july 2020 • BMJ

Intake of whole grain foods and risk of type 2 diabetes: results from three prospective cohort studies

Hu Yang, Ding Ming, Sampson Laura, Willett Walter C, Manson JoAnn E, Wang Molin, et al.

DOI: 10.1136/bmj.m2206

Content curated by:David Rodrigues

Key message

Qual a relação entre a ingesta de cereais integrais e o risco de desenvolver diabetes mellitus tipo 2? Estudo de coorte que procura entender a relação entre o consumo de alimentos integrais e o risco de desenvolver diabetes. Encontram que maior consumo de alimentos integrais (cereais matinais, aveia, pão preto, arroz integral, farelo adicionado) se associa de forma significativamente a menor risco de diabetes tipo 2. São resultados que devem ser interpretados com o cuidado que estudos de coorte baseados em questionários e auto-reporte dos mesmos obrigam (viéses e confundimento difíceis de analisar) mas que vão no sentido das recomendações das guidelines actuais: mais alimentos integrais nas dietas.

Analysis

Population

Adultos que quando entraram no estudo não tinham diabetes mellitus tipo 2; doença cardiovascular ou cancro. Contexto: EUA

Method

O que fizeram foi reunir dados de 3 estudos de coorte populacionais: O Nurses' Health study (1984- 2014), o nurses' Health study II (1991-2017) e o Health Professionals Follow-Up study (1986-2016). Dados colhidos por questionário. Avaliaram incidência de diabetes mellitus tipo 2 através de informação auto-reportada pelos doentes e confirmada e validada através de questionários adicionais.

Results

Em 4 618 796 pessoas-ano de acompanhamento, foram identificados 18 629 participantes com diabetes tipo 2. Depois de ajustar o estilo de vida e os fatores de risco dietéticos para diabetes, maior consumo total de alimentos integrais associou-se a uma taxa 29% menor de diabetes tipo 2 em comparação com menor consumo (IC95% 26% a 33%). Diferentes alimentos apresentaram diferentes riscos mas no global todos reduziram esse risco. Métodos estatisticos mais refinados indiciam uma associação dose-resposta não linear entre a ingestão total de alimentos integrais e o risco de diabetes tipo 2, em que a redução da taxa se estabilizou ligeiramente em mais de duas porções por dia (P <0,001 para curvatura). Quanto mais magra é a pessoa maior parece ser a redução do risco (obesidade como factor de confundimento). Não se encontrou efeito com diferentes níveis de atividade física, histórico familiar de diabetes ou tabagismo.

Abstract

Objective To examine the associations between the intake of total and individual whole grain foods and the risk of type 2 diabetes. Design Prospective cohort studies. Setting Nurses’ Health Study (1984-2014), Nurses’ Health Study II (1991-2017), and Health Professionals Follow-Up Study (1986-2016), United States. Participants 158 259 women and 36 525 men who did not have type 2 diabetes, cardiovascular disease, or cancer at baseline. Main outcome measures Self-reports of incident type 2 diabetes by participants identified through follow-up questionnaires and confirmed by a validated supplementary questionnaire. Results During 4 618 796 person years of follow-up, 18 629 participants with type 2 diabetes were identified. Total whole grain consumption was categorized into five equal groups of servings a day for the three cohorts. After adjusting for lifestyle and dietary risk factors for diabetes, participants in the highest category for total whole grain consumption had a 29% (95% confidence interval 26% to 33%) lower rate of type 2 diabetes compared with those in the lowest category. For individual whole grain foods, pooled hazard ratios (95% confidence intervals) for type 2 diabetes in participants consuming one or more servings a day compared with those consuming less than one serving a month were 0.81 (0.77 to 0.86) for whole grain cold breakfast cereal, 0.79 (0.75 to 0.83) for dark bread, and 1.08 (1.00 to 1.17) for popcorn. For other individual whole grains with lower average intake levels, comparing consumption of two or more servings a week with less than one serving a month, the pooled hazard ratios (95% confidence intervals) were 0.79 (0.75 to 0.83) for oatmeal, 0.88 (0.82 to 0.94) for brown rice, 0.85 (0.80 to 0.90) for added bran, and 0.88 (0.78 to 0.98) for wheat germ. Spline regression showed a non-linear dose-response association between total whole grain intake and the risk of type 2 diabetes where the rate reduction slightly plateaued at more than two servings a day (P<0.001 for curvature). For whole grain cold breakfast cereal and dark bread, the rate reduction plateaued at about 0.5 servings a day. For consumption of popcorn, a J shaped association was found where the rate of type 2 diabetes was not significantly raised until consumption exceeded about one serving a day. The association between higher total whole grain intake and lower risk of type 2 diabetes was stronger in individuals who were lean than in those who were overweight or obese (P=0.003 for interaction), and the associations did not vary significantly across levels of physical activity, family history of diabetes, or smoking status. Conclusion Higher consumption of total whole grains and several commonly eaten whole grain foods, including whole grain breakfast cereal, oatmeal, dark bread, brown rice added bran, and wheat germ, was significantly associated with a lower risk of type 2 diabetes. These findings provide further support for the current recommendations of increasing whole grain consumption as part of a healthy diet for the prevention of type 2 diabetes.