Whole grain foods for the prevention of type 2 diabetes mellitus

 

Abstract

Background

Diet as one aspect of lifestyle is thought to be one of the modifiable risk factors for the development of type 2 diabetes mellitus (T2DM). Information is needed as to which components of the diet could be protective for this disease.

Objectives

To asses the effects of whole-grain foods for the prevention of T2DM.

Search methods

We searched CENTRAL, MEDLINE, EMBASE, CINAHL and AMED.

Selection criteria

We selected cohort studies with a minimum duration of five years that assessed the association between intake of whole-grain foods or cereal fibre and incidence of T2DM. Randomised controlled trials lasting at least six weeks were selected that assessed the effect of a diet rich in whole-grain foods compared to a diet rich in refined grain foods on T2DM and its major risk factors.

Data collection and analysis

Two authors independently selected the studies, assessed study quality and extracted data. Data of studies were not pooled because of methodological diversity.

Main results

One randomised controlled trial and eleven prospective cohort studies were identified. The randomised controlled trial, which was of low methodological quality, reported the change in insulin sensitivity in 12 obese hyperinsulinemic participants after six-week long interventions. Intake of whole grain foods resulted in a slight improvement of insulin sensitivity and no adverse effects. Patient satisfaction, health related quality of life, total mortality and morbidity was not reported.
Four of the eleven cohort studies measured cereal fibre intake, three studies whole grain intake and two studies both. Two studies measured the change in whole grain food intake and one of them also change in cereal fibre intake. The incidence of T2DM was assessed in nine studies and changes in weight gain in two studies. The prospective studies consistently showed a reduced risk for high intake of whole grain foods (27% to 30%) or cereal fibre (28% to 37%) on the development of T2DM.

Authors' conclusions

The evidence from only prospective cohort trials is considered to be too weak to be able to draw a definite conclusion about the preventive effect of whole grain foods on the development of T2DM. Properly designed long-term randomised controlled trials are needed. To facilitate this, further mechanistic research should focus on finding a set of relevant intermediate endpoints for T2DM and on identifying genetic subgroups of the population at risk that are most susceptible to dietary intervention.

 

Plain language summary

Whole grain foods for the prevention of type 2 diabetes mellitus

Food products derived from cereal grains as wheat, rice, corn, rye, oat, and barley constitute a major part of the daily diet in many countries. In refined-grain products, the bran and germ of the grain, which contain the major amount of nutrients and dietary fibre, have been removed and only the starchy inner part of the grain (ca. 80% of the whole grain) is used. Whole grain foods contain either intact, flaked or broken grain kernels, coarsely ground kernels or flour that is made from whole grains (whole-meal flour). In this review the effect of whole grain foods and cereal fibre (as a marker of whole-grain food intake) on the prevention of type 2 diabetes mellitus (T2DM) was assessed using all available prospective cohort studies and randomised controlled trials. Only one randomised controlled trial was found which was of low methodological quality. This study investigated in 12 overweight persons during six weeks the effect of the consumption of refined grain foods versus that of whole grain foods on insulin sensitivity (risk factor for the development of T2DM). Intake of whole grain foods resulted in a slight improvement of insulin sensitivity, increased bowel movements and no adverse effects. No information was given about patient satisfaction, health related quality of life, total mortality and morbidity. In addition eleven prospective cohort studies were found. One study was conducted in Finland and the rest in the United States of America of which seven were done in health care workers. Some of the studies were of limited quality. They consistently showed that a high intake of whole grain foods or cereal fibre is associated with a lower risk of the development of T2DM. However, evidence for a protective effect coming from prospective cohort studies only has to be considered as weak as with this design no cause and effect relationship can be established. Well-designed randomised controlled trials are needed to be able to draw definite conclusions about the preventive effects of whole grain consumption on development of T2DM.

 

摘要

背景

全穀類食品對於第2型糖尿病之預防

以生活形態的一部份而言，飲食被視為第2型糖尿病可改變的危險因子之一。至於飲食中的何種成分，對於此一疾病有保護效果，則需進一步瞭解。

目標

評估全穀類食品對於第2型糖尿病之預防效果。

搜尋策略

我們搜尋了CENTRAL，MEDLINE，EMBASE，CINAHL及AMED等資料庫。

選擇標準

我們選擇了分析攝取全穀類食物或穀類纖維與第2型糖尿病發生率之間的關係且持續至少5年的世代研究(cohort studies)。此外，我們也選擇了比較富含全穀類食物的飲食及富含精製穀類食物的飲食對於第2型糖尿病及其主要危險因子的影響且持續至少6週以上的隨機對照試驗(randomised controlled trials; RCTs)。

資料收集與分析

2位作者分別選擇納入相關的研究，分析研究品質及摘錄數據。由於方法學上的差異，各個研究的數據並未被集中在一起。

主要結論

共有1個隨機對照試驗及11個前瞻性世代研究被選出。其中，隨機對照試驗(研究方法品質等級較低)的結果指出：12位肥胖且有高胰島素血症的受試者，在經過6週的介入之後，其胰島素敏感度有所變化。攝取全穀類食物使得胰島素敏感度輕微改善，且未發生副作用。然而，試驗結果並未提及患者滿意度、與健康相關的生活品質，及總體的死亡率和致病率。在11個世代研究中，4個研究著眼於穀類纖維攝取，3個研究著眼於全穀類的攝取，而有2個研究包括兩者。在2個著眼於全穀類食物攝取改變的研究中，1個亦同時包括穀類纖維攝取的改變。共有9個研究分析第2型糖尿病的發生率，而有2個研究分析體重的改變。前瞻性研究的結果一致指出：大量攝取全穀類食物(27%到30%)或穀類纖維(28%到37%)，均能減低第2型糖尿病的發生。

作者結論

僅由前瞻性世代試驗的證據，即斷定全穀類食物對於第2型糖尿病有預防效果，其立場仍嫌薄弱。因此，仍需要適當設計的長期隨機對照試驗。為促成此目的，未來於機制方面的研究，應著重於第2型糖尿病相關中間終點的發現，並在有風險的族群中，識別出對飲食介入最有反應的基因次群體。

翻譯人

本摘要由臺灣大學附設醫院林志弘翻譯。

此翻譯計畫由臺灣國家衛生研究院(National Health Research Institutes, Taiwan)統籌。

總結

目前仍需更多的研究來證實全穀類食物對第2型糖尿病預防的潛在效果。在許多國家中，由穀類，諸如小麥、稻米、玉米、裸麥、燕麥和大麥等所製成的食物製品構成了日常飲食的主要部份。於精製穀類食品中，富含膳食纖維的糠及胚芽均被除去，而僅有富含澱粉的內部(約佔全穀的80%)被使用。全穀類食物含有完整、切薄片、被打碎、被粗磨的仁，或是由全穀類所製成的麵粉(全餐麵粉)。在本篇回顧中，我們藉由所有可及的前瞻性世代研究和隨機對照試驗，來分析全穀類食物和穀類纖維(全穀類食物攝取之指標)對於第2型糖尿病(T2DM)預防的效果。我們僅找到1篇於方法學上品質不佳的隨機對照試驗。這篇研究調查了攝取6週之精製穀類食品或全穀類食物，對12位超重受試者之胰島素敏感度(第2型糖尿病發病的危險因子)的影響。攝取全穀類食物可輕微改善胰島素敏感度，改進排便狀況，同時亦無副作用發生。而有關病患滿意度、健康相關的生活品質，及總死亡率/罹病率的資料則付之闕如。我們亦找到另外11篇的前瞻性世代研究。僅有1篇研究是在芬蘭進行；其餘在美國進行的研究中，有7篇是在健康照護者的身上進行。其中有些研究的品質較為受限。這些研究的結果一致地指出：大量攝取全穀類食物或穀類纖維，與較低的第2型糖尿病發病風險有關。然而，因為前瞻性世代研究的設計並不能有效地建立因果關係，故要以此結果作為有保護效果的證據仍然過於薄弱。我們仍需有設計良好的隨機對照試驗來為攝取全穀類的預防效果與第2型糖尿病發病之間的關係下達定論。