Co-ingested vinegar-soaked or preloaded dried apple mitigated acute postprandial glycemia of rice meal in healthy subjects under equicarbohydrate conditions

Abstract

This study investigated 2 possible approaches to dietary control of acute postprandial responses to a rice-based meal under equicarbohydrate conditions: (1) a dried apple (DA) preload and (2) co-ingestion of vinegar-soaked DA. We hypothesized that both approaches would counteract hyperglycemia with no negative effect on satiety, possibly explained by an inhibitory effect on digestive enzyme activity and/or the effect of the sugar component of the DA. Fifteen healthy female subjects consumed (1) rice, (2) co-ingestion of DA and rice (DA + R), (3) DA preload and rice (PDA + R), (4) rice with sugar solution (same sugar profile as in DA) preloaded (PSS + R), or (5) co-ingestion of rice with vinegar-soaked DA (VDA + R) in a randomized crossover trial. Acute postprandial glycemic response tests and subjective satiety tests were conducted for each test meal. Compared with rice reference, the PA + R and PSS + R achieved 31.4% and 36.3% reduction of the incremental area under the curve_0-120, 24.3% and 27.0% decreases in the average glucose peak, along with 21.6% and 27.0% decreases in glycemic excursion in 240 minutes, whereas the VDA + R resulted 42.4%, 27.0%, and 29.7% reductions in the incremental area under the curve_0-120, peak, and glycemic excursion, respectively. The DA-containing meals had no effect or a favorable effect on satiety. The in vitro assay found larger resistant starch and smaller rapid digestible starch fractions in DA + R and VDA + R meals compared to those of the rice reference (P < .001). The result of this study supported the research hypothesis, and the DA-containing meals could be considered as a potential dietary approach for glycemic management.

Introduction

Dried fruits, the dehydrated products of fresh fruits, are good source of minerals, dietary fibers, and antioxidants to daily diets [1]. They are regarded as high–nutrient density choices for daily snacks and sweet foods [2]. Accumulating evidence indicates that dried fruits might have the potential of playing a role in cardiovascular health, bone health maintenance, and constipation alleviation [[3], [4], [5]].

Studies showed that partial substitution of high–glycemic index (GI) staple foods with fruits or dried fruits improved postprandial glycemic responses (GRs) [6,7], insulin responses [7], and HbA1c levels [8]. An isocarbohydrate exchange of dried apple (DA) for half of the rice meal lowered the GI and maximum amplitudes of glucose excursion (MAGE) in 240 minutes [6]. Preloads of kiwi fruit and apple significantly reduced GRs in acute trials [7,9]. However, the glycemic effect of preloaded dried fruit on high-GI diet was rarely reported.

In rice consumption areas such as East Asia, there is a long tradition of adding sour-tasting side dishes to rice diets. Organic acid–containing side dishes such as the salted plums, vinegar-pickled sliced cucumbers, sushi rice rolls, and algae salad with vinegar sauce in the traditional Japanese diet could decrease the GI of rice meals [10]. In China, vinegar-soaked raisins are believed to be beneficial to obesity prevention. Meta-analysis research confirmed that dietary vinegar consumption could effectively improve postprandial blood glucose and insulin responses [11], reduce appetite [12], and enhance satiety [13]. However, the combined effect of dried fruits and vinegar on glycemic responses and satiety has not yet been studied. Our study investigated the possible effects of DA and vinegar-soaked DA, either consumed as a preload or co-ingested, on acute GR and satiety of a rice meal compared with the isocarbohydrate rice reference.

As a good source of pectin, polyphenols, as well as fructose [14], DA was reported to have the lowest GI among tested dried fruits [15]. Based on isoenergetic comparisons, low-GI carbohydrate foods usually have a high satiety compared to their high-GI counterparts [16]. However, the isoenergetic or isocarbohydrate substitution of fruit or dried fruit for cereal foods will inevitably lead to a decrease in protein content and energy density, which may affect the satiety of test meals [17]. In an acute feeding trial, decreased self-reported appetite was demonstrated after a DA-containing meal [18]. In another study, adding vinegar to high-GI carbohydrate meals improved acute satiety [13]. Considering both the GI and protein content, we evaluated the satiety characteristics while exploring the glycemic effects of fruits and dried fruits.

This study investigated 2 possible approaches to dietary control of acute postprandial responses to a rice-based meal under equicarbohydrate conditions: (1) a DA preload and (2) co-ingestion of vinegar-soaked DA. The possible impact of DA on carbohydrate digestion was explored via an in vitro assay. This study's research hypotheses were as follows: (1) in an equal-carbohydrate partial substitution study design, the DA administered as preload would elicit more pronounced hypoglycemic effect compared with its co-ingestion counterpart; (2) compared with the co-ingested DA, the vinegar-soaked DA would further reduce the postprandial glycemia due to the addition of acetic acid; (3) co-ingested vinegar-soaked DA would not decrease the rice meal's satiety score; and (4) the glycemic effect of meals containing DA could be partly explained by the DA's sugar profile and its impact on carbohydrate digestion.