Grass seeds were plentiful, but the tough outer shell the husk made the seeds difficult to chew and digest. Early humans outsmarted the seeds by grinding them between stones, crushing the outer layers to get at the goodness inside. The result — a coarse powder — was the first whole-grain flour. The downside was spoilage. Crushing the germ released its oils, which quickly turned rancid when exposed to air. With the advent of industrial milling in the late s, machines began filtering out the germ and pulverized the remaining endosperm into a fine, white powder that lasted on the shelf for months.
And so all-purpose white flour was born — along with a host of health problems. Beneath their rigid architecture, whole-kernel grains conceal an array of vitamins, minerals, phytonutrients and fiber. Flour, as opposed to whole-kernel grains, is easy to overconsume because most flour-based foods require little chewing and go down rather quickly.
Blood-Sugar Blues. Smashing a whole-kernel grain to smithereens means it digests faster. Rapid-fire digestion causes blood sugar to spike, which causes a rise in insulin. The result? Not only are you hungry two hours later, but you are also paving the way for insulin resistance and diabetes.
Foods made with wheat flour are particularly damaging. A carbohydrate in wheat, called amylopectin A, is more easily converted to blood sugar than just about any other carbohydrate.
Two slices of bread made with whole-wheat flour raise blood sugar higher than six teaspoons of table sugar and higher than many candy bars.
Food Cravings. Over the past 50 years, the amber waves of grain our grandparents enjoyed have been replaced with modern, high-yield dwarf strains of wheat that produce more seeds and grow faster. Their safety has never been tested. Caloric Overload. By definition, a refined grain packs more calories than a whole-kernel grain because it is more concentrated.
And foods that are high in grains also tend to be high in sugar and industrialized fats. These are the foods, say many experts, that are causing our obesity and diabetes epidemic. Metabolic Slowdown. Research shows that the body may shift nutrients into fat storage and away from muscle burning in the presence of high-glycemic-index foods. In , Ludwig and his colleagues at Harvard conducted a study, published in the journal Lancet , in which they fed rats diets with identical nutrients, except for the type of starch.
By the end of the study, rats in both groups weighed roughly the same, but those eating a high-glycemic diet had 71 percent more fat than the low-glycemic-index group. A diet high in grains stokes inflammation. When blood sugar spikes, glucose builds up in the blood like so many standby passengers on a flight.
Choose whole grains instead of refined grains. These components have various effects on our bodies: Bran and fiber slow the breakdown of starch into glucose—thus maintaining a steady blood sugar rather than causing sharp spikes.
Fiber helps lower cholesterol as well as move waste through the digestive tract. Fiber may also help prevent the formation of small blood clots that can trigger heart attacks or strokes.
Phytochemicals and essential minerals such as magnesium, selenium and copper found in whole grains may protect against some cancers. The Whole Grain Stamp is a widely used marker on food products. The stamp, while designed to steer consumers towards healthy whole grains, identified products with more fiber and less sodium and trans fat but that were higher in sugar and calories than whole grain foods without the stamp.
The other three USDA criteria had mixed results in identifying healthier whole grain products, but criterion 4 the carbohydrate-to-fiber ratio of less than proved to be the most effective measure of healthfulness. Foods that met this criterion were higher in fiber and less likely to contain trans fats, sodium, and sugar. Because calculating the carbohydrate-to-fiber ratio may be difficult and not readily available for a consumer reading a label, the study suggests that labeling guidelines appearing on whole-grain foods should be improved.
Whole Grains and Disease As researchers have begun to look more closely at carbohydrates and health, they are learning that the quality of the carbohydrates you eat is at least as important as the quantity. References U. Department of Health and Human Services and U. Department of Agriculture. December Identifying whole grain foods: a comparison of different approaches for selecting more healthful whole grain products. Public Health Nutr. Association between dietary whole grain intake and risk of mortality: two large prospective studies in US men and women.
Jacobs DR, Jr. In a new study, researchers wanted to see how the consumption of refined grains and cereals, whole grains, and rice affects blood pressure, cholesterol levels, and the risk of heart disease and death.
The findings further validate a wealth of previous research linking diets high in refined carbohydrates with negative health outcomes.
The study, which involves 32 contributing researchers in 21 countries, appears in The BMJ. Carbohydrates are an essential nutrient. While we associate a diet of certain carbohydrates with health benefits, others raise the risk of health complications. When grains undergo the refinement process, they lose a nutrient, fiber-rich shell, and endosperm core, so they are quickly broken down into simple sugars when eaten. These simple sugars are rapidly absorbed into the bloodstream, causing sudden, temporary spikes in blood sugar levels.
This explains why most people only experience a short-term energy boost when eating refined carbohydrates. And because they lack fiber and are quickly digested, most people feel hungry relatively soon after eating simple carbohydrates.
Foods rich in simple carbohydrates also raise blood triglyceride levels, referring to blood fat. In addition, having high blood triglyceride levels increases the risk of diabetes, coronary artery disease , and fatty liver. Simple carbohydrates also contain many calories but have been stripped of their nutrition. So eating a lot of refined carbohydrates increases the risk of obesity and its associated health complications, as well as malnutrition. This is because complex carbohydrates contain grains that have their shell and endosperm core intact.
These layers are rich in nutrients and fiber, so they take much longer to break down and be absorbed. Because of this, consuming complex carbohydrates tends to provide a slow, steady release of sugar into the bloodstream, reducing the risk of blood sugar spikes and crashes.
This unhealthy, or Western, dietary pattern typically includes red and processed meat, sugar-sweetened foods and beverages, French fries, high-fat dairy products, and refined grains, and has been linked to an increased risk of a number of chronic diseases 12 , 15— An important question is whether each of the food groups in this dietary pattern is culpable for the increased disease risk. The discussion relies primarily on meta-analyses of relevant literature in which refined grain intake was analyzed separately, and not as part of a Western dietary pattern.
The Institute for Scientific Information's Web of Science was utilized to identify relevant meta-analyses of prospective cohort studies and randomized controlled trials RCTs.
Finally, reference lists and citation records of all identified articles were searched for additional studies not cited in meta-analyses. Five meta-analyses were identified that evaluated the association between refined grain intake and either CVD 2 , 5 or CHD 2 , 4 , 20 Table 1.
Collectively, these meta-analyses included a total of 12 publications 21— In both meta-analyses for CVD 2 , 5 and in 2 of the 3 meta-analyses for CHD 2 , 4 , no association was observed between refined grain intake and either outcome measure in comparisons of highest with the lowest intake groups and in dose-response analyses. Aune et al. Refined grain intake and relative risk of CVD, CHD, stroke, hypertension, heart failure, T2D, cancer, and all-cause mortality: results from meta-analyses of prospective cohort studies 1.
In the meta-analysis of Chen et al. However, this meta-analysis is flawed because the wrong outcome variable metabolic syndrome rather than CHD was used for 1 of the studies included in the meta-analysis In this study 27 , no association was observed between refined grain intake and CVD mortality. In fact, of the 12 studies included in the 5 meta-analyses, 11 reported no association between refined grain intake and risk of either CVD or CHD 21— The only study that reported an increased CHD risk associated with refined grain intake included Chinese adults who had very high total carbohydrate intake, primarily from white rice This is not a consistent finding because white rice intake was not associated with CVD or coronary artery disease CAD in an analysis of 3 large US cohorts In addition to these meta-analyses, refined grain was not associated with progression of CAD over a 3.
Also, the only study to date on refined grain intake and heart failure found no association between refined grain breakfast cereal intake and incident heart failure By comparison, with few exceptions meta-analyses have demonstrated that consumption of red meat and processed meat is associated with greater risk of CHD 4 , 40 , CVD 41 , 42 , and heart failure 4.
Four meta-analyses have been published on the association between refined grain intake and stroke risk, and all reported no association both when comparing the highest with the lowest intake groups and in dose-response analyses 2 , 4 , 33 , 34 Table 1. The lack of association between refined grain intake and stroke is consistent with the lack of association between refined grain intake and hypertension.
A meta-analysis that included 3 studies found no association between refined grain intake and incident hypertension both when comparing the highest with the lowest intake groups and in dose-response analyses 35 Table 1. By contrast, meta-analyses have reported increased risk of stroke associated with consumption of red and processed meat both when comparing the highest with the lowest intake groups 4 , 49 and in dose-response analyses 4.
One meta-analysis reported no significantly greater stroke risk associated with either red or processed meat intake, but intake of total meat was associated with higher stroke risk in a dose-response analysis Furthermore, the risk of hypertension was also shown to be higher in a meta-analysis comparing the highest and lowest intake groups for both red and processed meat consumption Two meta-analyses have been published on the association between refined grain intake and risk of T2D, and both demonstrated no association both when comparing the highest with the lowest intake groups and in dose-response analyses 3 , 13 Table 1.
Of the 12 publications included in these 2 meta-analyses, 5 reported no association between refined grain intake and T2D 51—55 and 3 reported a reduced risk of T2D associated with refined grain intake 56— In the Women's Health Initiative Observational Study, the reduced risk of T2D associated with refined grain intake in fully adjusted models was comparable to that for whole-grain intake Four of the studies included in the meta-analyses reported mixed findings, all pertaining to white rice intake 59— Another showed that white rice intake was associated with T2D risk in only 1 of 2 Iranian cohorts studied White rice intake was associated with T2D risk in Japanese women but not in Japanese men, whereas intakes of bread and noodles were not associated with T2D risk in either sex In the Melbourne Collaborative Cohort study of middle-aged men and women, white rice and pasta intake were not associated with risk of T2D, but white bread intake was Two meta-analyses have been published on the association between white rice intake and risk of T2D 3 , 63 Table 2.
The meta-analysis of Hu et al. It should also be noted that in a Spanish cohort white rice consumption was associated with a reduced risk of T2D White rice intake and relative risk of T2D and cancer: results from meta-analyses of prospective cohort studies 1. The results from most of the studies included in these meta-analyses 3 , 13 , i.
Additionally, refined grain intake was not associated with development of the metabolic syndrome Intake of red 13 and total 40 meat were also associated with higher T2D risk. Sugar-sweetened beverages, also included in the Western dietary pattern, have been reported to be associated with higher risk of T2D in most 13 , 67—69 , but not all 70 , meta-analyses.
This illustrates that the increased risk of T2D associated with a Western dietary pattern 15 is more likely attributable to consumption of red and processed meat, and possibly sugar-sweetened beverages, than to consumption of refined grains. Two meta-analyses on the association between refined grain intake and cancer risk have been published 2 , 36 Table 1. Both meta-analyses are limited by inclusion of few studies. In 1 of these analyses, a weak inverse association between refined grain intake and total cancer mortality in dose-response analysis was reported, but no association was found when comparing the highest and lowest intake groups 2.
White rice intake was not associated with total cancer incidence in the meta-analysis of Aune et al. In addition to the studies used in these meta-analyses, several other analyses from cohort studies have demonstrated no increased cancer risk associated with refined grain intake 30 , 71— By contrast, meta-analyses have shown higher total cancer mortality when comparing highest and lowest intake groups for consumption of processed meat 41 , 42 , red meat 42 , and total meat 41 , and higher total cancer mortality in dose-response analyses for both processed and red meat consumption A meta-analysis reported that consumption of red meat and processed meat was associated with significantly greater colon and colorectal cancer risk both when comparing the highest and lowest intake groups and in dose-response analyses, and greater rectal cancer risk in dose-response analyses Six studies have been published on the relationship between refined grain intake and all-cause mortality, 5 of which reported no association between refined grain intake and all-cause mortality 22 , 25 , 27 , 29 , 30 , and 1 that reported a slight, but statistically significant, inverse association between refined grain intake and mortality Two meta-analyses have been published that included 5 of these studies in their analyses 2 , 6 Table 1.
Not surprisingly, both reported no association when comparing the highest and lowest intakes. In the dose-response analysis, 1 reported no association 6 , whereas Aune et al. By contrast, the meta-analysis of Schwingshackl et al. Collectively, these studies show that mortality risk associated with the Western dietary pattern 76 is more likely attributable to consumption of red and processed meat, and not to intake of refined grains.
No meta-analyses on the association between refined grain intake and measures of body weight or body fat have been performed. Three systematic reviews reported no consistent relationship between refined grain intake and BMI or measures of adiposity 77— Most cohort studies show no association between refined grain intake and BMI 23 , 25 , 27 , 29 , 52 , 57 , 65 , 71 , 80— Although some studies indicate a positive association between refined grain intake and BMI 47 , 73 , 83 , 86—89 or body fat 87 , the magnitude of the difference between extremes of refined grain intake is typically very small.
Although statistically significant, the clinical relevance of this is not obvious. As reviewed above, meta-analyses consistently show that refined grain intake is not associated with increased risk of major chronic diseases and all-cause mortality. It is necessary to interpret these results from the perspective of how refined grains have been defined in most of the studies included in these meta-analyses.
In addition to staple grain foods such as bread, cereals and pasta, most of the studies that have examined refined grain intake separate from a Western dietary pattern have defined refined grains to include such foods as cookies 29 , 38 , 55 , 65 , 83 , cakes 25 , 29 , 31 , 38 , 44 , 47 , 52 , 53 , 55 , 65 , 86 , donuts 29 , 83 , brownies 29 , 83 , muffins 25 , 31 , 38 , 44 , 47 , 53 , 64 , 71 , 84 , 86 , sweet rolls or buns 25 , 31 , 44 , 52 , 53 , 55 , 83 , 86 , sweets or desserts made with grains 23 , 24 , 54 , 73 , and pizza 23—25 , 31 , 38 , 44 , 47 , 52—54 , 73 , 83 , 84 , 86 , These foods frequently contain high amounts of fat or sugar or both , consumption of which may offset any beneficial effects of staple grain foods.
Thus the generally neutral findings in most of the cohort studies of refined grain intake on health outcomes may be biased against yielding positive results. Meta-analyses have shown that total grain consumption is associated with reduced risk of T2D 3 , total cancer 2 , and all-cause mortality 2 Table 3. It should be noted that in both meta-analyses of grain intake and stroke risk 2 , 33 , the association between whole-grain intake and stroke risk was also not statistically significant.
Total grain intake and relative risk of CVD, CHD, stroke, T2D, cancer, and all-cause mortality: results from meta-analyses of prospective cohort studies 1. Only 1 meta-analysis has reported on the association between total grain intake and all-cause mortality 2.
The dose-response analysis, which included only 7 cohorts, produced a nonsignificant relative risk of 0. These results for total grain intake are not surprising in view of the consistently beneficial associations between whole-grain intake and chronic disease risk 2—9 and the largely neutral findings for refined-grain intake Table 1. Despite the consistent superiority of whole grains reported in observational studies, RCTs have not consistently produced expected findings. Four meta-analyses of RCTs comparing whole and refined grains have been published, with mixed results 7 , 90—92 Table 4.
These meta-analyses have included studies that determined the effects of diets higher in whole-grain foods compared with diets higher in refined-grain foods, or usual diet. Studies included in these meta-analyses were relatively short duration 2—16 wk.
Effects of whole-grain foods compared with refined-grain foods or usual diet on cardiovascular risk markers, blood pressure, body weight, and body fat: results from meta-analyses of randomized controlled trials 1. In 1 meta-analysis 92 , increased consumption of whole-grain foods had no effect on body weight or waist circumference compared with nonwhole-grain foods, but percentage body fat was reduced by 0.
The significance of a decrease in body fat of such small magnitude is questionable. In a Cochrane review and meta-analysis 90 , diets higher in whole-grain foods had no significant effect on body weight, BMI, total cholesterol, LDL cholesterol, HDL-C, triglycerides, or blood pressure.
The only meta-analysis of RCTs showing a superiority of whole-grain foods reported lower fasting glucose, total cholesterol, and LDL-C, and a trend for a reduction in fasting insulin, but no significant effect on blood pressure or body weight 7 Table 4.
0コメント