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In a pooled analysis of three large prospective American cohorts, people with the highest versus lowest total consumption of whole grain foods had a significantly 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,” wrote the authors led by Yang Hu, a doctoral student at Harvard School of Public Health, Boston.
Similarly, in a large European case-cohort study, people with higher values for plasma vitamin C and carotenoids (fruit and vegetable intake) had a lower incidence of type 2 diabetes.
“This study suggests that even a modest increase in fruit and vegetable intake could help to prevent type 2 diabetes ... regardless of whether the increase is among people with initially low or high intake,” wrote Ju-Sheng Zheng, PhD, University of Cambridge (England), and colleagues.
Individual whole grain foods
Previous studies have shown that high consumption of whole grains is associated with a lower risk of developing chronic diseases, including type 2 diabetes, cardiovascular disease, obesity, and some types of cancer, Mr. Hu and colleagues wrote.
Although research has shown that whole grain breakfast cereal and brown rice are linked with a lower risk of type 2 diabetes, the effect of other commonly consumed whole grain foods – which contain different amounts of dietary fiber, antioxidants, magnesium, and phytochemicals – has not been established.
Mr. Hu and colleagues analyzed pooled data from 158,259 U.S. women who participated in the Nurses’ Health Study (1984-2014) or the Nurses’ Health Study II (1991-2017) and 36,525 U.S. men who took part in the Health Professionals Follow-Up Study (1986-2016), who were free of diabetes, cardiovascular disease, and cancer.
Participants’ baseline consumption of seven types of whole grain foods – whole grain breakfast cereal, oatmeal, dark bread, brown rice, added bran, wheat germ, and popcorn – was based on self-replies to food frequency questionnaires.
During an average 24-year follow-up, 18,629 participants developed type 2 diabetes.
After adjusting for body mass index, lifestyle, and dietary risk factors, participants in the highest quintile of total whole grain consumption had a 29% lower risk of incident type 2 diabetes than those in the lowest quintile.
The most commonly consumed whole grain foods were whole grain cold breakfast cereal, dark bread, and popcorn.
Compared with eating less than one serving a month of whole grain cold breakfast cereal or dark bread, eating one or more servings a day was associated with a 19% and 21% lower risk of developing diabetes, respectively.
For popcorn, a J-shaped association was found for intake, where the risk of type 2 diabetes was not significantly raised until consumption exceeded about one serving a day, which led to about an 8% increased risk of developing diabetes – likely related to fat and sugar added to the popcorn, the researchers wrote.
For the less frequently consumed whole grain foods, compared with eating less than one serving a month of oatmeal, brown rice, added bran, or wheat germ, participants who ate two or more servings a week had a 21%, 12%, 15%, and 12% lower risk of developing type 2 diabetes, respectively.
Lean or overweight individuals had a greater decreased risk of diabetes with increased consumption of whole grain foods; however, because individuals with obesity have a higher risk of diabetes, even a small decrease in risk is still meaningful.
Limitations include the study was observational and may have had unknown confounders, and the results may not be generalizable to other populations, the authors note.