Canada Grains Council 1999 Statistical Handbook On Women
Whole grains Whole grain and fibre 09 July 2015Grains are the seeds of cereal crops such as wheat, rye, rice, oats or barley. They have been a staple food for humans for thousands of years.Nowadays, it is widely recognised that foods made with whole grains can make an important contribution to our health and wellbeing. Whole grains provide benefits relating to the many individual nutrients and bioactive compounds (also called phytochemicals) they contain. Extensive research has examined the link between regular consumption of whole grain foods and the risk of heart disease, certain types of cancer, type 2 diabetes, and body-weight management.This review looks at the definition of “whole grain” and what qualifies as a whole grain food. Current intakes of whole grains, and dietary guidelines in different countries are presented, along with data on current understanding of the health benefits of whole grain. What does whole grain mean?The term “grain” applies to the species of the grass family and includes the cereal grains wheat, rice, barley, maize (corn), rye and oats and the term “pseudocereals” applies to amaranth, buckwheat, quinoa and wild rice.
1 All these grains are structurally similar and are made up of three distinct sections: the outer fibre-rich bran, the micronutrient-rich germ and the starchy main ‘body’ of the kernel known as the endosperm. Oilseeds, and pulses and other legumes are not classed as grains.Historically there has been some variation in the definition of “whole grain”. However since 2010 the identified the need to develop a European definition. There is now a growing international consensus that whole grains “consist of the intact, ground, cracked or flaked kernel”, which, “after removal of the inedible parts such as the hull or husk”, must contain “the same relative proportions of starchy endosperm, germ and bran found in the intact kernel. Small losses of components, that is less than 2% of the grain or 10% of the bran, that occur through processing are allowed”.Whole grain can be a food on its own such as oatmeal, brown (red, black, or wild) rice or popcorn. Alternatively, it can be processed and used as an ingredient in a product.When whole grain ingredients are used to make breads, pasta, crackers, breakfast cereals, and other grain-based foods, inconsistency exists between countries as to what qualifies as a whole grain food product. 4 Discussions are ongoing to unify the definition of whole grain foods and provide consistent guidance for researchers, labelling purposes and dietary guidelines.
The 2, the follow-up organisation of the HEALTHGRAIN project, is currently working on a more comprehensive definition which is expected to be published in 2016. The nutritional composition of whole grainsThe bran is the multi-layered outer skin, which along with the husk, helps to protect the other two parts of the kernel from sunlight, pests, and water. The bran contains fibre, minerals such as iron, zinc, copper and magnesium, vitamin E, B vitamins, and a multitude of other bioactive compounds.
Bioactive compounds (such as flavonoids, carotenoids) have a beneficial biological action in the body, and emerging research suggests they may, together with fibre be responsible for many of the health effects of whole grains.The germ is the embryo, which will sprout into a new plant under favourable conditions. It contains essential unsaturated fats, B vitamins, vitamin E, selenium, antioxidants, plant sterols, and other bioactive compounds.The endosperm is the germ's initial food supply, providing essential energy. The endosperm is the largest portion of the kernel, and contains largely starchy carbohydrates, some proteins, and small amounts of fibre, vitamins and minerals.Although all grains have the same basic structure, the precise balance of nutrients and bioactive compounds they contain varies by species, the cultivar used, and the growing conditions. 6 Some examples comparing the nutritional composition of different grain species and their whole grain (green column) and refined (white column) varieties are in the table below.
The dietary fibre content is made up of different types of fibre which varies between grain species. Wheat and rye are higher in insoluble and less fermentable fibre like cellulose; oats and barley are rich in fermentable, soluble fibre like beta-glucans. The health benefits are explained in the section “Health effects of whole grains”.
, INTRODUCTIONCardiovascular diseases (CVDs) 6 have become the number one cause of death globally, and it is estimated that 23 million people will die of CVD annually by 2030. A reduction of circulating total cholesterol (TC) and LDL-cholesterol concentrations is an important public health aim for the prevention of CVD (, ). Prospective cohort studies consistently find that intake of whole grains is associated with a 20–25% reduced risk of CVD and with lower TC and LDL-cholesterol concentrations (, ).
Consequently, public health authorities have made recommendations on whole-grain intake for the maintenance of cardiovascular health (, ). First author, year of publication, country (ref)Design and duration, wkNo. First author, year of publication, country (ref)Design and duration, wkNo. First author, year of publication, country (ref)Design and duration, wkNo. First author, year of publication, country (ref)Design and duration, wkNo. Flow diagram showing the flow of articles through the search strategy and selection of studies.
CAB, Core Agricultural Serials; FSTA Food Science and Technology Abstracts. Participant characteristicsOverall, data from up to 2275 participants aged 18–75 y were included in the analyses. A total of 16 of the 24 studies report mean baseline TC concentrations 5.2 mmol/L (, –), which indicates hypercholesterolemia.
Most of the studies included both sexes, and only 3 studies included women only (, ) (M Kristensen et al., unpublished results, 2015). Four studies were conducted in East-Asian populations (, ), whereas the remaining studies were carried out in Western Europe or North America, predominantly in Caucasian populations—except for one study focusing on Hispanics in North America. Study designOf the 25 studies included, 6 studies evaluated whole grain compared with refined grain intake in a calorie-restricted background diet (–, ), whereas the remaining 19 studies aimed to maintain the subjects’ weight. The duration of the studies ranged from 2 wk to 16 wk (, ); most of the studies lasted 6–8 wk. Whole-grain interventionThe type of whole-grain intervention varied between studies. The daily whole-grain dose ranged from 28 g/d to 213 g/d.
Eight studies investigated an intervention diet of mixed whole-grain products such as bread, crisp bread, rolls, muesli, ready-to-eat (RTE) cereals, pasta, rice, snack bars, crisps, muffins, and cookies) compared with a mixed refined grain diet (containing the same but made using refined grain (, ) (M Kristensen, et al., unpublished results, 2015) or the participants’ habitual diet. Eight studies compared whole-grain oat e.g., oatmeal, instant oats RTE cereal, or Cheerios (General Mills), hot cereal, or oat incorporated into other foods with a refined-grain diet (with the avoidance of oat, grain cereals, participant’s habitual diet, including refined wheat, non-oat RTE cereal, or low-fiber breakfast and snack foods) (, –). Three studies compared whole-grain wheat (, ) (e.g., bread, muffins, crackers, RTE cereal, bread rolls, rusks, and biscuits) with refined-grain wheat (containing the same products but of refined wheat or non–whole-grain cereal). Two studies evaluated whole-grain rye breads, and crisp bread was compared with refined white-wheat bread and crisp bread (, ). The effect of whole-grain rice was investigated in 2 studies (, ): 1 compared brown rice with white rice and the other a brown and black-rice meal replacement with a white-rice meal replacement. Only one study compared whole-grain barley consumed as a staple food with white rice.
Intervention effects LDL cholesterolIn total, 22 studies were included in the analysis, of which 1 study investigated the effect of 2 different doses and another investigated 3 different doses. One study reported results for both normoglycemic/normoinsulinemic and hyperglycemic/hyperinsulinemic individuals and another reported results separately for participants with normal and elevated TC.
One study investigated both whole-grain wheat and a mixed whole-grain diet compared with control foods , which resulted in a total of 28 comparisons. Overall, whole-grain consumption led to decreased LDL-cholesterol concentrations compared with a control diet (weighted difference: −0.09 mmol/L; 95% CI: −0.15, −0.03 mmol/L; P “ 0.01). If the 11 studies on oat were removed from the analysis, the effect favoring whole grain disappeared (weighted difference: −0.01 mmol/L; 95% CI: −0.08, 0.07 mmol/L; P = 0.83).
The studies on oat accounted for ∼50% of the weight in the analysis; in the stratified analysis, these studies alone suggest an effect of greater magnitude with oat compared with all whole grains together (weighted difference: −0.17 mmol/L; 95% CI: −0.10, −0.25 mmol/L; P “ 0.0001). Forest plot of the results of the random-effects meta-analysis of change in LDL cholesterol (mmol/L) according to grain type shown as pooled mean differences with 95% CIs. For each study, the square represents the point estimate of the intervention effect. Horizontal lines join lower and upper limits of the 95% CI of this effect. The area of shaded squares reflects the relative weight of the study in the meta-analysis. Diamonds represent the subgroup mean difference and pooled mean differences.
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M Kristensen, AB Ross, F Thielecke, unpublished results, 2015. HGI, high glycemia/insulinemia; IV, inverse variance; NGI, normal glycemia/insulinemia; TC, total cholesterol. Forest plot of the results of the random-effects meta-analysis of change in LDL cholesterol (mmol/L) according to grain type shown as pooled mean differences with 95% CIs. For each study, the square represents the point estimate of the intervention effect. Horizontal lines join lower and upper limits of the 95% CI of this effect. The area of shaded squares reflects the relative weight of the study in the meta-analysis. Diamonds represent the subgroup mean difference and pooled mean differences.
M Kristensen, AB Ross, F Thielecke, unpublished results, 2015. Forest plot of the results of the random-effects meta-analysis of change in total cholesterol (mmol/L) according to grain type shown as pooled mean differences with 95% CIs. For each study, the square represents the point estimate of the intervention effect.
Horizontal lines join lower and upper limits of the 95% CI of this effect. The area of shaded squares reflects the relative weight of the study in the meta-analysis. Diamonds represent the subgroup mean difference and pooled mean differences. M Kristensen, AB Ross, F Thielecke, unpublished results, 2015. HGI, high glycemia/insulinemia; IV, inverse variance; NGI, normal glycemia/insulinemia; TC, total cholesterol. Forest plot of the results of the random-effects meta-analysis of change in total cholesterol (mmol/L) according to grain type shown as pooled mean differences with 95% CIs. For each study, the square represents the point estimate of the intervention effect.
Canada Grains Council 1999 Statistical Handbook On Women Education
Horizontal lines join lower and upper limits of the 95% CI of this effect. The area of shaded squares reflects the relative weight of the study in the meta-analysis.
Diamonds represent the subgroup mean difference and pooled mean differences. M Kristensen, AB Ross, F Thielecke, unpublished results, 2015. HGI, high glycemia/insulinemia; IV, inverse variance; NGI, normal glycemia/insulinemia; TC, total cholesterol.Compared with the control diets, whole grain consumption led to a decrease in TC (weighted difference: −0.12 mmol/L; 95% CI: −0.19, −0.05 mmol/L; P “ 0.001). The stratified analysis according to grain types found that only whole-grain oat lowered TC compared with control (weighted difference: −0.22 mmol/L; 95% CI: −0.11, −0.32 mmol/L; P “ 0.0001) —a result based on a total of 11 comparisons. As for LDL cholesterol, whole-grain oat accounted for most of the weight of the overall analysis (53.2%); hence, the effect of whole grain disappeared when the oat studies were excluded (weighted difference: −0.02 mmol/L; 95% CI: 0.10, 0.06 mmol/L; P = 0.64).
Stratification according to background diet (calorie restriction or not) did not change the result; however, a more pronounced effect was seen with whole grain for studies with calorie restriction (weighted difference: −0.17 mmol/L; 95% CI: −0.33, −0.1 mmol/L; P = 0.04) (, ) compared with studies without calorie restriction (weighted difference: −0.10 mmol/L; 95% CI: −0.19, −0.02; P = 0.02). The overall test for heterogeneity resulted in I 2 = 40% ( P = 0.1). Heterogeneity for LDL cholesterol was reduced when studies on oat were removed from the analysis ( I 2 = 0%, P = 0.59), which indicated that these studies were largely responsible for the observed heterogeneity. HDL cholesterolResults for HDL cholesterol were reported in 21 of the eligible studies. One study investigated the effect of 2 different doses and another investigated 3 different doses ; one study reported results for both normoglycemic/normoinsulinemic and hyperglycemic/hyperinsulinemic individuals , and another study investigated both whole-grain wheat and a mixed whole-grain diet compared with control , which resulted in a total of 26 comparisons. Forest plot of the results of the random-effects meta-analysis of change in HDL cholesterol (mmol/L) according to grain type shown as pooled mean differences with 95% CIs.
For each study, the square represents the point estimate of the intervention effect. Horizontal lines join lower and upper limits of the 95% CI of this effect. The area of shaded squares reflects the relative weight of the study in the meta-analysis. Diamonds represent the subgroup mean difference and pooled mean differences. M Kristensen, AB Ross, F Thielecke, unpublished results, 2015. HGI, high glycemia/insulinemia; IV, inverse variance; NGI, normal glycemia/insulinemia.
Forest plot of the results of the random-effects meta-analysis of change in HDL cholesterol (mmol/L) according to grain type shown as pooled mean differences with 95% CIs. For each study, the square represents the point estimate of the intervention effect.
Horizontal lines join lower and upper limits of the 95% CI of this effect. The area of shaded squares reflects the relative weight of the study in the meta-analysis. Diamonds represent the subgroup mean difference and pooled mean differences.
M Kristensen, AB Ross, F Thielecke, unpublished results, 2015. HGI, high glycemia/insulinemia; IV, inverse variance; NGI, normal glycemia/insulinemia.Overall, whole grain intake did not affect HDL cholesterol compared with control (weighted difference: −0.01 mmol/L; 95% CI: −0.03, 0.02 mmol/L; P = 0.59).The stratified analysis found that only the mixed-grain studies, which accounted for most of the weight (44.4%), resulted in a reduction in HDL cholesterol with whole grain compared with control (weighted difference: −0.04 mmol/L; 95% CI: −0.06, −0.01 mmol/L; P = 0.005). Whole-grain rice resulted in an increased HDL-cholesterol concentration compared with the control (weighted difference: 0.09 mmol/L; 95% CI: 0.01, 0.16 mmol/L; P = 0.02); however, this result is based on only 2 studies. Calorie restriction did not appear to have an effect on the result (data not shown). Overall, heterogeneity between the studies was small ( I 2 = 21%, P = 0.59). TriglyceridesThe same studies included in the meta-analysis for triglycerides were included for HDL cholesterol, with 1 additional study resulting in a total of 27 comparisons.
Compared with a control diet, whole-grain consumption showed only a weak tendency to lower triglycerides (weighted difference: −0.04 mmol/L; 95% CI: −0.08, 0.01 mmol/L; P = 0.10). The stratified analysis for TC and LDL cholesterol according to grain type showed that only whole-grain oat decreased TG significantly compared with the control (weighted difference: −0.14 mmol/L; 95% CI: −0.22, −0.05 mmol/L; P “ 0.01). Analyzing calorie-restricted and non-calorie-restricted studies separately did not change the result (data not shown). Again, little heterogeneity between studies was observed ( I 2 = 0%, P = 0.49).
Forest plot of the results of the random-effects meta-analysis of change in triglycerides (mmol/L) according to grain type shown as pooled mean differences with 95% CIs. For each study, the square represents the point estimate of the intervention effect. Horizontal lines join lower and upper limits of the 95% CI of this effect. The area of shaded squares reflects the relative weight of the study in the meta-analysis. Diamonds represent the subgroup mean difference and pooled mean differences. M Kristensen, AB Ross, F Thielecke, unpublished results, 2015.
HGI, high glycemia/insulinemia; IV, inverse variance; NGI, normal glycemia/insulinemia. Forest plot of the results of the random-effects meta-analysis of change in triglycerides (mmol/L) according to grain type shown as pooled mean differences with 95% CIs.
For each study, the square represents the point estimate of the intervention effect. Horizontal lines join lower and upper limits of the 95% CI of this effect. The area of shaded squares reflects the relative weight of the study in the meta-analysis. Diamonds represent the subgroup mean difference and pooled mean differences.
M Kristensen, AB Ross, F Thielecke, unpublished results, 2015. HGI, high glycemia/insulinemia; IV, inverse variance; NGI, normal glycemia/insulinemia. Sensitivity analysesCritical to the interpretation of these results, sensitivity analyses were carried out to determine whether results were dependent on level of attention given to the whole-grain compared with control groups, i.e., whether study products were provided only to the whole-grain intervention group. The difference in attention was interpreted as an indicator of whether supplementation or replacement of habitual intake of cereal foods occurred.
This was done by excluding studies assigned a B or C rating for “attention” in the risk of bias assessment. The results did not change for any of the outcomes when the analysis was restricted to the 20 studies, in which participants were provided with study products in all groups, which indicated that lack of equal attention to groups did not result in the observed effects.
Sensitivity analyses were also performed according to allocation concealment, regardless of whether an intent-to-treat analysis was applied or not, and selective outcome reporting. None of these potential sources of bias changed the results for any of the outcomes assessed (data not shown). Meta-regression analysesThe whole-grain dose used in the included studies ranged from 28 to 213 g/d; however, we found no significant associations for any of the outcomes included when we performed a meta-regression analysis to investigate whether dose could predict changes in blood lipids ( P 0.40), although the direction appeared to be for a positive rather than negative association between whole-grain dose and changes in blood lipids ( for LDL cholesterol and for TC); the data are not shown for other outcomes. Post hoc, we decided to perform a second analysis on these data to restrict the analysis to studies with whole-grain intake of “100 g/d, because this better reflects usual intake in whole-grain consumers. This resulted in a negative, albeit nonsignificant, association between whole-grain intake and change in LDL cholesterol (β = −0.002698 mmol/L × g/d; SE: 0.002475 mmol/L; z: −1.090; P = 0.276; Supplemental Figure 1A) and TC (β = −0.002727 mmol/L × g/d; SE: 0.003606 mmol/L; z = −0.756; P = 0.449; Supplemental Figure 1B). We speculated that this may be confounded by studies investigating whole-grain oat, because they generally used lower doses than mixed whole-grain studies in particular. Meta-regression of mean differences in changes in LDL cholesterol (A) and total cholesterol (B) according to whole-grain dose.
The size of the circles is proportional to the precision of the estimate used in the meta-regression. The individual studies are indicated as follows, according to grain type (thin solid line represents mixed grain, double solid line represents oat, triple solid line represents wheat, broken solid line represents barley, dotted line represents rice) and calorie restriction (red represents calorie restriction and black represents noncalorie restriction). Regression lines: LDL cholesterol (β = 0.0007648 mmol/L × g/d; SE: 0.0010307 mmol/L; P = 0.458) and total cholesterol (β = 0.0005906 mmol/L × g/d; SE: 0.0012757 mmol/L; P = 0.643). Meta-regression of mean differences in changes in LDL cholesterol (A) and total cholesterol (B) according to whole-grain dose. The size of the circles is proportional to the precision of the estimate used in the meta-regression. The individual studies are indicated as follows, according to grain type (thin solid line represents mixed grain, double solid line represents oat, triple solid line represents wheat, broken solid line represents barley, dotted line represents rice) and calorie restriction (red represents calorie restriction and black represents noncalorie restriction). Regression lines: LDL cholesterol (β = 0.0007648 mmol/L × g/d; SE: 0.0010307 mmol/L; P = 0.458) and total cholesterol (β = 0.0005906 mmol/L × g/d; SE: 0.0012757 mmol/L; P = 0.643).Interestingly, positive associations between duration of study and effect size were seen for both LDL cholesterol (β= 0.021141 mmol/L × g/d; SE: 0.009854 mmol/L; z = 2.145; P = 0.03192) and TC (β = 0.02818 mmol/L × g/d; SE: 0.01089 mmol/L; z = 2.588; P “ 0.01), which indicated that the favorable effect on LDL and TC was attenuated with longer study duration ( for LDL cholesterol and for TC).
However, as for the whole-grain dose, this may have been confounded by the studies that investigated whole-grain oat, because those studies were generally of shorter duration, although it could also indicate that compliance intervention diets may decrease over time. Meta-regression of mean difference in change in LDL cholesterol (A) and total cholesterol (B) according to study duration. The size of the circles is proportional to the precision of the estimate used in the meta-regression. The individual studies are indicated as follows, according to grain type (thin solid line represents mixed grain, double solid line represents oat, triple solid line represents wheat, broken solid line represents barley, dotted line represents rice) and calorie restriction (red represents calorie restriction and black represents noncalorie restriction). Regression lines: LDL cholesterol (β = 0.021141 mmol/L × week; SE: 0.009854 mmol/L; P = 0.0319) and total cholesterol (β = 0.02818 mmol/L × week; SE: 0.01089 mmol/L; P “ 0.01).