Is Whole Grain Intake Associated with Morbidity and Mortality?

Popular diets come and go. While no longer nearly as popular as it was a decade ago, a major emphasis of the Paleo Diet is to avoid grains, including whole grains. Although there is no scientific evidence to support this notion, Paleo enthusiasts claim that grains ‘cause inflammation’, which leads to an increased risk of chronic disease (morbidity) and early death (mortality). Before we look at what the science says, let’s review the basics regarding grains.

All grains contain 3 parts: the bran, germ, and endosperm. A whole grain uses all three parts of the grain. Refined grains only use the endosperm. This is important because different nutrients and phytochemicals* are found within each part of the grain plant. Thus, whole grains are nutritionally superior and contain significantly more fiber than refined grains.  

Several years ago, results from 161,737 women enrolled in the Nurses’ Health Study (NHS) were published. The study focused on dietary intake of whole grains, bran, and subsequent risk of developing type 2 diabetes. All women were healthy at baseline, and completed dietary questionnaires at regular intervals during the 12-18 year follow-up. During this time, 6,486 women developed type 2 diabetes. The women were assigned to one of five groups based on their average daily whole grain and bran intake.

Those women within the highest intake group were nearly 40 percent less likely to develop type 2 diabetes when compared to women within the lowest intake group.

These relationships were similar when dietary bran intake was evaluated. Based on pooled data from 5 additional published studies on this topic, researchers concluded that for every two serving per day increment in whole grain consumption, there was a 21% decrease in risk of developing type 2 diabetes.  

Although we know that increased whole grain intake is associated with a reduced risk of type 2 diabetes and cardiovascular disease (CVD), less is known about whole grains and risk of mortality. Accordingly, a major study was published in JAMA Internal Medicine. A total of 74,341 women from the NHS and 43,744 men from the Health Professionals Follow-up Study were enrolled; all subjects were healthy at baseline. Over a 25-year period, subjects completed validated food frequency questionnaires every 2-4 years. During the follow-up, there were a total of 26,920 deaths. At the completion of the data collection period, subjects were placed into five groups according to their average daily intake of whole grains. There was a 10% reduction in all-cause mortality among subjects with the highest intake of whole grains compared to subjects with the lowest intake of whole grains. The trend was even more significant with regard to CVD mortality, with subjects in the highest intake group enjoying a 15% reduction in the risk of CVD mortality compared to subjects in the lowest intake group. So now we have convincing evidence that increased consumption of whole grains is associated not only with significantly lower morbidity, but lower mortality risk as well. Strengths of these studies include large sample sizes, long follow-up periods, and significant numbers of events among the participants. Many factors such as age, smoking, and length of follow-up that may have ‘muddied the waters’ were carefully controlled for.  

As mentioned in previous Paleo blogs, there are some positive aspects to this dietary approach. It restricts simple sugars and sodium, while promoting physical activity and green tea consumption. Individuals with gluten intolerance comprise about 5% of the U.S. population. These individuals should avoid wheat, barley, and rye because of their high gluten content. No one would argue against that recommendation.

However, the notion that grains are ‘bad’ for us simply does not hold up in the research world, particularly when we look at whole grains.

The results of these studies and others are in line with current dietary recommendations to increase intake of whole grains and to decrease intake of refined grains in order to help prevent chronic disease and premature mortality.

In case you were wondering, ‘multi-grain’ and ‘7-grain’ on a label does not always mean whole grain! For example, a loaf of bread that is labeled multi-grain may be using only the endosperm (not the bran or the germ) from seven different grains. So, when examining the list of ingredients, always look for the words ‘whole grain’ at the very beginning of the list.  

In conclusion, enthusiasm for the Paleo Diet has been waning for several years. Among the many reasons for this trend is overwhelming evidence that increased consumption of whole grains decreases the risk of morbidity and mortality.

*phytochemicals are disease preventing non-nutrients that are only present in plant-based foods

References

De Munter JS, Hu FB, Spiegelman D, Franz M, van Dam RM. (2007). Whole grain, bran, and germ intake and risk of type 2 diabetes: a prospective cohort study and systematic review. PLoS Med. 4(8)e261. doi: 10.1371/journal.pmed.0040261.

Wu H, Flint AJ, Qi Q, et. al. (2015). Association between dietary whole grain intake and risk of mortality: two large prospective studies in US men and women. JAMA Internal Med. Doi.1001.6283. Epub ahead of print.

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