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.
Highlights
Higher consumption of whole-grain foods has been linked to a lower risk of type 2 diabetes mellitus (T2DM), cardiovascular disease (CVD) risk, and mortality in large prospective cohorts [1,2,3,4,5,6].While dietary fiber is a predominant nutritional attribute of whole grains, there are a host of potential phytochemicals present in whole-grains that might confer metabolic health benefits [7,8]
The exclusion criteria used to screen for eligibility included: (a) presence of cardiovascular, endocrine, gastrointestinal, and renal diseases; (b) use of estrogen, with or without progesterone; (c) use of medications known to affect lipid metabolism; (d) use of medications known or suspected to influence blood pressure (BP); (e) gastrointestinal diseases and conditions or medications influencing gastrointestinal absorption; (f) chronic kidney disease; (g) endocrine disorders including diabetes and untreated thyroid disease; (h) rheumatologic disorders; (i) active treatment for cancer of any type ≥1 year; (j) regular use of oral steroids; (k) systolic blood pressure
The present study examined whether an acute intake of muffins made with whole oat or barley flour would increase plasma phytochemical status and improve some biomarkers of CVD risk
Summary
Higher consumption of whole-grain foods has been linked to a lower risk of type 2 diabetes mellitus (T2DM), cardiovascular disease (CVD) risk, and mortality in large prospective cohorts [1,2,3,4,5,6].While dietary fiber is a predominant nutritional attribute of whole grains, there are a host of potential phytochemicals present in whole-grains that might confer metabolic health benefits [7,8]. Β-glucan is the predominant soluble fiber found in oats and barley and has been shown to reduce serum cholesterol and improve post-prandial insulin and glucose responses in healthy and diabetic adults [12,13]. It has been suggested these and other health benefits of whole grains may be the result of a synergistic effect of the fiber and the constituent phytochemicals [14]. 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 (OGTT)
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