Higher whole grain intakes are linked to smaller increases in waist size, improved blood pressure and blood glucose among middle-to older-aged adults, a new observational study reports.
Cardiovascular disease (CVD) is a frequent cause of death in the United States. Research has established diet as an important modifiable risk factor, which, once improved, may lower CVD risk.
Whole grains, defined as the intact, ground, cracked, or flaked fruits of the grain that contain the endosperm, germ and bran layers are an essential component of a healthy, balanced diet. Many observational studies have linked whole grain-rich diets to lower CVD risk, while others have linked refined grains containing only the endosperm layer to a higher CVD risk.
Unlike refined grains, whole grains are rich in fibre and nutrients, including magnesium, vitamin E, potassium and many other plant chemicals that may contribute to its cardiovascular health benefits.
Besides diet, blood pressure, waist circumference, cholesterol levels and fasting glucose are other factors contributing to CVD risk. Studies investigating the effect of a whole grain-rich diet on these factors have produced conflicting results. While some have demonstrated beneficial effects, others have not, possibly due to differences in study designs, studies being too small and short to detect changes.
A team of researchers sought to investigate the effect of regular whole grain consumption on blood pressure, waist circumference, high-density lipoprotein (HDL, ‘good’) cholesterol and fasting blood glucose levels in participants enrolled in the Framingham Heart Study (FHS).
FHS is a long-term, community-based population study that began in 1948 to study the risk factors of CVD. In 1971, children of the original participants were recruited into the Offspring cohort. Approximately every four years after that, they underwent medical tests and physical examinations and, from 1991, dietary assessments via food frequency questionnaires.
A total of 3121 participants followed for a median of 18 years with a medical history, physical examinations and dietary data were included in the study. Data from 1991-2014 were included in the analysis. The participants were a mean age of 55 years old, 54.5% were female, and 64% were overweight or obese.
Dietary guidelines recommend that adults eat at least three portions of whole grains daily. However, the study participants ate an average of one serving of whole grains and three refined grains daily. Only 3.8% of participates ate three servings of whole grains daily. Whole grains were mainly derived from dark or whole wheat bread and breakfast cereals, while white bread and pasta primarily contributed to refined grain intake.
Participants who ate more than three servings of whole grains daily had smaller increases in their waist circumference, blood glucose and blood pressure at each four-year interval. These associations remained even after adjusting for body mass index and other dietary factors. Whole grain consumption was also associated with greater increases in HDL cholesterol and reductions in triglycerides.
“Our findings suggest that eating whole-grain foods as part of a healthy diet delivers health benefits beyond just helping us lose or maintain weight as we age. In fact, these data suggest that people who eat more whole grains are better able to maintain their blood sugar and blood pressure over time. Managing these risk factors as we age may help to protect against heart disease,” Nicola McKeown, senior and corresponding author of the study, said.
In contrast, participants eating at least four servings of refined grains daily had significantly greater increases in waist size and smaller reductions in the triglyceride levels compared to those consuming less than two servings of refined grains.
“The average American consumes about five servings of refined grains daily, much more than is recommended, so it’s important to think about ways to replace refined grains with whole grains throughout your day. For example, you might consider a bowl of whole grain cereal instead of a white flour bagel for breakfast and replacing refined grain snacks, entrees, and side dishes with whole-grain options. Small incremental changes in your diet to increase whole-grain intake will make a difference over time,” McKeown said.
“Overall, these findings support recommendations to replace refined grain foods with whole grain equivalents, particularly as a dietary modification to attenuate abdominal [fat], hypertension and [high blood glucose], and thereby reduce the risk for cardiometabolic disease,” they concluded.
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