose challenge. These null results may be due, in part, to the inclusion criteria for the subjects, dose of the whole grains, and concurrent acute administration of the whole grains with the glucose bolus.