New research out this week from Tufts University in the US state of Massachusetts has highlighted more of the health benefits of whole grains.
Published in the American Journal of Clinical Nutrition, the first of the two studies looked at the effect of whole grains versus refined grains on gut microbiota.
Eighty-one participants were recruited for the eight-week randomized, controlled trial, and for the first two weeks were asked to consume a Western-style diet rich in refined grains and designed to maintain weight.
However for the next six weeks, 40 participants stayed on the diet while 41 participants switched to one rich in whole grains.
The diets were similar in total energy, total fat, and number of fruit, vegetable, and protein servings.
To measure the effect on gut microbiota, the bacterial content and concentration of short-chain fatty acids in the stool was measured, both considered to be vital for healthy immune and inflammatory functions.
Although improvements were modest, the results showed that those who ate the whole grain diet had an increase in Lachnospira, the bacteria that produces short-chain fatty acids, and a decrease in the pro-inflammatory bacteria, Enterbacteriaceae.
In addtion blood tests showed that participants on the whole grain diet showed modest improvements in levels of memory T cells and TNF-alpha production, both a measure of healthy immune response.
In a second study, the team looked at the effect of replacing refined grains with whole grains on weight management.
The team followed 81 men and women aged 40 to 65 during eight-weeks, with the participants once again following the same diet for the first two weeks.
After two weeks, participants were randomly assigned to eat a diet that included either whole grains or refined grains, with the energy, macronutrient composition, type of food, and meal structure similar in both diets.
Although hunger and fullness were not statistically different between diets, results showed that participants who ate the diet with whole grains, which matched the recommended dietary allowance (RDA) for fiber, lost nearly an extra 100 calories per day than those on the refined grain diet which contained less fiber -- equivalent to a brisk 30 min walk or enjoying an extra small cookie every day.
The team believe the results are due to a combination of the whole grain diet causing an increase in resting metabolic rate and greater loss of energy in feces. However the extra fecal energy losses were not due to the extra fiber itself but from the effect the fiber had on the digestibility of other food calories.
Whole grains include the outer nutritious layer of grains and include whole-wheat flour, oatmeal and brown rice, whereas refined grains, such as white flour, white bread and white rice, have been processed and the outer nutritious layer removed.
The recommended daily allowance of whole grains is a minimum of three ounces for women and four ounces for men, equivalent to consuming 1½ to 2 cups of brown rice or oatmeal each day.
Eating a diet rich in whole grains has also been associated with reduced risk of heart disease, type 2 diabetes, and some cancers.