What is the relationship between whole grain intake and body weight?

Moderate evidence shows that intake of whole grains and grain fiber is associated with lower body weight.

Seven articles met the inclusion criteria and were reviewed to determine the effect of whole grain consumption on body weight, body mass index (BMI) and measures of adiposity. Of these studies, one was a systematic review (Williams PG et al, 2008), one was a systematic review/meta-analysis (Harland JI and Garton LE, 2007), two were RCTs (Behall KM et al, 2006; Katcher HI et al, 2008) and three were cross-sectional studies. Of the seven articles, five were of positive quality (Behall KM et al, 2006; Harland JI and Garton LE, 2007; Lutsey PL et al, 2007; Van de Vijver LP et al, 2009; Williams PG et al, 2008 ) and two were of neutral quality (Katcher HI et al, 2008; McKeown NM et al, 2009).

Both systematic reviews found that whole grains were associated with lower BMI and protected against weight gain and adiposity. Harland and Garton (2007) reviewed 15 observational trials that included a total of 119,829 subjects. Pooled analysis of high vs. low whole grain intake, using a random-effects model, found a combined and weighted mean difference in BMI of 0.630kg/m² (P<0.0001). They also found reduced waist circumference (P=0.03) and lower waist:hip ratio (P=0.0001) with higher whole grain intakes. The authors concluded that a higher intake of whole grains (approximately three servings per day) was associated with lower BMI and central adiposity. Williams PG et al, (2008) found that 10 of 11 studies of dietary patterns reported that diets including higher whole grain intakes were associated with lower measures of obesity; two RCTs found greater weight loss with the whole grain intervention, while three RCTs showed significant weight loss in both interventions; three out of four observational studies reported greater weight loss with higher whole grain intake. The authors concluded that there was strong evidence that a diet high in whole grains was associated with lower BMI, smaller waist circumference and reduced risk of being overweight.

The randomized controlled feeding trial (Behall KM et al, 2006) compared the effects of three whole grain diets on blood pressure with weight as an ancillary outcome. Subjects (N= 25) consumed a controlled Step I diet for two weeks after which approximately 20% of energy was replaced with whole wheat or brown rice, barley or half wheat-rice and half barley, for five weeks each. Subjects lost approximately 1kg during the study (P<0.01). In the RCT by Katcher et al (2008), subjects were told either to avoid whole grains foods or obtain all of their grain servings from whole grains for 12 weeks. Body weight, waist circumference and percentage body fat decreased significantly in both groups over the study period, but there was a significantly greater decrease in percentage body fat in the abdominal region in the whole grain group compared to the refined grain group.

The three cross-sectional studies consistently found that whole grain intakes were associated with lower BMI and adiposity. Analysis of a MESA study cohort of 5,496 men and women comparing the extreme quintiles of whole grain intake found a mean difference in BMI of 0.6kg/m² (P<0.0001) (Lutsey et al, 2007). Similarly, McKeown et al (2009) found that in older adults, after multivariate adjustment comparing the extreme quartiles of consumption, whole grain intake was inversely associated with BMI (P=0.08), percent body fat (P=0.02) and percent trunk fat mass (P=0.02) measured by whole-body dual-energy X-ray absorptiometry. In the Netherlands, Van de Vijver et al (2009) assessed the association of whole grain and cereal fiber intake with BMI and the risk of being overweight in older adults. They reported an inverse association between whole grain consumption and BMI. Fiber and cereal fiber intake were inversely associated with BMI in men only.

Systematic Reviews (2)

Harland JI and Garton LE, 2007 (positive quality), a systematic review and meta-analysis conducted in the United Kingdom, examined the relationship between whole grain consumption and body weight. The review included 15 observational trials published between 1990 and 2006 that reported whole grain consumption, an appropriate control group and measures of body weight and adiposity. Subjects included a total of 119,829 males and females, aged 13 years or older. Pooled analysis of high vs. low whole grain intake, using a random-effects model, found a combined and weighted mean difference in BMI of 0.630kg/m² (95% CI: 0.460, 0.800kg/m²; P<0.0001). In subjects with higher whole grain intakes (six data sets, N=4,178), waist circumference was reduced by 2.7cm (95% CI: 0.2, 5.2, P=0.03). In four data sets (N=20.417), higher whole grain intake was associated with a lower waist:hip ratio of 0.023 (95% CI: 0.016, 0.030, P=0.0001). The authors concluded that a higher intake of whole grains (approximately three servings per day) was associated with lower BMI and central adiposity.

Williams PG et al, 2008 (positive quality), a systematic review conducted in Australia, evaluated existing evidence regarding the role of cereal grains and legumes in the prevention or management of overweight and obesity. A total of 53 studies met the inclusion criteria for review; 20 examined whole grain intake. Of those, 10 of 11 studies of dietary patterns found that diets that included higher whole grain intakes were associated with lower measures of obesity. Of five RCTs that included a whole grain were reviewed and results were mixed with two studies reporting greater weight loss in the whole grain intervention and three studies showing significant weight loss in both interventions. Three of four observational studies reported greater weight loss with higher whole grain intake. The authors concluded that there was strong evidence that a diet high in whole grains was associated with lower BMI, smaller waist circumference and reduced risk of being overweight.

Randomized Controlled Trials (2)

Behall KM et al, 2006 (positive quality), a randomized, controlled crossover feeding trial conducted in the United States, compared the effects of three whole grain interventions on blood pressure. Weight was an ancillary outcome. Subjects (N=25; seven males, nine premenopausal and nine postmenopausal women) consumed a controlled Step I diet for two weeks after which approximately 20% of energy was replaced with whole wheat and brown rice, barley, or half wheat-rice and half barley for five weeks each. Blood pressure was measured weekly and weight taken daily before breakfast. Replacing refined grain foods with whole wheat, barley or brown rice products lowered blood pressure and maintained or lowered body weight while increasing energy intakes (P<0.0138) in overweight or obese subjects. Although the energy intakes were adjusted weekly to maintain weight, subjects lost about 1kg during the study (P<0.01). The authors concluded that increasing whole grain foods may help to control weight.

Katcher HI et al, 2008 (neutral-quality), an RCT conducted in the United States, examined 50 obese men and women with metabolic syndrome who received dietary advice either to avoid whole grain foods or obtain all of their grain servings from whole grains for 12 weeks. All participants were given the same dietary advice in other respects for weight loss. Forty-seven subjects completed the study (94%). Body weight, waist circumference and percent body fat decreased significantly in both groups over the study period (P<0.001), but there was a significantly greater decrease in percentage body fat in the abdominal region in the whole grain group (P=0.03). Total, LDL and HDL-cholesterol decreased in both diet groups (P<0.05).

Cross-sectional Studies (3)

Lutsey PL et al, 2007 (positive quality), a cross-sectional study conducted in the United States, examined the association between whole grain intake and obesity, selected CVD risk factors and measures of subclinical atherosclerosis using baseline data from the Multi-Ethnic Study of Atherosclerosis (MESA Study). Subjects included 5,496 men and women free of CHD and previously known diabetes. A 127-item FFQ was used to obtain dietary information, including whole grain intake. Mean whole grain intake was 0.5 servings per day. After multivariate adjustment, the mean difference in BMI for the extreme quintiles of whole grain intake was 0.6kg/m² (P<0.0001). The authors concluded that there were strong cross-sectional associations between whole grain consumption and BMI.

McKeown NM et al, 2009 (neutral quality), a cross-sectional study conducted in the United States, examined the associations between whole and refined grain intake, dietary fiber and fiber sources, and body fat among older adults. Subjects included 434 free-living adults (177 men, 257 women) aged 60 to 80 years. Dietary intake was estimated from a 126-item semi-quantitative FFQ. Percent body fat and percent trunk fat mass were measured by whole-body dual-energy X-ray absorptiometry (DXA). After multivariate adjustment comparing the extreme quartiles of consumption, whole grain intake was inversely associated with BMI (26.8kg/m² vs. 25.8 kg/m²; P=0.08), percent body fat (34.5% vs. 32.1%; P=0.02) and percent trunk fat mass (43.0% vs. 39.4%; P=0.02 ). Cereal fiber was also inversely associated with BMI, body fat and trunk fat mass. The authors concluded that higher consumption of whole grains, and consequently cereal fiber, was associated in a dose-dependent manner with a significantly lower BMI and percentage of abdominal fat as determined by DXA.

Van de Vijver LP et al, 2009 (positive quality), a cross-sectional study conducted in the Netherlands, examined the associations between whole grain and cereal fiber intake with BMI and the risk of overweight or obesity (BMI higher than 25 to 30kg/m²). The study included 4,237 subjects (2,078 men and 2,159 women) aged 55 to 99 years. Multivariate regression analysis found an inverse association between whole grain consumption and BMI, as well as with the risk of overweight and obesity. The associations were stronger in men than in women. For each additional gram of (dry) whole grain intake, obesity risk was 10% lower for men and 4% lower for women. Fiber and cereal fiber intake were inversely associated with BMI in men only. The authors concluded that whole grain consumption might be protective against overweight or obesity, although the cross-sectional study design did not allow conclusions about the causality of the association.