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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.

Disclaimer: The beneficial effects of whole grains on human health are well accepted in the medical and nutrition communities with significant support from the scientific literature. However, some evidence exists calling into question these beneficial effects. While studies show whole grains are better than refined grains for many health outcomes, there is almost a complete lack of research on whether whole grains are better than no grains. Therefore we question if their health benefits apply equally to all individuals, especially since many of the potentially beneficial components of whole grains can be obtained from other foods. The beneficial effects of whole grains on human health are well accepted in the medical and nutrition communities with significant support from the scientific literature. However, some evidence exists calling into question these beneficial effects. While studies show whole grains are better than refined grains for many health outcomes, there is almost a complete lack of research on whether whole grains are better than no grains. Therefore we question if their health benefits apply equally to all individuals, especially since many of the potentially beneficial components of whole grains can be obtained from other foods. 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

: fiber Germ : contains some B vitamins, minerals, fat, and protein

: 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. 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:

Barley

Brown rice

Bulgur

Corn

Oats

Rye

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.

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, they aren’t necessarily nutrient-rich when considered in the context of their carbohydrate and calorie content.

For instance, a 40g (1/4 cup) serving 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 about 10-20% of daily thiamin, iron, magnesium, biotin, selenium and zinc requirements. However, it also contains about 46 to 48 grams of net carbs and 150 calories, 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 8 grams of (incomplete) protein, a quarter of your daily selenium needs, and small amounts of thiamin, niacin, and magnesium, which would come with approximately 180 calories, 35 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 fiber than rice or pasta. While this may be true, they too are relatively high in net carbs, meaning that you’d need to eat a number of portions a day (and a lot of carbs!) to meet micronutrient requirements. For people who would like to follow a lower carbohydrate way of eating, there are more suitable ways of getting the vitamins and minerals you need.

Whole grains contain phytonutrients, 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.

At the moment, we don’t know enough about phytonutrients to make them a priority for inclusion in our diets. In any case, many plant-derived foods contain these phytonutrients including olives, nuts and even oils. Therefore, it’s not necessary to eat whole grains to get these potentially beneficial compounds if that doesn’t suit your dietary pattern

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

Whole-grain research: weak evidence overall

Studies about whole grains seem to receive more than their fair share of media coverage. 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.

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 necessarily 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.

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

Learn more about observational vs. experimental studies:

Since whole grains are promoted as a healthy product – they are typically chosen and eaten by people who prioritize health – so these people not only eat whole grains, they tend to engage in a whole host of healthy behaviors too – like not smoking, eating lots of fruit and vegetables, and exercising. Thus, the association between 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.

Observational studies are also limited by “social desirability bias.” This is where people taking part in a study respond in a certain way in order to please the researchers. Since whole grains are promoted as healthy for us, many people may respond, “Yes, of course, every day!” to the question “Do you eat wholegrain bread?”— even when they prefer white bread! This makes it harder to rely on self-reported dietary intake of healthy foods.

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, including the Dietary Guidelines for Americans, keep sharing this message: “Eating plenty of whole grains, as part of an overall healthy diet, may help with weight management.” 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. A newer systematic review published in 2019 found no weight loss benefit from whole-grain consumption.

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.

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.

Bottom line: RCTs show that adding whole grains to the diet has minimal benefit on body weight. However, replacing refined grains with whole grains likely has more significant benefits. Therefore it is likely that some of the benefit of eating more whole grains comes from eating less refined grains, in addition to small, if any, beneficial effects of the whole grains themselves.

Whole grains and diabetes

Can eating whole grains on a regular basis help prevent type two 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)?

A randomized control trial specifically designed to test the effect of the fibers from whole grains on type 2 diabetes development found that wholegrain fibers were not significantly better than the control arm at lowering glucose or improving insulin sensitivity. There was no difference between the groups in the incidence of type 2 diabetes. This study suggests that the addition of whole grains to a diet would not be sufficient to prevent type 2 diabetes.

Results from other experimental trials looking at blood sugar response to whole grains have been mixed. A 2017 systematic review of RCTs found that whole grains don’t raise blood sugar and insulin levels as much as refined grains do, at least in healthy people.

However, an even more recent review of RCTs showed that individuals without diabetes 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.

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.

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. Systematic reviews of the RCTs confirm these results. And the American Diabetes Association (ADA) now endorses “Reducing overall carbohydrate intake for individuals with diabetes has demonstrated the most evidence for improving glycemia.”

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.

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. 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 we already mentioned, 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.

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.

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.

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.

At this point in time, we can probably say that eating whole grains instead of refined grains is a good idea based on the other health evidence available but we should not have the expectation that we need whole grains in the diet to reduce our risk of CVD.

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 findings.

A huge challenge in these studies is an accurate assessment of dietary intake. There are biomarkers for whole grain intake which have been studied but they have their own limitations too including a short half-life. This may be important when looking at bowel cancer prevention because a large amount of fibre might be needed, and this is hard to assess accurately currently.

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. 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).

: 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 instead of refined grains helped reduce the inflammatory markers C-reactive protein (CRP) and interleukin-6 (IL-6). 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.

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. It is possible the fiber content of the whole grains does play a role in these beneficial health effects – but you can get a wide range of different fibers within a low-carbohydrate diet including from nuts, seeds, avocados, low-carbohydrate fruits and non-starchy vegetables.