Substituting whole grains for refined grains in a 6-week randomized trial favorably affects energy balance parameters in healthy men and post-menopausal women

Authors: KARL, JAMES - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; MEYDANI, MOHSEN - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; BARNETT, JUNAIDAH - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; VANEGAS, SALLY - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; GOLDIN, BARRY - Tufts University; RASMUSSEN, HELEN - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; SALTZMAN, EDWARD - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; CHEN, CHUNG-YEN - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; DAS, SAI KRUPA - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; JONNALAGADDA, SATYA - The Bell Institute; MEYDANI, SIMIN - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; ROBERTS, SUSAN - Jean Mayer Human Nutrition Research Center On Aging At Tufts University

Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2016
Publication Date: 2/8/2017
Citation: Karl, J.P., Meydani, M., Barnett, J.B., Vanegas, S.M., Goldin, B., Rasmussen, H., Saltzman, E., Chen, C., Das, S., Jonnalagadda, S.S., Meydani, S.N., Roberts, S.B. 2017. Substituting whole grains for refined grains in a 6-week randomized trial favorably affects energy balance parameters in healthy men and post-menopausal women. American Journal of Clinical Nutrition. 105:589-599. doi: 10.3945/ajcn.116.139683.

Interpretive Summary: Higher intakes of whole grains have been associated with lower body weight and body fatness and improved blood sugar control in some studies. However, those studies have had limitations that prevent definitively demonstrating links between whole grain intake and improved health outcomes. This study aimed to determine whether substituting whole grains for refined grains in the diet favorably affects metabolism and blood sugar control in men and post-menopausal women. The primary findings were that substituting whole grains for refined grains was associated with a small increase in metabolism at rest and an increase in the amount of energy not lost in stool (i.e. not absorbed by the body.) Using a strong study design, these findings suggest that whole grains may favorably impact body weight and adiposity.

Technical Abstract: Background: The effect of whole grains on the regulation of energy balance remains controversial. Objective: To determine the effects of substituting whole grains for refined grains, independent of body weight change, on energy metabolism parameters and glycemic control. Design: A randomized, controlled, parallel-arm, controlled-feeding trial was conducted with 81 men and post-menopausal women (49M/32F, 40-65 yr, BMI <35.0 kg/m2.) Following a 2-wk run-in, participants were randomly assigned to consume one of two weight-maintenance diets for 6 wk. Diets differed in whole grain and fiber contents (WG: 207+/-39 g whole grains/d, 40+/-5 g dietary fiber/d versus RG: 0 g whole grains/d, 21+/-3 g dietary fiber/d), but otherwise were similar. Energy metabolism and body composition parameters, appetite, and markers of glycemic control were measured at 2 and 8 wk. Results: By design, body weight was maintained in both groups. Plasma alkylresorcinols, biomarkers of whole grain intake, increased in WG but not RG (diet-by-time interaction, P<0.001). Changes in RMR ([deltaWG vs. deltaRG, beta+/-SE] 43+/-25 kcal/d, P=0.04), fecal weight (76+/-12 g/d, P<0.001), and fecal energy content (57+/-17 kcal/d, P=0.003), but not fecal energy density, were higher in WG. When combined, the favorable energetic effects of WG translated into a 92 kcal/d [95% CI: 28, 156 kcal/d] higher net daily energy loss compared to RG (P=0.005). Perceived hunger (P=0.12), prospective consumption (P=0.07) and glycemia following an oral glucose tolerance test (P=0.10) trended towards being lower in WG compared to RG. Excluding non-adherent participants attenuated between-group differences in RMR and appetite, but increased between-group differences in stool energy content and glucose tolerance. Conclusions: These findings suggest positive effects of whole grains on RMR and fecal energy excretion that favorably influence energy balance, and may help explain epidemiological associations between whole grain consumption and reduced body weight and adiposity.