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Fishy Diets Boost “Good” HDL Cholesterol
Clinical trial found that eating more fatty fish raised HDL blood levels
3/3/2014By Craig Weatherby
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Does fish oil lower cholesterol levels? Does it matter?
 
Those were the questions we posed back in 2007, in an article whose title posed both queries.
 
As we wrote then, “It’s believed that the omega-3s in fish fat reduce the risk of strokes, sudden cardiac death, and second heart attacks by doing four things:
  • Lower blood triglyceride (fat) levels.
  • Raise levels of “good” (HDL) cholesterol.
  • Lower levels of all non-HDL cholesterol
  • Reduce risk of arrhythmias (conditionally, and not consistently)
And we noted that fish oil can raise levels of LDL cholesterol slightly in people with high blood levels of triglycerides.
 
However, omega-3s from fish are shown to improve the ratio of HDL (“good”) cholesterol to total cholesterol … and this ratio ranks high among the most accurate predictor of cardiovascular risks.
 
The body uses high-density lipoproteins (HDLs) to remove cholesterol from the blood, and it uses various kinds of low-density lipoproteins (LDLs) to carry cholesterol through the blood.
 
Having high levels of HDL cholesterol is generally good for cardiovascular health, while “high” levels of LDL cholesterol are not inherently unhealthful.
 
In fact, the links between LDL levels and heart risk are weak, with many persons dying from heart disease despite having “low” cholesterol levels, and vice versa.
 
Instead, two other factors matter much more:
  • The kinds of LDL that predominate in your blood
  • Oxidation of LDL cholesterol by free radicals, which result from inflammation in the artery wall and blood.
Researchers at the National Institutes of Health (and around the world) increasingly point to excessive – hence pro-inflammatory and artery-irritating – intake of plant-source omega-6 fatty acids as a key but under-recognized cause of cardiovascular disease.
 
Unlike plant-source omega-6 fatty acids, omega-3s from fish moderate and end chronic inflammation.
 
Now, researchers from Finland say they’ve made a crucial discovery about fish and hearth health, and it relates to the kinds of HDL cholesterol in your blood.
 
Large HDL particles are believed to protect against cardiovascular diseases. Why is this?
 
Compared with regular HDL (“good”) cholesterol, large HDL particles do a better job of clearing excess cholesterol off artery walls.
 
In fact, compared with small HDL, large HDL is more strongly linked to reduced risk of cardiovascular disease.
 
Diets rich in fish have long been considered good for heart health. However, the mechanisms by which omega-3 fish fats help are not fully understood.
 
The new trial clarifies how fish consumption affects the size and levels of lipoproteins in the blood.
 
Fish found to boost levels of large HDL cholesterol
The results of a recent clinical trial at the University of Eastern Finland bolster the heart-healthy image of fish and their omega-3 fatty acids.
 
In an earlier clinical trial, the Finnish group found that a diet rich in fish, whole grains, and bilberries produced significant positive changes in glucose metabolism and increased the proportion of omega-3s in blood triglycerides.
 
As they wrote, “… such a diet may have a beneficial effect in the efforts to prevent type 2 diabetes in high risk persons.” (Lankinen M et al. 2011)
 
For their new trial, the authors recruited 131 subjects (aged 40 to 70) with impaired glucose (blood sugar) metabolism and features of the metabolic syndrome for a 12-week trial.
 
The volunteers were randomly divided into three groups, each assigned to a different diet:
  • Healthy Diet – Fatty fish 3 times a week; 3 portions of bilberries per day; whole grains and low-glycemic index (GI) grain products daily.
  • Whole Grain Diet – Whole grain and low GI grain products
  • Control – Refined wheat breads and cereals.
Of the total recruited, 106 subjects completed the study. The participants in the Healthy Diet group ate fatty fish such as salmon, rainbow trout, herring, and vendace (a fatty freshwater whitefish).
 
The scientists examined the volunteers’ blood to identify its “metabolic profile”, including all fatty acids, 14 kinds of LDL and HDL cholesterol, and key lipid metabolites (metabolic breakdown products).
 
After three months, the participants in the Healthy Diet group had more large HDL particles in their blood, as well as lower levels of omega-6 fatty acids.
 
In fact, although their total HDL cholesterol levels remained stable, the Healthy Diet volunteers who ate the most fish developed the highest levels of large HDL particles, the largest-sized HDL particles, and the highest proportions of large HDL particles to total HDL.
 
And the participants in the Healthy Diet group who increased their fish intake the most showed the greatest positive metabolic changes.
 
The authors described the outcomes this way: “The results suggest that consumption of [a] diet rich in whole grain, bilberries, and especially fatty fish causes changes in HDL particles, shifting toward larger particles.” (Lankinen M et al. 2014)
 
As they concluded, “These changes may be related to known protective functions of HDL, such as reverse cholesterol transport, and could partly explain the known protective effects of fish consumption against atherosclerosis.” (Lankinen M et al. 2014)
 
It remains unclear whether similar benefits would have resulted had the participants mainly eaten lower-fat fish such as pike and perch.
 
(Low-fat fish may have other health benefits such as lowering of blood pressure, which was observed in an earlier study carried out at the University of Eastern Finland.)
 
The authors employed a new, state-of-the-art analytical technique called metabolomics to Identify 14 different kinds of LDL and HDL cholesterol.
 
As co-author Maria Lankinen said, “People shouldn't fool themselves into thinking that if their standard lipid levels are OK, there's no need to think about the diet, as things are a lot more complicated than that.” (UEF 2014)
 
She and her colleagues stressed that diet is central to the management of total, HDL, and LDL cholesterol levels.
 
The Finnish group plans more research, to compare health effects of fish-souce omega-3s (EPA and DHA) and plant-derived omega-3s (ALA), and the comparative health effects of fatty and low-fat fish.
 
 
Sources
  • Lankinen M, Kolehmainen M, Jääskeläinen, Paananen J, Joukamo L, Kangas AJ, Soininen P, Poutanen K, Mykkänen H, Gylling H, Orešič M, Jauhiainen M, Ala-Korpela M, Uusitupa M, Schwab U. Effects of Whole Grain, Fish and Bilberries on Serum Metabolic Profile and Lipid Transfer Protein Activities – a Randomized Trial (Sysdimet). PLOS ONE 2014
  • Lankinen M, Schwab U, Erkkilä A, Seppänen-Laakso T, Hannila ML, Mussalo H, Lehto S, Uusitupa M, Gylling H, Oresic M. Fatty fish intake decreases lipids related to inflammation and insulin signaling–a lipidomics approach. PLoS One. 2009;4(4):e5258. doi: 10.1371/journal.pone.0005258. Epub 2009 Apr 23.
  • Lankinen M, Schwab U, Kolehmainen M, Paananen J, Poutanen K, Mykkänen H, Seppänen-Laakso T, Gylling H, Uusitupa M, Orešič M. Whole grain products, fish and bilberries alter glucose and lipid metabolism in a randomized, controlled trial: the Sysdimet study. PLoS One. 2011;6(8):e22646. doi: 10.1371/journal.pone.0022646. Epub 2011 Aug 25.
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