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Prawns may contain cholesterol but are strong in nutrition
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Monday, 16 June, 2014, 08 : 00 AM [IST]
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V Venugopal Menon
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fiogf49gjkf0d Prawns may contain cholesterol at levels as high as 200mg per 100g. Some consumers have health concerns regarding the consumption of prawns due to its high cholesterol level. This article indicates that several nutrients present in the shellfish can alleviate the adverse effect of the steroid.
While the general public is encouraged to consume the shellfish due to its nutritive value, it is advisable to restrict shrimp in the diet by those having high levels of LDL cholesterol, as they may be at risk of cardiovascular disease.
Prawn (shrimp), perhaps, is the most popular shellfish, throughout the world caught from both marine and freshwater sources. The term prawn is more often used for larger forms, while shrimp is sometimes applied to smaller species.
No clear distinction
There is no clear distinction between both the terminologies; their usage is dependent on countries or regions. In this article, generally the term shrimp is used.
Some popular shrimp species in Asia, including India are black tiger prawn (Penaeus monodon); white leg shrimp (Penaeus vannamei); flower prawn (P indicus); brown shrimp (P semisulcatus); king prawn (Metapenaeus dobsoni); marine shrimp (Metapenaeus affinis Parapenaeopsis stylifera) and giant freshwater prawn [Macrobrachium rosenbergii (scampi)].
According to the United Nations’ Food and Agriculture Organisation, the consumption of shrimp and other shellfish has nearly tripled since 1970. It currently contributes about 25 per cent to the annual world per capita fish consumption (16kg).
To meet the demand for shrimp, the black tiger prawn and white leg shrimp are commercially farmed by aquaculture in many Asian countries.
The consumer appeal of shrimp is due to its unique texture and reddish colour, in addition to its taste and size, although many may not able to differentiate major shrimp varieties (white, brown, or tiger) or wild species as opposed to farmed ones.
Low fat content
The proximate composition of prawn (shrimp) meat is shown in Table 1. It has low fat content (up to two per cent on fresh weight basis), but has high cholesterol (between 150 and 200mg per 100g meat).
This is true for both marine and freshwater shrimp species, and also for other shellfish, such as cephalopod such as squid and also octopus.
Cholesterol is necessary for proper functioning of cell membranes and production of hormones.
As the steroid is metabolically synthesised in human body, dietary intake of it is not necessary. Deposits of significant amounts of low-density lipoproteins (LDL) (protein complexes with saturated fats and cholesterol) in the arteries contribute to atherosclerosis.
Therefore, excessive intake of cholesterol can lead to increase in LDL, in contrast, increases in high-density lipoproteins (HDL) reduce the risk of heart disease.
Cooking does not reduce cholesterol content significantly. Many dieticians, health professionals and consumers have reservations about the consumption of shrimp due to its high cholesterol and the possibility to enhance the level of LDL.
Many nutrients
Although high in cholesterol, shrimp meat also contains significant amounts of many nutrients, including well-balanced proteins, bio-active peptides, beneficial omega-3 fatty acids, antioxidants and minerals (Venugopal, 2014).
Many of these compounds can have a protective role against cholesterol absorption. Shrimp meat has a protein content of 17-22 per cent, that contains all the essential amino acids (leucine, isoleucine, lysine, valine, threonine, methionine, phenyl alanine and cysteine).
Digestion of shrimp in the human digestive system (digestibility of shrimp proteins is comparable to that of casein, the milk protein) gives protein hydrolysates containing small molecular weight peptides having interesting bioactivities, particularly antihypertensive activity, in addition to antimicrobial and antioxidant activities.
The anti-hypertensive activity is due to the ability of some peptides to inhibit angiotensin I-converting enzyme (ACE), which plays fundamental role in blood pressure homeostasis.
ACE inhibitors are widely used for the treatment of high blood pressure. A peptide having significant angiotensin-I-converting enzyme inhibitory activity has been recently isolated from shrimp meat (Kim and Wijesekaraa, 2010).
Good source of PUFA
Shrimp, although low in fat, are good source of polyunsaturated fatty acids (PUFA), particularly of the Omega-3 type, which are present at an average value of 300mg in 100g meat.
Omega-3 PUFAs are widely accepted as a part of modern nutrition because of their health benefits. An inverse relation between Omega-3 PUFA intake and risk of coronary heart disease has been well established.
Health organisations in the United States and other countries recommend a daily intake of EPA and DHA ranging between 250 and 1,000mg for the general population and people with heart disease.
The potential of PUFA to enhance brain function and the effect of medical treatment of important diseases, such as Alzheimer’s, multiple sclerosis and cancer, has also been reported.
Rich in carotenoids
Shrimp meat is also rich in carotenoids (the pigments that give colour to shrimp meat), which function as antioxidants, protect the immune system and serve as precursors of vitamin A.
Shrimp is rich in the trace element, selenium, which has excellent antioxidant properties. These anti-oxidants have the potential to control arteriosclerosis (cardio-vascular disease), in addition to prostate and colon cancers.
Further, shrimp also contains L-carnitine, a quaternary ammonium compound, which has been reported to protect against ischemic heart disease. Shrimp and also other shellfish contain non-cholesterol sterols (also known as plant sterols or plant stanols).
They are similar in structure to cholesterol, but have methyl, ethyl or other groups in their aliphatic side chains. These differences minimise their absorption compared to cholesterol. These compounds can decrease the absorption of cholesterol (Dong, 2001).
The concern regarding the high level of cholesterol needs to be weighed against the functional roles of the abovementioned nutritional elements.
Moderate consumption
Research showed that moderate shrimp consumption was unlikely to adversely affect the overall lipoprotein profile.
In a peer-reviewed scientific study, researchers looked at the effect of two diets, one which contained shrimp, and the other eggs, on the cholesterol levels of people with normal lipid levels.
It was observed that a diet containing upto 300g steamed shrimp per day (equivalent to about 600mg cholesterol) did not increase plasma cholesterol nor impair lipoprotein profiles of consumers.
Although the shrimp diet increased the harmful LDL by 7.1 per cent, the beneficial HDL was increased by 12.1 per cent.
In contrast, a diet containing two eggs per day with an intake of 581mg dietary cholesterol raised LDL by 10.2 per cent, while the HDL cholesterol increased only by 7.6 per cent (Chides, et al, 1990).
Similar observations have also been made with respect to diets containing other shellfish items, such as oyster and mussel (Hicks, 2013).
The conclusion is that moderate shrimp consumption by people with normal lipid level is not likely to affect the overall lipoprotein profile, presumably due to positive influence of many nutrients, particularly omega-3 PUFA, which alleviate the adverse effect of cholesterol present in shrimp meat.
References
Venugopal Menon, V. (2014), Health promoting compounds in shrimp meat, Infofish International, 2014 (in press)
Kim SK, Wijesekaraa I, (2010) Development and biological activities of marine-derived bioactive peptides: A review J, Functional Foods 9 1-9
Dong FM. (2001), The nutritional value of shellfish, http://www.wsg.washington.edu/communications/online/shellfishnutrition_09.pdf
Childs MT, Dorsett CS, King IB, Ostrer JG, Yamanaka WK (1990) Effects of shellfish consumption on lipoproteins in normolipidemic men Am J Clin Nutr 51 1020-1027
Hicks, D (2013) Seafood Health Facts: Making Smart Choices Balancing the Benefits and Risks of Seafood Consumption Resources for Healthcare Providers and Consumers, (www.SeafoodHealthFacts.org).
Dalal J S, Ponniah, A G, Imran Khan, H, Madhu Babu, E P, Ambasankar, K and Vasagam, KP (2013), Shrimps – a nutritional perspective, Current Science, 104, 1487-1491 (Referred as Source I. in Table 1)
Self-Nutrition Data Crustaceans, shrimp, mixed species, cooked, moist heat, http://nutritiondata.self.com/facts/finfish-and-shellfish-products/4174/2 (Referred as Source II in Table 1).
(The author is seafood technologist. He can be contacted at vvenugopalmenon@gmail.com)
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