Associations of RTEC consumption with daily intake of energy, macronutrients, cholesterol, dietary fiber (DF) and sodium.

For summarizing cross-sectional data about the association between RTEC consumption and daily intake of energy, macronutrients, cholesterol, DF and sodium in children/adolescents, 33 data sets from 24 studies were available. More data sets per study were available when the investigators reported their results per sex and/or in several age groups (S1 Table and Table 4). 18 of these studies were (in part) funded by food industry. Higher frequency (approximately ≥ 5 serving/week) of RTEC consumption in children/adolescents was associated with higher intake of DF, carbohydrates and total sugars in 75%, 65% and 63% of the data sets respectively and with lower intake of cholesterol and fat, expressed as total amount and as energy percentage in 83%, 50%, and 60% of the data sets respectively. Energy, saturated fat, sodium and protein intake was not associated with RTEC consumption in most data sets (in 77%, 75%, 81% and 86% respectively). Associations were similar in the 6 studies (9 data sets) [20;21;41;43;48;51] with no food-industry related funding, except that total amount of fat was only reduced in 22% of the 9 data sets and dietary fiber intake was only higher in 25% of the 4 data sets in which it was measured. In the other data sets (78% and 75%) no difference of fat and dietary fiber intake was reported.

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Table 4. Number and percentages of studies reporting higher, lower or equal daily consumption of energy and nutrients of frequent versus low/no RTEC consumers.

https://doi.org/10.1371/journal.pone.0164931.t004

For summarizing the results in adults 16 data sets from 12 studies were available (S1 Table and Table 4). One of these studies [28] received no food-industry related funding. Higher frequency (approximately ≥ 5 serving/week) of RTEC consumption in adults was associated with higher intake of DF, carbohydrates and total sugars in 93%, 100% and 100% of the data sets respectively and lower intake of fat expressed as energy percentage (in 100% of data sets) but not if expressed as total amount. The associations of RTEC consumption with saturated fat and cholesterol intake were not consistent, whereas most data sets (62%) did not show an association with energy and protein intake.

One study (funded by food industry) investigated the association between RTEC consumption and daily intake of energy, macronutrients, cholesterol, DF and sodium prospectively [54] (Table 2). In secondary analyses of a RCT, 8–10 y old children were followed for 7.5 y Higher frequency (3 vs 0 serving/3 days) of RTEC consumption at breakfast was associated in girls and boys with a higher percentage of energy intake from carbohydrates and protein as well as a lower percentage from total and saturated fats. In addition, an association with higher intake of DF and lower intake of cholesterol was found whereas energy and sodium intake was not related. For boys, but not for girls, RTEC consumption was associated with higher intake of total sugars.

Associations of RTEC consumption with the percentage of populations receiving inadequate amounts of vitamins and minerals.

17 studies (of which one [20] was not funded by food industry) investigated the association of frequency of RTEC consumption with the proportion of the population receiving inadequate vitamins and minerals, of which ten studies were conducted in children/adolescents [7;20;22;23;26;27;36;39;44;47], five studies in adults [24;25;33;37;46] and two in both categories [32;42] (Table 1).

Inadequate micronutrient intake was defined as “below the estimated average requirement (EAR)” in ten studies [22–25;27;32;36;37;44;46], as “receiving less than two-thirds of the recommended dietary allowance (RDA)” in three studies [20;33;42] and as “consuming less than 100% of RDA, “consuming less than 80% of RDA”, “probability of not achieving 100% of EAR “and “percentage who did not achieve LRNI” in one study each [7;26;39;47]. The EAR is defined as the intake adequate for 50% of the population, the RDA is the average daily dietary intake level that is sufficient to meet the nutrient requirement of nearly all (97 to 98 percent) healthy individuals and the LRNI is the amount estimated to meet the needs of 2.5% of the population with the lowest requirements.

The prevalence of inadequate vitamin and mineral intake by breakfast group (lowest vs highest RTEC consumption) for 14 micronutrients is given in S2 Table. 19 data sets were available for children/adolescents and 11 for adults. In 15 data sets it was assessed whether the prevalence of inadequacy between low and high RTEC consumers is significantly different.

Combining these results, significant reductions of prevalence of inadequacy associated with RTEC consumption were observed for all vitamins and minerals. Prevalence of inadequacy as well as magnitude of reduction varied depending on country, age group, sex and method of assessment (S2 Table).

To assess the nutrients for which the prevalence of inadequacy was reduced the most, those nutrients were scored which had the four highest reductions of inadequacy. In case that an equal percentage of reduction was observed for more micronutrients, all micronutrients were scored, thus more micronutrients per reduction level were possible (S2 Table). To reduce imbalance due to limited assessment of micronutrients, data of studies were excluded which reported less than eight micronutrients, resulting in 11 data sets for children and eight for adults. The scored micronutrients of different populations were then combined: data of adults in which significance was assessed (7 data sets), data of children in which significance was assessed (6 data sets), all adult and all children/adolescent data sets.

When using only data sets that assessed significance, in children/adolescents as well as in adults, reductions of prevalence of inadequacy due to RTEC consumption were highest for vitamin A (range: 7–21% and 5–37% respectively), calcium (17–39% and 6–40% respectively), folate (5–28% and 7–50% respectively), magnesium (7–11% and 4–26% respectively) and zinc (9% and 19–37% respectively). In adults, high reductions were also seen for vitamin B 6 (7–55%) and C (6–21%).

When combining all data sets, for children/adolescents as well as for adults consistently the greatest reductions of prevalence of inadequacy was observed for vitamin A (range: 7–28% and 5–37% respectively), calcium (17–39% and 6–43% respectively), folate (5–50% and 7–50% respectively), vitamin B 6 (31–37% and 7–55% respectively), magnesium (7–11% and 4–26% respectively) and zinc (9–15% and 19–37% respectively).

Associations of RTEC consumption with micronutrient status.

In two cross-sectional studies (of which one was funded by food industry [38]) micronutrient status (12 vitamins and minerals) was measured in populations with and without RTEC consumption [38;41] (Table 1). In Spanish and/or French children and adolescents consumption of RTEC was associated with higher plasma concentrations of vitamin A (0.10 μmol/l [41]), β-carotene (0.21 μmol/l [38]), serum folate (4.1 nmol/l [41]) and lower erythrocyte glutathione reductase (EGR, 0.07 [38;41]) which indicates a better riboflavin status. In Spanish adults, a better thiamine and riboflavin status (erythrocyte transketolase 0.03, EGR 0.06) as well as higher β-carotene (0.25 μmol/l) and serum folate concentrations (30 μg/l) were found in the RTEC group [38].

Another study (no industrial funding) investigated the contribution of consumption of folic-acid enriched RTEC to folate and vitamin B 12 status in US children and adolescents [49] (Table 1). Higher folate and vitamin B 12 concentrations were associated with consumption of enriched RTEC. However, only a very low percentage of this population (< 0.5%) had folate deficiency or low vitamin B-12 status, probably due to consumption of other grain products which are mandatory enriched with folate since 1996. The percentage of persons with marginally low folate and vitamin B-12 status decreased from 3.4% to 1.7% and from 9.6 to 6.6% respectively [49] due to additional consumption of RTEC.

The effect of RTEC consumption on macronutrient and DF intake.

In healthy adults substituting the habitual breakfast with RTEC (60 g for women/80 g for men) resulted in a higher percentage of energy from carbohydrates and a lower percentage from total and saturated fat [11] (Table 3) in this study funded by food industry. Intake of energy, protein and cholesterol stayed the same. No effect on DF intake was observed, but the RTEC administered were relatively low in DF, providing 3 and 4 g DF/day for women and men respectively.

Associations of RTEC consumption with risk factors for cardiovascular diseases.

One prospective study investigated the association of consumption of whole grain vs refined grain RTEC with incident heart failure in a large cohort of male physicians [56] (Table 2). Decreased risk of heart failure was found for frequent consumers of whole grain RTEC (HR: 0.78 (95% CI 0.64–0.96) for 2–6 servings/wk; HR: 0.72 (95% CI 0.55–0.88) for ≥ 7 servings/wk) but not for those consuming refined RTEC.

Another prospective study investigated the association of consumption of whole grain vs refined grain RTEC with incident hypertension in a large cohort of male physicians [52] (Table 2). Decreased risk of hypertension was clearly demonstrated for participants with a high consumption of whole grain RTEC (HR: 0.87 (0.81–0.94) for 2–6 servings/wk, HR: 0.80 (0.74–0.86) for ≥ 7 servings/wk), whereas the associations with consumption of refined RTEC was weak and not significant in all groups (HR: 0.86 (95% CI 0.76–0.98) for 2–6 servings/wk, HR: 0.86 (95% CI0.74–1.00) for ≥ 7 servings/wk).

One prospective study [54] (Table 2) investigated the association between low and high RTEC consumption (0 vs 3 servings/3 days) on blood lipids in a group of 660 children, aged 8–10 years at baseline and with serum LDL cholesterol levels between the 80th and the 98th percentile for sex and age. In the high RTEC group total cholesterol was lower in boys (0.10 mmol/l) but not in girls. LDL cholesterol was lower in boys (0.07 mmol/l) but in girls lower HDL cholesterol (0.05 mmol/l) was observed.

The two prospective studies reporting decreased risk of heart failure and hypertension were not funded by food industry [56; 52], whereas the last described prospective study [54] which was funded by food industry showed mixed results on blood lipids in children.

Effects of RTEC consumption on risk factors for cardiovascular diseases.

Two RCTs, one in children (overweight or at risk of overweight 6- to 12-year-old Mexican children [62]) and one in Finnish adults [11] investigated whether increased consumption of RTEC results in a reduction of blood lipids (Table 3).

Twelve weeks of RTEC consumption (≈ 33 g, different corn and rice based types) resulted in an increase in HDL concentrations (as compared to baseline and the control group) when combined with nutritional education [62] in children. The changes of other lipid parameters, however, were not different.

In adults with serum cholesterol concentrations above 5.0 mmol/l, six weeks of consumption of RTEC (60 g for women/80 g for men) mainly in the morning instead of the habitual Finnish breakfast resulted in a reduction in total cholesterol by 2.5% (0.16 mmol/l) which was partly due to a reduction in HDL cholesterol (LDL was not measured) [11]. Intake of saturated fat and total fat was decreased by 2.5 and 5.5 energy% respectively.

Both studies were (partially) funded by the food industry and showed mixed results on the parameters investigated.

The effect of RTEC enriched with different types of DF on blood lipids was investigated in five RCTs [10;58;69;71;72] (Table 3).

Six week consumption of DF-enriched RTEC providing 5.8 or 11.9 g soluble fiber/day consistently lowered total cholesterol and LDL (by 5.9 or 3,5% and 5.7 or 5.7% respectively) in persons with hypercholesterolemia consuming a low-fat diet [71;72]. The effective soluble fiber was mainly derived from psyllium whereas soluble fiber from pectin [72] or wheat bran [71] did not have a significant cholesterol lowering effect.

Three other, more short-term (3–4 wk), RCTs in healthy volunteers [10;58;69] investigated the effect of RTEC rich in various DF (inulin-enriched vs inulin-free, whole grain wheat vs wheat bran-based, whole grain maize vs refined maize) on various lipid parameters. No effect on total and HDL cholesterol was found, only the inulin-enriched RTEC (9 g inulin/day) was able to reduce LDL cholesterol compared to baseline (by 0.35 mmol/l, 8.3%) but not to control. However, concentrations of triacylglycerols were reduced compared to baseline and to control (by 0.23 mmol/l, 27.4%) [69].

Four RCTS were industrial funded, of which two [71;72] showed positive effects on blood lipids and two no effects [10; 58]. Another RCT [69], without industrial funding, showed mixed effects.

Three RCTs [66;68;77] investigated the effect of folate-fortified RTEC on plasma homocysteine (tHcy) (Table 3). It was found that cereals fortified with 200 μg per portion could increase plasma folate concentrations by about 12 nmol/l and lower tHcy by about 1 μmol/l in populations selected based on high plasma tHcy concentrations (≥ 10 μmol/l, [68]) or not consuming vitamin supplements and RTEC [77]. Consumption of RTEC with 200 μg folate in combination with other vitamins did not result in different effects [77]. Homocysteine lowering effects were most effective in subjects with lowest plasma folate concentrations and highest baseline tHcy (tHcy reduction- 1.58 μmol/l and -1.87 μmol/l respectively) [77]. Venn et al [68] also tested fortification with 100 and 300 μg folate/portion and found similar tHcy results, concluding that 100 μg folate would be sufficient in population with ≥ 10 μmol /l plasma tHcy. Consumption of RTEC enriched with 440 μg folate in combination with RDA amounts of vitamin B 6 and B 12/portion resulted in small differences in plasma folate (7,5 nmol/l) and homocysteine (-0.4 μmol/l) in a population with in general already relatively high baseline folate and low homocysteine concentrations [66]. In addition, the reduction of the percentage of persons with high homocysteine (>10.4 μmol/l for women or 11.4 μmol/l for men) was greater in the supplemented group (13% to 3.2%) compared to the control group (10.4% to 7.3%). All three RCTs were funded by industry and showed a positive effect of the intervention.

Associations of RTEC consumption with BMI/weight gain.

One prospective study in adults demonstrated that men consuming at least one portion of RTEC/day gained on average 0.59 and 0.46 kg less body weight after 8 and 13 years respectively than men consuming RTEC rarely [8] (Table 2). They also had a decreased risk of 22% and 12% to become overweight during 8 and 13 years of follow-up. Associations were also examined for whole grain and refined grain RTEC intake separately but these were not different.

Two prospective studies investigated the relationship between consumption of RTEC and BMI in children with a follow up of 7.5 [54] and 3 years [51] (Table 2). Both studies were secondary analyses of RCTs with 8–10 year old children including either both intervention groups [54] or the control group only [51]. Lower BMI was associated with more frequent RTEC consumption in both sexes in low-income minority children in one study [51] (every day of RTEC consumption decreased BMI by 2 percentiles), but only in boys in the other (BMI 20.4 vs 20.1, 0–3 times RTEC/week respectively) [54].

Negative associations of frequent RTEC consumption with body weight gain were found in all three RCTs, two of which [8;54] were funded by food industry.

Effects of RTEC consumption on body weight, satiety and food intake.

Two RCTs, one in children (overweight or at risk of overweight [62]) and one in adults [11] investigated whether increase of consumption of RTEC results in a reduction in body weight (Table 3). Twelve weeks of RTEC consumption (≈ 33 g, different corn and rice based types) in combination with nutritional education not only prevented the weight gain observed in the other groups but it decreased weight (mean -1.01 kg) and body fat gain (0.8%) [62]. As these changes were different to that observed after the RTEC intervention without nutritional education, it can be assumed that nutritional education is responsible for this positive effect.

In adults, six weeks of consumption of RTEC (60 g for women/80 g for men) mainly in the morning instead of the habitual Finnish breakfast did not result in change in body weight (secondary objective) [11].

Both RCTs were funded by food industry and showed no effect of RTEC consumption (alone) on body weight reduction.

Seven RCTs [12;57;59;61;65;73;76] examined the effect of low DF vs high DF RTEC and/or wholemeal RTEC [65] on postprandial satiety and five of them also on subsequent energy intake [12;57;59;61;73] (Table 3). The amount of DF administered with the high DF RTEC varied between 2.3 g and 33 g whereas the control RTEC contained 0–4 g. The types of DF were wheat bran [12;61;65;73], b-glucan [59;76] and 2 types of arabinoxylans (AX): hydrolysed wheat bran AX and unhydrolysed flax AX [57]. Visual analog scales were applied in most studies to measure satiety and/or appetite and a questionnaire in one trial [73]. Three trials reported a significant difference in satiety/appetite measures. The degree of hunger was lower after ingestion of high versus low DF RTEC [73]. Furthermore, the average appetite score was highest after the high bran RTEC [12] and the ß-glucan RTECs resulted in a lower combined appetite score independent from dose [59].

Positive effects on satiety/appetite measured were found in two industrial funded [12; 59] and one not industrial funded RCT [73]. No effects were found in three industrial funded RCTs [57; 61;76] and one RCT without industrial funding [65].

In two trials [12;61] it was found that a large portion of RTEC (71 and 60 g) containing 33 and 28 g of mainly insoluble wheat fiber can reduce subsequent energy intake (Table 3). After breakfasts providing the same energy, food intake at an early subsequent meal (75 min) was reduced by 160 kcal [12]. In the other trial the lower caloric value of the high DF RTEC was not compensated at lunch (3 h later) resulting in lower cumulative energy intake (93 kcal) [61]. In another trial [73] two experiments were conducted with RTEC containing different amounts of wheat bran. In the first experiment a significant difference in cumulative (breakfast and lunch 3.5 h later) energy intake (≈ 140 kcal) was found after the RTECs with the highest (22 and 20 g) compared to that with the lowest DF content (0 g). In the second experiment comparing the RTEC with the lowest and highest amount of DF, a decrease of energy intake at lunch and of cumulative energy intake was observed after the high DF RTEC (≈ 100 and 200 kcal respectively). In a trial with overweight women consumption of RTEC enriched with 15 g AX (19 g total DF) did not result in decreased energy intake at lunch (4 h later) nor decreased cumulative energy intake compared to the low DF RTECs (4 and 3 g DF) [57]. In addition, RTEC enriched with a low amount of β-glucan (2.3–5.9 g) did not result in lower energy intake at lunch (4 h later) in overweight persons [59].

Positive effects of consumption of fiber-rich RTEC on subsequent food intake were found in two RCTs [12;61] funded by food industry and one RCT without industry-related funding [73], whereas the other two funded RCTs [57;59] showed no effect. One RCT (industry funded) investigated the effect of modifying the processing procedure of wheat flakes (sour-dough prefermentation, steam cooking omission, reduction sucrose content) on satiety. Modified wheat flakes successfully reduced hunger feelings at 120, 150 and 180 min after ingestion compared to conventionally produced wheat flakes and white wheat bread [60] (Table 3). The test meals had similar energy content and differed slightly in macronutrient and DF composition.

Associations of RTEC consumption with development of type 2 diabetes.

One prospective study investigated the association between RTEC (cold breakfast cereals) consumption and incident diabetes in male physicians [55] (Table 2). Decreased risk of diabetes was clearly demonstrated for participants with a high consumption of whole grain RTEC (HR: 0.76 (95% CI 0.66–0.87) for 2–6 servings/wk, HR: 0.60 (95% CI 0.50–0.71) for ≥ 7 servings/wk), whereas the associations with consumption of refined RTEC were not significant in all groups (HR: 0.69 (95% CI 0.53–0.90) for 2–6 servings/wk, HR: 0.95 (95% CI 0.73–1.3) for ≥ 7 servings/wk) [55].

Another prospective study investigated the association between consumption of whole grain foods and incident diabetes in women [50] (Table 2). Analyses of HR of specific whole grain foods showed decrease risk of diabetes for high consumption of whole grain breakfast cereals ((HR: 0.71 (95% CI 0.62–0.82) for 5–6 servings/week and HR: 0.66 (95% CI 0.55–0.80) for ≥ 1/day).

Both these prospective studies showing associations between high consumption of whole grain RTEC and decreased risk of diabetes were not industry funded.

Effects of RTEC consumption on risk factors for type 2 diabetes.

Two RCTs examined to what extent postprandial insulinemia is changed in response to RTEC with different content of DF and different GI [64;74] (Table 3). 136 g whole grain wheat RTEC enriched with corn bran (GI: 49, 50 g available carbohydrates, 63.5 g DF) compared to 60 g low DF RTEC (GI: 125, 50 g available carbohydrates, 2 g DF) consumed with water reduced postprandial the 2h-AUC of insulin by 50% in healthy volunteers [64]. Half the portion of those RTEC was administered with milk in the other trial in which 2h-AUC of insulin was only decreased (by 14%) in volunteers with high fasting insulin but not in those with normal insulin values [74]. Both those industrial funded RCTs found positive effects of fiber-rich RTEC on postprandial insulinemia.

Two RCTs investigated whether addition of soluble fiber to RTEC with the same carbohydrate content results in decreased postprandial glucose and insulin responses [59;70] (Table 3). In overweight volunteers, corn based RTEC with 4–6 g oat β-glucan did not reduce blood glucose but only decreased the 2h-AUC insulin by 14–17% compared to RTEC without β-glucan [59]. In healthy volunteers, however, addition of 4.5 g soluble fiber from guar gum to wheat RTEC decreased both the 2 h- AUC glucose and insulin by 47% and 34% respectively compared to control [70]. The industry funded RCT [59] found mixed results of consumption of RTEC rich in soluble fiber on postprandial glucose and insulin, whereas the RCT without industry-related funding [70] found reduction of both parameters.

One RCT (food-industry funded) investigated the effect of modified processing of wheat flakes (sourdough pre-fermentation, suppressing steam cooking) and reduced sucrose content on GI and insulinemic index (reference food was white wheat bread) [60] (Table 3). The GI of modified whole wheat flakes and standard whole wheat flakes was not different. However, the 90 min and 180 min insulinemic index of the modified flakes was decreased by 20 and 12% respectively.

Another RCT (food-industry funded) investigated whether the low GI of a DF-rich RTEC is caused by a slower rate of appearance of starch-derived glucose (Ra_gluc, reflecting starch digestion) or a higher glucose uptake from the blood by tissues (Rd_gluc) [67] (Table 3). The Ra_gluc of the high GI RTEC and low GI RTEC was not different. However, the Rd_gluc at 30–60 min was 31% higher after the low GI RTEC which was associated with a 125% higher 0–30 min insulin response. It was hypothesized that the higher protein content of the low GI RTEC (11 g) contributed to the higher insulin response and thereby increased Rd_gluc which could explain the low GI despite the same rate of starch digestion.

Effect of RTEC consumption on the composition of the colonic microbiota and on bowel function.

One RCT (without industry-related funding) investigated the effect of 4-wk consumption of inulin-rich (9 g inulin/day) compared to inulin-free RTEC on the composition of the microbiota using selective growth media [69] (Table 3). It was found that the amount of bifidobacteria was higher after the inulin-rich RTEC compared to control, but only after correction for total anaerobes.

Two RCTs (food-industry funded) investigated the effect of 3-wk consumption of one portion whole grain RTEC/day on the composition of the microbiota with fluorescence in situ hybridization [10;58] (Table 3). One trial compared whole wheat RTEC (48 g, 5.7 g DF) to a wheat- bran based RTEC (48 g, 13 g DF) [10], whereas the other compared whole grain maize RTEC (48 g, 7 g DF) to refined maize RTEC (48 g, 0.4 g DF) [58]. In both trials, only whole grain RTEC consumption increased the amount of Bifidobacterium spp. compared to baseline. The increase in Bifidobacterium spp compared to control, however, was only significantly different in the wheat RTEC trial [10]. In this trial, also the numbers of Lactobacillus/Enterococcus were higher after the intervention with whole wheat RTEC compared to that with the wheat bran based RTEC.

The same three trials, which assessed the effect of DF-rich RTEC on the composition of the microbiota [10;58;69] (Table 3), monitored also bowel function as secondary outcome. A daily increase of DF in form of 9 g inulin or 7 g maize fiber did not change bowel habits [58;69]. During the intervention with wheat-bran based RTEC stool frequency was increased compared to that with whole wheat RTEC, and frequency of soft stools and flatulence increased [10]. Consumption of whole wheat RTEC resulted in more formed stool [10]. Consumption of DF-rich RTEC did not have an effect on bowel habits in one industrial funded RCT [58] and one without industry-related funding [69]. Another industrial funded RCT [10] reported improved bowel habits.

Association between RTEC consumption and cognitive decline.

One prospective study (food-industry funded) investigated the association between frequency of RTEC consumption and cognitive decline in elderly subjects over 11 years [53] (Table 2). Daily consumers of RTEC had a pattern of cognitive decline similar to infrequent consumers.

Effect of RTEC consumption on acute cognitive performance.

One RCT in children [75] and one in adolescents [63] investigated the effect of RTEC with low and high GI on acute cognitive performance (Table 3). The low GI RTEC (GI 30 [63] and 42 [75]) provided a lower amount of energy and carbohydrates, but higher amounts of protein than the high GI RTEC (both GI 77). In children, after the low GI RTEC secondary memory performance was better and decline in accuracy of attention was attenuated. Speed of attention and memory as well as working memory was not affected by GI [75]. In adolescents verbal episodic memory tasks were performed under divided attention which measured immediate, short-delay and long-delay memory [63]. No differences were found comparing the raw data scored after high and low GI RTEC consumption. However, when calculating remembering/ forgetting indices for each participant, it was shown that high GI RTEC improved long-delayed memory. Both RCTs were without industry-related funding and showed either positive [75] or negative effects [63] of consumption of low GI RTEC on specific cognitive tasks.

Risk factors for CVD.

Prospective studies that examined associations of low and high consumption of RTEC with health outcomes mostly differentiated between whole grain and refined grain RTEC. No studies were found that investigated associations of whole grain RTEC with cardiovascular disease directly. However, the associations with hypertension [52] and heart failure [56] were assessed and a decreased risk of 20 and 28% respectively was found. The inverse association of whole grain RTEC consumption with hypertension is consistent with that of a number of studies investigating associations with whole grain intake in general (women 0.89 [88], men 0.81 [89], young adults 0.83 HR [90]) whereas the magnitude of effect on heart failure was not comparable with that of a study examining the association with whole grain intake in general (0.93 HR [91]). Beneficial effects of whole grain products are related mainly to the bran fraction of the grain and its high content of micronutrients, like magnesium and zinc, and bioactive components, like phytic and ferulic acid, many having antioxidant properties [92;93]. Magnesium is one of the micronutrients linked to the prevention of hypertension [93;94] and oxidative stress is involved in the pathophysiology of cardiovascular disease and heart failure [95;96]. Furthermore, it is postulated that synergetic effects can occur as different components of whole grain act together to beneficial influence processes involved in development of disease [92].

In addition, hypocholesterolaemic properties of whole grain have been postulated that are mainly ascribed to viscous soluble fiber [97]. Reductions in total cholesterol and LDL were seen due to psyllium-enriched RTEC [71;72] but not with wheat bran RTEC in hypercholesterolemic men [71]. In normocholesterolemic persons RTEC based on whole grain maize [58], whole grain wheat and wheat bran [10] did not affect blood lipids. This is in agreement with the findings of a recent meta-analysis summarizing results of lipid-lowering effects of whole-grain interventions in apparently healthy [98]. Whole grain products based on wheat did not consistently exert lipid lowering effects in contrary to products based on barley and oat [48]. Psyllium fiber, like fiber in oat and barley, are soluble whereas wheat or corn fiber are mainly insoluble, which can explain these results.

Elevated plasma concentrations of homocysteine are suggested to be an additional risk factor for the development of cardiovascular disease [99], although not consistently [100]. Higher plasma folate concentrations are implicated with lower homocysteine [101] as well as a reduced risk of developing CVD [102]. Three studies consistently demonstrated that consumption of RTEC fortified with folate could increase plasma folate concentration and lower plasma homocysteine [66;68;77]. The effects were most pronounced in persons with low plasma folate and high homocysteine concentrations.

In summary, studies investigating whether RTEC consumption can reduce the risk of development of CVD addressed different risk factors. Prospective studies suggest that consumption of whole grain RTEC may reduce the risk of hypertension and heart failure, which so far has not been assessed in RCTs. RCTs demonstrated that RTEC with soluble fiber from psyllium have lipid lowering potency and folate-enriched RTEC can reduce plasma homocysteine concentrations. These prospective studies did not have industrial funding, whereas the effect of psyllium and folate-enriched RTEC were only investigated in RCTs which were industrial funded.

Weight gain/BMI, satiety and food intake.

Lower weight gain (0.59 and 0.46 kg during 8 and 13 y respectively) and a lower risk of becoming obese (22 and 12%) was associated with frequent RTEC consumption in men without being different between refined and whole grain RTEC [8]. The magnitude of effect was similar in two prospective studies that examined the association between whole grain food and refined grain food intake [103;104]. Consumption of whole grain food resulted in 0.49 kg less weight gain during 8 y in men [103] and 0.39 kg less weight gain during 12 y in women [104]. In contrary to the RTEC study [8] refined grain intake was associated with an increase in weight in women (0.43 kg during 12 y) [104]. However, differences in weight gain found in these studies are quite small and its health impact is difficult to judge.

In 8–10 y old children frequency of RTEC consumption was associated with slightly lower BMI in boys in two prospective studies [51;54] but in girls only in one study (low-income minority children) [51]. These studies did not differentiate between types of RTEC. Similar associations between BMI and consumption of breakfast cereals in general (9–10 y girls [105]) or whole grain foods (13–15 y old boys and girls [106]) were found, with no sex-related differences. Explanations for these beneficial effects postulated are the more healthy eating pattern of RTEC consumers with increased intakes of whole grain, DF and reduced fat or increased satiety [51;54] and higher insulin sensitivity in case of whole grain consumers [106]. Results of two RCTs [11;62] investigating the effect of high vs low RTEC consumption on body weight do not substantiate results from prospective studies. However, in both trials RTEC with a low content of DF were administered and one was of relative short duration.

Other RCTs explored the effect of DF-rich RTEC on postprandial satiety and food intake. From these trials it seems that postprandial satiety and/or appetite is not affected by higher DF content of RTEC, as only three from seven studies reported a decrease [12;59;73]. However, consumption of wheat bran RTEC decreased energy intake at a subsequent meal in normal weight subjects [12;61;73].

In summary, consumption of RTEC (all types) is associated with modest reduction in weight gain or BMI in adults and children in prospective studies, which so far is not substantiated with RCTs. There are indications that RTEC enriched with wheat bran can decrease energy intake at a subsequent meal in normal weight persons, with RCTs without industry-related funding showing similar results as industrial funded RCTs. However, long term RCTs are needed to demonstrate that this results in decreased weight gain. Furthermore, it seems of great interest to not only assess body weight but also fat mass as the results of a recent meta-analyses demonstrated that whole grain interventions can decrease fat mass, despite no effect on body weight [107].

Type 2 diabetes and risk factors.

Consumption of whole grain RTEC 2–6 times weekly was associated with a decreased the risk of the development of type 2 diabetes by 24% and 29% and ≥ 7 servings/week by 40 and 43% [55;50]. These finding are consistent with that of studies investigating associations with total whole grain intake (0.79 HR [108], 0.67 [109], 0.72 [110]). Increased intake of bran-derived micronutrients like magnesium and zinc as well as bioactive components may contribute to beneficial effects [92;93]. Magnesium for example, plays an important role in insulin sensitivity [94;111;112] and recently the property of zinc to influence synthesis, secretion and the action of insulin has become clear [113]. In addition, chronic low-grade inflammation and oxidative stress are factors involved in the development of type 2 diabetes, which can be alleviated by certain micronutrients as well as by bioactive compounds,—possibly through synergistic action [92].

Reduction of postprandial glucose and/or insulin concentrations are considered beneficial as repeated high glucose concentrations and related high insulin concentrations can lead to decreased insulin sensitivity and β-cell function in susceptible persons [114;115]. Reductions of postprandial glucose and insulin concentrations have been demonstrated for viscous soluble fiber [116]. The property of RTEC enriched with soluble fiber to decrease postprandial glucose and insulin was shown for guar gum (4.5 g) in healthy [70], whereas in overweight persons only the insulin response was reduced after RTEC with oat b-glucan [59].

Evidence from prospective studies, which were all without food-industry related funding, indicates a reduced risk of development of type 2 diabetes due to consumption of whole grain RTEC. However, RCTs investigating the effect of whole grain versus refined grain RTEC on risk factors related to the development of type 2 diabetes are needed to draw a definite conclusion. Addition of soluble fiber seems a promising strategy to reduce not only postprandial glucose but also insulin concentrations (independent from funding sources) and deserves further evaluation. Lower postprandial insulin response is considered beneficial because this would be less demanding for the pancreatic β-cells [115] and could play a role in preventing insulin resistance [117]. In addition, more recently, diets with a low insulin load were reported to be associated with lower body fat during puberty [118] and with lower energy intake in obese adolescents with features of insulin resistance and/or prediabetes [119].