As part of the Nurse's Health Study, researchers from Harvard University measured the relationship between consumption of grain foods and body weight and changes in body weight over a 12-year period in over 74,000 US women (Liu et al, 2003). Women who consumed more wholegrains and fibre gained less weight over the time of the study, and were less likely to become overweight or obese. Women who consumed the most refined grain products tended to weigh more and gain more weight. The authors of the study concluded that increasing fibre intakes and focussing wholegrain products could play an important role in controlling body weight.
In an analysis of data from the Iowa Women's Health Study, those consuming more wholegrains had a lower BMI and waist:hip ratio compared to women consuming the least amount of wholegrains (Jacobs et al, 1998). Similarly, findings from the Framingham Offspring Study of almost 3,000 subjects also demonstrated that a higher intake of wholegrain foods was associated with a lower BMI (McKeown et al, 2002).
Similar results were also recently observed in males when researchers examined the intakes of wholegrains in over 27,000 men participating in the Health Professionals Follow Up Study (Koh-Banerjee et al, 2004). After adjusting for a range of factors, increasing intakes of wholegrains over 8 years was associated with less weight gain. After adjusting the findings for added bran and fibre, the findings persisted, suggesting that other components of wholegrains besides bran and fibre may beneficially influence long-term weight. The results also showed that for every 40g per day increase in wholegrain intake, long term weight gain was reduced by 1.1kg. Higher intakes of dietary fibre from cereal and fruit was also related to less weight gain, and intakes of breakfast cereals with greater than 51% wholegrains protected against weight gain, and this relationship was statistically significant.
In multicenter population study of young adults, a higher intake of wholegrains was associated with a lower Body Mass Index (BMI) at the start of the study and after seven years of follow-up (Pereira et al, 1998). No relationship was observed between wholegrain intakes and waist:hip ratio in this study.
The exact mechanisms for the protective effect of wholegrains on weight gain may relate to the effects of wholegrains on insulin sensitivity, the high fibre content and antioxidant profile.
Wholegrain intakes were negatively associated with fasting insulin levels in young adults after seven years of follow-up, even with adjustment for BMI (Pereira et al, 1998). Interestingly, those consuming higher intakes of wholegrain bread and cereals tended to have lower insulin levels, despite the high glycemic index value of these foods.
In the Framingham Offspring Study, higher intakes of wholegrains were inversely associated with fasting insulin levels, particularly among subjects who were overweight (McKeown et al, 2002).
It is thought that high insulin levels may promote obesity by altering adipose tissue, increasing appetite and encouraging fuel storage rather than oxidation.
The high fibre content and lower GI value of wholegrains may also explain the lower risk of weight gain associated with wholegrain intakes (Koh-Banerjee & Rimm, 2003). High fibre foods tend to have a lower energy density and promote satiety due to the bulk of fibre.
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- Liu S et al, Relation between changes in intakes of dietary fibre and grain products and changes in weight and development of obesity among middle-aged women, Am J Clin Nutr 2003;78:920-927.
- Jacobs DR, Meyer KA, Kushi LH et al, Wholegrain intake may reduce the risk of ischemic heart disease deat in postmenopausal women: the Iowa Women's Health Study, Am J Clin Nutr 1998;68:248-257.
- Koh-Benerjee P, Rimm EB, Whole grain consumption and weight gain: a review of the epidemiological evidence, potential mechanisms and opportunities for future research, Proc Nutr Soc 2003;62:25-29.
- Koh-Banerjee P et al, Changes in whole-grain, bran and cereal fiber consumption in relation to 8-y weight gain among men, Am J Clin Nutr 2004;80:1237-1245.
- McKeown N, Meigs J, Liu S et al, Whole-grain intake is favourably associated with metabolic risk factors for type 2 diabetes and cardiovascular disease in the Framingham Offspring Study. Am J Clin Nutr 2002;76(2):390-398.
- Pereira MA, Jacobs DR, Slattery ML et al, The association of wholegrain intake and fasting insulin in a Biracial cohort of young adults: The CARDIA study, CVD Prev 1998;1:231-242.
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