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REVIEW
Review of human studies investigating the post-prandial
blood-glucose lowering ability of oat and barley food products
SM Tosh
Oat and barley foods have been shown to reduce human glycaemic response, compared to similar wheat foods or a glucose
control. The strength of the evidence supporting the hypothesis that the soluble fibre, mixed linkage b-glucan, reduces glycaemic
response was evaluated. A search of the literature was conducted to find clinical trials with acute glycaemic response as an end
point using oat or barley products. Of the 76 human studies identified, 34 met the inclusion and exclusion criteria. Dose response
and ratio of b-glucan to available carbohydrate as predictors of glycaemic response were assessed. Meals provided 0.3–12.1 g oat or
barley b-glucan, and reduced glycaemic response by an average of 48±33 mmol min/l compared to a suitable control. Regression
analysis on 119 treatments indicated that change in glycaemic response (expressed as incremental area under the post-prandial
blood-glucose curve) was greater for intact grains than for processed foods. For processed foods, glycaemic response was more
strongly related to the b-glucan dose alone (r
2
¼0.48, Po0.0001) than to the ratio of b-glucan to the available carbohydrate
(r
2
¼0.25, Po0.0001). For processed foods containing 4 g of b-glucan, the linear model predicted a decrease in glycaemic response
of 27±3 mmol min/l, and 76% of treatments significantly reduced glycaemic response. Thus, intact grains as well as a variety of
processed oat and barley foods containing at least 4 g of b-glucan and 30–80 g available carbohydrate can significantly reduce
post-prandial blood glucose.
European Journal of Clinical Nutrition advance online publication, 20 February 2013; doi:10.1038/ejcn.2013.25
Keywords: glycaemic response; oat; barley; b-glucan
INTRODUCTION
It has long been established that post-prandial glucose response
to carbohydrate meals is not determined by the amount of
available carbohydrate alone.
1,2
The proportions of different
nutrients, particularly protein and fat, as well as food
microstructure can affect the rate of glucose absorption. The
presence of soluble dietary fibre in carbohydrate foods also
influences the glycaemic response after a meal. Oat and barley
b-glucans have been widely studied for their health benefits,
including their ability to reduce post-prandial glucose alone and in
a wide variety of food formats.
3
The mechanism of action has been well established. Oat and
barley b-glucans, in their native state, are very high molecular-
weight polysaccharides that exhibit high viscosities at low
concentrations.
4
Consumption of viscous polysaccharides
increases the viscosity of the meal bolus in the stomach,
5
which
reduces mixing of the food with digestive enzymes and delays
gastric emptying. Increased viscosity also retards the absorption of
glucose.
6,7
In vitro digestion studies demonstrate that b-glucan
slows the rate of starch digestion.
8–10
Owing to its solubility,
b-glucan is easily fermented by the gut microbiota, which
produces short-chain fatty acids, including acetate, propionate
and butyrate.
11,12
A study designed to keep viscosity in the small
intestine constant, while the b-glucan was fermented in the large
intestine, showed that slowed glucose absorption by viscosity
development in the gut was responsible for acute effects.
13
However, fermentation products may affect post-prandial glucose
at subsequent meals. After evening meals containing barley,
post-prandial glucose response to a standardized breakfast was
reduced and inversely correlated with colonic fermentation as
indicated by increased breath hydrogen.
14
It was also inversely
related to plasma butyrate and acetate concentrations.
15
Recently, the European Food Safety Authority, Panel on Dietetic
Products, Nutrition and Allergies issued an opinion that ‘reduction
of post-prandial glycaemic responses (as long as post-prandial
insulinaemic responses are not disproportionally increased) may
be a beneficial physiological effect’.
16
The panel recognized that a
cause and effect relationship between consumption of oat and
barley b-glucans and a reduction of post-prandial glycaemic
responses has been established. Based on six studies, the panel
concludes that ‘in order to obtain the claimed effect, 4 g of
b-glucans from oat or barley for each 30 g of available
carbohydrates should be consumed per meal’. This condition of
use is likely to be difficult for food processors to meet.
To aid in elaborating the strength of the evidence, a summary
of the human trials that have been undertaken, focusing on
glycaemic responses in relation to the b-glucan and available
carbohydrate doses, is presented here.
METHODS
Outcome measures
Post-prandial glucose response is generally measured by determining
blood-glucose concentration several times over a 2 h interval after a test
meal is consumed and calculating the incremental area under the curve
(AUC). In two studies, the AUC was measured over 1 h
17
or 4 h,
18
but as
blood glucose returned to base line after 1 h in the first instance, it was felt
that the difference in time interval did not affect the measurement greatly,
Guelph Food Research Centre, Agriculture and Agri-Food Canada, Guelph, Ontario, Canada. Correspondence: Dr SM Tosh, Guelph Food Research Centre, Agriculture and
Agri-Food Canada, 93 Stone Road West, Guelph, Ontario N1G 5C9, Canada.
E-mail: Susan.Tosh@agr.gc.ca
Received 3 May 2012; revised 20 November 2012; accepted 17 December 2012
European Journal of Clinical Nutrition (2013), 1–8
&
2013 Macmillan Publishers Limited All rights reserved 0954-3007/13
www.nature.com/ejcn
and for the second study a 2 h value was calculated. Although the
physiological response most frequently reported was area under the post-
prandial blood-glucose curve (AUC), some studies reported glycaemic
index (GI), which is AUC as a percentage of response to a standard glucose
drink or white bread test (GI ¼AUC
test meal
/AUC
standard meal
100).
Another useful measurement is the peak blood-glucose rise. Oat
b-glucan and other viscous soluble polysaccharides tend to slow the
initial blood-glucose absorption, resulting in a flatter peak and sustained
glucose uptake. Therefore, even when AUC is not decreased, the blood-
glucose uptake may be blunted, avoiding large fluctuations in blood
glucose and insulin.
Search strategy
A search of the literature was conducted on 14 November 2012 using the
search string ‘(oat* or barley) and (glycaem* or glycem* or (blood and
glucose))’ using the PubMed and SCOPUS search engines. The searches
returned 437 matches from PubMed and 602 matches from Scopus. From
this list, 79 human studies, published in English, were extracted based on
the titles and abstracts.
Inclusion criteria
Studies were included if they were controlled, randomized, blinded,
crossover or parallel human studies, which included information on
available carbohydrate dose, b-glucan or soluble fibre dose and post-
prandial blood-glucose response.
Where it was available, information concerning peak blood-glucose
response and insulin response was extracted from either graphs or tables.
Information on number of subjects, food format and food processing was
also collected.
Exclusion criteria
Studies were excluded if they did not have an appropriate control, used
subjects with type 2 diabetes (including non-insulin-dependent diabetes
mellitus), used low viscosity extracts or the b-glucan was deliberately
depolymerized.
It has been demonstrated that depolymerization of b-glucan affects its
efficacy as related to post-prandial blood-glucose reduction.
19
Therefore,
10 treatments where the b-glucan molecular weight (MW) was reduced
deliberately to o250 kDa, either to demonstrate loss of efficacy or to
produce a low viscosity extract, were excluded from further
analysis.
7,10,19,20
One paper included six treatments with high levels of
resistant starch in addition to b-glucan.
21
Only the treatments with low
levels of resistant starch were considered.
Data analysis
Extracted data were used to calculate change in AUC or GI compared to an
appropriate control. For 12 studies, AUC was calculated from tables or
graphs.
6,21–28
Data extracted from the papers were tabulated. Ranges,
averages and s.d.’s were calculated. Various plots and regressions were
produced to represent the relationships among the parameters. Where a
glucose drink was used as a control for solid foods,
21,28–31
the data were
adjusted to simulate a hypothetical control of white bread with a GI of 71.
Statistical analysis
Statistical analyses were performed using Graph Prism v. 5.0 (GraphPad
Software, La Jolla, CA, USA). Regression analysis was performed to
determine significant relationships among b-glucan dose or bG/AC (mixed
linkage cereal b-glucan/available carbohydrate) ratio and the post-prandial
glucose response measures. One data point, with the highest b-glucan
dose, 14.1 g per serving and the highest ratio of bG/AC, was excluded
because it was an outlier and the dose was too high to be of commercial
interest.
8
RESULTS
Of the 76 studies reviewed in full, 34 studies that comply with
inclusion and exclusion criteria were included in the analysis: 18
on oat products, 10 on barley products and 6 including both oats
and barley foods. Thus, the analysis was conducted on a total of
119 treatments from these 34 studies. The treatments included 55
oat products and 64 barley products.
A solution containing 50 g of glucose was included as a control
in 15 of the studies. The mean AUC for the standard glucose
solutions was 184±31 mmol min/l (range 122–240 mmol min/l).
Glycaemic response in relation to available carbohydrate dose
Between 5 and 20 participants were recruited to determine the
post-prandial response. Table 1 summarizes the data extracted
from the studies that comply with the inclusion and exclusion
criteria. The dose of b-glucan in the treatments ranged from
0.3–12.1 g per meal and the dose of available carbohydrate
ranged from 25 to 100 g per meal. Of the 119 treatments, 74 used
50 g of available carbohydrate and the change in glycaemic
response ranged from 1.4 to 147 mmol min/l for these
treatments. This large variation shows that available carbohydrate
dose is not the dominant factor determining glycaemic response.
The range of b-glucan to available carbohydrate ratios (bG/AC)
was 0.004–0.305 with an average of 0.101±0.063.
For oats, 69% of treatments (38/55) reported significant
reduction in AUC and/or GI, and 71% of treatments (29/41)
reporting information on peak blood-glucose rise indicated a
significant reduction. One data set (four treatments) reported
significant differences in peak blood-glucose rise and insulin, but
did not specify for AUC or GI changes.
26
For barley, 64% of
treatments (41/64) demonstrated significant reductions in AUC
and/or GI, and 68% (21/31) of treatments reporting peak rise data
showed significant reductions. Oat and barley products were not
significantly different in terms of the average reduction in AUC
(P¼0.17) or GI (P¼0.19), therefore the data for oats and barley
were combined for the regression analyses.
Typically, foods with a GI 470 are considered high GI, whereas
those with GI o55 are considered low GI.
2
Therefore, for the
purposes of this paper, a reduction equivalent to the difference, or
change in GI 415 units, will be considered of biological relevance.
Back-calculating for a control glucose solution with an average
AUC of 184 mmol min/l, 15 GI units corresponds to a change in
AUC of 27 mmol min/l. For oat and barley combined, the average
reductions in AUC and GI were 48±33 and 31±17 mmol min/l,
respectively. These values represent substantial reductions and
reinforce the certainty that oat and barley b-glucans consistently
reduce post-prandial glucose. The treatments represented a wide
range of oat and barley formats using a number of food-
processing technologies. These products could serve as
prototypes of functional foods for the consumer market.
In Figure 1, each treatment was plotted on a grid, indicating
their relative b-glucan and available carbohydrate composition,
and whether there was a significant lowering of AUC. An
assumption was made by the EFSA Panel on Dietetic Products,
Nutrition and Allergies
16
that there is a linear relationship between
bG/AC and efficacy. A dot is plotted to represent the condition of
use recommended by the panel. A product containing 4 g
b-glucan per 30 g of available carbohydrate and presumably any
product with a bG/AC ratio X0.133 shown by the dashed line
could make a claim. If efficacy was dependent on bG/AC ratio, a
diagonal pattern would be observed with non-significant
treatments falling below the line and significant treatments
above the line. This pattern is not apparent in the data;
moderate doses of b-glucan appear to be effective at higher
available carbohydrate doses.
All 29 of the treatments that are plotted above the dashed line
were effective in reducing post-prandial blood glucose. Addition-
ally, 51 products which also exhibited significant reduction fell
below the line. This suggests that the recommendation is overly
restrictive.
However, 76% of the treatments (48/63) with 4 g or more
b-glucan showed significant reduction in post-prandial glucose,
independent of their available carbohydrate content (Table 3).
The average carbohydrate dose for these 63 treatments was
Post-prandial blood-glucose lowering ability of oat and barley foods
SM Tosh
2
European Journal of Clinical Nutrition (2013) 1 – 8 &2013 Macmillan Publishers Limited
Table 1. Included studies using oat or barley products
First author Food format Subjects
n
bG
dose
(g)
AC
dose
(g)
Change in AUC
(mmol min/l)
sig.
a
Change in
GI values
Peak
Change
sig.
a
Insulin
change
sig.
a
Aldughpassi
32,33
Whole grain boiled barley 10 3.0 50 104 Yes 41
Pearled boiled barley 10 2.8 50 80 Yes 30
Whole grain pasta 10 3.0 50 10 No 5
Pearled barley pasta 10 2.8 50 24 No 14
Whole grain boiled barley 10 3.7 50 92 Yes 35
Whole grain boiled barley 10 3.8 50 102 Yes 43
Whole grain boiled barley 10 3.4 50 100 Yes 42
Whole grain boiled barley 10 3.1 50 98 Yes 42
Whole grain boiled barley 10 4.3
b
50 118 Yes 46
Pearled boiled barley 10 4.2
b
50 101 Yes 38
Whole grain boiled barley 10 8.4
b
50 128 Yes 49
Pearled boiled barley 10 8.9
b
50 111 Yes 41
Whole grain boiled barley 10 5.7
b
50 105 Yes 45
Whole grain boiled barley 10 4.9
b
50 111 Yes 47
Whole grain pasta 10 4.3
b
50 14 No 5
Pearled barley pasta 10 4.2
b
50 36 No 14
Alminger
29
Oat tempe 13 1.8 25 79 Yes 37 Yes Yes
Barley tempe 13 1.7 25 147 Yes 70 Yes Yes
Behall
30
Pudding with oat flour 10 3.23
b,c
73.7
d
62 Yes Yes No
Pudding with oatmeal 10 3.23
b,c
73.7
d
49 Yes Yes No
Pudding with barley flour 10 12.1
b
76.1
d
101 Yes Yes Yes
Pudding with barley flakes 10 12.1
b
76.1
d
111 Yes Yes Yes
Behall
21
Oat bran muffins 18 0.3
c
72
d
3No NoNo
Oat bran muffins 18 0.9
c
72
d
5No NoNo
Oat bran muffins 18 3.7
c
72
d
26 No Yes Yes
Braaten
6
Oat b-glucan isolate gel 10 11.3
b
50 64 Yes 48 Yes Yes
Brummer
34
Oat bran cereal (high MW) 12 8.6
b
31 56 Yes 56 Yes
Oat bran cereal (medium MW) 12 8.3
b
31 46 Yes 46 Yes
Oat bran cereal (medium MW) 12 8.7
b
31 64 Yes 44 Yes
Oat bran cereal (medium MW) 12 8.4
b
31 65 Yes 27 Yes
Casiraghi
35
Barley crackers 10 3.6 40 15.9 No 25.3 No Yes
Barley cookies 10 3.5 40 32.8 Yes 47.8 Yes Yes
Cavallero
22
Bread with barley fraction 8 1.8 50 18.7 No 0.8
Bread with barley fraction 8 3.3 50 37.9 No 18.3
Bread with barley fraction 8 4.9
b
50 41.9 Yes 27.8
Chillo
20
Pasta with barley concentrate 9 1.5 50 21.4 No 19.3
Pasta with barley concentrate 9 3.0 50 28.5 No 25.7
Pasta with barley concentrate 9 4.4
b
50 35.4 No 31.9
Pasta with barley concentrate 9 6.1
b
50 47.2 No 42.6
Pasta with barley concentrate 9 7.7
b
50 57.1 Yes 51.6
De Angelis
23
Sourdough bread with oat fibre 15 3.9 50 35. Yes 18.3 Yes
Finocchiaro
24
Bread 40% waxy barley flour 9 5.3
b
50 22.9 No 12.7
Bread 40% non-waxy barley flour 9 4.8
b
50 46.1 Yes 25.6
Granfeldt
36
Oat bran muesli 9 3.3
c
50 23.6 No 11 No No
Oat porridge 9 3.3
c
50 11.5 No 7No No
Boiled oat kernels 9 3.5
c
50 80.0 Yes 40 Yes No
Granfeldt
9
Boiled barley kernels 10 4.5
b,c
50 73.6 Yes 35 Yes Yes
Boiled barley flour 9 4.7
b,c
50 36.2 Yes 61 Yes Yes
Boiled barley kernels 10 6.6
b,c
50 68.5 Yes 34 Yes Yes
Boiled barley flour 9 6.8
b,c
50 45.3 Yes 55 Yes Yes
Boiled barley kernels 10 6.2
b,c
50 79.9 Yes 29 Yes Yes
Granfeldt
37
Oat bran muesli 19 3 50 16.7 No No No
Oat bran muesli 13 4
c
50 29 .3 Yes Yes Yes
Hallfrisch
31
Oat bran 20 3.7 83.9
d
71 Yes No Yes
Oat extract 20 3.8 83.9
d
44 Yes No Yes
Barley flour 20 7.4
b
83.9
d
49 Yes No Yes
Barley extract 20 5.2 83.9
d
60 Ye s Ye s Ye s
Ha¨to¨nen
38
Oatmeal porridge 12 4
b
50 29.4 Yes 24
Hlebowicz
39
Wholemeal oatflakes 12 0.5 31.5 23 No No
Hlebowicz
17
Oat bran muesli 12 4
b
32.7 15.5
e
Yes Ye s
Holm
40
Oat bran fettucini 10 5.2
b
54.2 4.5 Yes Yes
Juntunen
41
Rye bread with oat b-glucan
concentrate
10 5.4
b
50 48 Ye s Ye s Ye s
Lan-Pidhainy
42
Oat bran muffin 11 8
b
50 79 Yes Yes
Previously frozen oat bran muffin 11 8
b
50 66 Yes Yes
Previously frozen oat bran muffin 11 8
b
50 48 Yes Yes
Oat bran muffin 11 12
b
50 73 Yes Yes
Previously frozen oat bran muffin 11 12
b
50 68 Yes Yes
Previously frozen oat bran muffin 11 12
b
50 63 Yes Yes
Liljeberg
8
Bread with coarse boiled oats 10 2.1
c
50 15.6 Yes 6.7 Yes Yes
Wholemeal barley bread 10 2.8
c
50 13.7 No 5.1 No No
Bread with coarse boiled barley 10 2.4
c
50 29.5 Yes 16.7 Yes Yes
Bread with coarse scalded barley 10 2.5
c
50 38.5 Yes 26.3 Yes Yes
Liljeberg
43
Barley bread (80% scalded kernels) 8 4.5
b,c
50 92.6 Yes 66.8 Yes Yes
Barley bread (40% scalded kernels) 8 2.8
c
50 54.4 Yes 34.4 No No
Wholemeal barley bread 8 4.1
b,c
50 11 No 1.2 No Yes
Sourdough wholemeal barley bread 8 4.0
b,c
50 29.2 No 15.8 No Yes
Scalded wholemeal barley bread 8 3.8
b,c
50 3 No 10.1 No Yes
Liljeberg
25
Oat porridge 9 2.1
c
35.5 7.1 No 5.8 No No
Barley porridge 9 2.3
c
35.5 2.5 No 3No No
Barley porridge (50% PW
f
)97.6
b,c
35.5 18.2 Yes 22.3 Yes Yes
Barley bread (50% PW
f
)98.0
b,c
31.5 23.7 Yes 29 Yes Yes
Barley bread (80% PW
f
) excluded 9 14.1
c
31.5 31.9 Yes 39.1 Yes Yes
Post-prandial blood-glucose lowering ability of oat and barley foods
SM Tosh
3
&2013 Macmillan Publishers Limited European Journal of Clinical Nutrition (2013) 1 – 8
51.1±13.6 g, much higher than the recommended 30 g of
available carbohydrate. In fact, nearly half (43%) of products with
2–4 g b-glucan per meal showed significant reduction in post-
prandial blood glucose as well.
Regression analysis
To compare the predictive value of the ratio of b-glucan to
available carbohydrate versus b-glucan dose alone, regression
analyses against AUC were performed.
When the data were considered as a whole, neither the ratio nor
the dose data set passed the D’Agostino and Pearson omnibus
test of normality performed within the statistical software.
Examination of the data indicated that the whole boiled grains
gave markedly lower values than the processed foods, therefore
the data were divided into two sets. Subsequently, both the
processed and intact grain groups passed the normality tests. A
test for non-linear behaviour showed that the data did not exhibit
significant curvature, therefore a linear model was employed.
There was a large scatter in the data, but significant slopes of
relationships were observed. Statistical parameters are reported in
a Supplementary Table available at the European Journal of
Clinical Nutrition’s website.
Figure 2a shows the data for bG/AC plotted against glycaemic
response. The bG/AC ratio for processed foods was weakly
correlated with the AUC (Po0.0001, r
2
¼0.24). The low r
2
values
mean that there is a small chance that post-prandial glycaemic
response can be reliably predicted by the bG/AC ratio for a given
product. For all processed food treatments, the average bG/AC
ratio was 0.137±0.065. The intact grains had a much lower AUC
than the processed foods, including porridge. There was a
significant relationship between AUC and the bG/AC ratio
(P¼0.011, r
2
¼0.26) and average change in AUC of the intact
grains was 83±29.
The dashed line shows where products containing 4 g b-glucan
and 30 g available carbohydrate (bG/AC ¼0.133) would fall. All 29
treatments (27 processed and 2 intact kernals), with a bG/
AC40.133 significantly reduced glycaemic response. However,
55% (16 processed and 23 intact kernals) of treatments with bG/
ACo0.133 also showed significant reductions in post-prandial
blood glucose. Moreover, this suggests that the recommended
condition of use may be too stringent.
Figure 2b shows the dependence of glycaemic response on
b-glucan dose. The data for processed products show a significant
(Po0.0001) drop in AUC with increasing dose. Compared to bG/
AC ratio, b-glucan dose showed a stronger association with AUC
(r
2
¼0.48). The regression predicts a reduction in AUC of
5.2±0.6 mmol min/l for each gram of b-glucan included in a
meal. The physiologically relevant reduction of 27 mmol min/l
was attained with a dose of 4.0 g b-glucan. On the graph, a dashed
line indicates a dose of 4.0 g b-glucan. To the right of the line, 75%
of the processed treatments (45/60) and 95% (21/22) of the intact
boiled barley treatments demonstrated a significant reduction in
AUC with an average reduction of 51±29 mmol min/l.
Peak blood-glucose rise
The development of viscosity in the gut caused by oat and barley
b-glucan tends to slow the absorption of glucose. As the post-
prandial blood-glucose curves tend to be low broad peaks, after
Table 1. (Continued )
First author Food format Subjects
n
bG
dose
(g)
AC
dose
(g)
Change in AUC
(mmol min/l)
sig.
a
Change in
GI values
Peak
Change
sig.
a
Insulin
change
sig.
a
Ma¨kela¨ inen
26
Oat bran drink 10 2 50 26.9 ? 16.3 Yes No
Oat bran drink 10 4
b
50 68.8 ? 41.7 Yes No
Previously frozen oat bran drink 10 4
b
50 58.9 ? 35.7 Yes No
Oat bran drink 10 6
b
50 60.6 ? 36.7 Yes No
Nilsson
44
Boiled oat kernels 12 2.9
c
50 40.4 No 15
Boiled barley kernels 12 2.9
c
50 76.8 Yes 51
Bread with barley fibre 12 6.3
b,c
50 29.4 No 7
Barley porridge 12 2.6
c
50 10.8 No 12
O
¨stman
27
Barley bread (50%) 10 1.1 30 15.2
2
No 16.8 No
Barley bread (35% PW
f
)102.93018.6
2
No 25.2 Yes
Barley bread (50% PW
f
)104.6
b
30 17.8
2
Yes 35.5 Yes
Barley bread (75% PW
f
)109.2
b
30 26
2
Yes 45.3 Yes
Panahi
7
Glucose drink with oat extract 11 6
b
75 39 Yes
Regand
45
Oat porridge (high MW) 12 4
b
43 37 No Yes
Oat crisp bread (medium MW) 12 4
b
64 11 No No
Oat granola (high MW) 12 4
b
44 29 No Yes
Oat pasta (medium MW) 12 4
b
42 7No No
Regand
10
Oat grannola product (high MW ) 12 6.2
b
38 35 Yes Yes
Oat grannola product (medium MW ) 12 6.2
b
38 28 Yes Yes
Oat grannola product (high MW ) 12 6.3
b
60 33 Yes Yes
Oat grannola product (medium MW ) 12 6.3
b
60 0 No No
Throndre
46
Barley chapattis 8 2 50 1.4 No 0 No No
Barley chapattis 8 4.1
b
50 40.9 Yes 43 Yes No
Barley chapattis 8 6
b
50 16.3 No 16 No No
Barley chapattis 8 7.8
b
50 48.3 Yes 47 Yes No
Throndre
28
Barley porridge (high fibre) 10 2.7 50 112 Yes 61 Yes
Barley porridge (medium fibre) 10 2.7 50 105 Yes 57 Yes
Tos h
19
Oat bran muffin (medium MW) 10 4
b
50 26 No
Oat bran muffin (medium MW) 10 4
b
50 44 Yes
Oat bran muffin (high MW) 10 4
b
50 50 Yes
Oat bran muffin (medium MW) 10 8
b
50 49 Yes
Oat bran muffin (medium MW) 10 8
b
50 74 Yes
Oat bran muffin (high MW) 10 8
b
50 76 Yes
Ulmius
47
Beverage with oat bran 18 5
b
75 40 No 40 Yes
Wood
48
Oat bran porridge 9 8.8
b
60 54 Yes 38
Cream of wheat þoat b-glucan isolate 9 8.6
b
60 57 Yes 40
Yokohama
18
Barley pasta 5 12
b
100 92 Yes Yes No
Abbreviations: AC, available carbohydrate; bG, mixed linkage cereal b-glucan; MW, molecular weight. The italicized row indicates the excluded data point.
a
Yes
means significant reduction detected (Po0.05).
b
Treatment included in table 3.
c
Soluble fibre measured.
d
1 g AC/kg body weight, average given.
e
1hAUC data
reported.
f
PW—high b-glucan, prowashonupana variety. The italized row indicates the excluded data point.
Post-prandial blood-glucose lowering ability of oat and barley foods
SM Tosh
4
European Journal of Clinical Nutrition (2013) 1 – 8 &2013 Macmillan Publishers Limited
consumption of oat and barley foods, peak blood-glucose rise is
often a more sensitive measure of efficacy than AUC or GI. Peak
blood-glucose rise was reported for 72 treatments (41 for oat and
31 for barley) (Table 2). In these studies, 69% of the treatments
had a peak blood-glucose rise significantly smaller than the
control meal.
Of the 43 treatments with at least 4 g of b-glucan where peak
rise was reported, 81% (35/43) significantly reduced the peak
blood-glucose rise (Table 3). The available carbohydrate dose
ranged from 30 to 100 g. This result is further evidence of the
ability of moderate doses of oat and barley b-glucan to modulate
glucose absorption, independent of available carbohydrate dose.
Insulinaemic response
Information concerning the insulin response was given in tables or
graphs for 56 of the 119 treatments. The insulin did not rise
significantly in any of the measurements. This shows that ‘post-
prandial insulinaemic responses are not disproportionally
increased’.
16
For treatments using 4 g b-glucan or more, 72%
(18/25) processed foods and all four intact barley treatments
confirmed a significant reduction in area under the insulin curve
(Table 3).
Figure 1. Plot of b-glucan dose against available carbohydrate dose
for included treatments. Whether a treatment significantly reduced
AUC or GI (J), or not ( ) is indicated. Dot represents b-glucan and
available carbohydrate ratio recommended in condition of use, and
the line shows the cutoff for products with a ratio of 4 g b-glucan
per 30 g of available carbohydrate (0.133).
Figure 2. Relationship between (a) ratio of b-glucan/available
carbohydrate (bG/AC) or, (b)b-glucan dose and post-prandial
blood-glucose responses (AUC). Processed (J) and intact grain
(&) treatments are indicated. The solid line is a trendline with the
95% confidence limits shown as dotted lines. The dashed line
represents the cutoff point for (a) ratio 4 g bG/30 g AC ¼0.133, or (b)
4g b-glucan.
Table 2. Attributes of oat and barley foods included in analysis
Oats Barley Combined
Average b-glucan
dose (g)
5.4±2.9 4.7±2.5 5.0±2.7
Average AC (g) 51.7±13.6 49.1±12.8 50.3±13.2
Average bG/AC
ratio
0.113±0.072 0.090±0.052 0.101±0.063
Treatments (no.
reported)
55 64 119
No. of significant
reductions
38 (69%) 41 (64%) 79 (66%)
Non-significant
treatments
17 (31%) 23 (36%) 40 (34%)
AUC change
Range
(mmol min/l)
7.1 – 80 1.4 – 147 7.1 – 147
Average
(mmol min/l)
41±24 54±39 48±33
GI change (no.
reported)
18 47 65
Range 6 – 48 10 – 70 10 – 70
Average 27±14 33±19 31±17
Peak rise (no.
reported)
41 31 72
No. of significant
reductions
29 (71%) 21 (68%) 50 (69%)
Non-significant
treatments
12 (29%) 10 (32%) 22 (31%)
Insulin Change (no.
reported)
23 33 56
No. of significant
reductions
10 (43%) 24 (73%) 34 (61%)
Non-significant
treatments
13 (57%) 9 (27%) 22 (39%)
Abbreviations: AUC, area under the curve; bG, mixed linkage cereal
b-glucan; GI, glycaemic index. Treatments containing 0.3–12.1 g b-glucan
per meal.
Post-prandial blood-glucose lowering ability of oat and barley foods
SM Tosh
5
&2013 Macmillan Publishers Limited European Journal of Clinical Nutrition (2013) 1 – 8
DISCUSSION
The 119 treatments included in the review used 92 processed
products bread, pasta, hot and cold breakfast cereals, beverages
and other food products as b-glucan sources, and represented a
wide variety of processing conditions, as well as 25 intact oat and
barley grains.
The regression analysis indicates that for processed products
glycaemic response is more strongly dependent on b-glucan dose
than the ratio of bG/AC. Although there is evidence that glycaemic
response depends on the amount of starch in a meal,
10,37,43
it also
depends on the characteristics of the starch. Resistant starch can
lower the glycaemic responses
21
as does an increase in slowly
digestible starch
10
or an increase in the amylose to amylopectin
ratio.
9,24
Thus, simply considering the bG/AC ratio is too simplistic
and adds error to the model.
The statistical analysis predicts a reduction of
5.2±0.6 mmol min/l in AUC for each gram of b-glucan added
to a processed product, or 8.4±2.7 mmol min/l for intact oat and
barley treatments as indicated by the slopes of the trendlines in
Figure 2b. The dose at which the model predicts a physiologically
relevant decrease of 27 mmol min/l (equivalent to 15 GI units)
was 4.0 g b-glucan for processed products. All of the intact oat and
barley treatments reduced AUC by more than 27 mmol min/l
compared to the control.
Table 3 shows the characteristics of the 72 treatments from 27
studies, which contain at least 4 g of b-glucan. Products containing
at least 4 g of oat or barley b-glucan significantly reduced
glycaemic response in 76% of the treatments tested. Peak
blood-glucose rise was significantly reduced in 79% of the
reported observations. The average reduction in AUC was
45±24 mmol min/l for processed products and
99±20 mmol min/l for intact boiled grains. The products
considered had an average carbohydrate dose of 51.1±13.6 g
(range 30–100 g).
Implications for persons with type 2 diabetes
Although studies conducted on subjects with type 2 diabetes
were not included in the statistical analysis, the outcomes of those
studies suggest that type 2 diabetics would benefit from
consuming oat and barley foods as well. A study where type 2
diabetics consumed 3 g of b-glucan in muesli containing extruded
oat bran
49
resulted in a 204 mmol min/l reduction in AUC
(Po0.01) compared to a whole wheat cereal. Research
conducted on a commercial oat bran breakfast cereal (3.7 g
b-glucan per serving), a b-glucan-enriched breakfast cereal (7.3 g
b-glucan per serving) and a cereal bar (6.2 g b-glucan per serving)
showed that they had significantly lower GI values compared to
white bread.
50
The b-glucan in the oat products tested reduced
the AUC (180 min) of type 2 diabetic subjects by 74, 372 and
332 mmol min/l when they consumed the oat bran breakfast
cereal, high b-glucan cereal and bar, respectively. A dose-response
study using extruded breakfast cereals with 4.0, 6.0 or 8.4 g b-
glucan per serving showed significant reductions in both glucose
and insulin response.
51
The 4.0 g dose reduced the AUC and peak
blood-glucose rise by 33% (Po0.05) compared to a whole wheat-
based continental breakfast, whereas the 6.0 and 8.4 g of doses
reduced glycaemic response by 60% (Po0.001). Therefore,
although incorporating more b-glucan into the diets of healthy
individuals is effective in maintaining healthy blood-glucose
levels, it appears that it also ameliorates blood-glucose levels in
persons with type 2 diabetes.
Food formats
Intact boiled kernels were used in six studies, as is, fermented,
pearled or baked into wheat bread.
9,29,32,36,43,44
Where the
integrity of the kernel was maintained, 96% (21/22) treatments
showed efficacy with an average reduction in AUC of
99±20 mmol min/l. The glycaemic response to intact boiled
barley was shown to be related to total dietary fibre and slowly
digestible starch, rather than b-glucan content.
32
This difference
from processed products suggests that, for cooked kernels, the
intact cell walls act as a physical barrier to starch-degrading
enzymes.
The effects of food processing are frequently questioned in
regard to maintaining the efficacy of soluble fibre in oat and
barley products. A wide variety of food formats were used in the
clinical studies considered here. Foods were divided into different
categories based on the type of processing they received and
treatments, which provided at least 4 g of oat or barley b-glucan,
were assessed. Raw flours, flakes and bran mixed into beverages
or puddings were used in four of the experiments
30,31,47
and 75%
demonstrated effectiveness with an average change in AUC of
75±33 mmol min/l (Table 1). All seven of the treatments that
used 44gb-glucan from isolates or extracts, significantly reduced
the glycaemic response with an average reduction of
58±39 mmol min/l.
6,7,26,31,48
This may be because it is easier to
achieve higher concentrations of b-glucan in a meal. The dose for
these studies was 4–11.3 g per meal. Porridge is considered a
minimally processed food, and often thought to be better than
more highly processed foods. However, 6 of the 12 porridge
products studied contained less than 4 g b-glucan. Of those that
contained at least 4 g b-glucan, 83% significantly lowered the
glycaemic response, with an average reduction in AUC of
38±10 mmol min/l.
25,36,38,45,48
Thus, porridges were not
particularly better than other products. Granola, muesli and
breakfast cereal are products where the moisture content is
kept relatively low during processing, and hydration of the b-
glucan may be inhibited. For cereal products containing at least
4gb-glucan, 82% of test meals showed significant results with an
average change in AUC of 32±15 mmol min/l.
10,17,34,36,37,45
Muffin batter has a higher water content allowing b-glucan to
better solubilize, and disperses through the crumb.
42,52
For
muffins with at least 4 g b-glucan, 92% (11/12) of the treatments
significantly reduced blood glucose with an average reduction of
60±16 mmol min/l.
19,42
There were 26 tests run on oat and
barley breads, which was the largest group of food products.
Despite concerns that b-glucan may be partially degraded by
enzyme activity during bread production,
45,53
64% of bread
products containing at least 4 g b-glucan (9/14) showed significant
decreases in glycaemic response with an average AUC reduction
Table 3. Attributes of oat and barley foods with at least 4 g b-glucan
Processed Intact grain
Number of treatments 63 9
b-glucan dose (g) 6.6±2.5 6.0±1.7
AC dose (g) 51.1±13.6 50.0
bG/AC ratio 0.137±0.060 0.078±0.030
Change in AUC (mmol min/l) 45±24 99±20
Significant treatments 48 (76%) 9 (100%)
Non-significant treatments 15 (24%) 0
Peak rise
Significant treatments 31 (79%) 4 (100%)
Non-significant treatments 8 (21%) 0
Insulinaemic response
Significant treatments 18 (72%) 4 (100%)
Non-significant treatments 7 (28%) 0
Abbreviations: AC, available carbohydrate; AUC, area under the curve; bG,
mixed linkage cereal b-glucan.
Post-prandial blood-glucose lowering ability of oat and barley foods
SM Tosh
6
European Journal of Clinical Nutrition (2013) 1 – 8 &2013 Macmillan Publishers Limited
of 29±13 mmol min/l.
22,24,25,27,41,43,46
In pasta products, where
depolymerization has also been observed,
45
three of the eight
tests showed significant reductions.
18,20,32,40
Therefore, the main
concern with regard to the effects of processing on efficacy is
maintaining the MW of the b-glucan.
Relation to viscosity development in the gut
Five of the studies reported viscosity of an in vitro digestion
extract in addition to physiological data.
10,19,34,42,45
Samples of the
foods used in the clinical trials were treated with digestive
enzymes, with appropriate pH changes at 37 1C in a shaking water
bath. The liquid containing the soluble b-glucan was removed by
centrifugation and the viscosity of the extract was measured. The
sample to buffer ratio was doubled in Regand experiments.
10,45
To
account for this difference in concentration, the 4.4th root of
viscosity values was used because Ren et al.
4
showed that a
doubling in concentration results in an exponential increase in
viscosity of that order.
The control whole wheat products (muffins, crispbread, pasta,
granola and cereal) all had low viscosity extracts (Figure 3). The oat
products were modified to change the b-glucan content,
solubility, MW and processing conditions which resulted in a
range of extract viscosities from 1.2 to 2900 mPa s. The glycaemic
response for the control and oat pastas was lower than for the
other test foods, 96 and 89 mmol min/l, respectively. Pasta is
known to have lower GI than other food products,
54
possibly
because of its compact microstructure, which restricts enzyme
access to starch.
55
For the other 33 meals, the AUC ranged from
175 mmol min/l for whole wheat muffins and granola to
53 mmol min/l for extruded oat bran cereal, with 8.6 g high MW
b-glucan per meal. A significant linear relationship was found
between AUC and log(viscosity) (r
2
¼0.69, Po0.0001). For each
decade of increase in viscosity, the model predicts a decrease in
AUC of 32±4 mmol min/l. This correlation between viscosity and
reduction in glycaemic response supports the hypothesis that b-
glucan influences blood-glucose concentrations by increasing
viscosity in the upper gut.
Summary
The results of 119 treatments from 34 publications were reviewed
to determine the dose of oat or barley b-glucan necessary to
achieve a consistent post-prandial blood-glucose lowering effect.
The b-glucan content ranged from 0.3 to 12.1 g, and the available
carbohydrate content ranged from 30 to 100 g, resulting in a
bG/AC range of 0.004–0.305. The statistical analysis, as indicated
by the correlation coefficients (r
2
values), shows that efficacy was
more strongly related to b-glucan content alone than to the ratio
of bG/AC. This is reassuring, as oat and barley foods are often
eaten as part of a meal including additional carbohydrates. Based
on the data analysed, it is suggested that intact cooked or
fermented grains containing at least 3 g b-glucan per meal is
sufficient to significantly lower glycaemic response. Processed oat
or barley foods, where the b-glucan is soluble and has a MW
4250 000 g/mol, containing at least 4 g b-glucan per meal is
sufficient to reduce post-prandial by AUC 27±3 mmol min/l for
meals with B30–80 g of available carbohydrate. This reduction in
glycaemic response is sufficient to be considered a physiologically
relevant effect.
CONFLICT OF INTEREST
The authors declare no conflict of interest.
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Supplementary Information accompanies the paper on European Journal of Clinical Nutrition website (http://www.nature.com/ejcn)
Post-prandial blood-glucose lowering ability of oat and barley foods
SM Tosh
8
European Journal of Clinical Nutrition (2013) 1 – 8 &2013 Macmillan Publishers Limited
