The Healthy Skeptic: Do Grains Help or Harm Health?
Gluten is troubling or toxic for some, and white flour ain't good … but new studies find whole grains healthful
Gluten is troubling or toxic for some, and white flour ain't good … but new studies find whole grains healthful
White flours and other starchy, refined grain products are problematic.
Like sugars, they raise blood sugar (glucose) levels sharply … which tends to promote diabetes and inflammation.
Doctor-penned bestsellers like Grain Brain (David Perlmutter, M.D.) and Wheat Belly (William Davis, M.D.) advise readers to avoid grains.
Both authors say that we are not adapted to eating grains and high-carb diets, and that this leads to brain problems related to blood sugar control and gluten.
Let's consider the evidence for these claims.
Human aren't adapted to grains ... or are they?
Advocates of grain avoidance also assert that our prehistoric ancestors did not eat grains, so we have not adapted to eating them, with unhealthful results.
However, recent studies undermine that claim. Some of our Paleolithic forebears not only ate grasses – the ancestors of today's cereal grains – but were grinding them as long as 30,000 years ago (Piperno DR et al. 2000; Revedin A et al. 2010; Liu L et al. 2013).
Research suggests that Paleolithic diets varied widely, so we can't say anything defintitive about the proportions of carbs eaten by prehistoric people ... see “Is the Paleo Diet Based on Myths?”.
There's also ample evidence that humans can adapt to dietary changes within a few thousand years or less … such as Northern Europeans' increasing lactose tolerance over time, in response to animal milk.
Gluten and brain health
Gluten occurs only in rye, barley, wheat, and wheat ancestors like spelt, teff, triticale, and kamut.
Gluten does not occur naturally in oats, rice, corn, quinoa, or buckwheat (which is actually a fruit), and is not normally added to baked goods that contain only these naturally gluten-free grains.
Advocates of grain-avoidance point to rising rates of Celiac disease and gluten sensitivity, and cite evidence that gluten promotes “leaky gut” syndrome.
They also cite evidenced that people with Celiac disease show higher rates of dementia.
In leaky gut syndrome, large molecules normally retained in the intestines pass into the blood stream, sparking an immune response that includes inflammation and other harmful effects.
Celiac disease devastates sufferers' health unless they avoid all gluten. And gluten appears to cause intestinal upset and other adverse symptoms in some people without Celiac disease.
However, many who believe they are sensitive to gluten may actually be reacting to complex carbohydrates called FODMAPs, which occur in grains, garlic, onions, milk products, and foods naturally high in fructose (honey, apples, mangoes, and watermelon) … see “Is Gluten Really so Guilty?”.
Blood sugar control and brain health
In Grain Brain, neurologist Dr. David Perlmutter cites recent evidence that chronically high blood sugar levels lead to dementia ... especially a study by an international team of academic scientists (Crane PK et al. 2013).
Its authors stated the background and the resulting question as follows: “Diabetes is a risk factor for dementia. It is unknown whether higher glucose levels increase the risk of dementia in people without diabetes.”
They compared blood sugar levels in 2,067 people with the risk for developing dementia in the next seven years ... and their conclusion seems to support Dr. Perlmutter's case against carbohydrate-rich diets: “Our results suggest that higher glucose levels may be a risk factor for dementia, even among persons without diabetes.”
Which foods raise blood sugar levels?
Glycemic index or GI is the standard (albeit crude) measure of how much a food raises blood sugar levels. It ranges from 1 to 100, and foods with high GI numbers raise blood sugar the most.
High-GI foods (70 and above) include:
Low-GI (55 or below) foods include:
Medium-GI (56 to 69) foods include:
Fat and fiber tend to lower the GI of a food, while cooking or processing tends to raise a food's GI.
However, traditional cultures with diets higher in carbs than the standard American diet don't seem to suffer from high rates of dementia. These include the Hadza of Tanzania, the Kuna of Panama, the Kitava in the Pacific Islands, and the Tukisenta people of Papua New Guinea, whose diet is over 90 percent carbs.
(Of course, these rural people probably get more exercise than we do, which matters to blood sugar control.)
Advocates of grain avoidance also cite evidence that – because they raise blood sugar levels – grains and other starchy carbohydrates spark the inflammation that drives degenerative disorders like diabetes, dementia, and cardiovascular disease.
For example, a recent evidence review found that diets low in sugars and rapidly-absorbed starches reduce key markers for inflammation (C-reactive protein) and blood sugar control (fasting insulin).
However, the same review found no reductions in two other key indicators of diabetes risk: levels of HbA1c levels and fasting glucose (Schwingshackl L, Hoffmann G 2013).
And another review detected no consistent benefit from low-carb diets, in terms of cardiovascular risk factors (Kristo AS et al. 2013).
Two earlier evidence reviews from the Harvard School of Public Health linked diets rich in whole grains to a reduced risk for stroke and diabetes (Liu S et al. 2000; de Munter JS et al. 2007).
It's important to note that – unlike white flour products – whole grains and coarsely ground whole grain breads do not raise blood sugar sharply … see our sidebar, “Which foods raise blood sugar levels?”.
Advocates of grain-avoidance also tend to gloss over the big nutritional differences between whole grains – rich in fibers and antioxidants – and nutritionally “empty” refined grain foods such as white bread.
Now, three new studies suggest that advice to avoid all grains is misguided, and may lead to unnecessary diet restrictions.
Study #1: Glycemic index may not indicate a diet's healthfulness
Last month, researchers at the National Institutes of Health (NIH) published the surprising results of a very well-designed clinical trial.
They recruited 163 mostly overweight people with high blood pressure … a combination that raises the risk of heart disease and Type 2 diabetes.
The subjects were assigned to eat four different diets, each diet lasting five weeks. Importantly, all of their food was provided, to ensure compliance.
Each diet included plenty of fruits, vegetables, beans, fish, poultry, lean meat, and grains.
Two of the diets were slightly higher in carbs compared with the average American's diet, and two were slightly lower in carbs.
The researchers then altered the types of carbs in each diet:
- Low glycemic diets included whole grain bread and cereal, apples, steel-cut oats, and non-starchy vegetables.
High glycemic diets included white bread, carrot and bran muffins, instant rice and instant oatmeal, honey, and sweet snacks like bananas and apricots in heavy syrup.
When the overall amount of carb intake was lowered, this reduced cardiovascular risk factors like cholesterol, triglycerides and blood pressure.
This outcome affirmed the idea that lower-carb diets are generally healthier than higher-carb diets … a key principle of the Paleo diet and other low-carb approaches.
But when the two diets provided equivalent amounts of carbs and calories, the low glycemic approach did not improve insulin sensitivity, cholesterol or blood pressure levels.
Critics noted that this trial was fairly short in duration, and that the benefits of a low-GI diet may take longer to manifest … a good point that may lead researchers to conduct longer-term studies.
Study #2: Large study links whole grains to lower death risk
A very large population study from Harvard links diets higher in whole grains to reduced mortality rates … especially a cut in deaths due to cardiovascular disease (CVD).
Whole grains are recommended in official U.S. diet guidelines ... but it's been unclear whether, or how much, diets high in whole grains impact death risk.
The study was led by Hongyu Wu, Ph.D., of the Harvard School of Public Health. He and his coauthors examined data from two large studies:
- The Nurses' Health Study (1984-2010), involving 74,341 women
- The Health Professionals Follow-Up Study (1986-2010), involving 43,744 men
All the participants were free of cancer and CVD when the studies began.
After the data were adjusted to account for potential confounding factors, the results linked diets higher in whole grains with lower risk of death and death from CVD … but not to reduced risk of death from cancer.
The authors estimated that every serving (28 grams/per day) of whole grains dropped the risk of death by five percent, and reduced the risk of death from CVC by nine percent.
As they wrote, “These findings further support current dietary guidelines that recommend increasing whole grain consumption … and [suggest that] a diet enriched with whole grains may confer benefits toward extended life expectancy.” (Wu H et al. 2015)
Study #3: Nordic diet rich in whole rye found healthful
We've all heard of the Mediterranean diet ... but what about the Nordic diet?
Researchers in Nordic countries have been studying the health effects of the so-called “healthy Nordic diet”, and have found that it exerts beneficial health effects similar to those of the Mediterranean diet.
They define the Nordic diet as one rich in these components:
Low-fat dairy products
Berries and other fruits
Fish (three servings per week)
Green vegetables and root vegetables
Whole grain products – whole wheat, but more whole rye
Canola oil – High in healthful omega-3 and monounsaturated fats, but low in pro-inflammatory omega-6 fats. (Note: Extra virgin olive oil is a better choice, because it is high in healthful monounsaturated fats but low in pro-inflammatory omega-6 fats, and is rich in potent antioxidants linked to good vascular health.)
A newly published study from the University of Eastern Finland was designed to discover whether the Nordic diet affects the expression of inflammation-related genes in fatty (adipose) tissue under the skin, where diet-driven inflammation usually manifests (Kolehmainen M et al. 2015).
The study participants were middle-aged men and women with at least two characteristics of metabolic syndrome, such as high blood pressure or fasting blood sugar levels, abnormal blood-fat profiles, or being at least slightly overweight.
For a period of 18 to 24 weeks, half of the study participants followed the health-promoting Nordic diet.
The control group consumed refined, starchy, low-fiber grain products, butter-based spreads, and relatively little fish.
The participants were not asked to try to lose weight during the study, and no significant weight changes occurred.
Samples of the study participants' adipose tissue were taken at the beginning and end of the study, and examined to detect any changes in the expression of genes related to metabolism and inflammation.
At the end of the study, the researchers found differences in the function of up to 128 different genes in the adipose tissue of the Nordic diet group and the control group.
Despite it being high in whole grains, the expression of several inflammation-associated genes was lower in the Nordic diet group than in the control group.
The researchers also conducted a separate controlled clinical trial in 158 middle-aged people with metabolic syndrome, to see whether the whole-grain-rich Nordic diet would have any effect on blood-fat risk factors for cardiovascular disease.
They measured the participants' blood levels of compounds called alkylresorcinols (AR) … a marker for whole grain wheat and rye intake.
After adjusting for other factors that would affect blood fats, they linked higher AR blood levels to improved blood-fat profiles: lower blood levels of LDL cholesterol, non-HDL cholesterol, apolipoprotein B, triglycerides, and a lower LDL/HDL cholesterol ratio, lower.
As they wrote, “Increased proportion of whole grain rye … is associated with favorable blood lipid outcomes …”. (Magnusdottir OK et al. 2014).
An earlier trial from the same research team found that the Nordic diet improved participants' blood-fat profiles and reduced markers for inflammation (Uusitupa M et al. 2013)
Our takeaway: Whole grains are generally healthful
These and other studies suggest that two things are generally true:
Diets low in starchy carbs are generally healthier than ones high in such foods.
The case for eliminating or avoiding whole grains and whole grain products is weak, at best.
It's tempting to believe that extreme diets are magic bullets.
But the evidence suggests that traditional whole-food diets – ones featuring vegetables, fruits, beans, dairy, fish, grass-fed meats and poultry, and whole grains – are reliably healthful.
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