Claims of Multiple Health Benefits of Papaya

The following lengthy and unedited article written by an unknown person was sent to me by Ir. CK Cheong via e-mail for my comment.

“Papaya was the only studied food found to halt breast cancer

Scientists studied 14 plant foods commonly consumed in Mexico to determine their ability to halt breast cancer cell growth. These included avocado, black sapote, fuava, mango, prickly pear cactus (nopal), pineapple, grapes, tomato, and papaya. They also evaluated beta-carotene, total plant phenolics, and gallic acid contents and antioxidant capacity. They found that only papaya had a significant effect on stopping breast cancer cell growth. (International Journal of Food Science and Nutrition, May)

Papaya is a store-house of cancer fighting lycopene

The intense orangey-pink color of papaya means it is chock full of cancer fighting carotenoids. Not only beta carotene, but lycopene is found in abundance. The construction of lycopene makes it highly reactive toward oxygen and free radicals. Scientists at the University of Illinois think this anti-oxidant activity contributes to its effectiveness as a cancer fighting agent. Epidemiological studies have indicated an inverse relationship between lycopene intake and prostate cancer risk. They showed that oral lycopene is highly bioavailable, accumulates in prostate tissue, and is localized in the nucleus of prostate epithelial cells.

In addition to antioxidant activity, other experiments have indicated that lycopene induces cancer cell death, anti-metastatic activity, and the up-regulation of protective enzymes. Phase I and II studies have established the safety of lycopene supplementation. (Cancer Letter, October 8, 2008)

Prostate cancer was the subject of a study in Australia that looked at 130 prostate cancer patients and 274 hospitalized controls. The scientists found that men who consumed the most lycopene-rich fruits and vegetables such as papaya were 82% less likely to have prostate cancer. In this study, green tea also exerted a powerf! ul anti-cancer effect. When lycopene-rich foods were consumed with green tea, the combination was even more effective, an outcome the researchers credited to their synergy. (Asia Pacific Journal of Clinical Nutrition, 2007)

Isothiocyanates found in papaya restore the cell cycle to eliminate cancer

Organo-sulfur compounds called isothiocyanates are found in papaya. In animal experiments, isothiocyanates protected against cancers of the breast, lung, colon pancreas, and prostate, as well as leukemia, and they have the potential to prevent cancer in humans. Isothiocyanates have shown themselves capable of inhibiting both the formation and development of cancer cells through multiple pathways and mechanisms. (International Journal of Oncology), October, 2008)

Researchers in Japan clarified the mechanisms of action in a type of isothiocyanate found in papaya known as BITC that underlies the relationship between cell cycle regulation and appropriate cell death. When cancerous cells die on schedule, they are no longer a problem. The researchers established that BITC exerted cancer cell killing effects that were greater in the proliferating cells than in the quiescent cells. Cancer cells that are proliferating are much more dangerous than cancer cells that are in a state of dormancy. (Forum of Nutrition, 2009)

Enzymes from papaya digest proteins including those that protect tumors

The fruit and other parts of the papaya tree, also known as the paw paw tree, contain papain and chymopapain, powerful proteolytic enzymes that facilitate chemical reactions in the body. They promote digestion by helping to break down proteins from food into amino acids that can be recombined to produce protein useable by humans. Proteolytic enzymes protect the body from inflammation and help heal burns. They do a good job of digesting unwanted scar tissue both on the skin and under its surface.

Research has shown that the physical an! d mental health of people is highly dependent on their ability to produce proteins they can use effectively. However, as people age, they produce less of the enzymes needed to effectively digest proteins from food and free needed amino acids. They are left with excessive amounts of undigested protein which can lead to overgrowth of unwanted bacteria in the intestinal tract, and a lack of available amino acids.

Eating papaya after a meal promotes digestion, and helps prevent bloating, gas production, and indigestion. It is quite helpful after antibiotic use to replenish friendly intestinal bacteria that were the casualties in the war against the unwanted bacteria. When the intestinal tract is well populated with friendly bacteria, the immune system is strengthened, and can better protect against flu and cancer.

Being a proteolytic enzyme, papain is able to destroy intestinal parasites, which are composed mostly of protein. To rid the body of intestinal parasites, half a cup of papaya juice can be alternated each hour for twelve consecutive hours with the same amount of cucumber or green bean juice.

Papaya contains fibrin, another useful compound not readily found in the plant kingdom. Fibrin reduces the risk of blood clots and improves the quality of blood cells, optimizing the ability of blood to flow through the circulatory system. Fibrin is also important in preventing stokes. Proteolytic enzymes containing fibrin are a good idea for long plane rides to minimize the potential of blood clots in the legs. People who sit at a desk all day might want to use proteolytic enzymes too.

Proteolytic enzymes are able to digest and destroy the defense shields of viruses, tumors, allergens, yeasts, and various forms of fungus. Once the shield is destroyed, tumors and invading organisms are extremely vulnerable and easily taken care of by the immune system.

Undigested proteins can penetrate the gut and wind up in the bloodstream where they are treated by the immune system as invaders. If too many undigested proteins are floating around, the immune system becomes overburdened and unable to attend to the other tasks it was meant to do. Proteolytic enzymes can digest these rogue proteins, freeing up the immune system.” (End of article)

Dear Dr Lim,

You are the only source of medical expert.

I heartily look up for professional advice other than my own brother-in-law who is a G P.

What is you expert opinion on this issue. Could this be a fake?

Warmest regards,

C K Cheong


Dear Ir. Cheong,

Thank you for your e-mail seeking my advice.

Correct! Most of the claims about papaya are reasonable, but a lot are still in the hypo-theoretical stage. Most of them seem scientifically reasonable based on our current knowledge on the nutritive, prophylactic values of papaya.

Nutraceutical and biological effects of some of the active ingredients such as lycopenes and the carotenoids need further study and evaluation. It is true for instance that lycopenes have been demonstrated in a number of studies as a prophylaxis (prevention) against prostate cancers. However, there are vegetables like tomatoes that are richer in lycopenes (a class of carotenoids) than in papaya. Of course I do understand that the subject in discussion was on papaya, and not on tomatoes or other fruits and vegetables.

However, I am unaware if papaya contains isothiocyanates as claimed in the article. This active principle is quite pungent as in mustard where isothiocyanates are present in abundance. If this is present in papaya, it would give papaya quite a pungent taste like mustard. But papaya does not have pungent mustard-like taste. So we need to study this carefully and analyze the phytochemicals present before we support this claim

Papain:

Papaya does contain a proteolytic enzyme called papain. This enzyme specifically cleaves the peptide covalent bonds between certain types of amino acids in a protein polymer (protein chain). In simple words, it helps to break down proteins and helps in the digestion of proteins.

Papaya contains fibrin?

However, I am not too happy by the statement that it also contains fibrin. This is actually a fibrous protein involved in the clotting mechanism of blood. In a slightly more technical language, this means it contains a fibrillar protein that is joined up (polymerized) to form a kind of mesh-work so that it forms a haemostatic plug or a blood clot in conjunction with thrombocytes or platelets (non-cellular fragments) over a wound site.

In very simple English, this simply means papaya contains a substance called ‘fibrin’ (as claimed in that article) which actually promotes blood clot. Our question is, how is it possible for papaya to contain an enzyme called papain that dissolves a protein clot, and at the same time contains fibrin that promotes a protein clot?

The article clearly says that ‘fibrin is also important in preventing strokes.’ This is just the opposite. A stroke or medically called cerebral vascular accident (CVA) is primarily caused by either a blood clot in one of the cerebral vessels in the brain, or its rapture – both compromising blood and oxygen perfusion to the brain.

Contradictory claims:

Thus you can clearly see that article contradict itself by saying that it contains a proteolytic enzyme (papain) that can dissolve a clot, but at the same time it claims to contain a fibrin that actually promotes a blood clot. To make the statement worse, it states there in red lettering ‘fibrin is also important in preventing stokes’. The author actually does not know what he was talking about. He was actually contradicting himself.

The clotting process essentially involves the conversion of a soluble plasma protein, fibrinogen, into strands of the insoluble protein fibrin, which forms a mesh that traps platelets

The situation would have been the reverse had the author the above claimed that papaya contains an anti-fibrin factor that prevents the clotting of blood that causes stroke or deep vein thrombosis (DVT). Such substances would be called fibrinolytic agents or anti-thrombotic substances that promote fibrinolysis, meaning it breaks down a clot or the fibrin. But the author did not. He clearly said in the above attached article that it contain a fibrin which is a protein clot itself. He even emphasized the word ‘fibrin’ in red lettering. Clearly he does not understand clinical biochemistry well and hence contradicted himself.

Normally in a normal physiologically induced thrombosis, this is counterbalanced by intrinsic antithrombotic properties and fibrinolysis. Fibrinolysis means, it is a process wherein a fibrin clot, the product of coagulation, is broken down. Its main fibrinolytic enzyme plasmin cuts the fibrin mesh at various places, leading to the production of circulating fragments that are cleared by other proteases or by the kidney and liver.

There are at least two questionable things we need to ask here.

Firstly:

Even if papaya contains an anti-coagulating (anti-thombocytic, anti-platelet aggregating, anti-fibrinogen or anti-fibrin substance(s) as he claimed, I suspect it will be at very low concentration to have any physiological effect against DVT or as a prophylaxis against stroke.

Secondly:

Even these substances are present in papaya; I doubt it would be effective if taken orally. Most of these anti-fibrinogens are protein in nature, and if taken orally as when we eat a papaya, the protein-digesting intestinal juices, the proteases from the pancreas will instantly destroy any proteins, including the soluble fibrinogen, insoluble fibrin or any fibrinolytic agent that is of protein in nature, rendering it biologically inactive. Even in the stomach, the proteins are already beginning to be broken down by the gastric juices the stomach is broken down by the action of the gastric juice containing hydrochloric acid and a protein-digesting enzyme called pepsin.

An example of a fibrinolytic factor which is a protein is obtained from certain giant leeches like Haementeria ghilianii. The anti-clotting proteins from this leech have molecular weights under about 100,000, and are isolated from the salivary glands of H. ghilianii. When a leech bites, the anti-coagulant goes directly into site of the bite. It will not be effective if it is taken orally like eating a papaya.

Such substances need to be injected directly into the blood stream to bypass the destructive actions of the digestive juices.

For instance, there are three major classes of fibrinolytic drugs: tissue plasminogen activator (tPA), streptokinase (SK), and urokinase (UK). While drugs in these three classes all have the ability to effectively dissolve blood clots, they differ in their detailed mechanisms in ways that alter their selectivity for fibrin clots. But none of these clot-buster drugs can be given orally. They need to administered via intra-venous route

Thirdly:

Even if papaya contains an fibrinolytic substance as claimed, it cannot exist inside the papaya in the original form per sec because the papaya itself has papain, a proteolytic enzyme that will destroy the anti-fibrin principles, unless it occurs in the form of a precursor trapped in the cells, and can only be released when the papaya is crushed by mastication.

In the first instance, I do not think such an anti-clotting substance exist in papaya. I have not come across any published literature on this.

If there are foods that have anti-coagulating and anti-platelet aggregating properties that may have health benefits against stroke, cardiovascular risk, and DVT, I would suggest foods that contain high levels of salicylates (Aspirin). Aspirin is the acetylated form of salicylic acid known as acetylsalicylic acid.

Cardio-protective, as well as cancer-protective foods:

Foods with medicinal values against cardiovascular risks would be capsicum, hot pepper, tomatoes, all curry powder, and spices, and curry leaves, guava, oranges, pineapples, grapes, plums, prunes, almonds, water chestnuts, teas, etc. Not only are these foods cardio-protective, but because of their high salicylate content, they were also shown to be preventive against colorectal cancer. So far I have not come across any published literature showing papaya can prevent heart, CVA and other vascular diseases. Neither have I come across research papers demonstrating anti-cancer properties in papaya.

Garlic, onions, leeks, mok yee (black fungus), oats, asparagus, whole grains and cereals, green leafy vegetables and plenty of fresh fruits can also do a very good job in preventing a lot of cardiovascular related diseases. It is not just papaya mentioned in the article.

This is the problem when we get things sent to us through chain e-mails, or from websites. Most people will believe them as gospel truth. They become blind to a lot of these hoaxes. Most of the claims have not undergone intensive well-designed scientific studies.

The authors’ names, qualifications and academic credentials, place of work and professional position are not given in all these claims.

Anyone can literally write and claim just about anything in the Internet and chain e-mails. They then send them out, and ask recipients of such mails to be forwarded to other people. So lies are spread like wild fires this way without editing and policing.

There are a lot more nutritional and medicinal claims mentioned in that article on papaya, but I do not think I should waste a lot of my time that needs a lot more evidence-based studies.

Lots of claims, little references:

Nevertheless, it will take me a lot of time and effort to discuss all those claims and details there. There were a few references there which as a medical research scientist and research nutritionist, I appreciate, but there were far more claims in the lengthy article than citations quoted. So those claims cannot be supported by scientific evidences, at least not at the moment.

However, the background hypotheses are attractive, and may be used as a basis for further studies, or as a thesis for a Masters degree in Nutrition, Medicine or Biomedical Sciences.

Regards

lim ju boo

Chief and Special Medical and Science Adviser
Head of Technical Advisory Board
Dynapharm In’tl Pharmaceutical Group
Malaysia

Dear Dr Lim,

Thank you so much for the expert advice and research information regarding the benefit of Papaya.

May you be well & happy always!

Metta

C K Cheong