The Cooper Institute
 

Founded in 1970 by the "Father of Aerobics"
Kenneth H. Cooper MD, MPH

Loading
 
 

New Studies Bolster Existing Support for Whole Grains!

Posted in
Eat better

Tuesday, Aug 29, 2017

In most developed countries, cardiovascular disease and cancer are the two leading causes of death. It is indisputable that dietary intake is an important lifestyle component for determining the risk of developing these two conditions.

The First Amendment in U.S. Constitution guarantees the right of free speech. Thus, anyone can write a diet book and say whatever they please. Due in large part to this, fad diets are a dime a dozen. A couple of somewhat popular diet crazes claim that all grains should be avoided because they cause inflammation, leading to increased risk of chronic disease and early death. Worldwide, grains are a major component of the diet, providing approximately half of the energy and protein intake. Thus, the claim by authors of diet books that grains increase the risk of disease and death warrants very careful scientific scrutiny!

All grains contain three parts: the bran, germ, and endosperm. The bran is the outer layer of the grain plant, and is a good source of fiber, B vitamins, and a few trace minerals. The germ contains B vitamins, vitamin E, and antioxidants. The endosperm contains carbohydrate and protein. While whole grains use all three of these parts, refined grains use only the endosperm. Previous studies have consistently shown that higher intakes of whole grains are associated with a reduced risk of type 2 diabetes, coronary heart disease, and obesity. However, studies on whole grain intake and risk of total cancer death are mixed. Additionally, the dose-response relationship between whole grain intake and various other diseases and causes of death has not been carefully examined. 

Accordingly, in a recent study published in the British Medical Journal, researchers combined 45 published studies in order to determine the dose-response relationship (this simply means that the greater the number of daily servings of whole grains consumed, the greater the reduction in mortality risk) between whole grain intake and the risk of cardiovascular disease, cancer, and various causes of mortality (death). This technique of combining similar well-controlled studies into one very large study is known as a meta-analysis. The individual studies were performed in the U.S., Europe and Asia. At baseline, all of the participants in these studies were apparently healthy, and their dietary intake of whole grains was carefully examined. Smoking status, height/weight, age, physical activity, alcohol intake, sugar-sweetened beverage intake, and other factors that might ‘muddy the waters’ were carefully controlled for. We will summarize the results below.

Whole Grains and Coronary Heart Disease (CHD)

Among 316,491 participants, 7068 cases of CHD occurred during the follow-up period. Across the spectrum of whole grain intake, a significant dose:response relationship was seen. As whole grain intake increased, a reduction in risk was seen up to an intake of 7 servings/day*. There was no further reduction in risk beyond this point. When comparing individuals with the highest and lowest whole grain intake, a 20% reduction in CHD risk was seen in the former group. 

Whole Grains and Stroke

Among 245,012 participants, 2337 strokes occurred during the follow-up period. A dose:response relationship was observed up to an intake of 5 servings of whole grains/day. There was no further reduction in risk beyond this point. When comparing individuals with the highest and lowest whole grain intake, a 14% reduction in stroke risk was seen in the former group. 

Whole Grains and Cardiovascular Disease (CVD)

Among 704,317 participants, 26243 cases of cardiovascular disease occurred during the follow-up period. When comparing individuals with the highest and lowest whole grain intake, a 16% reduction in cardiovascular disease deaths was seen in the former group. The greatest reduction in risk was seen when comparing individuals who consumed 1.5 servings per day with individuals who consumed no whole grains. There were slight further reductions in CVD risk with intakes up to 7 servings/day; with no further reduction in risk beyond this point.  

Whole Grains and all-cause Mortality

Among 705,253 participants, 100726 deaths from all causes occurred during the follow-up period. A dose:response relationship was observed, with the lowest risk seen among individuals consuming 7 servings per day. There was no further risk reduction beyond this point. When comparing individuals with the highest and lowest whole grain intake, a 17% reduction in all-cause deaths was seen in the former group. 

Whole Grains and Total Cancer Mortality

Among 640,065 participants, 34346 total cases of cancer death occurred during the follow-up period. A dose:response relationship was observed, with the lowest risk seen among individuals consuming 8 servings/day. There was no further risk reduction beyond this point. When comparing individuals with the highest and lowest whole grain intake, an 11% reduction in cancer deaths was seen in the former group. 

Whole Grains and Diabetes Mortality

Among 632,849 participants, 808 deaths from diabetes occurred during the follow up. A dose:response relationship was observed, with the lowest risk seen among individuals consuming approximately 4 servings/day. There was no further risk reduction beyond this point. When comparing individuals with the highest and lowest whole grain intake, a 36% reduction in diabetes deaths was seen in the former group. 

How Do These Findings Relate to Childhood Obesity?

It’s no secret that the prevalence of childhood obesity in the U.S. has been on the rise over the past few decades. In fact, recent data from the National Health and Nutrition Examination Survey (NHANES) indicates that 17% of youth ages 2-19 years are obese. It’s important to note that the criterion for obesity in youth is very different than the criterion used for adults. Among youth, obesity is defined as a body mass index (BMI) at the 95th percentile or higher when compared to other youth of the same age and gender. Obesity in children carries with it many of the same health risks that are seen in obese adults. These include high blood pressure and high blood cholesterol, type 2 diabetes, breathing problems and joint problems, as well as fatty liver disease and heartburn. The behaviors that influence excess weight gain in youth include consuming too many high-calorie/low nutrient foods and beverages and inadequate levels of physical activity. Kids and adults should strive to consume a healthy diet; one which follows the 2015-2010 Dietary Guidelines for Americans (DGA). The DGA places a strong emphasis on consuming a wide variety of fruits and vegetables, whole grains, various lean sources of protein, fatty fish, and reduced-fat dairy products. At the same time, consumption of foods and beverages containing added sugars (e.g. non-diet soda and fake fruit juice), or high amounts of solid fats and sodium should be limited. So, whoever does the grocery shopping in your household should be seeking out whole grain breads, cereals, rice, and pasta as opposed to their refined versions whenever possible. Doing so will benefit all family members!   

Conclusion

In this large meta-analysis, significant dose:response relationships were seen between whole grain intake and outcomes of several major chronic diseases and causes of death. The ‘sweet spot’ for reduction of overall risk seems to be 6-8 servings of whole grains/day. So, despite the ranting and raving from the authors of some popular diet books, there is overwhelming scientific evidence that an increased intake of whole grains is strongly associated with a reduced risk of disease and death. Some would argue that associations do not prove cause and effect. I would be the first to agree. Without plausible biological mechanisms, it would be incorrect to state that whole grains cause a decreased risk of disease and death. However, many plausible biological mechanisms have been identified. For example, the fiber in whole grains helps to decrease blood levels of LDL cholesterol and triglycerides. Fiber also helps to minimize increases in blood glucose and insulin levels following a meal. Contrary to the claims of some fad diet proponents, whole grains have been shown to decrease several inflammatory markers. Finally, whole grains also contain a wide variety of phytochemicals, which are naturally occurring non-nutrients that help to prevent disease. Obviously, those with gluten intolerance or celiac disease need to meet with their physician to discuss limitations on their grain intake.  However, these individuals make up a very small percentage of the overall population. 

*What Constitutes a Serving of Whole Grains?

For grains, a serving is commonly identified as an ‘ounce-equivalent.’ First, be sure to look for the words ‘whole grain’ at the very beginning of the list of ingredients. If you don’t see this, then it’s not a whole grain. Each of the following is considered to be 1 ounce-equivalent (1 serving) of grains: 

One slice of bread, ½ hamburger bun, ½ bagel, one 6-inch diameter tortilla, 1/2 cup cooked rice or pasta, 1 cup ready to eat cereal, 1 packet instant oatmeal, 1 small pancake.

 

References

Aune, D., Keum, N., Giovannucci, E.,…Norat, T. (2016). Whole grain consumption and risk of cardiovascular disease, cancer, and all-cause and cause-specific mortality: systematic review and dose-response meta-analysis of prospective studies. BMJ, 353, doi.10.1136/bmj.i2716. 

Centers for Disease Control and Prevention. (2016). Childhood obesity: causes and consequences. www.cdc.gov/obesity/childhood/causes.html

 

Did you know that The Cooper Institute is one of only a handful of organizations that has a nationally accredited Personal Trainer Certification? If you have a passion for health and fitness and enjoy working with people, or if you are already working as a personal trainer, click here to learn more about the CI-CPT (Cooper Institute Certified Personal Trainer)!