Acute ingestion of snake fruit jelly improves glycemic response, enhances endurance performance and antioxidant defense, and reduces inflammatory markers in healthy adults

ABSTRACT

Background

Snake fruit is rich in vitamin C, carotene, phenolic compounds, flavonoids, and monoterpenoids – bioactive constituents known for their potent antioxidant properties. Based on these components, the present study investigated the potential effects of snake fruit jelly ingestion on glycemic control, endurance performance, alongside its impact on antioxidant status, inflammatory responses, and metabolic biomarkers in healthy individuals.

Methods

A randomized crossover design was used in two separate experiments involving 48 healthy sedentary men and women aged 19–35 years. All participants ingested 140 g of both control jelly and snake fruit jelly on separate occasions. Experiment 1 (n = 25): Blood glucose (BG) concentrations were measured at baseline and every 30 minutes for 2 hours post-ingestion. Experiment 2 (n = 23): Following each jelly ingestion, participants performed leg cycling at 60% of peak oxygen consumption until exhaustion. Blood samples were collected before and after exercise to measure BG, insulin, cortisol, and biomarkers of antioxidant status and inflammation.

Results

In Experiment 1, BG concentrations at 30 and 60 minutes post-ingestion, as well as the incremental area under the BG curve at 30, 60, 90, and 120 minutes, were significantly lower following snake fruit jelly ingestion compared with control (all p < 0.05). In Experiment 2, post-exercise superoxide dismutase (SOD) activity was significantly increased, while tumor necrosis factor-alpha (TNF-α) and cortisol concentrations were significantly decreased after snake fruit jelly ingestion (all p < 0.05). Between-group analysis revealed that endurance time and SOD activity were significantly higher, whereas BG, insulin, and TNF-α concentrations were significantly lower following snake fruit jelly ingestion compared with control jelly ingestion (all p < 0.05). Cortisol and interferon-gamma concentrations showed no significant differences between conditions.

Conclusion

Acute ingestion of snake fruit jelly enhances glycemic control, endurance performance, and antioxidant activity, while reducing blood glucose, insulin, and pro-inflammatory markers in response to endurance exercise.

Clinical trial registration

Retrospectively registered at ClinicalTrials.gov (Identifier: NCT06227260).

1. Introduction

The global sports nutrition market is a multibillion-dollar industry, projected to nearly double in value by 2030 [1]. Dietary supplements are widely used by athletes across various disciplines – including speed, power, and endurance sports – as part of their training regimens or during competition. Notably, approximately 85% of elite track and field athletes report supplement use [2]. The primary motivations for supplement use include enhancing athletic performance, promoting faster recovery, and supporting overall health [1].

Sports supplements are generally classified into several categories, including sports foods, medical supplements, ergogenic aids, functional foods and superfoods, and miscellaneous supplements [3]. Among ergogenic aids, commonly used supplements include vitamins, minerals, protein, creatine, and various other compounds [2]. In recent years, antioxidant supplementation has attracted increasing attention as a potential strategy to enhance athletic performance. This interest arises from evidence that intense physical activity elevates free radical production, leading to oxidative stress, which is linked to muscle inflammation, tissue damage, fatigue, and impaired performance [4].

During exercise, the elevated oxygen consumption of muscle cells promotes excessive free radical generation. In particular, strenuous and prolonged exercise can induce oxidative damage to cellular components such as lipids (lipid peroxidation), proteins (protein oxidation), and DNA (DNA oxidation) within contracting myocytes. These processes contribute to contractile dysfunction, muscle fatigue, tissue damage, and reduced performance capacity [5]. Moreover, muscle fatigue and damage can further stimulate pro-inflammatory responses, exacerbating performance decline [6] and delaying muscle recovery [7].

Snake fruit, or salak (Salacca edulis Reinw.), is a tropical fruit native to Indonesia and widely cultivated in other Southeast Asian countries such as Thailand, Malaysia, and Brunei. Nutritionally, snake fruit contains higher levels of dietary fiber, crude protein, and crude fats compared to kiwi fruit [8]. It is also a rich source of natural sugars, essential minerals, and vitamins, including ascorbic acid (vitamin C) and carotene [9]. Numerous in vitro and in vivo studies have demonstrated the medicinal potential of snake fruit, which includes antioxidant, anticancer, antihyperlipidemic, and antihyperuricemic effects. These properties are primarily attributed to its high content of phenolic compounds, flavonoids, and monoterpenoids, which possess significant antioxidative activities [10,11].

Notably, several antioxidant compounds present in snake fruit have been proposed to exert ergogenic benefits, particularly under exercise conditions. These effects may involve improvements in cellular redox balance and reductions in oxidative modifications to DNA, lipids, and proteins, ultimately supporting contractile function, delaying fatigue, and prolonging exercise performance [12]. For example, Bentley et al. [13] demonstrated that a single dose of an antioxidant supplement (Lactaway® containing pycnogenol) significantly improved endurance performance, as measured by time to fatigue, in trained athletes. Similarly, evidence suggests that dietary polyphenols – the most abundant antioxidants in the human diet – may promote mitochondrial adaptation and enhance blood flow, thereby improving endurance capacity [14]. In addition, both animal and human studies indicate that polyphenols improve glycemic control by attenuating postprandial hyperglycemia and hyperinsulinemia through enhanced insulin signaling and sensitivity [15]. Supporting this, a randomized, double-blind, placebo-controlled clinical trial by Bumrungpert et al. [16] showed that nutraceutical supplementation containing antioxidant compounds improved glycemic control, insulin sensitivity, and oxidative stress in individuals with hyperglycemia.

Despite substantial evidence supporting the antioxidant properties of snake fruit, human studies investigating its potential antioxidant, anti-inflammatory, and performance-enhancing effects remain limited. Therefore, the present study aimed to develop an ergogenic supplement derived from snake fruit and evaluate its effects on glycemic control and endurance performance. In addition, physiologically relevant mechanisms – including antioxidant capacity, inflammatory responses, and metabolic changes – were examined to provide a more comprehensive understanding. We hypothesized that acute ingestion of snake fruit jelly would enhance glycemic control and endurance performance by improving antioxidant status, modulating inflammatory markers, and promoting favorable metabolic responses.

2. Materials and methods

2.1. Study design and sample size

This study was designed as a randomized, single-blind, crossover, placebo-controlled trial. It was divided into two experiments: the first examined blood glucose (BG) responses to acute ingestion of snake fruit jelly (n = 25), and the second investigated the efficacy of snake fruit jelly on endurance performance (n = 25). The sample size for each experiment was determined using the crossover study formula described by Machin and Campbell [17]. Based on a previous study evaluating the acute effects of passion fruit juice supplementation on BG levels in healthy individuals [18], a mean difference of 16.4 mg/dL between treatment and control conditions was observed, with a standard deviation of 9.0. Using a type I error (α) of 0.05 and a type II error (β) of 0.20 (power = 80%), the required sample size was calculated to be 22 participants. To account for a potential 10% drop-out rate, the final sample size was increased to 25 participants per experiment.

2.2. Ethical considerations

All participants provided written informed consent before undergoing any screening procedures. They were thoroughly informed – both verbally and in writing – about the study objectives, experimental protocol, potential risks and benefits, and their rights and responsibilities as research participants. The study protocol was approved by the Human Ethics Committee of Burapha University (Approval No. IRB1-028/2566; approval date: 20 March 2023). This trial was also retrospectively registered with ClinicalTrials.gov (Identifier: NCT06227260; registration date: 17 January 2024).

2.3. Participants and screenings

A total of fifty healthy sedentary men and women aged 18–35 years were enrolled in the study. Participant recruitment occurred between 21 March and 9 September 2023. The inclusion criteria were: (a) age between 18 and 35 years; (b) normal body mass index (BMI) of 18.5–24.9 kg/m²; (c) absence of any diagnosed health conditions; and (d) willingness to consume snake fruit products. Exclusion criteria were: (a) known allergy to snake fruit or carrageenan; (b) regular smoking or alcohol consumption (defined as at least once per week); (c) regular physical activity exceeding 150 minutes per week or more than two days per week; (d) regular use of dietary supplements (e.g. vitamins or antioxidants) more than two days per week; (e) musculoskeletal conditions that could interfere with leg cycling; and (f) presence of current signs or symptoms of inflammation or infection, including fever, hyperpnea, dyspnea, or palpitations. Participants were withdrawn from the study if they: (a) exhibited abnormal symptoms during the exercise test or following jelly ingestion; (b) were unable to complete both jelly ingestion conditions in either experiment; or (c) voluntarily discontinued participation. Screening questionnaires were used to collect information on demographics, medical history, food allergies, physical activity levels, and dietary supplement use. Physical and physiological assessments included height, BM, BMI, blood pressure, heart rate, and body temperature. Additionally, all participants consumed a small sample of snake fruit jelly (approximately 50 mg) to assess for any allergic reactions or adverse symptoms related to acute ingestion.

2.4. Experiments

2.4.1. Experiment 1

In the first experiment, as illustrated in Figure 1, 25 participants consumed 140 g of either the control jelly or the snake fruit jelly in a randomized sequence. BG concentrations were measured at baseline (T0) and subsequently at 30, 60, 90, and 120 minutes post-ingestion (T30, T60, T90, and T120). After completing the first intervention arm, participants underwent a one-week washout period before crossing over to the alternate jelly condition. In the second arm, participants consumed the other jelly formulation, and BG measurements were repeated following the same protocol as in the first arm.

Figure 1.

CONSORT flow diagram for Experiment 1.

2.4.2. Experiment 2

In the second experiment (see Figure 2), 25 participants were randomly assigned to ingest 140 g of either the control jelly or the snake fruit jelly. Following ingestion, endurance performance was assessed using a leg cycling test conducted at 60% of each participant’s peak oxygen consumption (VO₂peak) until exhaustion. Blood samples were collected immediately before and after the endurance test to measure concentrations of BG, insulin, and cortisol, as well as biomarkers of antioxidant status and inflammation, including superoxide dismutase (SOD), interferon-gamma (IFN-γ), and tumor necrosis factor-alpha (TNF-α). After a one-week washout period, participants crossed over to consume the alternate jelly and underwent the same endurance test and biomarker assessments as in the first session.

Figure 2.

CONSORT flow diagram for Experiment 2.

All participants completed both Experiment 1 and Experiment 2 during the same time period and under similar environmental conditions, including consistent room temperature and humidity. Additionally, participants were instructed to maintain their usual daily routines – particularly with regard to dietary intake and physical activity – throughout the study period and during both arms of the crossover design.

2.5. Preparation of snake fruit jelly and control jelly

The snake fruit used in this study was sourced from Song Salueng Sub-district, Klaeng District, Rayong Province – a region in Eastern Thailand renowned for cultivating and distributing high-quality snake fruit. To prepare the snake fruit jelly, the fruits were processed using a fruit extractor to separate the juice from the pulp. The extracted juice was then double-filtered through a filter cloth to obtain a clear liquid. Sucrose powder and carrageenan were added to the juice, and the mixture was heated at medium temperature until fully homogenized. It was subsequently cooled at room temperature (22–28 °C) for approximately 30 minutes and then refrigerated at 2–4 °C until use. The preparation protocol was adapted from a Thai publication on fruit jelly development, with modifications to accommodate the unique characteristics of snake fruit, as no established recipe for snake fruit jelly currently exists. To ensure standardization and batch-to-batch consistency in product quality, all snake fruit was harvested from the same crop, and all jelly batches were prepared by a single skilled cook. The control jelly was prepared using the same procedure, except that glucose and fructose powders were used in place of snake fruit juice to match the sugar composition and total caloric content of the snake fruit jelly [8].

2.6. Analysis of snake fruit jelly constituents

According to the Thai Food Composition Database 2015 (THAI FCD 2015), a 140 g serving of snake fruit jelly provides approximately 245.08 kilocalories, primarily from carbohydrates (59.47 g; 237.88 kilocalories), with minor contributions from protein (1.20 g; 4.80 kilocalories) and fat (0.30 g; 2.40 kilocalories). In comparison, the control jelly provides approximately 245.00 kilocalories, derived solely from carbohydrates (61.25 g). To further characterize its chemical composition, the snake fruit jelly was lyophilized using a freeze dryer (Christ Alpha 2–4 LSCbasic, Martin Christ Gefriertrocknungsanlagen GmbH, Germany), and the resulting powder was subjected to gas chromatography – mass spectrometry (GC-MS) analysis. For this, 100 mg of the lyophilized powder was dissolved in 1 mL of ethanol, and a 2 µL aliquot was injected into an Agilent 7890A gas chromatograph coupled with an Agilent 7000B mass spectrometer (Agilent Technologies, Santa Clara, CA, USA), equipped with an HP-5 capillary column (30 m × 0.32 mm i.d., 0.25 µm film thickness). The injection was performed in split mode (split ratio 5:1) with an injector temperature of 250 °C. Helium was used as the carrier gas at a constant flow rate of 1.0 mL/min. The oven temperature program began at 40 °C (held for 5 min), ramped to 200 °C (held for 25 min), and finally increased to 280 °C (held for 61 min). Mass spectrometry was performed using electron ionization at 70 eV with an ion source temperature of 230 °C. Spectral data were acquired over a mass range of 50–650 m/z. Compound identification was carried out using GC-QQQ software in conjunction with the NIST MS Search 2.0 library.

2.7. Biochemical assays

In Experiment 1, BG concentrations were measured using the Accu-Chek® Guide BG monitoring system (Roche Diabetes Care Inc., Indianapolis, IN, USA), following the procedure previously described by Prasertsri et al. [18]. In Experiment 2, approximately 10 mL of venous blood was collected in the morning (between 8:00 and 9:00 a.m.) following an overnight fast of at least 8 hours. Of this, 6 mL was drawn into glucose and clotted blood collection tubes for analysis of BG, insulin, and cortisol concentrations. BG was measured using the VITROS Chemistry Products GLU Slides and the VITROS GLU Slide technique (Ortho Clinical Diagnostics, San Diego, CA, USA). Insulin concentration was determined using the ARCHITECT Insulin assay (Abbott Laboratories, Abbott Park, IL, USA). Cortisol levels were measured using the VITROS Immunodiagnostic Products Cortisol Reagent Pack via a competitive immunoassay technique (Ortho Clinical Diagnostics, San Diego, CA, USA). All biochemical analyses were conducted by RIA Laboratory Co., Ltd., Thailand.

2.8. Inflammatory cytokines assay

Approximately 3 mL of blood collected in clotted blood tubes was used for the analysis of inflammatory biomarkers. Serum concentrations of IFN-γ and TNF-α were measured using the OptEIA™ ELISA Sets for human IFN-γ and TNF-α, following the manufacturer’s instructions (BD Biosciences Pharmingen, San Diego, CA, USA).

2.9. Antioxidant biomarker assay

Approximately 1 mL of blood collected in clotted blood tubes was used for the analysis of antioxidant biomarker. SOD activity was measured in serum using the SOD Assay Kit-WST and a colorimetric method, following the manufacturer’s instructions (Dojindo Laboratories, Kumamoto, Japan).

2.10. Endurance performance test

During the first visit, participants underwent a submaximal exercise test using the Åstrand-Rhyming cycle ergometer protocol to estimate their VO₂peak and to determine the corresponding 60% VO₂peak workload [19]. On the subsequent visit, participants ingested either the control jelly or the snake fruit jelly and then performed an endurance performance test. This involved leg cycling at 60% of their VO₂peak until exhaustion, defined as the onset of maximal symptoms of dyspnea and fatigue or the inability to maintain a pedaling cadence of at least 60 revolutions per minute. Endurance performance was quantified by the total duration of the cycling effort (endurance time).

2.11. Statistical analyses

Data were assessed for normality using the Shapiro-Wilk test, homogeneity of variance using Levene’s test, and sphericity using Mauchly’s test. In Experiment 1, differences in BG concentrations across time points (T0, T30, T60, T90, and T120) within and between ingestion conditions were analyzed using repeated measures analysis of covariance (ANCOVA), with baseline BG (T0) included as a covariate. In Experiment 2, differences in outcome variables between ingestion conditions (control vs. snake fruit jelly) were analyzed using two-way repeated measures analysis of variance (ANOVA). The Bonferroni post hoc test was employed for multiple comparisons, and results were further validated using paired (dependent) t-tests. All statistical analyses were performed using IBM SPSS Statistics for Windows (IBM Corp., Armonk, NY, USA). Data are presented as mean ± standard deviation, and a p-value of < 0.05 was considered statistically significant.

3. Results

3.1. Experiment 1

3.1.1. Participant characteristics

In Experiment 1, all 25 participants completed the study. Of these, 4 participants (16%) were male and 21 (84%) were female. The average age, height, BM, and BMI of the participants were 22.60 ± 3.33 years, 159.52 ± 7.12 cm, 52.89 ± 8.68 kg, and 20.64 ± 2.15 kg/m², respectively (Table 1).

Table 1.

Baseline physical and physiological characteristics of participants before participating in Experiment 1.

Characteristics	Mean ± SD	Minimum	Maximum
Sex (n, male – female)	4:21	–	–
Age (years)	22.60 ± 3.33	19	35
Height (cm)	159.52 ± 7.12	148	174
Body mass (kg)	52.89 ± 8.68	40.80	72.10
Body mass index (kg/m2)	20.64 ± 2.15	18.51	24.89
Heart rate (/min)	78.62 ± 12.52	56	97
Systolic blood pressure (mmHg)	103.02 ± 10.41	88	131
Diastolic blood pressure (mmHg)	66.30 ± 7.99	54	85

Data are presented as mean ± standard deviation (SD).

3.1.2. Blood glucose and incremental area under the blood glucose curve

Following control jelly ingestion, BG concentrations at T30 and T60 were significantly elevated compared to baseline (T0) (p < 0.001). A similar trend was observed after snake fruit jelly ingestion, with significant increases in BG at T30 and T60 relative to T0 (p < 0.001). When comparing between the two ingestion conditions, BG concentrations at T30 and T60 were significantly lower in the snake fruit jelly group compared to the control jelly group (T30: 124.12 ± 15.52 vs. 143.16 ± 20.98 mg/dL, p = 0.001; T60: 98.04 ± 11.24 vs. 110.72 ± 16.52 mg/dL, p = 0.003) (Figure 3A).

Figure 3.

Blood glucose (A) and incremental area under the blood glucose curve (iAUC) (B) at baseline and subsequently at 30, 60, 90, and 120 minutes post-ingestion following the ingestion of either control jelly or snake fruit jelly. *, p < 0.05 vs. baseline; ^#, p < 0.05 vs. control jelly.

Additionally, analysis of the incremental area under the BG curve (iAUC) showed that BG responses from T30 to T120 were significantly lower in the snake fruit jelly condition compared with the control jelly condition (T30: 453.00 ± 221.01 vs. 762.00 ± 268.96 mg/dL·min, p < 0.001; T60: 576.60 ± 625.06 vs. 1312.80 ± 622.59 mg/dL·min, p < 0.001; T90: 718.20 ± 1314.61 vs. 2019.00 ± 1220.04 mg/dL·min, p < 0.001; T120: 1332.60 ± 2754.74 vs. 3789.00 ± 2124.20 mg/dL·min, p = 0.001) (Figure 3B).

3.2. Experiment 2

3.2.1. Participant characteristics

In Experiment 2, 23 of the 25 enrolled participants (92%) completed the study, while 2 participants (8%) withdrew because they were unable to attend the second ingestion session. Of the 23 completers, 2 (8.7%) were male and 21 (91.3%) were female. Their mean age, height, BM, and BMI were 21.57 ± 1.88 years, 159.52 ± 7.12 cm, 53.26 ± 6.71 kg, and 20.86 ± 1.52 kg/m², respectively (Table 2).

Table 2.

Baseline physical and physiological characteristics of participants before participating in Experiment 2.

Characteristics	Mean ± SD	Minimum	Maximum
Sex (n, male – female)	2:21	–	–
Age (years)	21.57 ± 1.88	20	29
Height (cm)	159.52 ± 7.12	148	174
Body mass (kg)	53.26 ± 6.71	41	69
Body mass index (kg/m2)	20.86 ± 1.52	17.60	23.60
Heart rate (/min)	100.83 ± 12.96	69	120
Systolic blood pressure (mmHg)	110.48 ± 9.75	90	126
Diastolic blood pressure (mmHg)	68.57 ± 6.97	59	81
Oxygen saturation (%)	98.70 ± 1.02	96	100
Peak oxygen consumption (L/min)	1.00 ± 0.14	0.90	1.60
Maximum workload (watts)	58.91 ± 10.87	50	105
Workload at 60% VO2peak (watts)	35.35 ± 6.52	30	63

Data are presented as mean ± standard deviation (SD). VO2peak, peak oxygen consumption.

3.2.2. Endurance performance

Following ingestion of snake fruit jelly, participants demonstrated a significantly greater endurance time compared to the control jelly condition (33.37 ± 1.91 vs. 25.73 ± 1.71 minutes; p < 0.001) (Figure 4). Among the 23 participants, 19 individuals (82.61%) exhibited an improvement in endurance performance. The average percentage increase in endurance time was 35.27 ± 48.86%.

Figure 4.

Endurance time following the ingestion of either control jelly or snake fruit jelly. ^#, p < 0.05 vs. control jelly.

3.2.3. Blood glucose, insulin, and cortisol

Following control jelly ingestion, both BG and insulin concentrations were significantly elevated (p < 0.001). In contrast, these elevations were not observed after snake fruit jelly ingestion. Furthermore, post-exercise concentrations of BG (86.13 ± 13.83 vs. 101.22 ± 17.90 mg/dL; p = 0.003) and insulin (37.30 ± 25.49 vs. 68.30 ± 50.94 µU/mL; p = 0.010) were significantly lower in the snake fruit jelly condition compared to the control jelly condition (Figure 5). Cortisol concentrations were significantly reduced after ingestion of both jelly types (p < 0.001); however, there was no significant difference between the two conditions (p = 0.589).

Figure 5.

Blood glucose (A), insulin (B), and cortisol (C) concentrations at baseline (pre-exercise) and immediately post-exercise following the ingestion of either control jelly or snake fruit jelly. *, p < 0.05 vs. before endurance test; ^#, p < 0.05 vs. control jelly.

3.2.4. Antioxidant biomarker

SOD activity significantly increased following snake fruit jelly ingestion (p = 0.005), whereas no significant change was observed after control jelly ingestion (p = 0.746). Additionally, post-exercise SOD activity was significantly higher in the snake fruit jelly condition compared to the control jelly condition (47.30 ± 14.21% vs. 39.38 ± 9.05%; p = 0.041) (Figure 6).

Figure 6.

Blood superoxide dismutase (SOD) activity at baseline (pre-exercise) and immediately post-exercise following the ingestion of either control jelly or snake fruit jelly. *, p < 0.05 vs. before endurance test; ^#, p < 0.05 vs. control jelly.

3.2.5. Inflammatory cytokines

TNF-α concentration significantly decreased following snake fruit jelly ingestion (p = 0.004), whereas no significant change was observed after control jelly ingestion. Moreover, post-exercise TNF-α levels were significantly lower in the snake fruit jelly condition compared to the control jelly condition (0.94 ± 1.47 vs. 13.54 ± 12.47 pg/mg; p < 0.001) (Figure 7). In contrast, IFN-γ concentrations did not change significantly after ingestion of either jelly. No significant differences were observed between the two conditions.

Figure 7.

Blood tumor necrosis factor-alpha (TNF-α) (A) and interferon-gamma (IFN-γ) (B) concentrations at baseline (pre-exercise) and immediately post-exercise following the ingestion of either control jelly or snake fruit jelly. *, p < 0.05 vs. before endurance test; ^#, p < 0.05 vs. control jelly.

3.3. Snake fruit jelly powder constituents

GC-MS analysis revealed the presence of 17 phytochemical compounds in the snake fruit jelly powder, as illustrated in Figure 8. Among these, 5-hydroxymethylfurfural (RT 15.31 min) was the most abundant, with a peak area of 58.74%, followed by propanoic acid (RT 50.46 min, 10.34%), pyranone (RT 13.22 min, 4.80%), and 2,5-furandione (RT 6.55 min, 2.17%). Additionally, butanoic acid was detected at two retention times – RT 7.02 min (0.69%) and RT 7.36 min (0.58%) – along with hexadecanoic acid at RT 25.40 min (1.03%). These findings indicate that the snake fruit jelly powder contains a diverse range of bioactive phytochemicals, including organic acids, furanoids, and fatty acids.

Figure 8.

GC-MS chromatogram showing the chemical profile of snake fruit jelly powder. The analysis identified 17 major compounds, with 5-hydroxymethylfurfural being the most abundant.

4. Discussion

This study hypothesized that ingestion of snake fruit jelly – a novel ergogenic supplement – would enhance endurance performance by improving antioxidant status, modulating inflammatory responses, and optimizing metabolic parameters. The results support this hypothesis, demonstrating that acute ingestion of snake fruit jelly significantly improved endurance performance. These effects appear to be mediated, at least in part, through better regulation of BG, enhanced antioxidant activity, and reduced inflammatory responses.

Reactive oxygen species (ROS) are recognized contributors to premature muscular fatigue during sustained contractions and exercise. Skeletal muscle contains several endogenous sources of ROS, and their accumulation within active fibers impairs muscle function and promotes fatigue [20,21]. Accordingly, exogenous antioxidant supplementation has been proposed as a strategy to delay fatigue and enhance endurance performance [22]. Reid [20] further suggested that antioxidant therapy may be particularly beneficial for individuals prone to early fatigue. The benefits of antioxidant supplementation are thought to arise from improvements in cellular redox balance and reductions in oxidative damage to DNA, lipids, and proteins. Although snake fruit is well established for its antioxidant properties, its ergogenic potential in humans has remained unexplored. Nutritionally, snake fruit is a rich source of polyphenols, organic acids, vitamin C, and other bioactive compounds [23]. Vitamin C, the predominant antioxidant in plasma, modulates key enzymes such as nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and SOD [24]. Consistent with this, several studies have shown that acute vitamin C intake in various forms enhances antioxidant capacity and reduces oxidative stress [25–27].

Beyond oxidative stress, inflammation is increasingly recognized as an additional contributor to exercise-induced fatigue. The interplay between oxidative stress and inflammation – termed oxinflammation [28]—is particularly relevant, as inflammation can disrupt the balance between muscle protein synthesis and degradation. Proinflammatory cytokines such as TNF-α impair muscle function by suppressing muscle-specific expression of insulin-like growth factor 1 (IGF-1) [29]. Consequently, both oxidative stress biomarkers (e.g. antioxidant capacity) and inflammatory markers (e.g. TNF-α) are commonly used to evaluate muscle fatigue [30].

In this study, the reduction in TNF-α concentration following snake fruit jelly ingestion suggests that key constituents of the fruit – particularly vitamin C – may contribute to mitigating muscle inflammation and thereby enhancing endurance performance. These findings are in line with previous reports. For example, Nakhostin-Roohi et al. [31] demonstrated that supplementation with 1,000 mg of vitamin C attenuated exercise-induced lipid peroxidation and muscle damage after 30 minutes of endurance exercise at 75% VO₂max, although no significant effects on inflammatory markers were observed. More recent meta-analyses further support the anti-inflammatory potential of vitamin C, showing reductions in lipid peroxidation and IL-6 after acute exercise bouts [32]. In addition, combined supplementation with vitamins C and E has been shown to decrease post-exercise IL-6, cortisol, creatine kinase (CK), and lipid peroxidation [33].

The observed increase in SOD activity may also reflect adaptive responses triggered by exogenous antioxidants, which stimulate antioxidant enzyme expression. Supporting this, polyphenol supplementation has been shown to improve redox homeostasis and enhance skeletal muscle function [34], partly by activating the extracellular signal-regulated kinase/nuclear transcription factor erythroid 2–related factor 2 (ERK/Nrf2) signaling pathway. Another possibility is that exercise-induced antioxidant responses contributed to the effect, since SOD is most noticeably upregulated in oxidative muscle fibers (type I and type IIa), which are critical for endurance performance [35].

Importantly, the improvement in endurance performance occurred despite comparable total sugar content between the experimental and control jellies, suggesting that other bioactive compounds in snake fruit contributed to the ergogenic effect. Vitamin C, for example, is essential for carnitine biosynthesis, which supports fatty acid β-oxidation, and serves as a cofactor for catecholamine synthesis, thereby promoting carbohydrate oxidation and energy production during exercise [36]. Although the evidence for direct performance-enhancing effects of vitamin C remains mixed, several studies have reported reductions in muscle damage markers such as CK after intense exercise [37–39]. In addition, both conventional antioxidants (e.g. vitamins C and E, quercetin, resveratrol, α-lipoic acid) and targeted antioxidants (e.g. Mitoquinol) have been shown to support mitochondrial adaptations and improve circulation, potentially enhancing exercise capacity [12,40]. Vitamin A – also present in snake fruit – has further been implicated in regulating mitochondrial biogenesis and muscle fiber composition via the p38 MAPK – PGC-1α signaling pathway [41]. Enhanced mitochondrial biogenesis through PGC-1α activation, largely mediated by AMPK, improves endurance capacity, endothelial nitric oxide synthesis, and blood flow [12].

Overall, the effects of acute antioxidant supplementation on exercise-induced oxidative stress and physical performance appear to be context-dependent, influenced by factors such as dosage, timing, supplementation duration, exercise modality, participant fitness level, and baseline redox status [4]. Regarding dosage, Braakhuis [42] highlighted that high vitamin C intakes ( > 1 g/day) may impair performance by attenuating mitochondrial biogenesis, whereas more moderate intakes (~200 mg/day) – commonly obtained through fruit and vegetable consumption – are sufficient to reduce oxidative stress and promote health benefits without compromising training adaptations.

Phytochemical profiling further supports snake fruit’s ergogenic potential. Hlásná Čepková et al. [8] identified high total phenolic content (257.17 μg/mL), including chlorogenic acid, epicatechin, procyanidin B2, neochlorogenic acid, ferulic acid, quercetin, isoquercetin, and apigenin. Its antioxidant activity (10.56 μM Trolox/g of pulp) is comparable to that of black mulberry (Morus nigra L.). Chlorogenic acid, the most abundant phenolic compound, is a potent antioxidant that also inhibits α-amylase and α-glucosidase, enzymes critical to carbohydrate digestion and glucose absorption, thereby contributing to antidiabetic effects [43]. Chlorogenic acid has been shown to improve fasting BG, glucose tolerance, insulin secretion, and insulin sensitivity in both animal and human studies [44,45]. Mechanistically, it activates the Nrf2 pathway to strengthen antioxidant defenses and the AMPK pathway to regulate glucose and lipid metabolism [46], restoring expression of genes encoding enzymes such as SOD and glutathione peroxidase [47]. By stimulating AMPK, chlorogenic acid also promotes GLUT4 translocation, thereby enhancing glucose uptake and peripheral disposal [48].

Other polyphenols present in snake fruit, such as epicatechin, may provide additional cardiometabolic benefits. Dicks et al. [49] reported that epicatechin supports cardiovascular and metabolic function, while Cremonini et al. [50] found that epicatechin improved insulin sensitivity and glucose tolerance, likely by reducing oxidative stress and enhancing insulin signaling. Collectively, these bioactive compounds suggest that snake fruit exerts complementary antioxidant, anti-inflammatory, and insulin-sensitizing effects that synergistically regulate postprandial BG.

GC-MS analysis of snake fruit jelly powder identified 17 phytochemicals, including 5-hydroxymethylfurfural (5-HMF). 5-HMF exhibits antioxidant, anti-allergenic, and cytoprotective effects, and has been reported to suppress oxidative stress and the expression of JNK2/3 and IL-8 induced by hyperglycemia [51]. In animal models simulating low-pressure, oxidative-stress conditions, 5-HMF reduced muscle superoxide production, prevented declines in isometric force, enhanced mitochondrial fusion, and preserved mitochondrial membrane potential [52]. When acting in combination with other phytochemicals detected in snake fruit jelly (e.g. propanoic acid, pyranone, butanoic acid), 5-HMF may contribute to glycemic control and ergogenic properties. However, since 5-HMF is also a common byproduct of heating carbohydrate-rich foods, its true bioactivity in this context remains uncertain.

In Experiment 2, post-exercise insulin levels increased in both the snake fruit jelly and placebo trials, reflecting the physiological need to replenish glycogen stores after exercise [53]. Notably, insulin levels were significantly lower following snake fruit jelly ingestion compared with placebo, suggesting improved insulin sensitivity or reduced insulin demand. Beyond chlorogenic acid, epicatechin may also contribute to this effect, as it has been shown to lower BG and fasting insulin by enhancing insulin sensitivity [54] and inhibiting α-glucosidase [55]. These findings indicate that multiple phenolic compounds in snake fruit may act synergistically to improve glycemic control and metabolic efficiency, thereby supporting endurance performance.

Another mechanism underlying these effects may involve vitamin C. Plasma vitamin C has been proposed to enhance insulin sensitivity by facilitating nonoxidative glucose metabolism [56], which could partly explain the improvements in BG regulation and metabolic efficiency observed in this study. Although the evidence on vitamin C’s role in BG regulation is mixed [57–60], several studies support its potential benefits. Structurally, vitamin C resembles glucose and can substitute for it in certain biochemical reactions [61], enabling it to scavenge free radicals generated during postprandial hyperglycemia and exhaustive exercise [62,63].

Finally, with regard to cortisol, post-exercise levels were attenuated in both experimental and control conditions. Exercise at intensities above ~60% VO₂peak typically activates the hypothalamic – pituitary – adrenal axis, eliciting a cortisol response proportional to exercise intensity. Because participants exercised at 60% VO₂peak, this intensity may not have been sufficient to trigger a cortisol rise, possibly explaining the observed post-exercise decreases [64]. These results are consistent with studies reporting decreased cortisol immediately after exercise and lasting up to 1–2 hours [65–67]. However, conflicting evidence suggests that cortisol responses depend not only on intensity but also on methodological factors such as blood sampling time and measurement techniques [68].

This study has several limitations that should be acknowledged. First, blood vitamin C levels were not measured, limiting our ability to directly attribute the observed changes in antioxidant, inflammatory, and metabolic parameters – as well as endurance performance – to the bioactive compounds in snake fruit jelly. Second, insulin concentrations were not assessed in Experiment 1 due to resource limitations and a focus on readily measurable outcomes. Although BG data may indirectly reflect insulin action, as insulin sensitivity and secretion can sometimes be estimated from parameters such as fasting BG or oral glucose tolerance tests [69], the absence of insulin data restricts a more comprehensive understanding of the jelly’s effects on BG regulation, particularly in relation to type 2 diabetes mellitus. Third, Experiment 2 did not include measurements of muscle damage markers (e.g. CK, myoglobin, or blood urea nitrogen), which prevented a clearer interpretation of the mechanistic links among oxidative stress, inflammation, muscle damage, and endurance performance. Fourth, due to the complexity of snake fruit components, the control jelly could only mimic one main feature – the sugar content – relevant to the key outcomes. No dietary fibers or bulking agents were added to reproduce the physical properties of snake fruit jelly. As such, the absence of other phytochemicals and properties (e.g. soluble and insoluble fibers, organic acids, viscosity, taste, and appearance) that may also influence glycemic or ergogenic responses limits the completeness of our interpretation. Lastly, the sex distribution of participants was unbalanced, with a predominance of female participants in both experiments (21 vs. 4 in Experiment 1; 21 vs. 2 in Experiment 2). Given that sex-related differences are known to influence metabolism and inflammation in the context of exercise and nutrition [70,71], this imbalance should be considered when interpreting the findings.

Future research should address these limitations by incorporating measurements of blood vitamin C, insulin levels in glycemic studies, and muscle damage biomarkers in exercise protocols. Given the sex imbalance in the present study, the findings are most applicable to healthy, sedentary young women; further investigations in male participants are needed to confirm sex-specific responses. As this study investigated only a single ingestion, future research should examine the effects of long-term consumption at optimal dosages in both athletic populations and individuals with type 2 diabetes, thereby providing deeper insights into the potential of snake fruit jelly as an ergogenic aid and functional food in clinical nutrition. In addition, future trials should refine the formulation of the control jelly to more closely match the biochemical and physical properties of snake fruit jelly – by incorporating dietary fibers, bulking agents, or organic acids, and by adjusting viscosity, taste, and appearance – in order to more accurately isolate the bioactive effects of snake fruit constituents and minimize potential bias.

5. Conclusions

Acute ingestion of snake fruit jelly significantly improves glycemic control and endurance performance in healthy sedentary young adults. These effects may be attributed to enhanced antioxidant defense (as indicated by increased SOD activity), reduced inflammatory responses (evidenced by lower TNF-α levels), and improved metabolic regulation (reflected in reduced BG and insulin concentrations) following endurance exercise. Collectively, these findings highlight the potential of snake fruit jelly as a novel ergogenic aid and suggest its applicability as a functional supplement to support exercise performance and recovery in physically active individuals and athletes.

Funding Statement

This research was funded by the Burapha University (BUU); the Thailand Science Research and Innovation (TSRI); and the National Science Research and Innovation Fund (NSRF) (Fundamental Fund 2023), grant number [31/2566].

Author contributions

Conceptualization, P.P. and M.T.; methodology, P.P.; software, P.P.; validation, P.P.; formal analysis, P.P.; investigation, P.P., O.B., P.C., T.P., Y.T., and S.K.; resources, P.P.; data curation, O.B.; writing – original draft preparation, P.P. and O.B.; writing – review and editing, P.P. and O.B.; visualization, P.P.; supervision, P.P.; project administration, P.P.; funding acquisition, P.P., O.B., P.C., and M.T. All authors have read and agreed to the published version of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data are available upon request from the corresponding author.

Ethical statement

This study was conducted in accordance with the Declaration of Helsinki, and approved by the Institutional Review Board of Burapha University (approval number IRB1-028/2566, approval date 20 March 2023).