In this study, we investigated the effects of a lactose-free milk drink, a novel fibre-enriched lactose- and fat-free milk drink and regular fat-free milk on glucose and insulin responses and satiety levels in healthy subjects. The insulin response was markedly lower after the consumption of the fibre-enriched milk-drink compared to the other products. Although there was no significant difference in the AUC response of glucose between the study products, the fibre-enriched milk drink appeared to equalize the glucose response.
The metabolic syndrome is characterized by insulin resistance and hyperinsulinemia, as well as several detrimental symptoms, such as hypertension, fatty liver disease and impaired glucose disposal [36
]. In addition, continuously elevated insulin concentrations impair normal vascular function [37
]. Although the effect of the novel milk-drink on glucose response did not differ from the other studied drinks, it produced a significantly lower postprandial insulin concentration. The novel milk drink has the lowest carbohydrate content, which can partly explain the lower insulin response. Another potential explanation for the lower insulin response is the fibre added in the milk drink. Polydextrose, the soluble fibre used in the present study, is a polysaccharide, but it has physiologic effects comparable to other dietary fibres [38
]. In several studies, fibre-rich foods have been shown to lower insulin responses in healthy and diabetic subjects [39
]. On the other hand, Gruendel et al
. observed that when 5 or 10 g of insoluble carob fibre are consumed with a glucose drink, the insulin response increases compared to drinking only a glucose drink [46
]. To our knowledge, the effect of fibre enrichment in milk on insulin levels has not been studied before. Because the milk carbohydrate, lactose, is totally removed from the novel milk drink using the chromatographic technique, the energy and monosaccharide content of the milk drink is further reduced. Therefore, in addition to the added polydextrose, the low-energy and low-carbohydrate content of the milk drink have most likely contributed to the observed effect. Epidemiological studies have shown high vitamin D status to be inversely associated with insulin resistance [47
]. Regardless of this interesting finding, it is unlikely that the vitamin D content of the drink contributed to the lower insulin response in this study, since all three study drinks contained the same amount of vitamin D.
The present study does not support the earlier studies which indicate that fibre and fibre-enriched products stabilise postprandial glucose levels [22
]. However, a trend towards a more balanced glucose response was observed after the consumption of the fibre-enriched milk drink. Generally, dairy products have a low glycaemic response [48
], which is due to their low carbohydrate and high protein content [49
]. The fibre enrichment and the low calorie and carbohydrate content of the milk drink might explain the shape of the glucose curve. Furthermore, the lack of significant difference in the postprandial glucose response could also be due to the selection of healthy, glucose-tolerant individuals who show only minor fluctuation in glucose levels due to a well-preserved insulin secretion capacity.
Dietary fibre may enhance satiety by slowing gastric emptying and by delaying absorption [35
]. Soluble fibres absorb water, form a gel and may increase abdominal distension, which creates a sensation of fullness [34
]. We used a Visual Analogue Scale (VAS) questionnaire to study the effect of milk products on satiety, because it is the most commonly used satiety measurement and makes comparison to other studies possible [51
]. Another rating scale, Satiety Labeled Intensity Magnitude (SLIM) [52
], was also used. In the present study, fibre enrichment did not increase satiety. Furthermore, neither differences in the energy intake at the subsequent breakfast meals or in the energy intake during the rest of the study day were found. The reason for not finding a satiating effect in this study might be due to the moderate amount of fibre in the study product and the fairly small amount of product consumed. In a study by King et al
], the effects of polydextrose and xylitol on appetite were examined independently and together with a greater amount of fibre than in this study. King et al
. used 25 g of polydextrose or 25 g of xylitol or 12.5 g of polydextrose and 12.5 g of xylitol. In the present study, the amount of polydextrose was only 3 g. In the study by King et al
., the combination of the studied carbohydrates significantly increased the feeling of fullness. Used alone, polydextrose significantly suppressed food intake compared to a control product. Similarly, another soluble fibre (oligofructose, 16 g/day) significantly reduced energy intake, hunger and prospective food consumption and increased satiety compared to placebo treatment [54
]. The products studied in the present study were beverages, which may have different effects on satiety compared to solid foods [55