3.3. Glycemic Excursions in 48-h CGM
The effects of NBS
vs. DCS on glycemic characteristics in 48-h CGM are illustrated in
Table 2. Mean blood glucose (MBG) and the total glucose AUC-48 h were both significantly reduced after NBS supplementation in comparison with DCS in all of the groups (
p < 0.0001 for MBG, and
p < 0.05 for AUC-48-h). No statistical differences were observed between NBS and DCS supplementation on GV indexes, including SD, CV, MAGE, and MAG
5 changes between groups.
Table 2.
Effects of beverages containing native banana starch (NBS) or digestible corn starch (DCS) in glycemic characteristics based on continuous glucose monitoring (CGM).
Table 2.
Effects of beverages containing native banana starch (NBS) or digestible corn starch (DCS) in glycemic characteristics based on continuous glucose monitoring (CGM).
Characteristic | Lean | Obese | Lean and Obese |
---|
DCS | NBS | p | DCS | NBS | p | DCS | NBS | p |
---|
MBG (mmol/L) | 5.83 ± 0.95 | 5.15 ± 0.71 | <0.0001 | 6.28 ± 0.82 | 5.44 ± 0.63 | <0.0001 | 6.06 ± 0.89 | 5.29 ± 0.67 | <0.0001 |
AUC (mmol.h/L) | 4.43 ± 0.49 | 3.97 ± 0.45 | 0.0329 | 5.85 ± 0.29 | 5.06 ± 0.20 | 0.0121 | 5.16 ± 0.32 | 4.51 ± 0.27 | 0.0007 |
SD (mmol/L) | 1.00 ± 0.44 | 0.77 ± 0.25 | 0.1229 | 1.13 ± 0.39 | 1.07 ± 0.46 | 0.7651 | 1.07 ± 0.41 | 0.92 ± 0.40 | 0.2440 |
CV (%) | 16.81 ± 5.88 | 15.14 ± 4.88 | 0.3904 | 17.74 ± 4.60 | 20.25 ± 9.64 | 0.5028 | 17.28 ± 5.16 | 17.70 ± 7.88 | 0.8374 |
MAGE (mmol/L) | 2.32 ± 0.67 | 2.26 ± 0.76 | 0.8780 | 2.27 ± 1.07 | 1.77 ± 0.61 | 0.2100 | 2.30 ± 0.87 | 2.02 ± 0.72 | 0.2960 |
MAG5 (mmol/L) | 0.12 ± 0.04 | 0.10 ± 0.02 | 0.2176 | 0.12 ± 0.03 | 0.15 ± 0.08 | 0.3095 | 0.12 ± 0.04 | 0.13 ± 0.07 | 0.7622 |
When comparing obese and lean subjects, the obese group exhibited a far greater AUC-48-h in comparison with lean subjects in both NBS and DCS supplementation (p = 0.034 and p = 0.026, respectively). However, no changes were observed in any of the GV indexes between obese and lean groups.
3.5. Meal Tolerance Test (MTT)
To better control postprandial glucose and insulin responses a standardized MTT was conducted on day 5. A reduction in glycemic and insulin responses after NBS was observed in all of the studied groups. Total glucose AUC-180 min and total insulin AUC-180 min were both reduced following NBS compared to DCS group (
Figure 2). When comparing obese and lean subjects (
Figure 3), no differences were appreciated in glucose AUC-180 min or insulin AUC-180 min after DCS. Likewise, there was not significant difference in the glycemic response between groups after NBS. However, insulin response (AUC-180 min) tended to be significantly decreased in lean subjects following NBS (
p = 0.051).
Figure 2.
Effects of beverages containing native banana starch (NBS) (red) in comparison with digestible corn starch (DCS) (blue) at the Meal Tolerance Test (MTT) (a,b) in lean group; (c,d) in obese group; (e,f) in lean and obese group. Notes: Beverages were administered 5 min before the standardized food. Areas under the curve (AUC) were compared using a paired Student t test or Wilcoxon test. In (a) ANB vs. DCS p = 0.0098; in (b) p = 0.0018; in (c) p = 0.0223; in (d) p = 0.0394; in (e) p < 0.0001; in (f) p = 0.0002.
Figure 2.
Effects of beverages containing native banana starch (NBS) (red) in comparison with digestible corn starch (DCS) (blue) at the Meal Tolerance Test (MTT) (a,b) in lean group; (c,d) in obese group; (e,f) in lean and obese group. Notes: Beverages were administered 5 min before the standardized food. Areas under the curve (AUC) were compared using a paired Student t test or Wilcoxon test. In (a) ANB vs. DCS p = 0.0098; in (b) p = 0.0018; in (c) p = 0.0223; in (d) p = 0.0394; in (e) p < 0.0001; in (f) p = 0.0002.
Figure 3.
Differences between lean and obese subjects in glycemic and insulin responses during a Meal Tolerance Test (MTT) (a,b) Beverage containing digestible corn starch (DCS). (c,d) Beverage containing native banana starch (NBS). Notes: Beverages were administered 5 min before the standardized food. Areas under the curve (AUC) were compared using an unpaired Student t test. In (a) Obese vs. Lean p = 0.0853; in (b) p = 0.8892; in (c) p = 0.0749; in (d) p = 0.051.
Figure 3.
Differences between lean and obese subjects in glycemic and insulin responses during a Meal Tolerance Test (MTT) (a,b) Beverage containing digestible corn starch (DCS). (c,d) Beverage containing native banana starch (NBS). Notes: Beverages were administered 5 min before the standardized food. Areas under the curve (AUC) were compared using an unpaired Student t test. In (a) Obese vs. Lean p = 0.0853; in (b) p = 0.8892; in (c) p = 0.0749; in (d) p = 0.051.
3.6. Discussion
We showed that acute supplementation of NBS significantly reduces glucose excursions measured by 48-h CGM and also diminished glycemic and insulin responses during a MTT in both lean and obese subjects. However, no changes on GV indexes were observed between groups. In comparison with previous studies, the experimental design of this work is novel in that it employed CGMS to estimate glucose excursions and GV over several days in subjects under conditions similar to those of everyday life.
All of the participants were included with normal fasting glycemia and normal HbA1c values, however, we could observe that some participants were undergoing excursions into glucose intolerant and/or diabetes range during the 48-h CGM. These results confirm previous observations that dysglycemia may be underestimated by traditional methods such as fasting glycemia and HbA1c, and that CGM could serve as a better tool to detect early alterations [
23,
24,
25]. Likewise, this study also confirmed altered glucose management in obese subjects with normoglycemia and normal HbA1c. Obese subjects exhibited a far greater glycemic burden in comparison with lean subjects regardless of the supplement employed. This disturbance is based on the fact that obese subjects exhibit an early decline in beta cell function, predisposing to an insulin resistance status several years prior to the onset of diabetes.
In both lean and obese subjects, NBS supplementation induced a significant reduction in 48-h glycemic excursions in comparison with DCS. However, in order to better control the postprandial response, an MTT was performed on day 5. In contrast with OGTT, which utilized a pure glucose load, the mixed meal has the advantage of mimicking the “real life” condition. In this test, we observed that NBS significantly reduced glycemic and insulinic postprandial responses in obese and lean subjects. This finding is very important because a recent study in overweight/obese subjects demonstrated that postprandial glycemia is the main contributor to overall 24-h hyperglycemia. Moreover, these authors reported that the contribution is higher when HbA1c values are low, as is the case of many obese subjects with unknown dysglycemia, such as those included in the present study [
26].
This effect of NBS in controlling postprandial glycemia under real-life conditions provides great interest with regard to clinical prevention, because it is known that high postprandial glycemia levels occur prior to the deterioration of fasting glucose levels and diabetes onset [
27]. Moreover, postprandial hyperglycemia has greater consequences than increased fasting glycemia. In a previous report, increased mortality was observed in subjects with abnormal 2-h postprandial glycemia, but not in those with increased fasting glycemia [
28]. In general, it is accepted that hyperglycemic peaks and hyperinsulinemia increases the risk for cardiovascular disease (CVD) in patients with prediabetes [
29,
30]. A reduction in postprandial responses over long periods could be a preventive factor for reducing the onset of diabetes in high-risk subjects and could diminish the incidence of cardiovascular events in individuals with T2DM [
31]. The dietary intervention using products manufactured with NBS might be implemented in order to prevent diabetes and improve cardiovascular prognosis.
Despite altered postprandial glucose excursions, no increased GV indices were observed in the obese subjects group and no effect of NBS on GV was detected. Some of the GV index values, such as SD, CV, and MAGE from this group, were similar to those reported in healthy Chinese population measured in 434 individuals 20–60 years old [
32]. The lack of alterations in GV indexes could be partially explained by the relatively youth of the subjects and because only 6 of 10 exhibited a moderated abdominal obesity. Indeed, few studies have investigated GV in normoglycemic populations. Ma Chung-Ming
et al. in 2011 [
33] reported increased GV in abdominally obese subjects with normal glucose tolerance (NGT). However, this study was performed in males, and our study included predominantly women.
Diminished glucose and insulin response after NBS could be partially explained by the reduced rate of digestion [
12,
34]. However, it could also be attributed to increased short chain fatty acids (SCFA) after RS fermentation in the colon. In previous studies, we demonstrated increased SCFA production in rodent intestine after NBS [
14]. Colonic SCFA production has been linked with increased secretion of incretin hormones, such as GLP-1 and PYY, from enteroendocrine cells [
19,
35]. Plasma SCFA have also shown to inhibit adipose tissue lipolysis
in vivo: thus, RS might modulate insulin sensitivity through alterations in this fatty acid flux [
10,
11]. In a recent study in humans, Robertson
et al. [
36] suggested that the most important effect of chronic supplementation with Hi-Maize
® was due to an improvement of the adipose tissue physiological function. As a secondary effect, increased glucose uptake into skeletal muscle was followed. The authors found that Hi-Maize
® 8-week supplementation induced stimulation of the expression of lipoprotein-lipase (LPL), adipose triglyceride lipase (ATGL), and hormone-sensitive lipase (HSL) in adipose tissue. From these observations, it is clear that further mechanistic studies are required to investigate the effects of NBS.
Some limitations merit consideration. First, we did not perform an OGTT to rule out glycemic alterations such as diabetes and IGT. Second, this study was conducted predominantly in females because in Mexico, diabetes prevalence is higher in women; thus, the results cannot be extrapolated to male population. Third, we matched the supplements only for total carbohydrates. The advantages of our study, however, comprised the use of a reliable CGMS to investigate glycemic profiles under conditions similar to those of everyday life and the crossover design, which permitted reducing inter-subject variability.