Lean fish like cod have been overshadowed by the acclaimed health benefits of fatty fish. But lean fish may be better for your health, especially for overweight men, a new study suggests. (Photo: Shutterstock / NTB / Scanpix)
Lean fish like cod have been overshadowed by the acclaimed health benefits of fatty fish. But lean fish may be better for your health, especially for overweight men, a new study suggests. (Photo: Shutterstock / NTB / Scanpix)

Cod may be healthier than salmon for overweight men

When researchers looked at the diets of northern Norwegian men over a 13-year period, they found that lean fish was good for both cholesterol and blood pressure levels. But not everyone is sure this is true.

We all know it’s important to eat fish, especially varieties that are high in heart-healthy omega-3 fatty acids, such as trout and salmon. This, combined with the explosive growth of the salmon farming industry in Norway, has made salmon in particular the go-to fish for many an evening meal.

But what of lean white-fleshed fish, such as cod and pollock? A Norwegian study just published in the academic journal Nutrients shows that lean fish may be as good for your health as salmon, especially if you are an overweight man.

Cod good for bad cholesterol

The researchers wanted to find out if eating fish can reduce some of the different factors that make up metabolic syndrome. This is not a disease but a number of conditions that mean a person has an increased the risk of diabetes and cardiovascular disease.

The conditions include large waist circumference, high blood pressure and high blood sugar. You may also have metabolic syndrome if you have an unhealthy blood lipid profile with high triglyceride levels and low levels of good HDL cholesterol.

The researchers looked at roughly 13,000 participants from the 1994-1995 Tromsø Study 4 who also participated in the 2007-2008 Tromsø Study 6. Data for the studies were collected using questionnaires on food consumption, non-fasting blood samples, and physical examinations.

The results showed that those who ate lean fish such as cod more than once a week improved their metabolic syndrome conditions over the study period.  In particular, they had an improved blood lipid profile, with less bad and more good cholesterol. This was true for both sexes.

Decreased blood pressure, waistline in men

The researchers also saw that both blood pressure and waistline measurements were lower in men who consumed lean fish, but not for women. While it’s true that the decrease in waistline circumference they found was just one centimetre, the same decrease did not occur in those who ate mostly fatty fish.

Those who ate fatty fish actually had larger waistlines over the 13 years.

"The results show that consumption of lean fish has a beneficial effect on several of the criteria used to define metabolic syndrome, while we did not find this same association for fatty fish," says Christine Tørris, a senior lecturer at Oslo and Akershus University College.

She is also a PhD candidate at the University of Oslo’s Faculty of Medicine.

Food can affect men and women differently

The researchers also found that consumption of fatty fish was linked to higher levels of good HDL cholesterol among men.

Why should there be gender differences in how lean fish affected blood pressure and waist circumference? 

Tørris said it’s well known that women and men have different blood lipid profiles and different hormones.

“Women bear children and breastfeed,” she said. “Thus, the food we eat may affect women and men differently.”

Fish is a good, healthy protein source

“This study hardly represents a major international breakthrough in showing that lean fish is healthier than fatty fish," said Professor Geir Bjørkøy, from the Norwegian University of Science and Technology in Trondheim.

He points out that there are already several thousand studies that suggest that diets that include fish are better for our health.

One of the reasons he is somewhat sceptical of the results is that the study relies on an epidemiological investigation, where people are asked about their diets.

“This study does not necessarily show any causal connection that proves that individual components in the diet have a beneficial effect on health,” he noted. “They could have also shown a connection between a decreased intake of bad foods and better health.”

Even though the studies show a lower risk of disease among those who ate fish, it might be because they ate less of the foods that are harmful to your health, such as saturated fat from meat, he says.

“Many of these studies also do not distinguish between whether people have eaten lean or fatty fish. But if you eat fish fingers, for example, that’s not necessarily so much healthier than red meat, since fish fingers may be cooked in unhealthy fat,” he said.

Bjørkøy investigates the beneficial effect of omega-3 fatty acids on the body's autoimmune inflammatory reactions.

He said the best way to uncover causal relationships between food consumption and health effects is to use a clinical blind trial, where information about which participant is getting which treatment is hidden from both participants and those administering the treatments.

“There are measurable, beneficial effects from consuming fatty fish. But since lean fish contain very little omega-3, I'm sceptical about whether consuming this type fish in itself has health effects, aside from keeping us from eating less meat,” Bjørkøy says.

See if you have metabolic syndrome:

Metabolic syndrome means that you have a number of risk factors for cardiovascular disease and type 2 diabetes.

A person is considered to have metabolic syndrome if they meet at least three of the five criteria listed below. The only thing you can check yourself is your waistline. But if your waistline measurement exceeds these numbers, you should consider going to the doctor to check your blood pressure, blood sugar levels and your cholesterol and triglyceride levels. Here are the five criteria:

Waistline: 94 cm or more for men, 80 cm or more for women.
Blood pressure: 130/85 mm Hg or more.
Blood sugar: 5.5 mmol / L or more
Triglycerides: 1.7 mmol / L or more
HDL cholesterol: less than 1.0 mmol / L for men and less than 1.3 mmol / L for women.


Read the Norwegian version of this article at forskning.no

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