4. Discussion and Conclusions
gastrointestinal hormones, gastrointestinal tract, weight gain, metabolic disorders, TG, hunger sensation
MINOR, SECONDARY, METABOLIC DISORDERS
The present work studied the effects of two different doses of oat polar lipids (15.0 g and 7.5 g) incorporated into a solid food matrix (bread) on cardiometabolic test variables. The biomarkers were investigated in the postprandial period after the breakfasts and also after a subsequent standardized lunch meal. Our results revealed that 15.0 g, and to a minor extent also 7.5 g, of oat polar lipids may improve acute and second meal glucose tolerance, increase gut hormones important in appetite and glycaemic regulation, and improve the postprandial blood lipid profile compared to both an isolipidic amount of a rapeseed oil-containing meal and/or a close to fat-free reference meal.The results from the present study support previous observations from this research group demonstrating the health effects of 12 g of oat polar lipids as part of a carbohydrate-rich liquid breakfast meal [In the present investigation, we found that the high dose (15.0 g) of oat polar lipids significantly improved most of the variables assessed in comparison to rapeseed oil, whereas only a few variables managed to reach a statistically significant improvement after the low dose of oat polar lipids (7.5 g). However, it is noteworthy that, in comparison to rapeseed oil, the 7.5 g dose significantly increased the gut hormone GLP-1 and significantly decreased the hunger sensation hormone ghrelin. When compared to WWB, the low dose of polar lipids significantly decreased glycemia; nevertheless, it was not significantly different when compared to rapeseed oil. It would be interesting to investigate the effects of PL administered at doses lying between those used in the current study.Both PLH and PLL resulted in significantly decreased acute postprandial glucose responses after the breakfast compared to WWB, whereas no significant effects were observed after RSO. The PLH meal also resulted in a significantly reduced glucose response compared to the RSO meal. These results show that not all lipids are equally potent to lower the acute postprandial glucose concentrations. In addition, the results demonstrate that a dose equal to 7.5 g of oat polar lipids is sufficient in this respect. Interestingly, the PLH breakfast also resulted in improved glucose tolerance after the standardized lunch meal. The insulin responses followed the same pattern as glucose. Consequently, the PLH breakfast resulted in lower postprandial insulin concentrations after both the breakfast and the standardized lunch periods compared to the WWB and RSO breakfasts. The beneficial modulation by oat polar lipids of second meal glucose tolerance is an interesting health effect. These observations confirm the glycemia-modulating properties of oat polar lipids that goes beyond the known action of dietary fats in general [Food matrices play an important role in the bioavailability and absorption of nutrients. Numerous studies have shown that the food matrices, calorie content, kinds of accessible macronutrients, volume, and complexity of the meal all have an impact on the degree to which the macronutrients are digested [In accordance with previous observations [The mechanisms behind the beneficial modulation of glucose tolerance by oat polar lipids are not yet clear. Ohlsson et al., in their study on oat polar lipids-enriched liposomes, suggested a slow digestion of these lipids in vivo, which could potentially result in an enhanced release of gut hormones in the gastrointestinal tract [GIP appears to have a bifunctional role, promoting both insulin secretion and adipogenesis, which potentially contribute to weight gain and the development of metabolic disorders [In the present study, ghrelin was significantly reduced in the postprandial period (0–210 min) after both the PLH and PLL breakfast meals compared to the WWB and RSO. Ghrelin stimulates appetite and accelerates gastric emptying, which triggers hunger sensation [As energy providers and carriers of dietary fat, TGs are essential to metabolism. Postprandial increased TG have, however, been suggested among cardiometabolic risk factors [To fully understand the underlying mechanisms behind these encouraging health benefits of oat polar lipids, further research is required. Since the PLL breakfast resulted in some, but limited, beneficial effects compared with the PLH, it would be interesting to investigate the dose-response effects of PL with doses in between the PLL and PLH breakfasts to find a dose as low in total fat as possible, but still efficient in improving cardiometabolic risk variables. Although the results indicate the metabolic beneficial effects of a low dose (7.0 g) of oat polar lipids on postprandial insulin and ghrelin responses, a dose closer to 15.0 g seems necessary to obtain more convincing effects on postprandial glycaemia, TG and other gut hormone responses. Future studies should also investigate whether the present observations with oat polar lipids can be extrapolated to plant polar lipids in general. It would be interesting as well to explore the long-term effects of oat polar lipids.The current study had two major limitations. The first one relates to the collection of capillary blood, which limited the sample volume. This, in turn, restricted the possible number of test points and test markers to be evaluated. Moreover, the sample size of the study was calculated to detect significant changes in blood glucose levels. However, the sample size might lack statistical power for the secondary outcomes. Studies in other populations, larger cohorts, and longer-term trials are desirable to confirm the results.In conclusion, this research demonstrates the beneficial effects of polar lipids from oats on acute and second meal postprandial glycaemic control, blood lipids, and gastrointestinal hormones in healthy volunteers. The results suggest that these lipids may have anti-obesogenic and anti-diabetic properties, and thus may be included in innovative foods with the purpose of preventing cardiometabolic illnesses. The recorded effects are probably independent of the type of food matrix (solid or liquid).