In a recent study published in The American Journal of Clinical Nutrition, researchers compared the cardiovascular outcomes of refined grains to wholegrains in children. Their randomized cross-over study comprised a cohort of 55 Danish children who were given diets containing either wholegrain or refined oats and rye for eight weeks. Their study findings revealed that wholegrain consumption significantly reduced low-density lipoprotein (LDL) cholesterol, triacylglycerol, and the ratio of total:high-density lipoprotein cholesterol. Wholegrain diets were additionally found to promote the growth of beneficial gut microbiota and reduce fatigue without any negative impacts on child health.

Study: Effects of Wholegrain Compared to Refined Grain Intake on Cardiometabolic Risk Markers, Gut Microbiota and Gastrointestinal Symptoms in Children: A Randomized Crossover Trial. Image Credit: created with the assistance of DALL·E 3

The cardiovascular benefits of wholegrains

Wholegrains contain high concentrations of β-glucans, arabinoxylans, fructans, lignins, and cellulose. β-glucans and arabinoxylans are known to upregulate bile acid secretion and reduce intestinal nutrient absorption, which may improve weight control, lipid profiles, and glycemic response. Lignins and cellulose are known to benefit the gastrointestinal tract by increasing the stool water content, thereby reducing transit time. β-glucans, fructans, and, to a lesser extent, arabinoxylans undergo fermentation in the gut, which is thought to promote the growth of beneficial gut bacteria.

Given these properties, research has hypothesized that wholegrain diets in adults can reduce the risk of cardiovascular disease (CVD) and may prevent type 2 diabetes (T2D). While studies aimed at confirming this hypothesis are confounding, most randomized trials report beneficial outcomes on blood lipids, body weight, and glucose homeostasis. This research, however, has focused on adults, with hitherto only two observational studies on school-going children.

Recent studies have highlighted that cardiometabolic risk factors, including overweight, obesity, and poor lipid profiles during childhood, significantly increase the risk of CVD later in life, necessitating research aimed at improving cardiovascular health as early as possible during an individual’s life.

About the study

In the present study, researchers employed a randomized cross-over study design to elucidate the outcomes of wholegrain rye and oats (WG) on cardiometabolic risk markers, body composition, and body mass index (BMI) of children aged 8-13. To verify the potential benefits of wholegrains, they compared these outcomes to those from a refined grain (RG) diet.

The study was conducted at the University of Copenhagen and comprised healthy but overweight (BMI +1 standard deviation [SD] above Danish median) Danish children who consumed cereal and bread daily. Children with allergies to whole- or refined grains and those consuming supplements altering their lipid or cardiometabolic profiles were excluded from the study. Recruitment for the study was carried out between August through December 2020.

Wholegrain products consisted of standard breakfast, lunch, and dinner snacks, wherein wholegrains comprised at least 50% of their dry weight. Refined grain products, in contrast, had low quantities of wholegrain and high amounts of refined wheat, corn, and rice. The nutrient and fiber content of WG and RG were separately measured via the Uppsala method at the Swedish University of Agricultural Sciences.

“Children were instructed to eat the provided products ad libitum, with a product intake goal of 150-200 g/day corresponding to 75 g wholegrain and 14-19 g dietary fiber in the WG period.”

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Daily intake of study products (WG or RG) was recorded in grams using kitchen weight balances. Additionally, prior to follow-up examinations, a 4-day dietary record of all food and beverages consumed was reported using the web-based Madlog Classic software. Using the Likert scale, a questionnaire was used to record and assess stool frequency and seven predefined gut symptoms.

Anthropomorphic measurements included weight, height, waist circumference, blood pressure (systolic and diastolic), age, body composition (using dual-energy X-ray absorptiometry [DXA]), and sex-adjusted BMI z-scores. Blood samples were collected for plasma analyses.

“The BMI z-scores were separated into BMI categories based on conventional intervals: normalweight (-1 SD to +0.99 SD), overweight (+1 SD to +1.99 SD) and obese (≥2 SD).”

Statistical analyses comprised linear mixed models for continuous variables and cumulative link mixed models for ordinal variables.

Study findings

Weight classification for the 55 included children reported 22% as normal weight, 60% as overweight, and 18% as obese. Of these, 52 completed the study, 26 (50%) of whom were male. Self-reported dietary compliance was high, which was clinically confirmed by plasma alkylresorcinols (AR). Blood analyses revealed that WG diets were associated with lower energy, lower carbohydrates, higher protein, and higher fat than RG diets.

Whole grain diets were observed to reduce plasma LDL cholesterol, triacylglycerol (TG), and total cholesterol while increasing acetate and propionate compared to RG diets. Feces showed an increase in butyrate during the WG diet, but no differences in insulin or glucose could be found between diets. Serum C-reactive protein (CRP) was found to be lower in WG diets, but no changes in BMI or adiposity were found.

Gut microbiota analyses from feces revealed that WG diets resulted in an increase in Faecalibacterium and Dialister populations and a reduction in Collinsella and Ruminococcus.

“WG reduced the odds of self-reported fatigue (P=0.017) and tended to increase stool frequency compared to RG.”

Conclusions

In the present study, researchers investigated the effects of wholegrains on the cardiovascular health and gut microbiota compositions of Danish children between the ages of 8-13. Their findings reveal that compared to refined grains, WG diets are associated with lower cholesterol and triacylglycerol levels, which previous research has reported are beneficial to long-term cardiovascular health. WG diets also result in improved energy levels and lower fatigue while leaving other body composition metrics unchanged.

“This study contributes to a growing body of research, demonstrating cardiometabolic benefits of replacing refined grain with wholegrain, even in children, and regardless of effects on body weight. Further randomized trials among children, including long-term studies and trials focusing on specific wholegrain types, are necessary to gain a deeper understanding of the underlying mechanisms.”

Journal reference:

• Madsen, M. T. B., Landberg, R., Nielsen, D. S., Zhang, Y., Anneberg, O. M. R., Lauritzen, L., & Damsgaard, C. T. (2023). Effects of Wholegrain Compared to Refined Grain Intake on Cardiometabolic Risk Markers, Gut Microbiota and Gastrointestinal Symptoms in Children: A Randomized Cross-over Trial. The American Journal of Clinical Nutrition. DOI – https://doi.org/10.1016/j.ajcnut.2023.10.025, https://www.sciencedirect.com/science/article/pii/S000291652366229X