“Healthy” whole grains: What the evidence really shows
You hear about them all the time: those 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 live up to their reputation as a superfood? Let’s take a closer look at the 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.
This guide is our attempt at summarizing what is known. It is written for adults who are concerned about whole grain intake and health.
Discuss any lifestyle changes with your doctor. Full disclaimer
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.
Wild grains appear to have been eaten by hunter-gatherers in certain regions during the paleolithic era, including the areas known today as Southern Italy and Africa.2 During the Agricultural Revolution, larger quantities of wheat, barley, rice and other grains were grown and became a part of the human diet in many other areas.
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:
- Brown rice
- Whole wheat
- Wild rice
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.
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.3
Nutrition in whole grains
Are whole grains really a nutrient-packed energy source? That depends what we compare them to. While some types contain a bit more protein and micronutrients than others, their nutrition profiles aren’t very impressive overall, especially when compared to a diet with a variety of vegetables and meats.4
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 this is considered “incomplete” protein since it lacks some of the essential amino acids), 8 grams of fiber (daily recommendations are around 30 grams per day), 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 (compare that to the recommended less than 20 grams of net carbs for very low carbohydrate diets, and less than 50 for low carb diets).
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 even lower in protein and fiber.
Additionally, newly popular grains like quinoa and farro are often lauded for being higher in protein and easier to digest than other grains. While this may be true, they too are relatively high in net carbs, low in fiber, and lacking many key nutrients thus making them nutritionally poor as stand alone foods.
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.5 Indeed, we just don’t know enough about polyphenols to make them a priority for inclusion in our diets.
Whole-grain research: weak evidence overallnews 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.6
We wrote about that study when it came out, noting that it compared diets with whole grains to diets full of highly-refined grains. (We also addressed the erroneous myth that low-carb diets are low-fiber diets. They are not!) And we wondered aloud how the results would have been different if the comparison group ate a low-carb, no grain diet.
Importantly, the evidence for whole grains’ beneficial health effects are largely based on epidemiological or observational studies. This kind of evidence cannot prove cause and effect and we should not rely upon these studies to draw any firm conclusions. Nutritional epidemiology is complicated by healthy user bias, poor data collection, and other factors, as Stanford professor John Ioannidis has repeatedly pointed out.
First of all, epidemiological studies rely on self-reporting and the potentially inaccurate food-frequency questionnaire. These questionnaires ask people to recall how many times they ate certain foods within a specific period of time — a tough task for just about anyone.7
Also, since the studies are observational, they cannot claim that eating more whole grains actually leads to improved health; they can just say that they observed a correlation. Remember the oft-said phrase “correlation is not causation”? Learn more about observational vs. experimental studies:
Guide to observational vs. experimental studies
Guide In this guide, we discuss the differences between observational and experimental studies, the advantages and disadvantages of each.
What’s more, the observational associations between eating whole grains and being healthy are statistically weak. When an observational study’s hazard ratios are less than 2, any evidence tying a behavior to an outcome is marginal.8 In observational studies looking at whole grains and health, hazard ratios have consistently been well below 2, meaning that any relationship between the two may be due to other factors rather than a true cause and effect.
The association between frequent whole-grain consumption and good health is a perfect example of the “healthy user bias.” Take the example of the “Blue Zones,” sections of society where people live to be 100 years old far more frequently than the general population. They are reported to eat lots of whole grains. But we don’t know if they are healthier because of the whole grains 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.
How do we understand this better? Let’s examine the higher-quality randomized control trial (RCT) evidence to see how well it supports the claim that whole grains can improve your health.
RCTs are designed to compare an intervention (such as consuming more whole grains) with a control (consuming refined grains or a standard diet). In these whole grain RCT studies, we need to know what the whole grains were compared to. Did they compare eating whole grains to eating refined grains? Or was it a standard diet? Or even better, low-carb vegetables? As you will see, it makes a difference.
Whole grains and weight loss
Many nutrition authorities, such as on the ShareCare site, keep sharing this message: Eating plenty of whole grains can help you achieve and maintain a healthy body weight. But how strong is the evidence linking high whole-grain intake and weight loss?
A 2013 systematic review of RCTs — considered the strongest type of evidence — found slightly higher fat loss (less than 0.5% difference) with no difference in overall weight loss in groups who consumed diets high in whole grains compared to groups who consumed refined grains.9 A newer systematic review published in 2019 found no weight loss benefit from whole-grain consumption.10
In other words, RCTs show the effect of whole grains on weight loss to be small at best. However, some studies show beneficial effects beyond just weight loss.
Several RCT studies have found that among normal weight and overweight adults, those who consumed whole grains compared to refined grains for four to 16 weeks experienced greater increases in resting metabolic rate and greater decreases in belly fat, insulin resistance, inflammation and body weight.11
In one study, people who ate whole rye products had greater fat loss compared to those who consumed refined grains. The same was not found for wholegrain wheat.12
Whole grains and diabetes
Can eating whole grains on a regular basis help prevent diabetes and blood sugar spikes?
Once again, observational trials show a relationship between eating whole grains and having a lower risk of developing type 2 diabetes. However, we have already reviewed the weakness in this level of data and explained how it does not prove a beneficial effect from whole grains. How does the claim hold up under scrutiny of higher quality randomized controlled trials (RCTs)?
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 raise blood sugar and insulin levels less than refined grains do, at least in healthy people.13
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 was much higher after eating white rice compared to whole-grain rice, though.14
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 grains with whole grains improves blood sugar and insulin regulation.15
So is this a good strategy for diabetes reversal or even adequate glycemic control? That depends. If you are replacing highly refined grains, then whole grains are likely beneficial. But how does that compare to diabetes control without grains?
Multiple randomized trials show better glycemic control with carbohydrate restriction. This by definition means they excluded grains. Systemic reviews of the RCTs confirm these results. 16 And the American Diabetes Association (ADA) now endorses “Reducing overall carbohydrate intake for individuals with diabetes has demonstrated the most evidence for improving glycemia.”17
Bottom line: Replacing refined grains with whole grains likely has significant benefits for blood sugar control. However, even whole grains raise blood glucose, so completely avoiding grains likely results in even better blood sugar control.
Whole grains and heart disease
Whole grains are often referred to as “heart-healthy” foods.
Indeed, many epidemiology studies show those who eat whole grains have lower risk of heart disease. However, as mentioned earlier, this does not prove that whole grains directly improve heart health, and given the inherent weakness of the data, it is just as likely due to healthy user bias (healthier people choose to eat whole grains and therefore have other healthy habits that contribute to a lower risk of heart disease).
On the other hand, higher-quality experimental studies frequently 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 (0.09mmol/L) and triglycerides (0.04 mmol/L) in groups who consumed whole grains compared to groups who consumed refined grains, with oats appearing to have the most cholesterol-lowering power.18
However, reducing isolated risk factors does not necessarily translate into improved health, especially if one marker improves while others worsen (such as LDL improving but insulin resistance worsening.) That is why we need experimental studies looking at the end points that really matter- heart attacks, strokes and death- rather than less certain outcomes. To date, those studies are lacking.
Moreover, in 2017, the Cochrane Database performed a systematic review of nine RCTs and concluded 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.19
This highlights the importance of understanding how low-quality research has influenced the support for the “heart-healthy” claim for whole grains. When scrutinized with a higher level of scientific integrity, the data doesn’t seem to hold up.
Whole grains and cancer risk
Cancer agencies and other groups often promote whole grains as a food that helps prevent cancer. This is based on mostly observational studies showing that people who eat the most whole grains are at lower risk for certain cancers, especially colorectal cancer. However, these studies are weakened by their low hazard ratios and by the fact that many other epidemiology studies fail to confirm those finding.20
What’s more, experimental research (RCTs) testing the effect of consuming whole grains on cancer risk is entirely lacking. Remember, since observational studies show associations and not causation, they’re considered a very low quality of evidence. We don’t know if healthier people chose to eat more grains, or if eating the grains made them healthier, or if whole grains are simply a surrogate for food quality and fiber when compared to a diet full of refined and processed foods.
Bottom line: If whole grains replace refined grains and highly processed foods, then eating whole grains may be associated with reduced cancer incidence. However, based on the conflicting results of lower-quality observational trials and lack of RCT evidence, at this point there’s no convincing evidence that whole grains by themselves are protective against cancer.
Whole grains and other attributed health benefits
Whole grains have also been linked to a few other health improvements:
- Reduced inflammation: Inflammation is believed to be at the root of many chronic diseases, including heart disease.21 Two meta-analyses of RCTs found that consuming whole grains instead of refined grains helped reduce the inflammatory markers C-reactive protein (CRP) and interleukin-6 (IL-6).22
- 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.23
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. In the end, it is possible all the benefits came from eliminating the refined grains and not from adding the whole grains.
Dietary guidelines videos
Comparing whole grains to no-grains
To recap, the RCTs to date around whole grains demonstrate that, yes, eating a less-processed food is better than eating a highly-processed one.
What if studies compared consuming three servings of whole grains to three servings of non-starchy vegetables per day on a low-carb diet? It could be that under such an RCT whole grains might not show any benefit. But we don’t know that yet because such a trial has never been done, at least not one that we can find in the research literature.
One RCT, however, suggests that the no-grain approach might be superior. Although not a head-to-head trial pitting whole grains vs. no grains, back in 2007 researchers compared a grain-free, very-low-carb ketogenic diet to a low-glycemic-index (low-GI) diet, which included whole grains, in adults with type 2 diabetes.
At the end of the six-month trial, people in the grain-free keto group had significantly greater weight loss and reductions in blood sugar than the low-GI group.24
In order to strengthen the evidence, we need more RCTs comparing the health effects of low-carb grain-free diets to whole grain diets in both healthy people and those with diabetes.
Whole grains don’t provide unique nutritional benefits
While it’s true that whole grains contain vitamins, minerals, fiber, and polyphenols, these nutrients are found in many other foods, often in greater concentrations:
- Fiber: Looking for fiber? Eat cruciferous vegetables, flaxseed, chia seeds, nuts, avocados, blackberries and raspberries — all of which provide more fiber than whole grains and far fewer digestible carbohydrates.
- Magnesium: Although most whole grains are considered a good source of magnesium, mackerel, cooked greens, almonds, hemp seeds, pumpkin seeds and sunflower seeds contain equivalent or greater amounts per serving.
- Thiamin: Seafood has the edge over whole grains for thiamin, and pork is higher in this B vitamin than any other food.
- Niacin: Chicken, turkey, red meat (especially liver), fatty fish and avocado are better sources of niacin than whole grains.
- Polyphenols: The jury is still out when it comes to the effects of plant phenols on health. However, you certainly don’t need to consume whole grains to get them. Vegetables, berries, olive oil, tea, spices, coffee, and dark chocolate contain an array of potentially beneficial polyphenols.25
Tolerance for whole grains varies among individuals
Some people can eat whole grains regularly without experiencing any issues. Others, however, cannot.
Individuals with celiac disease need to avoid gluten-containing whole grains. Gluten — a protein found in wheat, barley, rye and the wheat derivatives farro, spelt and triticale — can cause damage to the digestive tract and other symptoms when consumed in even small amounts by those with celiac disease.
People with celiac disease or non-celiac gluten sensitivity must eat a gluten-free diet in order not to experience symptoms.26 These individuals may be able to tolerate other types of whole grains like brown rice or quinoa. However, they might benefit from avoiding all grains, as even types that don’t naturally contain gluten are sometimes cross-contaminated with those that do during processing and packaging.27
There are also people for whom whole grains might cause other problems, such as IBS and skin problems.28 In addition, although not widely accepted among everyone in the scientific community, some researchers suggest that removing grains from the diet could be beneficial for people with certain mental health issues.29
While there isn’t much published research about adverse reactions to whole grains, many people report that they feel better and notice health benefits, such as improved digestive function when they minimize or avoid grains of all types.30
Whole grains can increase blood sugar more than commonly believed
Whole grains rank surprisingly high on the glycemic index (GI), the scale that measures how much a specific food raises blood sugar.31
The amount of processing grains undergo will influence their GI. Yet even minimally processed steel-cut oats have a moderate GI of 55, and quick-cooking oatmeal has a GI over 70.32 By contrast, cabbage and spinach have very low GIs of 15 and 6, respectively, and meat, fish, cheese, and fats are zero-GI foods.
As discussed earlier, whole grains have been shown to raise people’s blood sugar levels less than refined grains do in most experimental studies. But what is the blood sugar response to an entirely grain-free diet?
The paleo diet, which excludes grains, was found to be more effective than conventional dietary recommendations for lowering blood sugar and insulin levels in people at risk for metabolic syndrome, according to a 2015 meta-analysis of RCTs.33
In fact, there are many online personal stories of people with diabetes who have achieved normal blood sugar control for the first time in years as a result of adopting an entirely grain-free low-carb or keto diet.34 Of course, this isn’t surprising, given that whole grains are so high in carbohydrates.
Moreover, even people without diabetes or prediabetes can experience blood sugar elevations after eating whole grains. Recently, Lily Nichols — a young, healthy non-diabetic dietitian — wore a continuous glucose monitor (CGM) for ten days in order to learn more about her own blood sugar patterns in response to various foods.
After consuming her typical lower-carb meals, she could see that her blood sugar increased only minimally. However, when she experimented with eating a small portion of old-fashioned oats as part of a low-fat meal, the CGM revealed that her blood sugar more than doubled within an hour.
Summary: should we eat whole grains or avoid them?
Whole grains have a clear edge over refined grains, with many studies showing they can be an integral part of a beneficial diet. However, there’s a lack of evidence comparing eating a diet high in whole grains to eating a grain-free diet.
This means that for people who tolerate grains and enjoy eating them, minimally processed and whole grain types are likely best. But if you don’t feel a need to eat grains, there is no nutritional need and likely no health need for them.
Keep in mind that whole grains don’t offer any unique nutritional benefits that can’t be found in other foods. Recommendations to consume them regularly to promote better health are not based on high-quality scientific evidence.
What’s more, given their high carbohydrate counts, they probably shouldn’t be consumed very often on a low-carb lifestyle, if at all. Fortunately, Diet Doctor has plenty of tasty grain-free low-carb bread and porridge recipes available that can be enjoyed instead.
Do you need whole grains? In all likelihood, no. At the end of the day, why not experience the benefits of eating a wide variety of keto-friendly whole foods that are delicious, satisfying, and often nutritionally superior to whole grains?
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The Lancet 2019: Carbohydrate quality and human health: a series of systematic reviews and meta-analyses [Mixed observational and randomized clinical trial data; very weak evidence for significant health benefits] ↩
Hazard ratios, also referred to as relative risks, tell us how much something was observed in one group compared to another. A relative risk of 2 means something is twice as likely to occur in the observed group. However, anything less than two is considered a weak statistical correlation and has a high likelihood of being due to other factors. As an example of strong observational studies, the hazard ratio or relative risk for smoking and cancer varies between 10 and 40.
International Journal of Cancer: Cigarette smoking and lung cancer – relative risk estimates for the major histological types from a pooled analysis of case-control studies [meta-analysis of observational studies with a very high relative risk; moderate evidence] ↩
American Journal of Clinical Nutrition 2013: Whole grain and body weight changes in apparently healthy adults: a systematic review and meta-analysis of randomized controlled studies [strong evidence] ↩
Resting metabolic rate
American Journal of Clinical Nutrition 2017: Substituting whole grains for refined grains in a 6-wk randomized trial favorably affects energy-balance metrics in healthy men and postmenopausal women [moderate evidence]
Inflammation and body weight
Gut-British Medical Journal 2019: Whole grain-rich diet reduces body weight and systemic low-grade inflammation without inducing major changes of the gut microbiome: a randomised cross-over trial [moderate evidence] ↩
European Journal of Clinical Nutrition 2017: Wholegrain rye, but not wholegrain wheat, lowers body weight and fat mass compared with refined wheat: a 6-week randomized study [moderate evidence] ↩
American Journal of Clinical Nutrition 2018: The effects of whole-grain compared with refined wheat, rice, and rye on the postprandial blood glucose response: a systematic review and meta-analysis of randomized controlled trials [strong evidence] ↩
American Journal of Clinical Nutrition 2014: Effects of whole and refined grains in a weight-loss diet on markers of metabolic syndrome in individuals with increased waist circumference: a randomized controlled-feeding trial [moderate evidence] ↩
The advantage of a low-carb diet in type 2 diabetes has been recognized in several systematic reviews and meta-analyses or RCTs. Here are two recent examples:
Here are five RCTs demonstrating the benefits of low-carbohydrate diets in people with type 2 diabetes:
Nutrition & Diabetes 2017: Twelve-month outcomes of a randomized trial of a moderate-carbohydrate versus very low-carbohydrate diet in overweight adults with type 2 diabetes mellitus or prediabetes [moderate evidence]
Journal of the American College of Nutrition 2018: Effects of whole-grain consumption on selected biomarkers of systematic inflammation: a systematic review and meta-analysis of randomized controlled trials [strong evidence] ↩
American Journal of Clinical Nutrition 2017: Substituting whole grains for refined grains in a 6-wk randomized trial has a modest effect on gut microbiota and immune and inflammatory markers of healthy adults [moderate evidence]
British Journal of Nutrition 2015: Increased gut hormones and insulin sensitivity index following a 3-d intervention with a barley kernel-based product: a randomised cross-over study in healthy middle-aged subjects [moderate evidence] ↩
Nutrition & Metabolism 2008: The effect of a low-carbohydrate, ketogenic diet versus a low-glycemic index diet on glycemic control in type 2 diabetes mellitus [randomized trial; moderate evidence] ↩
Nutrition Research 2018: Oat safety for celiac disease patients: theoretical analysis correlates adverse symptoms in clinical studies to contaminated study oats [review of clinical studies; moderate evidence] ↩
American Journal of Clinical Nutrition 2009: Glycemic index, postprandial glycemia, and the shape of the curve in healthy subjects: analysis of a database of more than 1000 foods [non-randomized trial; weak evidence] ↩