Are oysters good for you?
This article provides some detailed information about health benefits, side effects and possible medical uses of oysters. Find out whether oysters are good for you or not. You will also learn about various types of oysters.
Oyster is the name given to the different families of bivalve molluscs and saltwater calms that live in the marine environment. The valves become hard in some species and get an irregular shape. Many oysters belong to the family Ostreoidea. Some types of oysters are eaten and consumed in raw or cooked form. Some pearl oysters are harvested for pearls, which is made inside their mantle. The most commonly used oysters are windowpane oysters, which are harvested for their translucent shells and different decoration pieces are made from them. The word oyster was first used in the 14th century, which is derived from the Old French word ‘oistre’. This French word is in turn derived from the Latin word ‘ostrea’.
Types of oysters
There are many types of oysters that include:
- True Oysters – True Oysters are members of the family Ostreidae. Edible oysters are included in this family which belong to the genera Saccostrea, Ostreola and crassostrea. Some popular examples of true oysters include eastern oyster, Olympia Oyster, Pacific oyster and Belon oyster.
- Pearl Oysters – Pearls are secreted by most shell-bearing mollusks. But many of them may not be of that much value. The true oysters and pearl oysters aren’t related to each other. The natural pearls and the cultural pearls can be obtained from pearl oysters, but some molluscs such as fresh water mussels also have some commercial value. The marine Pinctada maxima is the largest pearl bearing oyster. It is about the size of a dinner plate. Pearls aren’t found in all the oysters. The truth is that only three to four oysters have pearls in a harvest of two tons of oysters.
- Other Types – There are some bivalve molluscs which are also sometimes called oysters because they taste similar to oysters or they have pearls inside them. Some other types of oysters include Windowpane oysters, Saddle oysters, Dimydarian oysters and thorny oysters. Another species of oyster is quite popular in the Philippines and is known as Tikod Amo. It is eaten as a favorite food in Philippines but has a slightly higher price.
Oysters are filter feeders, which means that they breathe when their cilia beats. Plankton and other particles are stopped in the gill where they move through the mouth and are eaten and digested and are expelled out of the body in the form of feces. Mostly oysters are quite active above 10 degrees Celsius.
Health benefits of oysters
Now let us look at some of the health benefits of oyster. Some major health benefits of oysters have been mentioned below:
Oysters are aphrodisiac. This means that they are the foods which boost the sexual drive. They can boost the libido and sexual performance in men. The zinc content in oysters is quite high. There are more than 1500% of the daily requirements of this mineral present in a single serving. Zinc deficiency is closely related with sexual and erectile dysfunction in men. Eating oysters can therefore enhance a person’s sexual performance and give him the feelings of masculinity.
An oyster has the most number of nutrients and the least number of calories present in it. So, people looking to lose weight can pack their body with the essential nutrients present in oysters without gaining much weight. Oysters have relatively lower calories as compared to an equal serving of chicken. They have, in fact, half number of calories. So using it might lead to weight loss.
Proteins are quite essential for a healthy life and oysters are a good source of proteins. Proteins are usually broken down by the enzymes present in the body and thenconverted into beneficial proteins for the body. The protein content in oysters is very helpful for the body as it helps in the tissue repair, cell growth, muscle strength and proper growth of muscles. Proteins have an undeniable importance for the human body and a single serving of oyster fulfills about 1/3 of the daily recommendations of protein intake.
Oysters also promote a healthy heart. They are quite beneficial for a healthy heart in many ways but the one thing which is the most beneficial for a healthy heart is that oysters are rich in omega 3 and omega 6 fatty acids content. Therefore, they have a great impact on the cholesterol levels in the body. Omega 3 comes under the category of good cholesterols and the fact that the good cholesterol is more in oysters as compared to the bad cholesterol makes oysters quite beneficial for heart health.
Oysters also aid in lowering the levels of bad cholesterol in blood and their sticking to arterial walls. This fact can reduce the chances of cardiovascular complications like heart attack, stroke and angina. Oysters also have high magnesium and potassium content in them. This is quite beneficial for the body as it helps to lower the blood pressure and relaxes the blood vessels. It also increases the circulation of the blood and reduces the strain produced on the cardiovascular system. Strength and flexibility is given by the vitamin E present in oysters which gives protection against different kinds of heart diseases.
Oysters have a high zinc content in them and due to this reason they are quite beneficial for the body and heal the wounds quickly. They also boost the immune system of the body and kill various microbes and viruses. Zinc is an essential mineral present in the oysters which is quite helpful for the growth of children and young adults. It is also essential for the maintenance of the bodily functions. Zinc can also reduce the risks of a person to suffer from common cold (1).
Blood circulation and volume
Oysters are an important source of iron for the human body. More than 90% of the daily requirements of the body are fulfilled by one serving of oyster. Iron plays an important role in the formation of red blood cells. It also provides protection to the body against anemia, which is also called iron deficiency. This can lead to fatigue, stomach disorders and general malfunctions in the body. High iron levels lead to high levels of oxygenated blood in the organ systems and good blood supply in the circulatory system. This boosts the overall metabolic rate of the body and helps in the efficient functioning of the body.
Oysters have a good quantity of mineral content in them and this is quite helpful for giving strength to the bones. Calcium is required for healthy bones (2). Oysters have high levels of calcium, zinc, iron, phosphorous, selenium and copper in oysters. All these minerals help in increasing the overall functioning of the bones and improve the durability and density of the bones. They also protect the body against different health conditions like osteoporosis (3).
Functioning of immune system
Consuming oysters boosts the functioning of immune system. Oysters have a good quantity of vitamin E and C in them. These vitamins defend the body against different free radicals, which are produced as a byproduct of cellular metabolism. These radicals are quite harmful for the body and they attack the healthy cells and produce cancerous cells in return. Different health problems like heart diseases, aging and body disrepair are produced by these radicals. These free radicals are eliminated by the vitamins present in the oysters and therefore, the immune system is strengthened. Also, some oysters contain C-type lectins, which also boost immune system by mediating immune response (4).
Increase in energy
B vitamins present in oysters which are also known as energy releasing vitamins. The reason behind this is that they breakdown carbohydrates for energy. The vitamin B12, which is called cobalamin, content in oysters is quite high and contain good amounts of niacin and riboflavin too. There is 362 percent of the recommended daily intake of B12 in a single serving of oyster. It also contains 11 percent of niacin and 13 percent of riboflavin. Vitamin B12 is quite essential for the body and helps in maintaining the myelin which surrounds the nerve cells and breaks down the amino acids and the fatty acids in order to produce energy (5). Vitamin B is eliminated from the body because it is water soluble. You should eat the foods which are rich in vitamin B to get more and more of this vitamin.
Strengthening the integumentary system
The Center for Disease Control and Prevention recommends that at least 46 grams of proteins per day are needed by women and 56 grams per day by men (6). There are 14 grams in one cup of oyster. This is quite beneficial for the people who are pescatarian, meaning people who don’t eat land animals but eat water animals. Protein plays an essential role as a macronutrient and protect and strengthens the integumentary system of the body, which includes the coverings of the outer side of the body including the nails, hairs and skin. Oysters can be called as complete protein package because they contain all the essential amino acids. The thing that is interesting about oysters is that they don’t need to be mixed with other protein sources to get the most benefits; they are quite beneficial on their own.
Reduced risk of diseases
Oysters are usually available in canned form and are packed in water or oil. The oil which is used is quite healthy for the body and is a form of monounsaturated fat. Mostly, olive oils are present in smoked oysters. Researchers suggests that olive oils contain a powerful blend of antioxidants which lowers the LDL or lower-density lipoprotein levels. LDL is a dangerous and bad kind of cholesterol which increases the risk of heart diseases. There are about 9 kilocalories per gram present in fats. So, canned oysters are higher in calories as compared to the raw oysters. The number of calories present in canned oysters are 180 to 200 calories.
Again, one oyster nutrient that is going to benefit your vision is zinc. Different studies have shown that zinc plays an important role in the normal ocular functioning (7). High quantities of zinc are present in ocular tissue, choroid and the retina. Zinc provides many other health benefits such as enhancing the immune system, repairing the damaged tissues and stopping cardiovascular diseases.
The recommended daily intake of zinc is about 11 mg for an adult man or 8 mg for an adult woman (8). The vision quality is improved when the body needs for zinc are fulfilled. Different age related macular degeneration are also reduced through the consumption of zinc. A research was conducted in which the researchers followed more than 3,600 individuals for about eight years. The ages of the participants was between 55 and 80. The effects of antioxidant supplements on AMD (age related macular degeneration) were examined through the research. The results of the study showed that the high levels of antioxidants and zinc significantly reduced the risk of AMD. It was also proved through the research that the supplements which contain zinc as predominant component, stop the vision loss which is accompanied by AMD. The research team suggested that the people suffering from AMD should take at least 80 mg of zinc on daily basis.
People who add zinc as a daily supplement in their diet should also add copper along with it. The experts are of the view that excess of zinc in the body can create copper deficiency and vice versa. So, the crux of all this is that you need to increase zinc in your diet. You should therefore eat oysters which have the highest quantity of zinc in them.
Medical uses of oysters
Now let us look at some of the medicinal uses of oysters. Following are some major medical uses of oysters.
Oysters for bones
It has been found that oysters are quite beneficial for the bones. Some French biologists are of the view that oysters produce nacre and they could be used in the preventive treatments for arthritis, skin complaints and osteoporosis. Experts have the view that the main thing that makes the oysters so special is biomineralisation. Both oysters and humans have the quality of self-repair. The oyster shell heals just like a human bone. The experts now believe that the nacre produced by oysters is quite beneficial for the bones and helps in bone growth. The process of biomineralisation is quite old and is as old as bivalve molluscs and is approximately a few million years old. Some oysters have better quality of biomineralisation as compared to the others. Only those oysters are beneficial for bone growth which contain the largest quantity of nacre in them. It is present in species like Pinctada oyster which produces pearls.
Oysters and cancer
Oysters are quite beneficial in fighting cancer. Experts suggest that oyster flesh and dry powder oyster are especially beneficial for the cancer patients who are undergoing the process of radiation. The addition of the herb can improve the effect of radiation in killing tumors. A study proved that eating oysters can reduce the cancerous cell tumors in the body and empower the immune cells (9).
Oysters and immunity
Oysters are also quite beneficial for the immune system. This has been found by Chinese researchers which found that the shell of oysters can boost the immune cells of the body. The Chinese researchers have claimed that oysters are quite beneficial in boosting the overall immune system of the body. The natural killer cells in the body are also improved which are actually the body’s defense against outside forces (10). So, this means that oysters are quite beneficial for different kinds of illnesses like flu and cold.
Oysters and stomach
Oysters are quite beneficial for the stomach. It has been found that oysters are beneficial in preventing stomach ulcers (11 - not available online, see PUBMED reference under the article). Oysters are especially beneficial against gastric ulcers, which is commonly occurs during the indigestion process.
Oysters and blood circulation
Oysters are quite beneficial for the circulation of the blood throughout the body. They are quite rich in iron content which is the main component of the hemoglobin which carries the oxygen to the cells of the body. The organs work efficiently and the overall immune system is boosted by a fair supply of oxygen. The iron content in oysters is quite high because it is an animal source.
Oysters and brain health
The zinc content, vitamin B12 content, iron content and Omega 3 fats content is quite high in oysters which makes them a good source of boosting the memory and the functioning of the brain. The concentration ability of a person is hindered due to low iron content and the memory is affected due to the low levels of zinc. Omega 3 fatty acids also play an important role in the proper functioning of the brain.
Other medical uses
There are some other medical uses of oysters other than the ones mentioned above. They are quite beneficial for sore throats, whooping cough and colds. They are also quite beneficial for nasal bleeding. It has also been found that oysters are quite beneficial against bacillary dysentery. They also have anti-inflammatory properties in them and are helpful for bleeding stools.
Side effects of oysters
Let us now view some of the side effects of eating oysters. Some major side effects of eating oysters have been mentioned below:
As oysters feed on plankton and help keep marine environment clean by removing various toxins, they might accumulate some dangerous poisons and toxins in their shells. These toxins are produced by microscopic algae such as dinoflagellates, diatoms and cyanobacteria and cause amnesic, paralytic and neurotoxic syndromes called Amnesic shellfish poisoning (ASP), Diarrheal shellfish poisoning (DSP), Neurotoxic shellfish poisoning (NSP) and Paralytic shellfish poisoning (PSP) (12).
Amnesic shellfish poisoning is caused by domoic acid produced by diatomes. In humans domoic acid acts as a neurotoxin and causes permanent brain damage (loss of short-term memory) and may be lethal in severe cases.
Diarrheal shellfish poisoning is caused by okadaic acid, which inhibits de-phosphorylation of cells in gastrointestinal system and causes diarrhoea, nausea and vomiting. It is not a life threatening disorder and symptoms generally stops after a certain time.
Causative agent of neurotoxic shellfish poisoning is brevetoxin (and substances similar to it). It is usually not fatal but may cause neurological symptoms such as speech problems (slurred speech, difficulty to talk). Also abdominal pain accompanied with diarrhoea, vomiting and nausea may be present.
Paralytic shellfish poisoning is caused by a neurotoxin called saxitoxin, which is produced by microscopic algae, such as diatoms, dinoflagellates and cyanobacteria. It can be fatal in extreme cases however it usually causes symptoms such as abdominal pain (accompanied by nausea, vomiting and diarrhoea), burning or tingling sensations (affecting mainly lips, tongue, gums, face, arms, legs and toes). Some other symptoms also include shortness of breath, choking feeling and dry of mouth.
Cyanotoxin is produced by cyanobacteria, may accumulate in oyster shells and can cause lethal poisoning.
Infection from bacteria
It is really important to know about the type of oysters. The reason behind this is that oysters obtained from certain areas can make you ill because they contain dangerous bacteria. One example of this is Vibrio Vulnificus bacterium which is usually found in the coastal regions and the total number of these bacteria is increasing day by day. There is a high probability that the oysters can get infected with bacteria, which can in turn infect humans when consumed. Some common side effects of eating bacteria infected oysters include vomiting, diarrhea, fever and skin reactions. A person can even go into a shock if not treated properly. In general heat can destroy the bacteria. So make sure that you never eat raw oysters and only eat properly cooked oysters to avoid bacterial infection.
Another side effect of oysters is that they can cause food allergies. A protein present in oysters by the name of tropomyosin is responsible for causing oyster allergy. Some major side effects caused by oysters in people who are sensitive to tropomyosin are facial swelling, skin rashes, abdominal pain and other side effects.
The iron content in oysters is quite high. A 3 ounce serving of oysters can fulfill 44% of your daily needs. Iron is important for the body but people suffering from hemochromatosis (a genetic condition which automatically increases the amount of iron in the body) shouldn’t eat oysters because they can cause dangerous side effects. Some of these side effects include lethargy, loss of hair, abdominal cramps and changes in skin color.
Eating oysters can also cause gastrointestinal problems caused either by toxins (see shellfish poisoning section above) or by high content of zinc in oysters, which can cause some gastrointestinal problems. Some of the major reactions include diarrhea, abdominal cramps and vomiting. These effects will be visible within five to six hours after consumption of oysters. But they end when the zinc levels in the body fall back to normal.
The bottom line
Now you know all you need about oysters, their health benefits, medical uses and side effects. As you can see oysters can be beneficial for your health but you should never eat them raw to prevent bacterial infection and you should always ask your physician for permission before eating them. If you do not feel well after eating oysters, get rash or any other skin problems or have difficulty in breathing or speaking, you should always go and see your doctor immediately as you might be suffering from shellfish poisoning.
|Written by:||Michal Vilímovský (EN)|
|Education:||Medical student, 3rd Faculty of Medicine, Charles University, Prague, Czech Republic|
|Article resources:||See numbered references within the article.
Additional resources not available online:
(11): Nie SQ, Li TL, Jiang WJ, Xue BY, Liang AH, Li GQ, Yang Q. [A comparative study on anti-ulcer action of unprepared and calcined oyster shell]. Zhongguo Zhong Yao Za Zhi. 1994 Jul;19(7):405-7, 446. Chinese. PubMed PMID: 7802944.
|Published:||July 29, 2015 8:31 AM|
|Last updated:||July 31, 2015 12:10 AM|
|Next scheduled update:||July 31, 2017 12:10 AM|