Abstract
Background: Both epidemiological studies and randomised controlled trials report a reduction in cardiovascular disease (CVD) risk with the regular consumption of nuts. Furthermore, nut consumption may improve glycaemic control and increase satiety. These beneficial effects are likely to be due to their low available carbohydrate content, favourable fat and protein profiles as well as the presence of bioactive compounds. Moreover, postprandial events have attracted much attention for the potentially important role they may play in CVD risk and diabetic complications. Importantly, to obtain health benefits, nuts must be consumed regularly and in sufficient amounts. To this end, the National Heart Foundation of New Zealand recommends the daily consumption of 30 g of nuts as a means to reduce CVD. However, the 2008/09 New Zealand Adult Nutrition Survey (2008/09 NZANS) showed that only 6.9% of New Zealanders consumed nuts on the day of the 24-hour diet recall, with a mean population intake of 2.8 g/d. Therefore, innovative strategies are required to increase nut consumption. One such strategy is to incorporate nuts into a staple food such as bread. An important consideration for the formulation of the bread is the form of nut. It is possible that bread enriched with sliced nuts, which require more chewing than ground nuts, may promote satiety, leading to a lower food intake and potentially improved body weight regulation. Conversely, the addition of semi-defatted nut flour, a by-product of nut-oil production, may provide a more cost effective option. To date, only few studies have assessed the effects of different forms of nuts on glycaemic control and no study has incorporated different forms of nuts into the bread. Therefore, it is important to compare the health and satiating effects of these bread forms, bearing in mind the cost effectiveness of such strategies.
Objective: To compare the effects of consuming three different forms of hazelnut-enriched bread (finely sliced hazelnut, semi-defatted hazelnut flour and a combination bread containing finely sliced hazelnuts and semi-defatted hazelnut flour) with a control bread without hazelnuts, on postprandial glucose concentrations, satiety, and gastrointestinal tolerance.
Design: Thirty-two healthy men and women with a mean (SD) age of 30.2 (11.4) years, and mean body mass index (BMI) (SD) of 24.08 (4.10) kg/m2 were recruited to take part in a 10-week, randomised controlled, 4-arm, single-blinded, cross-over study. The participants were allocated in random order to receive the four different breads: white control bread (no hazelnuts), finely sliced nut bread (30 g finely sliced hazelnuts per 120 g of bread), semi-defatted nut flour bread (30 g hazelnut flour per 120 g of bread) and the combination bread containing finely sliced nuts and semi-defatted nut flour (15 g finely sliced hazelnut and 15 g semi-defatted hazelnut flour per 120 g of bread). All three nut breads were designed to contain 30 g of different forms of hazelnut per 120 g of bread, which is the average daily amount of bread reportedly eaten by bread consumers in the 2008/09 NZANS. Each dietary phase lasted 8 days followed by a one week wash-out period. During each dietary phase, the acute glycaemic response (GR) to the breads was measured (days 1 and 8), along with a satiety test (day 2) where both appetite ratings and subsequent energy intake was assessed. In addition, a further one-day food diary was completed by participants to assess energy and nutrient intake. Participants consumed 120 g of bread for 5 days after days 1 and 2 (i.e. days 3-7), up to the next glycaemic response testing session. For the GR testing, the test breads were provided as portions equivalent to 50 g of available carbohydrate and for the satiety testing day, the amount was equal to the amount of bread the participant’s reported consuming at their usual breakfast. The acute GR of each of the breads was assessed on two separate occasions (to take into account the intra-individual variation in blood glucose response) over a 2-hour postprandial period. Participants were fed the test breads after a 10-12 hour overnight fast. Capillary finger prick blood samples for glucose analysis were obtained at 0, 15, 30, 45, 60, 90, and 120 minutes. Glycaemic responses of all breads were assessed by calculating the incremental area under the 2-hour glucose curve (iAUC) and glycaemic index (GI) of the nut breads was calculated using the white bread as a reference. Each GR testing session was separated by one week. During the first GR session participants also reported any gastrointestinal symptoms using a 100-mm visual analogue scale (VAS) at the same time points as the finger pricks. Appetite ratings were measured on day 2 of each dietary treatment using a 100-mm VAS. The participants consumed the amount of bread they reportedly consumed at a usual breakfast and recorded their appetite ratings at five different points in time; at baseline (pre-bread ingestion), immediately post-bread ingestion, and at 1, 2 and 3 hours post-bread ingestion. In addition, subsequent food intake was measured by weighed diet record (WDR) for the remainder of the day. A further diet record was completed on the Sunday of each treatment period.
Results: The incremental glucose area under the curves [mean (95% CI)] for the finely sliced nut bread, semi-defatted nut flour bread, combination bread containing finely sliced nuts and semi-defatted nut flour, and white control bread, were 152 (95% CI: 128, 176), 137 (95% CI: 115, 159), 154 (95% CI: 130, 177) and 179 (95% CI: 146, 212) mmol/L.min, respectively. There was a significant difference in area under the curve (AUC) between the nut breads and the white control bread (p<0.001) with no significant differences between the nut breads (p≥0.130 in all cases). The median GI (Interquartile range) for the finely sliced nut bread, semi-defatted nut flour bread and the combination bread containing finely sliced nuts and semi-defatted nut flour were 83.0 (68.5-120), 78.5 (63.5-110.5), and 85.5 (59.5-129.5) respectively, which is consistent with the AUC for the different breads. There were no overall significant differences in the mean GI between the nut breads (p=0.122). There were no significant differences in either satiety (p≥0.135 in all cases) or gastrointestinal symptoms (p≥0.102 in all cases) between the treatment breads. The consumption of hazelnut-enriched breads improved diet quality compared to the white control bread, namely resulting in an increase in monounsaturated fat, vitamin E and dietary fibre.
Conclusions: Our results suggest that consuming hazelnut-enriched bread has beneficial effects on glycaemic control. The finely sliced nut bread, semi-defatted nut flour bread and the combination bread containing finely sliced nuts and semi-defatted nut flour equally improved postprandial glycaemic response (PGR) in the participants, supporting their inclusion in a healthy diet. Hazelnuts in different forms can therefore be incorporated into the usual diet as a means of diminishing PGR. In addition there was no difference in satiety between the breads suggesting no short-term differences in energy regulation. The nut breads did not cause any gastrointestinal discomfort and hence were tolerable. Consuming the nut breads improved diet quality in a manner that would be positively associated with a reduction in CVD. While the findings of this study support a short-term benefit for nuts in terms of postprandial glucose response, more studies are required to determine whether these acute benefits result in a long-term improvements in glycaemic control, as well as a reduction in other markers of CVD. (Clinical Trials number: ACTRN12614000213640)