Research reportWholegrain vs. refined wheat bread and pasta. Effect on postprandial glycemia, appetite, and subsequent ad libitum energy intake in young healthy adults
Introduction
Wholegrains are defined as consisting of the intact, ground, cracked or flaked caryopsis, whose principal anatomical components – the starchy endosperm, germ and bran – are present in the same relative proportions as they exist in the intact caryopsis covering the Gramineae family as proposed by the American Association of Cereal Chemists in 2000 (AACC, 2000). While wholegrain foods are hypothesized to protect against obesity, the evidence to support this is scarce. A few observational studies indicate an inverse association between a high intake of wholegrain products and lowered risk of body weight gain (Bazzano et al., 2005, Koh-Banerjee et al., 2004), but interventions published in recent years show less promising results, most of which did not include body weight changes as primary endpoint (Andersson et al., 2007, Behall et al., 2006, Katcher et al., 2008, Melanson et al., 2006, Pereira et al., 2002, Rave et al., 2007). Various characteristics of wholegrain products have been highlighted as responsible for the potential health benefits, including a reduced energy density, increased volume and particle size, and a high content of dietary fiber and bioactive micro- and non-nutrients such as betain, magnesium (Mg), calcium (Ca), and B vitamins (Slavin, 2003). Some wholegrain foods are also characterized by inducing a low glycemic response, but not all and this is related to differences in particle size, which is not included in the wholegrain definition. Dietary fiber may regulate body weight through intrinsic effects and hormonal responses. High-fiber foods may promote satiation (intrameal satiety) and satiety (intermeal satiety) due to its bulking and lower energy density. Dietary fiber may also prolong the secretion of appetite regulating hormones from the small intestine and the ability of particularly viscous dietary fibers to increase the viscosity of the intestinal contents may delay gastric emptying and blunt nutrient uptake resulting in reduced postprandial glycemia (Benini et al., 1995, Dikeman and Fahey, 2006, Jenkins et al., 2000). However, it is not clear whether it is glucose per se or other factors which are responsible for the satiety-promoting effect, as insulin and incretin hormones co-vary with glucose (Bornet et al., 2007, Flint et al., 2007).
The majority of wholegrain products consumed in Western countries are wholemeal wheat products, a source of mainly non-viscous arabinoxylans (Virkki, Maina, Johansson, & Tenkanen, 2008). Although viscous dietary fibers are thought to exert the greatest effects, non-viscous wheat fiber has previously been shown to reduce appetite and subsequent food intake, however this effect was observed with a very large dose of dietary fiber (33 g/meal) (Samra & Anderson, 2007). Another study compared similar 22 g doses of viscous (guar gum) and non-viscous (wheat bran) to a low-fiber control (3 g) but found no significant difference between the two high-fiber meals (Delargy, O'Sullivan, Fletcher, & Blundell, 1997).
Here we test the hypothesis that in a postprandial setting, wholegrain wheat products high in dietary fiber induce satiety and reduce subsequent ad libitum energy intake and examine its relation with the glycemic response.
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Subjects
Twenty young subjects (10 female and 10 male) were recruited through advertising at university campuses in the Copenhagen area. The exclusion criteria were as follows: known chronic illnesses, diabetes, hypertension, hyperlipidemia, smoking, elite athletes (>10 h/week), regular use of medication (oral contraceptives were allowed), use of dietary supplements and food intolerances or dislikes of relevance to the composition of the meals. All study subjects gave written consent after having
Results
Of the twenty subjects, sixteen completed all four meal tests (10 women and 6 men). The four subjects that dropped out did so due to logistic problems and one because of dislike of the ad libitum meal. All subjects were young apparently healthy normal weight adults with normal fasting glucose (Table 2).
Discussion
The hypothesis was that wholemeal products would induce increased satiety and lower subsequent energy intake and glucose response. We were however not able to substantiate this hypothesis entirely. The results showed that WWB but not WWP increased satiety compared to RWB, but without a reduction in subsequent energy intake and without a concurrent reduction in postprandial glycemia. As expected, both pasta meals decreased the glycemic responses, but only GI for RWP was significantly lower than
Acknowledgements
This study is financially supported by a grant from BARILLA G. e R. Fratelli S.p.A., Parma, Italy, who also provided test breads and pastas, and by the European Commission in the Communities 6th Framework Program, Project HEALTHGRAIN (FOOD-CT-2005-514008), University of Copenhagen, Faculty of Life Sciences and LMC FOOD research school. It reflects the authors’ views and the Community is not liable for any use that may be made of the information contained in this publication. M.K. and G.R.
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