The reported role of citrulline which is present in small concentrations in Water Melon ( Citrullus lanatus) in fighting obesity has some interesting implications. This fruit finding mention in Egyptian history almost 5000 years ago has suddenly shot into fame because of some heath attributes assigned to it by a recent scientific study. Considered as a native of South America, Water Melon has a special type of fruit known as a pepo with thick rind (exocarp) and a fleshy center (mesocarp and endocarp), derived from an inferior ovary which is characteristic of the cucurbitaceae family. It is puzzling as to how this crop with 92% water can be an effective fighter against over weight syndrome in human beings. What ever be the active principle that may be responsible for the claimed advantages of consuming this fruit must be present in small concentrations.
100 g of edible portion of the fruit has about 6-7% sugar, 0.4% dietary fiber, vitamins and minerals providing 1-4% of RDA except for Vitamin C estimated at 8 mg (14% of RDA). Though it is claimed that Water Melon is rich in Citrulline one of the 20 amino acids of biological significance, the effective concentration does not exceed 150 mg per 100 g. Citrulline is converted in the body to Arginine which is supposed to be active principle that is implicated in some of the beneficial effects attributed to Water Melon. Arginine is one of the essential amino acids human body is incapable of making it on its own depending on supply through the diet. This chemical, first isolated in 1886 by Swiss scientist Ernst Schultze, is a 4-carbon aliphatic straight chain amino acid and plays important role in many body functions including cell division, healing wounds, removal of Ammonia from the body, maintaining immune functions and release of hormones. There is still some doubt regarding the essentiality of Arginine as body is known to synthesize this amino acid to a limited extent not considered adequate to meet the demand. But for growing infants it is an essential nutrient as they are not equipped to make the same during early stages of development.
Arginine is considered a precursor to nitric oxide which is known to help boost blood vessel dilation and consequently preventing blood pressure built up. Same principle is cited to suggest Arginine as an intervention agent in erectile dysfunction disabilities though no conclusive scientific evidence has been forthcoming except for indirect deductions. Dietary Arginine was also found to reduce serum concentration of branched chain amino acids which are known to cause insulin resistance in obese individuals. How come it can fight obesity itself? According some published scientific published works, if diets are supplemented with Arginine, it shifts 'nutrient partitioning' to promote skeleton-muscle growth and preempts body fat gains by as much as 65% in studies on mice. Whether same results will hold good remains to be seen by clinical trials with human subjects. How ever any dietary supplementation will have to keep in mind the some of the adverse consequences of arginine on some people as reported from some quarters. These include increased risk of heart diseases, altering Potassium levels in the blood, upsetting electrolyte balance, tendency to elevate blood sugar levels, lowering of BP and causing indigestion, nausea and head ache.
Some of the good food sources of Arginine include Sea foods, meat, nuts, algae, soy protein isolate, dairy foods, wheat germ, oat meal, sesame, sunflower seed, pumpkin seed, chick peas, etc. Water Melon obviously does not figure in the above list probably because Arginine is present in this fruit in the form of Citrulline. It is a debatable point whether Water Melon which is more than 90% water or comparatively drier sources like nuts and seeds would be a better option if the benefits of arginine are to be tapped for better health. For example sesame seeds contain more than 4000 mg of Arginine per a 200 kC serving size ( about 40 g) or 3800 mg from peanuts (40 g) while a Water Melon can yield only 1200 mg from more than 1 kg of edible portion. The only difference is that in Water Melon has the precursor Citrulline rather than in the form of Arginine itself and whether this confers any special benefit is not yet known.