Refined carbs pose real risks, but whole grains keep showing benefits
Needless to say, diet is one way to protect yourself against type-2 diabetes.
And protecting yourself from diabetes is a growing concern, for two reasons.
First, the rate of diabetes in the United States doubled between 1991 and 2007, and has continue to rise.
Second, it’s become clear in recent years that people can be relatively thin and still develop type-2 diabetes.
Some of the most effective protections are to stay active and minimize or avoid added sugars and starchy, nutrient-poor “white” foods such as cornstarch, white bread, pastries, white pasta, potatoes, and white rice.
But it’s neither necessary — nor necessarily healthful — to avoid whole grains, because there’s ample evidence that (for most people), moderate consumption is positively healthful.
For example, a large new population study underscores the power of whole grains to help prevent heart disease, high cholesterol, and diabetes.
Before getting to that big Scandinavian study, let’s quickly review the existing evidence that whole grains help prevent diabetes.
Then we’ll look at why it makes biological sense that whole grains would help protect against diabetes.
Earlier research supports the value of whole grains for reducing diabetes risk
Many large epidemiological (population) studies link diets rich in whole grains to reduced risk for diabetes.
For example, Australian researchers who reviewed the epidemiological evidence five years ago came to this conclusion: “Two to three servings daily of whole grain foods reduced the risk of T2D [type-2 diabetes] by 20-30% compared to about 1 serving a week.” (Belobrajdic DP et al. 2013)
Epidemiological studies can’t prove a cause-and-effect relationship between a food or nutrient and risk for a disease.
But the Australian researchers also reviewed the evidence from clinical and laboratory studies, and reported that it supports the epidemiological evidence: “Randomized, controlled dietary studies in humans and other experimental research provides evidence of a causal relationship between whole grain consumption and diabetes prevention.”
Two years ago, a team of scientists from Harvard University and universities in Norway and Britain reviewed the evidence from 45 epidemiological studies — and their analysis linked higher whole grain intakes to protection against cardio-metabolic diseases (Aune D et al. 2016).
They calculated that people who ate three whole-grain servings a day enjoyed these apparent benefits:
- 51% less likely to develop diabetes.
- 22% less likely to develop cardiovascular disease.
- 19% less likely to develop coronary heart disease.
They found even greater risk-reductions among people who ate 7.5 servings a day (8 ounces or 225 grams).
Their analysis also detected significant anti-diabetes benefits among people who went from eating no whole grains to consuming two servings per day (32 grams, or a little over one ounce).
Importantly, as we’ll explain, there are good reasons why whole grains — like colorful fruits and vegetables — would protect people’s metabolic health. (See “Are antioxidants key to the benefits of whole grains?”, below.)
Large Scandinavian study affirms whole grains as anti-diabetes allies
A new population study from Swedish and Danish scientists supports the findings of the many prior studies that have linked substantial whole grain intakes to reduced diabetes risk.
The 15-year study involved more than 55,000 Danish men and women who answered diet surveys and provided access to their medical records (Kyrø C et al. 2018).
Using the participants’ answers to dietary surveys, the researchers divided them into four groups based on how much whole grain they reported eating.
The highest-whole-grain group reported eating at least 1.8 ounces (50 grams) of whole grains daily — the equivalent of a single serving of oatmeal plus one slice of whole rye bread.
And, in line with many prior findings, those who reported eating the most whole grains ran the lowest risk of developing type-2 diabetes over the course of the study.
Compared with those who reported eating the least amount of whole grains, the men and women who reported eating the most whole grains ran substantially lower diabetes risks:
- Men who reported eating the most whole grain were 34% less likely to develop diabetes.
- Women who reported eating the most whole grain were 2% less likely to develop diabetes.
Importantly, the Scandinavian team found that whole grains were one of the most effective anti-diabetes dietary factors.
Drinking coffee and avoiding red meat were also linked to a reduced risk of type 2 diabetes in this study — but neither of those appeared as effective as eating ample amounts (1.8 ounces/50 grams) of whole grains daily.
Senior researcher Rikard Landberg of Sweden’s Chalmers University of Technology had this to say: “Our results are in line with [common] dietary advice, which recommends switching out foods containing white flour for whole grains. You get extra health benefits — white flour has some negative effects on health, while whole grain has several positive effects, beyond protection against type 2 diabetes.”
Landberg underscored the near-uniformity of research on whole grains — a record that defies the rigid positions taken by some anti-grain and Paleo diet advocates:
“When it comes to whole grains, the research results are clear: among the many studies which have been made, in varied groups of people around the world, there hasn't been a single study which has shown negative health effects.”
And, the results of this Swedish-Danish study showed that it didn’t matter what type of whole grains people said they ate, because all appeared to offer the same protection against type-2 diabetes.
One reason the team chose to study people in Denmark is the broad range of whole-grain foods popular in that country.
People in the high whole-grain group reporting eating locally popular whole-grain foods like ryebread, oatmeal, and/or muesli (an unsweetened, granola-like, whole-grain cereal).
In contrast, most population studies on whole grains and diabetes involved Americans, for whom whole wheat bread — typically made with significant amounts of white flour — is the biggest source of whole grains. Nonetheless, those U.S.-based studies also linked diets rich in whole grains to reduced diabetes risk.
Are antioxidants key to the benefits of whole grains?
The benefits of whole grains are typically attributed to their indigestible dietary fibers, which certainly are helpful.
In fact, whole grains provide a wide range of health-promoters, including fiber, vitamins, and minerals — especially selenium, which is essential to the body's own antioxidant network.
However, public perceptions — fueled by the anti-grain arguments made in recent bestsellers — haven’t caught up to the fact that, like colorful fruits and vegetables, whole grains are rich in polyphenol-type antioxidants.
And although that fact isn’t news to researchers in the field, it’s not well known among the public, and is typically ignored by anti-grain and Paleo diet advocates — probably because it’s inconvenient to their positions.
Five years ago, researchers from the University of Minnesota, Australia, and Britain stressed this critical but underrecognized attribute of whole grains: “It is generally poorly appreciated by clinicians and public alike that grains accumulate antioxidants … to levels comparable to that in fruits and vegetables.” (Lillioja S et al. 2013)
They noted that the antioxidant effects of whole grains can be attributed primarily to a polyphenol compound called ferulic acid, found in the aleurone layer of grain kernels: “Our contention is that it is the [antioxidants in the] aleurone, rather than the indigestible fiber, which presents the most potent element influencing chronic disease.”
The aleurone layer surrounds and feeds the “embryo”, which contains precursor tissues for a cereal grain's leaves, stem, and roots.
As they wrote, “Ferulic acid … possesses intrinsic antioxidant activity, but also activates cellular antioxidant systems.” That fits with persuasive evidence that the antioxidants in fruits and vegetables work indirectly, by stimulating the body's own "antioxidant network".
For more on this topic, see Food-Borne Antioxidants May Act Indirectly, Whole Grain Foods Found High in Antioxidants, and Whole Grains: Under-Sung Antioxidant Stars Get a Boost.
Baking doesn't eliminate a whole grain's antioxidants
Importantly, the polyphenol antioxidants in grains retain their antioxidant activity after the grains are milled into flour and baked to make bread.
As a team from the University of Maryland reported four years ago, “… the total [levels of] phenolic acids [polyphenols] did not change significantly when breads were prepared from refined and whole wheat flour. Thus, the potential phytochemical health benefits of total phenolic acids appear to be preserved during bread baking.” (Lu Y et al. 2014)
Scientists from South Korea reported similar results seven years ago: “Phenolic acids [polyphenols] retain their antioxidant activity after the baking process, which has potential health benefits for consumers.” (Han HM et al. 2011)
Easy to go whole-grain, even if you need or want gluten-free
These are some whole grains you can incorporate in your diet — it’s often possible to find whole-grain versions of your favorite foods.
- Whole rye
- Black rice*
- Whole wheat
- Bulgur (cracked wheat)
- Oatmeal and whole oats
- Brown, red/purple, or black rice*
- Quinoa (particularly high in protein)
- Corn (whole kernels or whole-corn meal only; red-purple corn is preferable)
*In general, darker color indicates that a rice has more antioxidants.
**Buckwheat isn’t a true grain. Instead, it’s the seed of a flowering plant. But, like whole grains, it’s rich in antioxidants and other healthful compounds.
If you’re sensitive to gluten or cannot consume any gluten due to celiac disease, you should of course avoid wheat, barley, rye, oats and triticale, which is a cross between wheat and rye.
While oats are naturally gluten-free, look for oats and oat products labeled gluten-free, which have supposedly not been cross-contaminated with gluten-containing grains.
However, for reasons that remain unclear, some people with celiac disease cannot tolerate oats, including oat products labeled gluten-free.
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