Acute Capillary Glucose Responses to Sweetened Beverages, Spice Infusions, and Mineral-Rich Water in Healthy Young Adults: A Randomized Parallel-Group Study

1. Introduction

Type 2 diabetes and related metabolic disorders continue to impose a substantial global health burden [1]. Dietary carbohydrate quality and quantity influence glycemic exposure, and beverages are particularly relevant because liquid sugars can be consumed rapidly and provide limited satiety. Habitual intake of sugar-sweetened beverages has been associated with weight gain and cardiometabolic risk [2], while fruit juice has also been associated with incident type 2 diabetes in prospective evidence [3]. Acute glucose excursions are therefore relevant when comparing beverages, although a single post-consumption value should not be equated with a diagnostic glucose-tolerance test or long-term glycemic variability [4].

Cinnamon and ginger are commonly used in traditional and functional beverages. Experimental work suggests that cinnamon-derived compounds may influence insulin signaling and carbohydrate-digesting enzymes [5], and trials in people with type 2 diabetes have reported modest improvements in selected glycemic outcomes after sustained cinnamon supplementation [6]. Gingerols may promote glucose uptake in experimental models [7], and longer-term ginger supplementation has been studied in people with diabetes [8,9]. These findings, however, do not establish that a single serving of an unsweetened spice infusion lowers glucose in healthy fasting adults. In the absence of a carbohydrate challenge, a neutral response may simply reflect the lack of digestible sugar.

Mineral composition may also influence metabolic physiology, but evidence that drinking water acutely alters glucose regulation is limited [10]. Zamzam water is naturally mineral-rich groundwater obtained from the Zamzam well in Makkah, Saudi Arabia. Published analyses indicate that its mineral composition may vary according to the source and sampling conditions [11,12]. Any acute difference therefore requires direct compositional measurement and an appropriate mineral-matched comparator before it can be attributed to total dissolved solids or to an individual electrolyte.

This study compared the acute capillary glucose response to two carbohydrate-containing beverages (honey drink and orange juice), two unsweetened spice infusions (cinnamon and ginger), mineral-rich Zamzam water, and plain bottled water after an overnight fast. We expected the carbohydrate-containing beverages to produce the largest increases, while the responses to the unsweetened beverages would be smaller. The comparison involving Zamzam water was exploratory.

2. Materials and Methods

2.1. Study Design, Setting, and Ethics

This randomized, controlled, parallel-group, single-session intervention study was conducted at Jouf University, Saudi Arabia, between February and April 2020. The protocol was approved by the Bioethics Committee at Jouf University (Approval No. JU-LCBE-8-18-9-40). All participants provided written informed consent before study procedures. The study was conducted in accordance with the ethical principles stated in the Declaration of Helsinki.

2.2. Recruitment and Eligibility

Participants were recruited through public advertisements displayed across the Jouf University campus. Interested students contacted the study PI and underwent eligibility screening before providing written consent. Inclusion criteria were current enrollment at Jouf University; age 19-25 years; self-reported good health; ability to complete the required overnight fast; and willingness to consume any of the six study beverages. Students were excluded if they reported diabetes or impaired glucose regulation; a chronic endocrine, metabolic, renal, hepatic, or gastrointestinal disorder; an acute illness at the study visit; current use of medication or supplements known to affect glucose metabolism; or allergy or intolerance to any study-beverage ingredient. Participants who did not complete the required fasting period or either glucose measurement, or whose pre-consumption fasting glucose value was outside the prespecified normal range, were excluded from the analysis. A total of 144 eligible students were enrolled. Enrollment was feasibility-based, with participants allocated equally across six.

2.3. Randomization, Allocation Concealment, and Blinding

Before recruitment, an investigator who was not involved in enrollment, intervention delivery, or outcome measurement generated the allocation sequence with a computerized random-number generator. Randomly permuted blocks of six were used, with one assignment to each beverage group within every block, to maintain a 1:1:1:1:1:1 allocation ratio (n = 24 per group). The assignments were placed in sequentially numbered, opaque, sealed envelopes by the independent investigator. After written consent, eligibility confirmation, and baseline glucose measurement, the enrollment coordinator opened the next envelope in sequence and notified only the staff member preparing the assigned beverage. Outcome assessors who performed and recorded the capillary glucose measurements were blinded to group assignment, and participants were instructed not to disclose their beverage to the assessor. Participants and beverage-preparation staff could not be blinded because the beverages differed visibly and in taste.

2.4. Beverage Interventions

After an overnight fast and baseline glucose measurement, each participant consumed 250 mL of the beverage assigned to their group. The orange-juice intervention used a commercial 250 mL KDD Orange Juice pack (The Kuwaiti Danish Dairy Co. K.S.C.C., Kuwait; product code FJUQL6ORNGRP) [13]. The study record reported 50 g sugar for the orange-juice serving, although the interpretation and analytical verification of this value were unavailable. The honey drink contained approximately 50 g (two tablespoons) of Black Forest honey per 250 mL serving (200 g/L). The ginger infusion was prepared using approximately 12 g (two tablespoons) of fresh ginger in 250 mL water (48 g/L), whereas the cinnamon infusion contained 2.6 g cinnamon per 250 mL serving (10.4 g/L). The Zamzam-water intervention consisted of 250 mL of commercially bottled Zamzam water sourced from the Zamzam Well in Makkah (Al-Zamazemah Company, Saudi Arabia). The plain-water comparator consisted of 250 mL of Nova natural drinking water (Health Water Bottling Co. Ltd., Riyadh, Saudi Arabia. The interventions are summarized in Table 1.

2.5. Capillary Glucose Measurement and Outcomes

Capillary whole-blood glucose was measured using four Contour Next glucometers (Ascensia Diabetes Care, Parsippany, NJ, USA) and manufacturer-compatible test strips. A baseline measurement was obtained immediately before beverage consumption, and a second measurement was obtained 60 min after consumption. The post-consumption measurement was not considered an oral glucose tolerance test (OGTT) because such testing requires administration of a standardized oral glucose load. A total of 288 measurements were recorded (144 baseline and 144 post-consumption measurements). Six CONTOUR NEXT glucose meters and test strips lot 7308 were used. Meter performance was verified using CONTOUR® control solution according to the manufacturer’s instructions. Before capillary sampling, participants washed their hands with soap and water and dried them completely; when alcohol was used, the selected puncture site was allowed to air-dry fully. Each glucose measurement was performed in triplicate, and the mean of the three readings was used for analysis. Used test strips were discarded as clinical waste.

The primary outcome was the within-participant change in mean capillary glucose, calculated as the mean post-consumption value minus the mean fasting baseline value (Δ glucose, mg/dL). The mean post-consumption glucose value was treated as a secondary outcome. No clinical diagnostic classification was assigned because measurements were obtained at only one post-consumption time point following a non-standardized beverage challenge, which does not constitute an OGTT or another diagnostic procedure.

2.6. Statistical Analysis

Analyses were performed using GraphPad software (GraphPad Software, Prism, San Diego, CA, USA; version 11). Continuous results were summarized as mean ± standard deviation. Within each group, baseline and post-consumption glucose values were compared using a paired t-test, and mean changes were reported with 95% confidence intervals. A one-way analysis of variance was used to test whether change scores differed across the six groups. All tests were two-sided, and p < 0.05 was considered statistically significant. Model assumptions were assessed to verify exact F statistics, degrees of freedom, and p values, and pairwise comparisons. Enrollment was feasibility-based, with 144 participants allocated equally across six groups (24 per group). A sensitivity analysis for a fixed-effects one-way analysis of variance, assuming six groups, a two-sided α of 0.05, and 80% power, indicated that this sample could detect an omnibus effect of Cohen’s f ≥ 0.304, equivalent to η² ≈ 0.085.

3. Results

3.1. Participant Data and Baseline Glucose

Outcome data were obtained for 144 participants, with 24 participants in each of the six beverage groups. All participants were included in the analysis, and participant flow is presented in Figure 1. Group-level demographic characteristics and information regarding protocol deviations, and intervention adherence. Mean fasting capillary glucose ranged from 79.17 mg/dL in the Zamzam-water group to 91.33 mg/dL in the cinnamon-infusion group (Table 2).

3.2. Within-Group Changes in Capillary Glucose

The two carbohydrate-containing beverages produced the largest mean increases. Glucose increased by 20.09 mg/dL after the honey drink (95% CI, 15.50 to 24.68; p < 0.0001) and by 17.33 mg/dL after orange juice (95% CI, 6.10 to 28.56; p = 0.0058). In contrast, changes after cinnamon infusion (-3.58 mg/dL), ginger infusion (-3.91 mg/dL), and plain water (-2.84 mg/dL) were not statistically significant. The Zamzam-water group showed a mean within-group increase of 9.83 mg/dL (95% CI, 5.20 to 14.46; p = 0.0003), from 79.17 to 89.00 mg/dL.

3.3. Between-Group Comparison

The mean change in capillary glucose differed across the six beverage groups (one-way analysis of variance, p < 0.0001). The distribution of mean changes and reported 95% confidence intervals is shown in Figure 1. The largest positive changes occurred in the honey-drink and orange-juice groups, whereas the mean changes for plain water and the two unsweetened spice infusions clustered around zero. Although Zamzam water (Mineral-Rich Water) showed a statistically significant within-group increase, a paired within-group test alone does not establish that its response differed from plain water or from the other beverage groups.

4. Discussion

4.1. Principal Findings

In healthy young adults studied after an overnight fast, the two carbohydrate-containing beverages produced the largest acute increases in capillary glucose. Plain water and the unsweetened cinnamon and ginger infusions showed small, non-significant mean decreases. Mineral-rich Zamzam water was associated with a modest within-group increase, but the mean post-consumption value remained within the range observed across the study groups and the design does not identify a mineral-mediated mechanism.

4.2. Interpretation in Relation to Previous Evidence

The responses to the honey drink and orange juice are biologically plausible because both beverages supplied rapidly available carbohydrate. This acute experiment is consistent with the broader evidence linking sugar-containing beverages with adverse glycemic and cardiometabolic outcomes [2,3]. However, the post-consumption values in this study should not be described as prediabetic or pathological: diagnostic thresholds for fasting glucose or standardized oral glucose tolerance testing do not apply to a single capillary measurement after non-standardized beverages.

The neutral responses to cinnamon and ginger should also be interpreted conservatively. Prior research on cinnamon and ginger has generally evaluated standardized extracts or supplements over weeks or months in people with diabetes [6,8,9,15,16]. In the present study, the infusions were unsweetened and prepared with ginger at 16 g/L and cinnamon at 10.4 g/L; no carbohydrate challenge was co-administered. The results therefore show that these particular unsweetened drinks did not acutely raise glucose; they do not demonstrate active glucose lowering, enhanced insulin sensitivity, inhibition of intestinal carbohydrate digestion, or prevention of a glycemic spike.

The Zamzam-water (Mineral-Rich Water) observation is hypothesis-generating. Published studies confirm that Zamzam water may contain a distinct mineral profile, but the composition varies across samples [11,12]. The water consumed in this study was characterized only by a reported TDS value, and no mineral analysis was performed. Moreover, the Zamzam group had the lowest baseline mean glucose, which increases concern about baseline imbalance and regression to the mean. Biological and analytical variation in sequential capillary glucose measurements may also be important when interpreting a change of this magnitude [17]. Consequently, the data do not support attributing the increase to calcium, magnesium, bicarbonate, sodium, taste-triggered hormonal release, hepatic glucose output, or any other specific pathway. A crossover study with direct mineral analysis, a mineral-matched control, venous plasma glucose, insulin, and multiple post-consumption time points would be needed to test such mechanisms.

Acute human trials further show that beverage composition, comparator selection, and sampling schedule can materially influence observed glycemia. In healthy participants, glycemic responses differed among honey varieties even when available carbohydrate was standardized [18]. A randomized crossover trial found that adding orange-pomace fiber attenuated the acute glycemic response to sugar-matched orange juice [19]. Cinnamon consumed with a carbohydrate meal reduced postprandial glucose and delayed gastric emptying in a small crossover trial [20], whereas a randomized trial of a standardized ginger aqueous extract in nondiabetic adults used repeated postprandial measurements to evaluate the response [21]. These protocols are not directly comparable with the present single-dose, parallel-group experiment, but they illustrate why exact ingredient dose, beverage composition, comparator selection, and multiple sampling times should be documented.

4.3. Strengths and Limitations

Strengths of the study include concealed random allocation with equal group sizes, blinded outcome assessment, controlled beverage volume, inclusion of both carbohydrate-containing and unsweetened comparators, and paired measurement of glucose before and after consumption. The study also addresses a practical question about beverages commonly consumed in the region. This study is reported with reference to the CONSORT 2025 guidance. The completed checklist is provided as Supplementary File S1, and participant flow is presented in Figure 1. [22].

Several limitations should be considered when interpreting the findings. First, although outcome data were available for all 144 randomized participants, group-specific demographic and clinical characteristics, pretest standardization of diet and physical activity, intervention-adherence data, protocol deviations, systematic adverse-event monitoring, and prospective trial registration were not documented. Second, the exact cinnamon and ginger doses and the complete nutritional and mineral compositions of the beverages were not verified. Third, capillary glucose was measured at only one post-consumption time point using handheld glucose meters. Consequently, the study could not characterize the peak glycemic response, incremental area under the curve, glycemic variability, or insulin dynamics. User technique and variation among monitoring systems or test-strip lots may also affect capillary glucose measurements, emphasizing the importance of documented quality-control procedures and replicate measurements [23]. Fourth, baseline glucose differed descriptively among the groups; a baseline-adjusted analysis of covariance may have provided a more precise estimate of the intervention effect than an unadjusted comparison of change scores [24]. Fifth, the retained statistical output did not include complete model diagnostics, exact omnibus test statistics, or multiplicity-adjusted pairwise estimates, preventing independent verification of the model assumptions and effect estimates. Finally, the sample comprised healthy university students aged 19–25 years, limiting the generalizability of the findings to older adults, other populations, and individuals with impaired glucose regulation.

5. Conclusions

Following an overnight fast, the honey drink and orange juice showed the largest mean increases in capillary glucose at 60 minutes, whereas the unsweetened cinnamon and ginger infusions and plain bottled water produced smaller changes. These findings are consistent with differences in available carbohydrates but do not establish antihyperglycemic effects for the spice infusions. Zamzam water also showed a within-group glucose increase. Published analyses—not measurements of the water administered in this study—have reported Zamzam mineral concentrations reaching approximately 42 mg/L magnesium, 93 mg/L calcium, and 210 mg/L sodium [11,12]. Although magnesium may support insulin-mediated glucose uptake and calcium contributes to pancreatic β-cell insulin secretion, the observed Zamzam-water response cannot be attributed to these minerals because beverage composition, circulating minerals, and insulin were not measured. Given the modified per-protocol analysis and single post-consumption measurement, these findings should be considered preliminary and hypothesis-generating. Future preregistered studies should directly analyze beverage composition, use a crossover design or baseline-adjusted analysis, and measure venous glucose, insulin, and relevant mineral biomarkers at multiple time points.