After the recent blog on "Pomegranate and Blood Glucose Control" was posted, I got asked by a friend if dragon fruit may have any benefits for blood glucose control. This friend suggested that I could write a blog series about nutritional foods related to glycemic control.

 

    Dragon fruit, also known as pitaya, is mainly cultivated in East and Southeast Asia, Central and South America, and northern Australia. The name of 'dragon fruit' in Asia is coming from the large green or red scales these medium-large berries are bearing. There are several varieties of pitaya fruit: red skin white flesh, red skin red flesh, and yellow skin white flesh.

 

    Dragon fruit is a good source of bioactive nutrients. The fruit flesh contains glucose and fructose, some oligosaccharides, and dietary fiber. It also contains plant pigments such as betacyanin (a red-colored pigment), lycopene, and β-carotene.  The fruit is a good source of vitamins such as vitamin E and C, and minerals like calcium and phosphorous. Many health benefits of dragon fruit have been reported, such as antioxidant, antimicrobial, anticancer, and antidiabetic effects (1).

 

    One meta-analysis paper looked at the effect of dragon fruit on glycemic control in pre-diabetic and type-2 diabetic people. From 401 studies identified from the literature search, only 4 randomized controlled trials involving 36 prediabetes subjects and 109 type-2 diabetes patients were selected in the analysis. In prediabetes, fasting plasma glucose reduction was significant with mean difference of -15.1 mg/dL (range: -23.8 to -6.5 mg/dL, P = 0.0006). Meta-analysis in type-2 diabetes showed no effect of dragon fruit on fasting plasma glucose (mean difference -26.5 mg/dL, range: -72.6 mg/dL to 19.6 mg/dL) and in 2 hours post-prandial glucose (mean difference -30.5 mg/dL, range: -80.9 mg/dL to 19.9 mg/dL); however, there was a trend towards greater glucose reduction achieved with higher dose since estimated treatment effect became greater with the higher dose (2).

 

    Since this meta-analysis paper (2) only included 4 studies, I decided to take a closer read at each of them. Two out of the 4 studies included were master or Ph.D. student dissertations, which are not peer-reviewed publications, so the values of their findings became somewhat in question. One of the remaining two published papers was published in a different language than English and I could not find it through an internet search. The only publication that could be found was the study done by Hadi et al. (3).

 

    Hadi et al. (3) studied the effects of red pitaya fruit (with red flesh) consumption on blood glucose level and lipid profile in type 2 diabetic subjects. A total of 28 subjects (14 males and 14 females; 21 diabetic subjects, and 7 healthy subjects) were randomly assigned into four treatment groups (n=7 per group). Group 1: diabetic patients were given 400 g of red pitaya per day; Group 2: diabetic patients were given 600 g of red pitaya per day; Group 3 (negative control): diabetic patients were given a normal diet; Group 4 (positive control): healthy subjects were given a normal diet. The seven-week study consisted of three phases: phase 1: one week of control phase, phase 2: 4 weeks of treatment, and phase 3: 2 weeks of wash-out. After four weeks of treatment, Group 1 showed a significant increase in HDL-cholesterol level (+3%) and significant decreases in blood glucose (-24%), LDL-cholesterol (-39%), and triglyceride (-37%) levels. Even though there was no statistically significant difference in Group 2, there was still an increasing trend in HDL-cholesterol level (+15%) and a decreasing trend in blood glucose (-35%), total cholesterol (-32%), triglyceride (-29%), and LDL-cholesterol (-41%) levels, with a higher percentage of changes than Group 1.

 

    The authors (3) postulated that the glucose-lowering and lipid-lowering effect observed in the study as a result of higher dietary fiber content from the red pitaya fruit. Since the soluble fibers absorb water, then forming viscous solutions in the digestive tract that slow the rate at which nutrients (such as glucose and lipids) would be absorbed. In this study, eating 400 g and 600 g red pitaya was almost equal to the intake of 40.4 g and 60.6 g fiber/day, respectively (10.1g fiber per 100g edible portion).

 

    Dietary fiber, particularly soluble type, is capable of trapping cholesterol and bile acids in the small intestine. The gel matrix formed by soluble fibers that are excreted in the feces may entrap some of the bile acids released from the gallbladder. This physical entrapment could prevent bile acids from being reabsorbed. Thus, the liver then has to use cholesterol from the blood to synthesize new bile acids, which may result in reducing blood cholesterol levels. The soluble fiber in red pitaya could be one of the factors in controlling and reducing both glucose and LDL-cholesterol among type 2 diabetic patients (3).

 

    Despite similar fiber contents between red and white pitaya, red pitaya had 2-4 times higher antioxidant activities than those of white pitaya (4). Even though the antioxidant capacity of white dragon fruit was found lower than that of the red dragon fruit, the white dragon fruit also seemed to offer some glucose-lowering effects. Song et al. (5) evaluated the effects of white pitaya juice on obesity-related metabolic disorders like insulin resistance. The mice were fed a high-fat diet to induce obesity. Insulin resistance developed because of obesity could be reduced as proved by decreased fasting serum glucose and insulin levels in mice treated with white pitaya.

 

    The initial glucose and lipid levels in Group 1 subjects were much lower than those in Group 2 subjects in Hadi’s study (3). The subjects in Group 2 perhaps had more advanced diabetic conditions, and with more insulin resistance. Despite the differences in the initial glucose and lipid levels, the red dragon fruit intake at 400 g or 600 g per day for four weeks resulted in relatively large glucose and lipid-lowering effects in both diabetic subject groups (3).

 

    No published paper compared the glucose-lowering effects between dragon fruits with red or white flesh in people with diabetes. I wish that there are more papers published on the dragon fruit's effects on glucose control. I would tell my friend that dragon fruit may have some glucose control benefits but supporting evidence is limited. Try to eat some dragon fruit every day for a few weeks and see if it may lower glucose levels.

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    Many of the plant pigments and bio-actives have nutraceutical benefits. You can find more information on healthy foods that can help with blood glucose management, such as Anthocyanins (Purple Foods) for Glucose Control, Ginger's Benefit of Lowering Glucose, Adding Milk to Breakfast for Glucose Management, and Eating More Leafy Greens (Vitamin K) for Diabetes Prevention.

 

References:

1. Joshi, M., Prabhakar, B. (2020). Phytoconstituents and pharmaco‐therapeutic benefits of pitaya: A wonder fruit. Journal of Food Biochemistry, 44(7):e13260.

2. Poolsup, N., Suksomboon, N., & Paw, N. J. (2017). Effect of dragon fruit on glycemic control in prediabetes and type 2 diabetes: A systematic review and meta-analysis. PLOS ONE, 12(9), e0184577.

3. Hadi NA, Mohamad M, Rohin MAK, Yusof RM. (2012). Effects of Red pitaya fruit (Hylocereus polyrhizus) consumption on blood glucose level and lipid profile in type 2 diabetic subjects. Borneo Science, 31:113–29.

4. Mahattanatawee, K., Manthey, J. A., Luzio, G., Talcott, S. T., Goodner, K., & Baldwin, E. A. (2006). Total Antioxidant Activity and Fiber Content of Select Florida-Grown Tropical Fruits. Journal of Agricultural and Food Chemistry, 54(19), 7355–7363.

5. Song, H., Zheng, Z., Wu, J., Lai, J., Chu, Q., Zheng, X. (2016) White Pitaya (Hylocereus undatus) Juice Attenuates Insulin Resistance and Hepatic Steatosis in Diet-Induced Obese Mice. PLoS ONE 11(2): e0149670.