Fish Oil May Not Be a Defence Against Heart Disease
You've probably heard about the heart benefits of oily fish - consume salmon, sardines, mackerel or tuna a couple of times a week as part of a balanced diet, and you'll be doing your heart a favour. Fish oil supplements, which are also rich in heart-healthy omega-3 fatty acids, are the next best thing if you can't stand eating fish.
This dietary guideline isn't new. It is based in part on a study by two Danish physicians, Hans Olaf Bang and Jorn Dyerberg in the 1970s, which revealed that the low incidence of coronary artery disease (CAD) among the Greenland Inuits was linked to the group's high consumption of marine fats like whale and seal blubber.
But when some researchers recently set out to re-examine the validity of Bang and Dyerberg's famous study, they noted that it was flawed, according to their findings, which were published in the Canadian Journal of Cardiology.
The heart health of the Greenland Inuits had not actually been investigated, so there was no evidence to back claims that a diet high in fish oils does indeed provide cardio-protective benefits. In fact, the typical Inuit diet - which was high in animal fats and low in fruits and vegetables - violated all principles of balanced and heart-healthy nutrition.
In reviewing the original Bang and Dyerberg study, lead investigator and cardiologist Dr George Fodor found that, "Inuits have a similar prevalence of CAD as non-Inuit populations, they have excessive mortality due to cerebrovascular strokes, their overall mortality is twice as high as that of non-Inuit populations, and their life expectancy is approximately 10 years shorter than the Danish population".
According to Fodor, who is also head of research for the Prevention and Rehabilitation Centre at the University of Ottawa Heart Institute, the fact that Bang and Dyerberg overlooked important details is a big deal because, for the past 40 years, their study has been blindly accepted by doctors, nutritionists and other health experts as gospel truth.
"Most readers, if they read the original papers inThe Lancet at all, obviously did not pay attention to the fact that, as to the frequency of heart disease in Greenland, Bang and Dyerberg rely on third-party information, and in one case on personal communication.
"My opinion is that many researchers assumed that, if a statement was published in such a highly esteemed journal as The Lancet, then it must be verified information," says Fodor.
He says that he has nothing against oily fish, and acknowledges its value as part of a balanced diet. But he adds that there is no evidence to show that consuming oily fish helps to prevent heart disease.
A few other studies and reviews have also questioned the heart-health benefits of omega-3 fatty acids in fish oil supplements.
One review, led by Dr Rajiv Chowdhury - a cardiovascular epidemiologist at the University of Cambridge in England - and published in March in theAnnals of Internal Medicine, revealed that fish oils do not provide any significant protection against CAD when compared to other types of dietary fats. Other large-scale studies yielded similar findings.
But many studies suggest otherwise. For example, one major international study, which appeared in March in the journal Heart, discovered that eating fish in amounts comparable to those of people living in Japan appears to have heart-protecting benefits. It was thought that the omega-3 fatty acids found in oily fish help to slow the formation of fatty plaques in the arteries.
"Enough studies have been done over the past 10 years which prove that adding omega-3 fatty acids to the diet can lower one's risk of heart disease," says Winsy Leung, a dietician in Central. "Yes, there's a lot of information out there, but in clinical trials, people who were at a high risk of developing heart disease reduced their triglyceride or blood fat levels after increasing their intake of omega-3 fatty acids, either in the form of fish or fish oil supplements. The point is, this issue of omega-3 fatty acids is still quite new for scientists.
"Years ago, doctors told us that fat should not make up more than 30 per cent of our diet. But they never said where this fat should come from. It was only later that we became aware of the dangers of saturated fats, so now we're advised to keep our saturated fat intake to a minimum and consume healthier fats," says Leung.
Leung believes that oily fish should be part of a heart-healthy diet. So, too, does Jessica See, a clinical nutritionist and health coach from Health Coach International in Singapore.
"Having high triglyceride levels puts you at risk of developing heart disease," she says. "Docosahexaenoic acid, or DHA is a long-chain fatty acid that belongs to the omega-3 fatty acid family, and this has been shown to bring high triglyceride levels down, as well as reduce 'stickiness' of the blood. DHA can be obtained from fish oils."
Oily fish also contains another omega-3 fatty acid called eicosapentaenoic acid, or EPA. Plant-based omega-3 fatty acids (alpha-linolelic acid or ALA), such as those found in flax are not the same as the fatty acids found in oily fish. While ALA is beneficial, it is not as potent as DHA and EPA in terms of heart-protective benefits.
"Omega-3 fatty acids cannot be produced by the body and must be obtained from food," Leung says. "If you don't like the taste of fish, or are allergic to fish, then fish oil supplements are useful, but you must see a doctor or dietician to get the proper recommended dosage.
"Fish oil supplements should be treated like medication. If you take more than you need, you may experience internal bleeding."
If you are on medication, you also need to make sure that the supplements do not interfere with them, and vice versa - and only your doctor can give you the right advice.
If you have not been diagnosed with cardiovascular disease, the American Heart Association recommends eating a variety of (preferably oily) fish at least twice a week. If you have been diagnosed with cardiovascular disease, you should consume approximately one gram of omega-3 fatty acids per day, preferably from oily fish, although supplements could be considered in consultation with your physician.
Patients needing triglyceride lowering should take two to four grams of omega-3 fatty acids per day, provided as capsules under a physician's care.
As some species of fish (particularly the older, larger, predatory kind) contain high levels of mercury, PCBs (polychlorinated biphenyls), dioxins and other contaminants, it's important to choose your fish wisely. Canned light tuna and salmon are generally low in mercury, while king mackerel is not.
Even if you do eat oily fish twice a week or take fish oil supplements daily, your heart won't thank you if your diet is generally poor - that is, high in sodium and saturated fats, like those found in red meat, butter, lard, cream and cheese.
It is vital to take care of your overall health, and that includes sticking to a diet that is low in salt, low in saturated fat and high in fibre, and exercising three to five times a week to boost your cardiovascular health.
You also have to look at the big picture when it comes to heart health, Leung says.
"There are many other risk factors involved with heart disease - stress, smoking, genetics, and diseases such as diabetes. So you can't just increase your omega-3 fatty acid intake and think that you're in the clear. Eating fish alone is not the magic bullet," she says.
This dietary guideline isn't new. It is based in part on a study by two Danish physicians, Hans Olaf Bang and Jorn Dyerberg in the 1970s, which revealed that the low incidence of coronary artery disease (CAD) among the Greenland Inuits was linked to the group's high consumption of marine fats like whale and seal blubber.
But when some researchers recently set out to re-examine the validity of Bang and Dyerberg's famous study, they noted that it was flawed, according to their findings, which were published in the Canadian Journal of Cardiology.
The heart health of the Greenland Inuits had not actually been investigated, so there was no evidence to back claims that a diet high in fish oils does indeed provide cardio-protective benefits. In fact, the typical Inuit diet - which was high in animal fats and low in fruits and vegetables - violated all principles of balanced and heart-healthy nutrition.
In reviewing the original Bang and Dyerberg study, lead investigator and cardiologist Dr George Fodor found that, "Inuits have a similar prevalence of CAD as non-Inuit populations, they have excessive mortality due to cerebrovascular strokes, their overall mortality is twice as high as that of non-Inuit populations, and their life expectancy is approximately 10 years shorter than the Danish population".
According to Fodor, who is also head of research for the Prevention and Rehabilitation Centre at the University of Ottawa Heart Institute, the fact that Bang and Dyerberg overlooked important details is a big deal because, for the past 40 years, their study has been blindly accepted by doctors, nutritionists and other health experts as gospel truth.
"Most readers, if they read the original papers inThe Lancet at all, obviously did not pay attention to the fact that, as to the frequency of heart disease in Greenland, Bang and Dyerberg rely on third-party information, and in one case on personal communication.
"My opinion is that many researchers assumed that, if a statement was published in such a highly esteemed journal as The Lancet, then it must be verified information," says Fodor.
He says that he has nothing against oily fish, and acknowledges its value as part of a balanced diet. But he adds that there is no evidence to show that consuming oily fish helps to prevent heart disease.
A few other studies and reviews have also questioned the heart-health benefits of omega-3 fatty acids in fish oil supplements.
One review, led by Dr Rajiv Chowdhury - a cardiovascular epidemiologist at the University of Cambridge in England - and published in March in theAnnals of Internal Medicine, revealed that fish oils do not provide any significant protection against CAD when compared to other types of dietary fats. Other large-scale studies yielded similar findings.
But many studies suggest otherwise. For example, one major international study, which appeared in March in the journal Heart, discovered that eating fish in amounts comparable to those of people living in Japan appears to have heart-protecting benefits. It was thought that the omega-3 fatty acids found in oily fish help to slow the formation of fatty plaques in the arteries.
"Enough studies have been done over the past 10 years which prove that adding omega-3 fatty acids to the diet can lower one's risk of heart disease," says Winsy Leung, a dietician in Central. "Yes, there's a lot of information out there, but in clinical trials, people who were at a high risk of developing heart disease reduced their triglyceride or blood fat levels after increasing their intake of omega-3 fatty acids, either in the form of fish or fish oil supplements. The point is, this issue of omega-3 fatty acids is still quite new for scientists.
"Years ago, doctors told us that fat should not make up more than 30 per cent of our diet. But they never said where this fat should come from. It was only later that we became aware of the dangers of saturated fats, so now we're advised to keep our saturated fat intake to a minimum and consume healthier fats," says Leung.
Leung believes that oily fish should be part of a heart-healthy diet. So, too, does Jessica See, a clinical nutritionist and health coach from Health Coach International in Singapore.
"Having high triglyceride levels puts you at risk of developing heart disease," she says. "Docosahexaenoic acid, or DHA is a long-chain fatty acid that belongs to the omega-3 fatty acid family, and this has been shown to bring high triglyceride levels down, as well as reduce 'stickiness' of the blood. DHA can be obtained from fish oils."
Oily fish also contains another omega-3 fatty acid called eicosapentaenoic acid, or EPA. Plant-based omega-3 fatty acids (alpha-linolelic acid or ALA), such as those found in flax are not the same as the fatty acids found in oily fish. While ALA is beneficial, it is not as potent as DHA and EPA in terms of heart-protective benefits.
"Omega-3 fatty acids cannot be produced by the body and must be obtained from food," Leung says. "If you don't like the taste of fish, or are allergic to fish, then fish oil supplements are useful, but you must see a doctor or dietician to get the proper recommended dosage.
"Fish oil supplements should be treated like medication. If you take more than you need, you may experience internal bleeding."
If you are on medication, you also need to make sure that the supplements do not interfere with them, and vice versa - and only your doctor can give you the right advice.
If you have not been diagnosed with cardiovascular disease, the American Heart Association recommends eating a variety of (preferably oily) fish at least twice a week. If you have been diagnosed with cardiovascular disease, you should consume approximately one gram of omega-3 fatty acids per day, preferably from oily fish, although supplements could be considered in consultation with your physician.
Patients needing triglyceride lowering should take two to four grams of omega-3 fatty acids per day, provided as capsules under a physician's care.
As some species of fish (particularly the older, larger, predatory kind) contain high levels of mercury, PCBs (polychlorinated biphenyls), dioxins and other contaminants, it's important to choose your fish wisely. Canned light tuna and salmon are generally low in mercury, while king mackerel is not.
Even if you do eat oily fish twice a week or take fish oil supplements daily, your heart won't thank you if your diet is generally poor - that is, high in sodium and saturated fats, like those found in red meat, butter, lard, cream and cheese.
It is vital to take care of your overall health, and that includes sticking to a diet that is low in salt, low in saturated fat and high in fibre, and exercising three to five times a week to boost your cardiovascular health.
You also have to look at the big picture when it comes to heart health, Leung says.
"There are many other risk factors involved with heart disease - stress, smoking, genetics, and diseases such as diabetes. So you can't just increase your omega-3 fatty acid intake and think that you're in the clear. Eating fish alone is not the magic bullet," she says.
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