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Eating more fruit, veggies and whole grains linked to lower risk of type 2 diabetes

More than one in 10 American adults — 34 million people — have diabetes, and more than 95 percent of them have type 2 diabetes.

vegetable produce aisle
The researchers calculated that the risk of type 2 diabetes fell by about 25 percent for every 66 extra grams — slightly more than a third of a cup — of fruit and veggies eaten daily.
Photo by Scott Warman on Unsplash

A diet rich in fruits, vegetables and whole grains is associated with a lower risk of developing type 2 diabetes, according to a pair of studies published Wednesday in The BMJ.

In fact, even a modest increase in the consumption of those foods — as part of an overall healthy diet — may help prevent the condition, the studies suggest.

Any scientific news on how to stem the rising tide of type 2 diabetes is welcomed. More than one in 10 American adults — 34 million people — have diabetes, and more than 95 percent of them have type 2 diabetes. If current trends continue, one in three Americans will have the condition by 2050, according to the Centers for Disease Control and Prevention.

Diabetes claims more than 83,000 lives in the United States each year, making it the seventh leading cause of death in the country. In addition, it’s a leading cause of disability, for the disease is associated with many serious complications, including heart disease, kidney damage, nerve damage (and resulting amputations of the feet or legs) and blindness.

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Having diabetes also puts people at increased risk of developing severe complications from COVID-19.

Genetics plays a role in the development of type 2 diabetes, but lifestyle-related factors, including diet, are also involved.

Focusing on fruits and veggies

Most past studies that have looked at the link between the consumption of fruits and vegetables and the risk of developing type 2 diabetes have relied on data collected from dietary questionnaires. The answers people provide when filling out those questionnaires may not be accurate, however.

The authors of one of the new studies in The BMJ decided to take a different approach. They used a more objective indicator of fruit and vegetable intake: blood levels of vitamin C and carotenoids (the pigments responsible for the bright red, yellow and orange colors in fruits and vegetables).

To do this they analyzed blood samples taken from participants in a long-running European study investigating the role of nutrition in the development of chronic diseases. They compared the blood levels of vitamin C and carotenoids in 9,754 people who developed type 2 diabetes while in the study with 13,662 people who didn’t. (Interestingly, participants in Germany had the highest levels of vitamin C, on average, while those in France has the highest levels of carotenoids.)

The analysis revealed that higher “composite biomarker” scores — a combination of both vitamin C and carotenoids levels — were associated with a lower risk of developing type 2 diabetes, even after adjusting for a variety of other risk factors known to be associated with diabetes, such as age, body mass index, educational level, physical activity levels and total calories consumed daily.

Specifically, people whose biomarker score was in the top 20 percent of all the study’s participants were 50 percent less likely to have type 2 diabetes than those in the lowest 20 percent.

The researchers calculated that the risk of type 2 diabetes fell by about 25 percent for every 66 extra grams — slightly more than a third of a cup — of fruit and veggies eaten daily.

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“The public health implication of this observation is that the consumption of even a moderately increased amount of fruit and vegetables among populations who typically consume low levels could help to prevent type 2 diabetes,” the study’s authors conclude.

“It should be noted that these findings and other available evidence suggest that fruit and vegetable intake, rather than vitamin supplements, is potentially beneficial for the prevention of type 2 diabetes,” they add.

Focusing on whole grains

In the other study, a team of researchers from the United States examined the relationship between type 2 diabetes and specific types of whole grain foods: whole grain cold breakfast cereal, oatmeal, dark bread, brown rice, popcorn, wheat germ and added bran. They wanted to focus on specific food sources because of their differing amounts of dietary fiber, antioxidants, magnesium and other ingredients, which may factor into their effects on the development of type 2 diabetes.

The study’s data came dietary questionnaires filled out by 158,259 women and 36,525 men who were taking part in three large, long-running U.S. health studies. None of the participants had diabetes when they entered the studies, but over an average follow-up period of 24 years, 18,629 of them were diagnosed with it.

An analysis of that data revealed an association between the consumption of whole grains and the relative risk of type 2 diabetes, even after adjusting for body mass index and other lifestyle and dietary risk factors for the disease. Specifically, the study found that participants who ate the most whole grain foods — about four to six servings a week — were 29 percent less likely to have developed type 2 diabetes than those who ate less than one serving per month.

In regard to individual foods, the researchers found that eating one or more servings a day of dark bread was associated with a 21 percent lower risk of type 2 diabetes, while eating that amount of  whole grain cold breakfast cereal was associated with a 19 percent lower risk, compared with consuming less than one serving a month.

Results also showed that eating two or more servings a week of oatmeal was associated with a 21 percent reduced risk of diabetes, while consuming that amount of added bran lowered the risk by 15 percent and of brown rice or wheat germ lowered it by 12 percent, again when compared to eating less than one serving a month.

The study found, however, that the benefits plateaued at around two servings a day for total whole grain intake, and at about half a serving a day for whole grain cold breakfast cereal and dark bread.

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The data also suggested that popcorn, despite its high fiber content, was associated with an increased risk of type 2 diabetes, perhaps, say the researchers, because most people eat popcorn with salt, butter and sometimes sugar or cheese. In addition, some microwave popcorns contain substances that have been linked to poor glucose metabolism, weight gain — and an increased risk of type 2 diabetes.

Limitations and implications

Both these studies are observational, which means they can’t prove a direct cause-and-effect relationship between a higher consumption of fruits, veggies and whole grain foods and a lower risk of type 2 diabetes. In addition, the whole grain study relied on dietary questionnaires, which, as already noted, can be inaccurate.

Still, these food categories are widely recognized as being healthful. They have been linked not only to a lower risk of type 2 diabetes, but other major chronic diseases, including heart disease and some types of cancer.

Giving them a central role in our diet is, therefore, a healthy move for most of us. (Some people have medical conditions, such as Crohn’s disease, that make eating some of these foods problematic.)  Just make sure you’re not consuming unhealthy ingredients (as exemplified by the popcorn findings) along with them.

FMI: You’ll find both studies on The BMJ website. You’ll find tips on shopping for fruits and veggies and on choosing whole grain products on the U.S. Department of Agriculture’s website.