Large study adds more evidence that omega-3s may help deter the kidney damage associated with diabetes
by Craig Weatherby
We've reported before on the promise of omega-3-rich diets in diabetes... and now there's more good news.
Population studies show lower rates of glucose intolerance and its eventual outcome—type 2 diabetes—wherever people consume large amounts of fish.
Almost certainly, the reason for this apparent reduced risk is the omega-3s in fish.
Controlled clinical studies show that consumption of marine omega-3s reduces heart risks in people with type 2 diabetes, without any adverse effects on blood sugar control or insulin activity (Nettleton JA, Katz R 2005).
And preliminary evidence suggests that for overweight people, increased consumption of omega-3s—along with reduced intake of saturated fat—may reduce the risk that impaired glucose tolerance will become type 2 diabetes.
Diets high in omega-3s are also associated with reduced risk of albuminuria, reduced inflammation, less oxidative stress, and less obesity.
For more on this topic, see “Diabetes Study Debacle: Can Fishy Nutrients Help?”, which contains links to prior articles on research into omega-3s and diabetes.
Fish linked to lower risk of diabetic kidney disease
An analysis of data collected from more than 22,300 middle-aged and older English men and women suggest that eating fish may reduce the risk of kidney disease pretty dramatically (Lee CT et al. 2008).
English researchers studied medical records of people who were part of a large European cancer study
Out of the 517 subjects who had diabetes
—mostly type 2 or “adult onset” diabetes
—those who reported eating fish twice a week were four times less likely to show the signs of kidney failure (albumin in their urine) compared with the diabetics who averaged less than one serving of fish per week.
As the authors concluded, “These findings merit confirmation in prospective studies and intervention trials and suggest that fish intake may be beneficial for albuminuria in people with diabetes” (Lee CT et al. 2008).
Unfortunately, they didn't ask about the type of fish people ate, but fish eaters in the part of England that provided the volunteers favor cod, haddock, canned tuna, fried fish, and plaice (a family of flat fish like flounder).
Of course, people who eat fish might have other healthier habits, but it wouldn't hurt diabetics to eat more fish, whose heart-health and other effects make sense for this group.
We know that fried fish is much less healthful than other kinds—because of the load of pro-inflammatory omega-6 fatty acids in the batter—so stick with poached, broiled, and baked recipes.
Omega-3s and the diabetic risk to kidneys
When we digest protein, the process creates waste products. In the kidneys, millions of tiny blood vessels (capillaries) with even tinier holes in them act as filters.
But the high levels of blood sugar in diabetics make the kidneys filter too much blood, causing the capillary filters to leak protein, which is lost in the urine.
Having small amounts of protein in the urine is called microalbuminuria. Having larger amounts is called macroalbuminuria. When kidney disease isn't caught until macroalbuminuria occurs, complete kidney failure usually follows.
The kidneys work hard to make up for the failing capillaries so kidney disease produces no symptoms until almost all function is gone.
Not everyone with diabetes develops kidney disease. Risk factors include genetics, poor blood sugar control, and high blood pressure.
Keeping blood sugar in a recommended target range reduces the risk of kidney disease by one third.
And evidence from animal and human studies suggests that dietary omega-3s reduce the risk and severity of albuminuria (Fujikawa M et al. 1994; Schmitz PG et al. 1995; Shimizu H et al. 1995).
- Fujikawa M, Yamazaki K, Hamazaki T, Wakaki K, Koizumi F, Yano S, Kobayashi M. Effect of eicosapentaenoic acid ethyl ester on albuminuria in streptozotocin-induced diabetic rats. J Nutr Sci Vitaminol (Tokyo). 1994 Feb;40(1):49-61.
- Lee CT, Adler AI, Forouhi NG, Luben R, Welch A, Khaw KT, Bingham S, Wareham NJ. Cross-sectional association between fish consumption and albuminuria: the European Prospective Investigation of Cancer-Norfolk Study. Am J Kidney Dis. 2008 Nov;52(5):876-86. Epub 2008 Jun 4.
- Nettleton JA, Katz R. n-3 long-chain polyunsaturated fatty acids in type 2 diabetes: a review. J Am Diet Assoc. 2005 Mar;105(3):428-40. Review.
- Schmitz PG, Lane PL, Dalal R, Zhang K, Majidi BJ. Omega-3 fatty acids attenuate glomerular capillary hydraulic pressure in rats with renal ablation. Kidney Int. 1995 Dec;48(6):1792-800.
- Shimizu H, Ohtani K, Tanaka Y, Sato N, Mori M, Shimomura Y. Long-term effect of eicosapentaenoic acid ethyl (EPA-E) on albuminuria of non-insulin dependent diabetic patients. Diabetes Res Clin Pract. 1995 Apr;28(1):35-40.