Diet & Weight Magazine

“Healthy” Whole Grains: What the Evidence Really Shows

By Dietdoctor @DietDoctor1

You hear about them all the time: those allegedly nutritious whole grains you should be eating every day if your goals include being slim and healthy - and whose goals don't include that?

Do whole grains, however, really live up to their reputation as a superfood? Let's take a closer look at the very weak scientific evidence behind the claims made about their benefits. Then you can decide whether you need a daily dose of grains in your diet or not.

First, what are whole grains?

Technically, whole grains are the seeds of cereal grasses. In their natural "whole" state, grains have a hard, inedible husk that covers three edible parts:

  • Bran: fiber
  • Germ: contains some B vitamins, minerals, fat, and protein
  • Endosperm: major portion of the grain; mainly starch with a small amount of protein, vitamins and minerals

Nutritionally speaking, whole grains have had their outer inedible husks removed but retain all three edible parts of the seed. By contrast, refined grains like white flour (including unbleached wheat flour) and white rice have their bran and germ removed during milling leaving only the endosperm.

Most whole grains have some processing. For instance, whole wheat is ground or crushed to create whole-wheat flour; old-fashioned oats are steamed and rolled in order to make them more palatable and easier to digest.

Although wild grains may have been eaten by hunter-gatherers in certain regions during the paleolithic era, wheat, barley, rice and other grain crops were first grown and introduced into the human diet after the agricultural revolution was well underway, between 9,000 BC and 6,000 BC.

Since then, people around the world have consumed a variety of grains based on cultural preferences and availability. Among the dozens of types of whole grains that exist, some of the most well-known and widely consumed include:

According to the Whole Grains Council, the most commonly consumed whole grains in the US are whole wheat, oats, and brown rice.

Buyer beware: over the past several decades, the term whole grains has become a buzzword among the health conscious. Knowing this, manufacturers often include bold, eye-catching messages like "Contains 14 grams of whole grains" on boxes of cereal, whole-wheat pasta, granola bars and similar products, which often contain high levels of added sugar or refined grains, too, as well as being very high in carbohydrates.

In fact, a 2013 review of more than 500 grain-based products found that those displaying a "whole grains" stamp contained more sugar - and were more expensive - than similar products without the stamp.

All of that hardly makes these "whole-grain" products a healthy choice despite their labels' claims.

Nutrition in whole grains

Are whole grains really a nutrient-packed energy source? While some types contain a bit more protein and micronutrients than others, their nutrition profiles aren't very impressive overall, aside from being very high in manganese (like many other foods).

For instance, a bowl of steel-cut oats - often suggested as an ideal meal to start your day - provides about 10 grams of protein (although lacking in some of the essential amino acids found in complete animal protein), 8 grams of fiber, and small amounts of thiamin, iron, magnesium, selenium and zinc. However, it also contains 46 to 48 grams of net carbs, even when prepared without milk, fruit, sweeteners or other additives.

How about using two slices of whole wheat bread to build your sandwich at lunch? This would provide about 7 grams of (incomplete) protein, half of your daily selenium needs, and small amounts of thiamin, niacin, and magnesium, which would come with 40 grams of net carbs and a comparably low 6 grams of fiber.

Brown rice's nutritional profile is similar to that of whole wheat bread and oats, although lower in protein and fiber.

Additionally, trendy grains like quinoa and farro are often lauded for being higher in protein and easier to digest than other grains, but they too are very high in net carbs, relatively low in fiber, and lacking substantial amounts of key nutrients.

Most whole grains contain a substance called polyphenols, which are compounds found in plants that might potentially help protect cells from damage and reduce inflammation in the body. However, higher-quality studies are needed to confirm this. Indeed, we just don't know enough about polyphenols to make them a priority for inclusion in our diets.

And that leads us to the quality of the existing research on whole grains and health.

Whole-grain research: weak evidence that is over-hyped

Studies about whole grains seem to receive more than their fair share of media coverage these days. One such study to make recent international news headlines was a series of systematic reviews and meta-analyses exploring the health effects of different types of carbohydrate, which was published in The Lancet early in 2019.

After analyzing 185 observational studies and 58 clinical trials, researchers concluded that eating more whole grains and fiber might be an effective strategy for preventing obesity, heart disease, diabetes, cancer, and reducing risk of early death. Headlines even blared that people would live longer if they ate more healthy grains and that the findings "were a blow to fashionable low-carb diets."

We wrote about that study when it came out, noting that it was not comparing diets with whole grains to low-carb diets, but rather to diets full of highly-refined grains. (And we addressed the erroneous myth that low-carb diets are low-fiber diets. They are not!)

Diet Doctor: A low-carb diet does not mean a low-fiber diet

Importantly, the claims made for whole grains' beneficial health effects are largely based on epidemiological or observational studies - the kind of evidence that isn't considered strong to start with. Especially in nutrition, this type of research can't be relied upon to draw conclusions due to bias, research methods and other factors, as Stanford professor John Ioannidis has repeatedly pointed out:

Video from Swiss Re "Food for Thought": The role of bias in nutritional research American Council on Science and Health: John Ioannidis aims his bazooka at nutrition science

Epidemiological studies rely on self-reporting and the notoriously inaccurate food-frequency questionnaire, in which people are asked to recall how many times they ate certain foods within a specific period of time - essentially an impossible task for almost anyone.

Additionally, since the studies are observational, they cannot claim that eating more whole grains actually causes people to have greater weight loss, health improvements or decreased risk of disease or death; they can just say that they observed a correlation. Remember the oft-said phrase "correlation is not causation"? Such studies cannot prove anything. Learn more about observational vs. experimental studies:

“Healthy” whole grains: What the evidence really shows

What's more, the observational associations between eating whole grains and staying slim and healthy are statistically very weak. When an observational study's hazard ratios are less than 2, any evidence tying a behavior to an outcome is marginal at best. In observational studies looking at whole grains and health, hazard ratios have consistently been well below 2, meaning that any relationship between the two is likely random and false.

An association between frequent whole-grain consumption and good health is a perfect example of the "healthy user bias." We don't know if the reason people who eat whole grains tend to be healthier than those who don't is solely because of this one aspect of their diet (highly unlikely) or because they tend to practice many other health-conscious behaviors like exercising regularly, drinking alcohol in moderation, avoiding sugar-sweetened beverages and cooking fresh food at home on a regular basis.

But whole grains just seem so healthy, you may be thinking. And it's certainly understandable to feel that way, given what we've all been hearing from various health organizations over the past several decades. However, let's examine the experimental (higher-quality) randomized control trial (RCT) evidence to see how well it supports the claim that whole grains are the solution to staying slim and disease-free.

RCTs are designed to compare an intervention (such as consuming more whole grains) with a control (consuming refined grains or a standard diet). A very important question to ask in these whole grain RCT studies is what were whole grains in the diet were compared to: Did they compare eating whole grains to eating refined grains or a standard diet? Or did they compare eating whole grains to eating low-carb vegetables? It makes a huge difference.

Virtually all the RCTs for whole grains have compared them to refined grains or a standard diet. Let's take a closer look.

Whole grains and weight loss

Mainstream nutrition authorities, such as on this website, keep touting this message: Eating plenty of whole grains can help you achieve and maintain a healthy body weight. But how strong is the (RCT) evidence linking high whole-grain intake and weight loss?

It is not surprising that whole grains have been shown to outperform refined grains in experimental weight-loss studies. RCT studies have found that among normal weight and overweight adults, those who consumed whole grains for periods ranging from four to 16 weeks experienced greater increases in resting metabolic rate and greater decreases in belly fat, insulin resistance, inflammation and body weight compared to those who consumed refined grains.

In one study, people who ate whole rye products had greater fat loss compared to those who consumed refined grains, whereas consuming whole wheat didn't seem to provide any fat-loss benefits over refined wheat.

However, a 2017 systematic review of RCTs - considered the strongest type of evidence, as it includes multiple RCT studies rather than relying on just one - found no differences in weight loss and only slightly higher fat loss (less than 0.5% difference) in groups who consumed diets high in whole grains compared to groups who consumed diets high in refined grains.

Whole grains and diabetes

Can eating whole grains on a regular basis help prevent diabetes and keep blood sugar from rising too high after meals?

Results from experimental trials looking at blood sugar response to whole grains have been mixed. A 2017 systematic review of RCTs found that whole grains seem to raise blood sugar less than refined grains do, at least in healthy people.

However, an even more recent review of RCTs showed that non-diabetic individuals had almost identical blood sugar responses after eating whole or refined wheat or rye. The blood sugar increase, however, was much higher after eating white rice compared to whole-grain rice.

Still, even though white rice raised people's blood-sugar levels more quickly, whole-grain (brown) rice was also found to raise blood sugar to some extent in these studies, with differences likely related to individual tolerance, different methods of measuring, and possibly other factors as well.

At this time, there are only a few RCTs comparing blood sugar responses to whole vs. refined grains in obese people and those with diabetes. Overall, they have shown that replacing processed with whole grains modestly improves blood sugar and insulin regulation.

So is this a good strategy for diabetes reversal or even adequate glycemic control? Not really. For instance, in one of these studies, when diabetic adults ate 50 to 100 grams of whole-grain oats on a daily basis, their HbA1c and fasting blood sugar levels were still well above target range after one month, as well as when researchers followed up with them one year later.

“Healthy” whole grains: What the evidence really shows

Whole grains and heart disease

Whole grains are often referred to as "heart-healthy" foods. So what is the evidence supporting the cardio-protective effects of whole grains?

Experimental studies often show improvements in certain heart disease risk factors when whole grains are substituted for refined grains. Two meta-analyses of RCTs found minor reductions in LDL cholesterol and triglycerides in groups who consumed whole grains compared to groups who consumed refined grains, with oats appearing to have the most cholesterol-lowering power.

However, reducing isolated risk factors does not necessarily translate into improved health, especially if one marker improves while others worsen (such as low-density lipoprotein improving but insulin resistance worsening.)

Moreover, in 2017, authors who performed a systematic review of nine RCTs concluded that there isn't enough evidence to support claims that whole grains lower CVD risk. They made that conclusion due to the lack of high-quality controlled research, including small sample sizes and a high risk of bias (including funding from pro-cereal organizations) found in some of the trials they assessed.

This highlights the importance of understanding how low-quality research has biased the support for the "heart-healthy" claim for whole grains. When scrutinized with a higher level of scientific integrity, the data did not hold up.

Whole grains and cancer risk

Whole grains are often promoted by various groups, such as cancer agencies, as a food that helps fight cancer, especially colorectal cancer. This is based on some observational studies with weak correlations suggesting that people who eat the most whole grains may be at lower risk for certain cancers, while others show no association at all.

Experimental research, however, that tests the effect of consuming whole grains on cancer risk is entirely lacking. Remember, because observational studies show associations and not causation, they're considered a very low quality of evidence. There currently are no good RCTs about whole grains and cancer risk.

So based on the lack of robust evidence and the conflicting results of lower-quality observational trials, it doesn't sound as though there's much convincing evidence that whole grains are protective against cancer, does it?

Whole grains and other attributed health benefits

Whole grains have also been linked to a few other health improvements:

  • Reduced inflammation: Chronic system-wide inflammation is believed to be at the root of many chronic diseases, including heart disease. Two meta-analyses of RCTs found that consuming whole grains helped reduce the inflammatory markers C-reactive protein (CRP) and interleukin-6 (IL-6) but did not change other markers of inflammation - again, compared to eating refined grains.
  • Better gut health: Bacteria that reside in your colon produce short-chain fatty acids as a byproduct of digesting fiber. Results from RCTs suggest that consuming whole grains seems to boost production of these short-chain fatty acids - which nourish the gut and may improve insulin sensitivity - that is, again, compared with consuming refined grains.

While these studies may sound convincing, keep in mind that they are not comparing whole grains to a grain-free, low-carb diet, but rather to the consumption of highly refined grains.

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