. Watermelon (Obesity Management and Anti-Diabetic )

 3. Watermelon as a Functional Food in Obesity Management and Anti-Diabetic Snack

Obesity is an alarming public health issue worldwide which is linked to crucial metabolic ailments including diabetes and lifestyle-related diseases. Modern lifestyle and un-healthy food habits including several fast foods and processed food with higher levels of sugar in routine diet are major contributing factors for obesity. According to the National Diabetics Statistics Report (2020) published by Centers for Disease Control and Prevention (CDC), 45.8% of adults in USA are obese, among which 10.5% of the population suffer with diabetes [33]. Diabetes can be classified into two types (1 and 2) depending on the etio-pathogenesis. Type 1 diabetes is characterized by the destruction of pancreatic B cells due to the autoimmune response of the body leading to the insulin deficiency, whereas type 2, the most common form of diabetes involving resistance to insulin [34]. The chronic hyperglycemia resulting from the diabetes leads to retinopathy, neuropathy, nephropathy, peripheral vascular diseases, cerebrovascular diseases, and ischemic heart diseases [35,36,37]. However, the oxidative stress level and inflammatory responses in the body play a vital role in the development of the abovementioned complications.

The prominent symptom of non-insulin-dependent diabetes is the reduction in endothelial NO synthesis and bioavailability, increase in glucose concentration in plasma, free fatty acid, homocysteine, and methylarginines [38]. Numerous studies suggest that the regulation of energy substrate oxidation, sensitivity to insulin and hemodynamics are influenced by NO in humans [24]. For the synthesis of NO, l-arginine acts as the precursor which is converted by tetrahydrobiopetrin (BH4)-dependent NO synthase [9]. Based on the results of various in vivo and in vitro studies, it has been demonstrated that the dietary intake of l-arginine decreased the glucose level in diabetic and obese rats [39,40,41]. In addition, the l-arginine enhanced the vascular reactivity in animal models [38,42,43] and hypercholesterol patients [44]. Thus, owing to the numerous health benefits of l-arginine, it has been recommended to alleviate the risk of obesity and diabetes. However, direct intake of l-arginine displayed gastro-intestinal problems therefore diets enriched with l-arginine have become the alternative.

Consumption of watermelon significantly increased the plasma l-arginine levels. According to Wu et al. [12], supplementation of watermelon juice in Zucker diabetic fatty rats (a widely used animal model for non-insulin dependent diabetes) elevated the l-arginine levels, decreased the amount of glucose, free fatty acid, homocysteine, and methylarginines [12]. On the other hand, it enhanced the activity of GTP cyclohydroxylase-1 and tetrahydrobiopterin levels in heart and acetylcholine-mediated vascular relaxation. In addition, Wu et al. [12] recommended the consumption of watermelon pomace juice as a functional food to combat diabetes and obesity based on their results in animal models.

In humans, the oral administration of watermelon juice can act as an effective alternative for the supplementation of arginine. Watermelon juice effectively aided in the regulation of whole body metabolism, and enhanced the cardiovascular and immune response in humans. A study by Figueroa et al. [45] in obese middle-aged adults with pre-hypertension revealed that the watermelon intake improved the arterial function and reduced the ankle blood pressure, brachial blood pressure, and carotid wave reflection. Similarly, consumption of watermelon elicited the satiety response, and reduced the body weight, body mass index (BMI), and waist to hip ratio in obese adults. Furthermore, Lum et al. [46] suggested that watermelon can effectively reduce the appetite and aid in the weight management on comparison to the conventional refined carbohydrate snacks.