Wholegrains: the whole story?

Nutritionists have embraced the concept of wholegrains with a passion claiming they are protective foods. But the evidence is inconsistent, which may be due to the methodology of the studies that have been undertaken so far. As the dietary fibres found in some grain foods are beneficial for bowel function and lowering blood cholesterol there is a case for basing cereal recommendations on fibre. Other aspects of the nutritional quality of cereal goods, such as nutrient density and glycaemic index are also relevant. Just recommending wholegrains is not enough.

When it comes to recommendations about grain foods the draft Australian Dietary Guidelines keep it simple: eat mostly wholegrain. The rationale is simple too: wholegrains are nutrient-rich and protective against a range of modern diseases such as cardiovascular disease, type 2 diabetes and obesity.

But is it true? How evidence-based is this advice?

Wholegrains and the prevention of disease

Superficially the wholegrain story looks very good. Prospective cohort studies consistently show that higher intake of wholegrains is associated with lower risk for cardiovascular disease, finding a reduction in risk of about 20 percent when high wholegrain-eaters are compared to those who eat little wholegrain. The risk for type 2 diabetes also appears to be lowered by eating wholegrains, the risk reduction being 27-30 percent. And higher wholegrain intake is associated with lower body mass index. In some studies higher intakes of wholegrains have also been associated with lower levels of inflammatory markers in the blood, suggesting that wholegrain consumption is damping down underlying disease processes. Based on studies such as these the draft Australian Dietary Guidelines report states: The evidence for the association of grain (cereal) foods (mostly wholegrain) with reduced risk of cardiovascular disease, type 2 diabetes and excess weight gain has strengthened …

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Reality check

It is important to remember that all of the above evidence is drawn from observational studies. They show associations between wholegrain consumption and health benefits but this type of study can’t prove that the wholegrains are actually responsible for the benefits. In fact, the results can be interpreted in two ways: (1) eating wholegrains makes people healthy, or (2) healthy people eat wholegrains.

As it turns out wholegrain-eaters are indeed healthy people – they tend to smoke less, exercise more and have better diets. Although researchers do their best to allow for these confounding factors in their analyses there is always the risk of a false signal about wholegrains that is actually due to the cluster of healthy behaviours typical of wholegrain-eaters.

Other lines of evidence need to be considered, so let’s look at the intervention studies. If wholegrains provide protection against cardiovascular disease and diabetes they would be expected to operate through the well-established risk factors for these diseases. So the task for the researcher is relatively straightforward – feed people wholegrains and measure changes in risk factors. The first large scale intervention study of this kind was the WHOLEheart Study conducted in the United Kingdom. The subjects substantially increased their wholegrain intake for four months and the researchers looked for effects on body weight, percentage body fat, waist circumference, blood lipids, glucose and insulin, and indicators of inflammation, coagulation and blood vessel function. The results? Nothing. Eating wholegrains had no significant effect on any of these markers of risk. There were similar findings in a more recent intervention study, although this study did find a beneficial effect of wholegrains on blood pressure.


Health benefits from wholegrains are sometimes attributed to phytochemicals – minor components found in the bran and germ of grains such as betaine, phenolic acids, carotenoids, tocotrienols and plant sterols. They are not essential nutrients but are biologically active and could conceivably affect health. However, the limited effects of wholegrains on risk factors for cardiovascular disease and diabetes seen in the intervention studies suggest any effects of these phytochemicals are relatively weak.

So rather than the evidence strengthening, it appears that the different lines of evidence linking wholegrains with prevention of disease are inconsistent. Importantly, a plausible mechanism for protection is yet to be identified.

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Dietary fibre and health

Lest this review be seen as a bit too sceptical we should consider the known health effects of one of the best-researched components of wholegrains – dietary fibre. The insoluble fibre found in the bran of wheat has a beneficial effect on bowel function, promoting the regular passing of soft stools. Bearing in mind the relatively high prevalence of constipation there is only benefit to be gained from dietary recommendations encouraging increased intakes of all sources of wheat fibre.

Another well-researched subject is the blood cholesterol-lowering effect of the soluble fibre in oats, achieved via changes in bile acid metabolism. This would be expected to lower the risk for coronary heart disease. In the draft Australian Dietary Guidelines the discussion on the mechanism by which wholegrains lower heart disease states Almost all the high level trials were conducted with oats. Therefore the benefit can be ascribed to oats or to soluble fibre, but cannot be generalised to wholegrains. Many wholegrains are not good sources of soluble fibre. All wholegrains are not alike.

The known health benefits of dietary fibre suggest that any effects of wholegrains may be due, at least in part, to their fibre content. In fact, some of the prospective studies showing that wholegrains are protective also show  that cereal fibre is protective, to a similar degree to wholegrains. Digging deeper, the definitions of wholegrain in these studies vary widely and in some instances include bran-based foods (which by definition are not made from whole grains). To muddy the waters further, wholegrain foods vary widely in their dietary fibre content.

So should dietary recommendations for cereal foods be based around the concept of wholegrains or dietary fibre? Or maybe both?

The shortcomings of wholegrains

There are a couple of shortcomings of wholegrains that nutritionists seldom mention but I will address them here. The draft Australian Dietary Guidelines refers to wholegrains as highly nutrient-dense and they are contrasted with low nutrient-dense foods like white bread. This statement is simply not true. All unfortified cereal foods are relatively nutrient-poor, with wholegrain foods being marginally better than refined cereals. White bread is actually more nutrient-rich than many wholegrains because it is enriched with nutrients. When dietary surveys find that cereal foods are major sources of B group vitamins and iron it is important to remember that this is largely due to the enrichment of breads and breakfast cereals with these nutrients.

Many wholegrain foods also have high glycaemic indices and when eaten in quantity contribute to a high glycaemic load. Evidence is accruing that this issue may be relevant to the risk for coronary heart disease, diabetes and weight management. I’ll address glycaemic index in depth next week.

When all the variables are considered it is apparent that the term wholegrain is not necessarily synonymous with good. For example, brown rice is a wholegrain and is a good source of fibre, but it is also a nutrient-poor food and has a high glycaemic index. Is it good?

Recommending cereal foods

The recommendation to eat mostly wholegrains sits comfortably with the dietetic mind-set that minimally processed, whole foods must be nutritious. But one has to question the wisdom of embracing the concept of wholegrains to the exclusion of other important aspects of the nutritional quality of grain-based foods, such as dietary fibre, nutrient density and glycaemic index. Several submissions on the recent draft Australian Dietary Guidelines encouraged the authorities to recommend both wholegrain and high fibre cereal foods. The latest Dietary Guidelines for Americans recommend wholegrains and enriched grains, which at least addresses the nutrient density issue.

8 thoughts on “Wholegrains: the whole story?

  1. Thank you for taking a more real view on foods, and not allowing commercial or scientific community norms influence your writing. I have been thinking these same things for some time, and it frustrates me that the mainstream is so reluctant to move from engrained held beliefs that are grandfathered by use.

  2. Bill, thank you for the very informative article and the discussion on the results of the intervention studies.
    Could you reveal what measure you use for overall nutrient density? A quick search showed that some people have developed and used measures of aggregate nutrient density (e.g. “ANDI”). On this scale, some whole grains have respectable scores, though not even coming close to the high nutrient density green vegetables.
    My own hand calculations indicate that oats are more zinc-dense (zinc per unit energy) than dairy & cooked eggs- foods commonly thought to be nutrient powerhouses.

    • Hello Robert. Firstly, there is no consensus on how nutrient density should be calculated. I suggest you read Drewnowski and Fulgoni (2008) to get a feel for the way this issue has been approached in the literature. In some work that a colleague and I recently completed we developed a nutrient density score based on six principles that Drewnowski and Fulgoni recommend:
      1. a focus on nutrients with accepted nutritional roles i.e. those with Nutrient Reference Values
      2. assessment of nutrient density within food groups
      3. identification of index (or distinguishing) nutrients for each food group
      4. development of an algorithm for nutrient density
      5. assessment against recognised standards, in this case the Nutrient Reference Values, and
      6. calculations of nutrient density be based on a fixed amount of energy for each food.

      Some models of nutrient density include negative terms for fat or sugar, but this doesn’t make sense to me. If fat and sugar dilute nutrients then this should be expressed through the model, as calculations are based on a fixed amount of dietary energy. Regards, Bill.

      Reference: Drewnowski A, Fulgoni V. Nutrient profiling of foods: creating a nutrient-rich food index. Nutr Rev 2008; 66: 23-39.

  3. Hi Bill,

    Thanks for an informative article. Could you elaborate on your rating of brown rice as a nutrient-poor food? This may come across as quite confusing to an every-day consumer.

    Do you think as dietitians we should we be recommending low GI foods over wholegrain foods? It certainly seems that there is more quality evidence for low GI, but I also think there is a place for wholegrains, even if the evidence is not quite there.



    • Hi Jemma.

      All cereals tend to have low nutrient densities i.e. they provide relatively few nutrients per kilojoule. Among the cereals, rice has the lowest nutrient density. White rice is particularly low but brown rice is not much better. That’s why I suggest that nutritionists need to be a bit cautious about arguing that wholegrain equals good.

      I agree that the GI evidence has improved in recent years (I’ll discuss this next week) and I think it should be considered when we advise people on carbohydrate-rich foods. But I don’t think GI or wholegrains provides the whole answer. Carbohydrate quality is complicated and I suggest that fibre/wholegrain, GI and nutrient density are all relevant. However, it would be a mistake to pick just one of these (say wholegrain) and suggest that’s the whole answer. Regards, Bill

  4. A very good read and an excellent insightful article. I enjoyed it very much. I’d have liked to have seen some example figures enabling nutrient comparison to re-enforce your points. Grains, whether whole or otherwise require substantial processing to make them edible and for the most part of human evolution were simple not available. How is it they have become the mainstay of a healthy diet?

    • Hello Nick. Good point, but now that grains are so much a part of the human diet I guess the question for nutritionists is what grain foods should be recommended. As with all carbohydrate-rich foods, the answer is not as simple as it would appear. Carbohydrate quality is a complex concept (more on this soon). Regards, Bill

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