fish oils and type II
INTERNATIONAL HEALTH NEWS DATABASE
Fish Oils and Diabetes
Summaries of the latest research concerning fish oils
and diabetes
Fish oil supplementation is safe for diabetics
PARIS, FRANCE. People suffering from type II diabetes
often have high blood levels of triglycerides and are
therefore prone to coronary heart disease. Fish oils
are known to be effective in lowering triglyceride
levels, but concern has been expressed that they may
also increase low-density lipoprotein (LDL) levels and
be deleterious to glucose control.
Medical researchers at the Hotel-Dieu hospital now
report the results of a study designed to investigate
these concerns. The study involved 10 men with type II
diabetes (average age of 54 years). The men were
randomized into two groups in the double-blind
crossover study. Group 1 supplemented with 6 grams/day
of fish oils (containing 320 mg of eicosapentaenoic
acid [EPA] and 215 mg of docosahexaenoic acid [DHA])
for two months while group 2 supplemented with 6
grams/day of sunflower oil (containing 65% linoleic
acid). At the end of the two months all participants
went through a 2-month wash-out period and group 1 was
then assigned to supplement with sunflower oil while
group 2 was given fish oil supplements. All
participants maintained their regular diet (55%
carbohydrates, 15% protein, and 30% fat) and continued
with their medications throughout the study except for
cholesterol-lowering drugs which were discontinued 2
months before the start of the trial.
The researchers noted a considerable increase in both
EPA and DHA content in blood plasma phospholipids and
in red blood cell membranes after two months on the
fish oil supplements. Triglyceride levels and the
level of plasma lipoprotein(a) were both significantly
lowered following fish oil supplementation. No adverse
effects on glucose control were observed; there was a
small increase in the LDL level, but this was
compensated for by a similar increase in the HDL
(high-density lipoprotein) level so that the important
LDL/HDL ratio remained unchanged. The researchers
conclude that fish oil supplementation is effective in
lowering triglyceride levels in type II diabetics and
has not adverse effects on glycemic control or overall
cholesterol levels.
Luo, Jing, et al. Moderate intake of n-3 fatty acids
for 2 months has no detrimental effect on glucose
metabolism and could ameliorate the lipid profile in
type 2 diabetic men. Diabetes Care, Vol. 21, May 1998,
pp. 717-24
Fish oils and fiber benefit diabetics
CLEVELAND, OHIO. Patients with non-insulin-dependent
diabetes mellitus (NIDDM) often suffer from abnormal
lipid (fat) and lipoprotein metabolism resulting in
unfavourable cholesterol levels and an accompanying
increase in the risk of heart disease. Numerous
studies have shown that fish oil supplementation
lowers the levels of very-low-density-lipoprotein
(VLDL) and triglycerides (triacylglycerol), but has
little effect on the levels of low-density-lipoprotein
(LDL) and total cholesterol. There has also been some
reports that fish oil supplementation may worsen
glycemic (glucose) control. Now medical researchers at
the Case Western Reserve University report that adding
soluble fiber to the fish oil supplementation regimen
is highly beneficial. Their experiment involved 15
non-obese NIDDM patients (12 men and 3 women) aged 32
to 74 years. For the first four weeks the patients
received 20 grams of fish oil per day (equivalent to
six grams of n-3 fatty acids). During the next four
weeks all patients received the fish oil plus 15
grams/day of soluble apple pectin. During the final
four weeks both supplements were withdrawn. The
patients continued their usual diabetic diet and
medication during the entire study period. Analysis of
blood samples showed that fish oil supplementation
alone lowered the levels of triacylglycerol and VLDL
cholesterol by 41 per cent and 36 per cent
respectively. No changes were observed in total
cholesterol, LDL cholesterol or HDL cholesterol. When
apple pectin was added to the treatment
triacylglycerol and VLDL cholesterol levels were both
lowered by 38 per cent, but in addition total
cholesterol levels decreased by 13 per cent and LDL
cholesterol by 7 per cent. There was no significant
change in HDL cholesterol level. Fasting and two-hour
postprandial plasma glucose concentrations were not
affected by the fish oil or fish oil/pectin
supplementation and no changes in serum levels of
zinc, magnesium, and copper were observed. Plasma
levels of triglycerides and cholesterols returned to
pre-treatment levels four weeks after discontinuation
of supplementation. The researchers conclude that a
combination of fish oil supplementation and increased
fiber intake (up to 40 grams/day total) may be a
beneficial addition to the conventional treatment of
high cholesterol levels in NIDDM patients.
Sheehan, John P., et al. Effect of high fiber intake
in fish oil-treated patients with
non-insulin-dependent diabetes mellitus. American
Journal of Clinical Nutrition, Vol. 66, November 1997,
pp. 1183- 87
Diabetics may benefit from fish oil supplementation
NAPLES, ITALY. Animal studies have shown that fish oil
supplementation has a beneficial effect on insulin
resistance and can prevent its development in animals
fed a high-fat diet. It is also known that a high fish
intake can delay the development of diabetes in
glucose-intolerant individuals. Researchers at the
Federico II University recently set out to investigate
if long-term supplementation with fish oils would
improve insulin sensitivity in patients with
non-insulin-dependent diabetes (NIDDM). The clinical
trial involved 16 NIDDM patients (average age of 56
years) who, after a 3 week run-in period during which
they received 3 olive oil capsules per day, were
assigned to receive either fish oil capsules or olive
oil capsules for a further 6-month period. For the
first two months the participants received either 3
fish oil capsules daily (320 mg eicosapentaenoic acid
[EPA] and 530 mg docosahexaenoic acid [DHA] per
capsule) or 3 placebo capsules (each containing 1 gram
of olive oil). During the last four months these
dosages were reduced to 2 fish oil or 2 placebo
capsules daily. The patients were evaluated at the
beginning and end of the trial and maintained their
usual diet and medications (except for cholesterol-
lowering drugs) during the entire trial period.
The researchers concluded that fish oil
supplementation induced a significant decrease in
triglyceride concentrations particularly in the level
of very-low-density lipoprotein (VLDL) triglycerides
(a reduction of 45%). There was also a significant
decrease in VLDL cholesterol levels (47% drop) and a
14% increase in LDL cholesterol. There was no
significant change in blood glucose control and,
contrary to expectations, no significant improvement
in insulin resistance despite the fact that red blood
cell levels of EPA and DHA increased significantly.
The researchers conclude that long-term fish oil
supplementation lowers triglyceride levels in NIDDM
patients without adversely affecting blood glucose
control. NOTE: This study was partially funded by
Pharmacia, Farmitalia Carlo Erba, Milan, Italy.
Rivellese, Angela A., et al. Long-term effects of fish
oil on insulin resistance and plasma lipoproteins in
NIDDM patients with hypertriglyceridemia. Diabetes
Care, Vol. 19, November 1996, pp. 1207-13
Diabetes and fish oil supplementation
EDMONTON, CANADA. Diabetics are at significantly
increased risk for cardiovascular disease and any
dietary intervention that could decrease this risk
would be of great importance. Studies have shown that
fish oil supplementation lowers triglycerides, very
low density lipoprotein (VLDL) levels, and blood
pressure in non-diabetic individuals and thereby
diminishes their risk of heart disease. Unfortunately,
some early experiments with fish oil supplementation
in type II diabetics reported adverse effects on
glycemic control and cholesterol levels.
Researchers at the University of Alberta have just
released the results of a new study aimed at
evaluating the overall effects of fish oil
supplementation in type II diabetics. Eleven subjects
with non-insulin- requiring type II diabetes took part
in the randomized, double-blind, crossover study. All
participants underwent a 3-month run-in period during
which they supplemented with olive oil capsules
(placebo). They were then randomized into two groups
with one group supplementing with fish oil capsules
(about 2.0 grams/day) and the other group
supplementing with flax seed oil capsules. After 3
months the participants underwent a crossover to the
alternative oil for a final 3 months of
supplementation.
All study participants had acceptable blood levels of
total cholesterol, triglycerides, high density
lipoproteins, low density lipoproteins, and low
density triglycerides prior to initiating
supplementation with fish oil or flax seed oil.
Supplementation did not change these levels except in
the case of triglycerides which were markedly reduced
after fish oil supplementation. Glycemic control was
not adversely affected by supplementation with either
oil and there was a trend towards decreased insulin
sensitivity in the group taking fish oils. The
researchers conclude that fish oil supplementation is
safe in type II diabetes and can help ameliorate
cardiovascular disease risk factors such as high
triglyceride levels. They also conclude that flax seed
oil supplementation, while having no adverse effects,
is not of significant benefit in type II diabetes.
NOTE: This study was partially funded by the Canadian
Dairy Bureau.
McManus, Ruth M., et al. A comparison of the effects
of n-3 fatty acids from linseed oil and fish oil in
well-controlled type II diabetes. Diabetes Care, Vol.
19, May 1996, pp. 463-67
Fish oils recommended for diabetes and hypertension
TROMSO, NORWAY. Fish and fish oils help protect
against the development of atherosclerosis and heart
disease. It is believed that fish oils exert their
protective effect by lowering blood pressure and the
levels of triglycerides and very-low-density
lipoprotein (VLDL). Fish oils are also believed to
reduce platelet aggregation and to suppress the growth
of smooth-muscle cells in the arterial walls. Many
people with hypertension also suffer from diabetes and
there has been concern that fish oil supplementation
may aggravate problems with glucose intolerance.
Researchers at the University of Tromso now report
that fish oil supplementation lowers blood pressure
significantly in people with hypertension and has no
effect on glucose control even in people with mild
diabetes. The study involved 78 obese volunteers with
essential hypertension. The participants were randomly
assigned to one of two equal-sized groups. The fish
oil group received four fish oil capsules a day
(containing a total of 3.4 grams of a mixture of
eicosapentaenoic acid and docosahexaenoic acid) for a
period of 16 weeks. The control group received four
corn oil capsules a day.
At the end of the test period the average (mean)
systolic blood pressure had dropped by 4.4 mm Hg and
the diastolic pressure by 3.2 mm Hg in the fish oil
group. The average blood pressure in the control group
did not change. The researchers also found that plasma
triglyceride and VLDL levels in the fish oil group
decreased significantly (by about 9 per cent) while
they increased significantly (by about 12 per cent) in
the control group. There were no changes in total or
low-density-lipoprotein levels in either group.
Extensive tests (oral glucose tolerance, hyperglycemic
and hyperinsulemic clamps) were done to evaluate the
effect of fish oil supplementation on glucose control.
No adverse effects were found. An editorial
accompanying the research report concludes that fish
or fish oil is useful in the prevention of vascular
disease in diabetics. Patients with diabetes should
eat fish two to three times a week or, as an
alternative, supplement with two to three one gram
capsules of fish oil per day.
Toft, Ingrid, et al. Effects of n-3 polyunsaturated
fatty acids on glucose homeostasis and blood pressure
in essential hypertension. Annals of Internal
Medicine, Vol. 123, No. 12, December 15, 1995, pp.
911- 18
Connor, William E. Diabetes, fish oil, and vascular
disease. Annals of Internal Medicine, Vol. 123, No.
12, December 15, 1995, pp. 950-52
Fish oil supplementation recommended for type II
diabetics
DALLAS, TEXAS. High cholesterol and triglyceride
levels are common among diabetics and are major
contributors to their increased risk of cardiovascular
disease. Researchers at the Texas Woman’s University
and the University of Texas Medical Center now report
that fish oil supplementation can markedly decrease
cholesterol and triglyceride levels without adversely
affecting glycemic control.
Their study involved 40 patients with
non-insulin-dependent diabetes mellitus (NIDDM) who
had abnormally high blood plasma levels of one or more
of the following lipids: total cholesterol (greater
than 5.17 mmol/L), LDL cholesterol (greater than 3.36
mmol/L), or triglycerides (greater than 6.47 mmol/L).
After a four-week baseline phase during which
cholesterol levels, weight, blood pressure, and
diabetes control were assessed every two weeks the
participants were randomly assigned to one of four
groups - daily dose of 9 grams of corn oil (57%
linoleic acid), 18 grams of corn oil, 9 grams of fish
oil (29% EPA and 27% DHA), and 18 grams of fish oil.
All participants were assessed every two weeks during
the 12- week supplementation period.
A significant reduction in the levels of
very-low-density lipoproteins, triglycerides and
very-low-density triglycerides was observed among the
participants supplementing with fish oils at both the
6-week and 12-week mark. There were no significant
differences in the effect of 9 grams/day versus 18
grams/day supplementation. The level of LDL
cholesterol increased temporarily at the 6-week mark,
but this effect was no longer present at the 12-week
examination. Neither fish oil nor corn oil
supplementation produced any significant changes (over
baseline values) in total cholesterol levels, HDL
cholesterol levels, fasting plasma glucose, weight or
blood pressure. A small increase in VLDL cholesterol
was noted in the corn oil group at the end of the
experiment.
The researchers conclude that fish oil supplementation
is useful in lowering triglycerides in diabetics with
excessive levels and has no deleterious effect on
glycemic control.
Morgan, Wanda A., et al. A comparison of fish oil or
corn oil supplements in hyperlipidemic subjects with
NIDDM. Diabetes Care, Vol. 18, January 1995, pp. 83-86