Effects of Daily Ingestion of Two SunGold Kiwifruit for 6 Weeks on Metabolic and Inflammatory Biomarkers: A Randomized, Cross-Over, Exploratory Intervention Study

Abstract

Kiwifruit contain many components, some considered beneficial, such as vitamins, phytochemicals and dietary fibre, and others potentially harmful, such as fructose and glucose in fruit sugars. In a 6-week, randomised, crossover study aimed at exploring the net effects of daily consumption of kiwifruit, 23 healthy participants consumed two Actinidia chinensis var. chinensis 'Zesy002' (marketed as Zespri™ SunGold™ Kiwifruit) per day as part of their customary diet (intervention) or without kiwifruit (control) as their customary diet for 6 weeks in a cross-over study. Anthropometric data, venous blood, and urine samples were collected at the start and end of the 6-week intervention and control periods for the measurement of physical changes, plasma glucose, insulin, glycated haemoglobin, short-chain fatty acids, blood lipids, uric acid, inflammatory biomarkers, and urinary ascorbic acid. Variables were measured between the start and finish of interventions, and between intervention and control periods. Food diaries were completed on the 3 days before blood sampling to estimate dietary ascorbic acid and dietary fibre intakes. Despite urinary vitamin C and food diaries indicating compliance, and good precision in measurements, there were no appreciable changes in biomarkers during the study, either within or between intervention and control periods, that would indicate a change in health status. Thus, the sizes of any effects of kiwifruit ingestion were too small to become significant under the test conditions used, indicating a high probability that daily ingestion of two SunGold kiwifruit is safe with respect to metabolic health.

Keywords: C-reactive protein; inflammation; kiwifruit; metabolic health; plasma lipids; plasma short-chain fatty acids; vitamin C.

Figure A1

Variables measured in 6-week kiwifruit intervention study (non-bold in boxes) and their relationship with possible physiological and metabolic effects of kiwifruit components (bold, unboxed). Abbreviations: AGE, advanced glycation end product; BMI, body mass index; BP, blood pressure; CRP, C-reactive protein; CVD, cardiovascular disease; RAGE, AGE receptor; HbA1c, glycated haemoglobin; HDL, high density lipoprotein, LDL, low density lipoprotein; IL-6, interleukin 6.

Figure A2

Two SunGold kiwifruit (200 g) alone had a moderate effect size, raising blood glucose concentrations significantly above baseline in healthy participants fed at breakfast time after an overnight fast (p < 0.001, n = 21). Means ± SEM. Points significantly higher than baseline are shown with an asterisk (LSD 0.38; Dunnett’s test). Blood glucose concentrations were monitored by capillary finger-prick analysis.

Figure A3

CONSORT diagram for the cross-over study of the effects of daily kiwifruit ingestion (intervention) compared with no-kiwifruit ingestion (control).

Figure A4

Change in daily ascorbic acid intake as a result of consuming two SunGold kiwifruit per day, compared with customary diet excluding kiwifruit, assessed for each participant who completed 3-day food diaries. Kiwifruit and control group comparison of means is in Table 2.

Figure A5

Urinary ascorbic acid concentration at end of kiwifruit intervention (+KF) and control (−KF) periods of the trial were significantly different (p = 0.033) (Means ± sem).

Figure A6

Plasma ascorbic acid concentrations at the end of no kiwifruit (−KF) and kiwifruit (+KF) interventions. BL = baseline, BL2 = baseline during crossover, WO = washout. Corresponding to periods A, B, C, D, and E in Figure 1. There were no statistically significant differences (p > 0.05) between treatments. (Means ± SD).

Figure A7

Change in daily dietary fibre intake as a result of consuming two SunGold kiwifruit per day, compared with customary diet with kiwifruit excluded, assessed from all participants who completed 3-day food diaries. Mean daily dietary fibre intake was 32 ± 2.3 g/day.

Figure A8

Plasma short-chain fatty acids (SCFA) at the end of different stages of long-term crossover study: A: LI = lead-in; B: +KF = first kiwifruit intervention arm; B: −KF = first control group arm; C: WO = wash out at crossover, all participants; D: +KF = second kiwifruit intervention arm; D: −KF = second control group arm; E: FU = post-trial follow up with all participants (Means ± SD). Differences between treatments were not statistically significant (p > 0.05).

Figure A9

Total plasma short-chain fatty acids (SCFA) measured as the sum of acetic, propionic, butyric and isovaleric acids (Figure A5) (Means ± SD).

Figure 1

Design of crossover study of the effects of ingesting two kiwifruit per day for 6 weeks. BMI = body mass index.

Figure 2

Intakes of vitamin C during the kiwifruit intervention and control periods for each participant based on 3-day food diaries.