Eating a diet rich in omega-3 fatty acids appears to protect seniors against the onset of a serious eye disease known as age-related macular degeneration (AMD). Researchers did a fresh analysis of a one-year dietary survey conducted in the early 1990s. The poll involved nearly 2,400 seniors between the ages of 65 and 84 living in Maryland’s Eastern Shore region, where fish and shellfish are eaten routinely.
While participants in all groups, including controls, averaged at least one serving of fish or shellfish per week, those who had advanced AMD had consumed less fish and seafood containing omega-3 fatty acids. After their food intake was assessed, participants underwent eye examinations. About 450 had AMD, including 68 who had an advanced stage of the disease, which can lead to severe vision impairment or blindness. Prior evidence suggested that dietary zinc is similarly protective against AMD, so the researchers looked to see if zinc consumption from a diet of oysters and crabs reduced risk of AMD, but no such association was seen.
The researchers believe that the low dietary zinc levels relative to zinc supplements could account for the absence of such a link. However, they cautioned against people to start taking omega-3 supplements to protect against AMD based on this study because they are not sure that the above results have sufficient power to draw any conclusions. The correlation is important but larger studies with longer term follow-up are needed before being able to properly assess the impact.
Women who eat more than three servings of fish per week are less likely to experience a stroke, a new study suggests. Specifically, fish-lovers in Sweden were 16 percent less likely to experience a stroke over a 10-year-period, relative to women who ate fish less than once a week. “Fish consumption in many countries, including the U.S., is far too low, and increased fish consumption would likely result in substantial benefits in the population,” said Dr. Dariush Mozaffarian of the Harvard School of Public Health. When choosing fish to eat, it’s best to opt for fish that are rich in omega-3 fatty acids, found most abundantly in fatty fish like salmon, mackerel and albacore tuna. “But any fish is better than none,” Mozaffarian noted.
“Indeed, these fatty acids likely underlie the benefits of fish on stroke risk”, said study author Dr. Susanna Larsson of the Karolinska Institute in Stockholm. “These fatty acids may reduce the risk of stroke by reducing blood pressure and blood (fat) concentrations.”
This is not the first study to suggest that people who eat more fish have a lower risk of stroke, and experts already recommend a fishy diet to reduce the risk of cardiovascular problems, Mozaffarian added. “This study supports current recommendations.” Earlier this year, for instance, a study showed that middle-aged and older men who eat fish every day are less likely than infrequent fish eaters to develop a suite of risk factors for heart disease, diabetes and stroke.
In the current study, published in the American Journal of Clinical Nutrition, Larsson and her colleagues looked at 34,670 women 49 to 83 years old. All were free of cardiovascular disease and cancer at the beginning of the study, in 1997. During 10 years of follow-up, 1,680 of the women (4 percent) had a stroke. Stroke caused by blockage of an artery that supplies blood to the brain — also known as a “cerebral infarction” or “ischemic stroke” — was the most common event, representing 78 percent of all strokes in the study. Other types of strokes were due to bleeding in the brain, or unspecified causes.
Women who ate more than three servings of fish per week had a 16 percent lower risk of stroke than women who ate less than one serving a week. “Not a small effect,” Mozaffarian said, noting that it was roughly equivalent to the effect of statin drugs on stroke risk. Furthermore, the researchers asked women about their diets only once, using a questionnaire, which might have caused errors that would underestimate the link between a fishy diet and stroke risk, he explained. “So, the true risk reduction may be larger.”
Interestingly, women appeared to benefit most from eating lean fish, when other research shows fatty fish is better for health. This finding may stem from the fact that most fatty fish, such as herring and salmon, is eaten salted in Sweden, Larsson explained. “A high intake of salt increases blood pressure and thus may increase the risk of stroke,” she said. “So the protective effects of fatty acids in fatty fish may be attenuated because of the salt.”
Indeed, when it comes to fish, not all have equal benefits, Mozaffarian noted – for instance, he said, research has not shown any cardiovascular benefits from eating fast food fish burgers or fish sticks. In addition, women of childbearing age should avoid certain types of fish known to carry relatively high levels of pollutants, such as shark and swordfish, Mozaffarian cautioned. “This is a very, very short list of fish to avoid or minimize — there are many, many other types of fish to consume,” he said. “Women at risk of stroke are generally beyond their child-bearing years, and so for these women, all types of fish can be consumed.”
Larsson and her team speculate that certain nutrients in fish, such as fatty acids and vitamin D, might explain its apparent benefits. The Swedish study cannot prove cause and effect for high fish consumption and lowered stroke risk, however. For instance, fish consumption could be a sign of a generally healthier lifestyle or some other mechanism at work. Last December, Larsson and colleagues published data from the same group of women in the journal Stroke showing that those who eat a lot of red meat may also be putting themselves at increased risk of stroke.
SOURCE: bit.ly/dKunk8 American Journal of Clinical Nutrition, online December 29, 2010.
Recent studies show that grapefruit and diabetes may share a close link. Researchers concluded that naringenin found in grapefruit may increase the body's sensitivity to insulin. This research was conducted only in the laboratory, and further studies are still needed. Grapefruit and diabetes may share a close link given some recent studies suggesting that eating of the fruit can help in controlling the disease. One recent report suggests that grapefruit may become an effective part of the treatment for type 2 diabetes as it contains the antioxidant Naringenin that can break down fats and increase a person's sensitivity to insulin.
The study also concluded that grapefruit is also capable of treating abnormal levels of cholesterol, warding off metabolic syndrome and improving a person's tolerance to glucose, factors that are all associated with diabetes. The study was conducted by scientists from the Massachusetts General Hospital Center for Engineering in Medicine and Hebrew University of Jerusalem. Although more research needs to be completed, grapefruit is a safe source of vitamins for diabetics. One-half of a grapefruit contains 52 calories and 13g of carbohydrates, and the fruit has a low rating on the glycemic index, indicating a lower propensity to drive up blood sugar levels.
The antioxidant Naringenin is found in grapefruit and has been largely credited for its ability in heping to treat type 2 diabetes. Naringenin is specifically noted for being able to break down fatty acids in the liver, similar to what happens when a person undergoes fasting. Yaakov Nahmias, PhD of the Hebrew University of Jerusalem reports that the results of their study indicate that Naringenin antioxidant was found to be capable of breaking down fatty acids similar to those induced by significant amounts of fasting. It does so by activating nuclear receptors, a family of proteins that can cause the liver to break down fatty acids instead of storing them.
Another study conducted by researchers at the University of Western Ontario showed that Naringenin can correct increases in triglyceride and cholesterol levels, while resisting insulin resistance and normalizing glucose metabolism. The said study showed that Naringenin genetically reprograms the liver to burn up more excess fat, instead of storing it. The said study also showed that Naringenin is able to suppress appetite and decrease food intake, which are common strategies in controlling diabetes.
The study of MGH and Hebrew University scientists also noted that Naringenin can lower bad cholesterol called vLDL while able to cure several symptoms of type 2 diabetes.
Research on grapefruit and diabetes, however, has not yet been conducted on humans, and were only done in the laboratory on the liver cells of humans and rats. Until further studies are done to confirm the effects of grapefruit in the treatment of diabetes type 2 in humans, it is still not safe to conclude that the naringenin in grapefruits can indeed cure diabetes. Further studies are still needed to establish its efficacy as well as its overall effects in the body, including the negative effects it might have.
Thus, many health experts do not encourage patients with diabetes to increase their consumption of grapefruits or increase grape juice intake, especially if they are also taking medications. There are patients prescribed with some type of drugs to lower their cholesterol level who are advised not to drink grapefruit juice as it can increase risk of side effects.
Nutrition experts at Oregon State University have essentially “cured” laboratory mice of mild, diet-induced diabetes by stimulating the production of a particular enzyme. The findings could offer a new approach to diabetes therapy, experts say, especially if a drug could be identified that would do the same thing, which in this case was accomplished with genetic manipulation.
Increased levels of this enzyme, called fatty acid elongase-5, restored normal function to diseased livers in mice, restored normal levels of blood glucose and insulin, and effectively corrected the risk factors incurred with diet-induced diabetes. “This effect was fairly remarkable and not anticipated,” said Donald Jump, a professor of nutrition and exercise sciences at Oregon State, where he is an expert on lipid metabolism and principal investigator with OSU’s Linus Pauling Institute. “It doesn’t provide a therapy yet, but could be fairly important if we can find a drug to raise levels of this enzyme,” Jump said. “There are already some drugs on the market that do this to a point, and further research in the field would be merited.”
The studies were done on a family of enzymes called “fatty acid elongases,” which have been known of for decades. Humans get essential fatty acids that they cannot naturally make from certain foods in their diet. These essential fatty acids are converted to longer and more unsaturated fatty acids. The fatty acid end products of these reactions are important for managing metabolism, inflammation, cognitive function, cardiovascular health, reproduction, vision and other metabolic roles.
The enzymes that do this are called fatty acid elongases, and much has been learned in recent years about them. In research on diet-induced obesity and diabetes, OSU studied enzyme conversion pathways, and found that elongase-5 was often impaired in mice with elevated insulin levels and diet-induced obesity.
The scientists used an established system, based on a recombinant adenovirus, to import the gene responsible for production of elongase-5 into the livers of obese, diabetic mice. When this “delivery system” began to function and the mice produced higher levels of the enzyme, their diet-induced liver defects and elevated blood sugar disappeared.
“The use of a genetic delivery system such as this was functional, but it may not be a permanent solution,” Jump said. “For human therapy, it would be better to find a drug that could accomplish the same thing, and that may be possible. There are already drugs on the market, such as some fibrate drugs, that induce higher levels of elongase-5 to some extent.”
There are also drugs used with diabetic patients that can lower blood sugar levels, Jump said, but some have side effects and undesired complications. The potential for raising levels of elongase-5 would be a new, specific and targeted approach to diabetes therapy, he said. While lowering blood sugar, the elevated levels of elongase-5 also reduced triglycerides in the liver, another desirable goal. Elevated triglycerides are associated with “fatty liver,” also known as non-alcoholic fatty liver disease. This can progress to more severe liver diseases such as fibrosis, cirrhosis and cancer.
Further research is needed to define the exact biological mechanisms at work in this process, and determine what the fatty acids do that affects carbohydrate and triglyceride metabolism, he said. It appears that high fat diets suppress elongase-5 activity.
“These studies establish a link between fatty acid elongation and hepatic glucose and triglyceride metabolism,” the researchers wrote in their report, “and suggest a role for regulators of elongase-5 activity in the treatment of diet-induced hyperglycemia and fatty liver.”
The study was published in the Journal of Lipid Research. The research was supported by the National Institutes of Health and the National Institute for Food and Agriculture of the U.S. Department of Agriculture.
The new study looked into the effects of four different diet combinations on blood lipid metabolism, in 117 patients with metabolic syndrome.
In accordance with previous suggestions, the researchers found that a low-fat, high-complex carbohydrate diet had “several detrimental effects”, including significantly increasing total triglyceride levels, and triglyceride rich lipoprotein cholesterol levels.
In contrast, intake of the same diet supplemented with omega-3 was found to have no effects on blood lipid levels, with researchers observing that a diet rich in monounsaturated fats, or a low-fat diet rich in complex carbohydrates and omega-3 fatty acids, resulted in lower circulating blood lipid levels than a diet rich in high saturated fats or a diet low in fats and high in complex carbohydrates.
The data from the study suggest a place for higher omega-3 intake in people with metabolic syndrome, and supports previous research that suggests monounsaturated fatty acids can have a positive effect on blood lipid levels.
“The long-term effect of the low-fat, high-complex carbohydrate diet, pre vs. post intervention phases, showed several beneficial effects of long chain omega-3 PUFA supplementation,” stated the researchers.
“Our data suggest that long-term intake of an isocaloric, low-fat, high-carbohydrate diet supplemented with long chain omega-3 … have beneficial effects on postprandial lipoprotein response in patients with metabolic syndrome,”
Source: The Journal of Nutrition
“A Low-Fat, High-Complex Carbohydrate Diet Supplemented with Long-Chain (n-3) Fatty Acids Alters the Postprandial Lipoprotein Profile in Patients with Metabolic Syndrome”
Authors: Y. Jimenez-Gomez, C. Marin, P. Perez-Martinez, et al
“It may be that the amount of omega-3 fatty acids in fish oil supplements are higher than most people would typically get from their diet,” White said.
However, White cautioned against gleaning any recommendations from the results of one study.
“Without confirming studies specifically addressing this,” she said, “we should not draw any conclusions about a causal relationship.”
Edward Giovannucci, M.D., Sc.D., professor of nutrition and epidemiology at the Harvard School of Public Health and an editorial board member of Cancer Epidemiology, Biomarkers & Prevention, agreed.
“It is very rare that a single study should be used to make a broad recommendation,” said Giovannucci. “Over a period of time, as the studies confirm each other, we can start to make recommendations.”
Still, fish oil continues to excite many, as evidence emerges about its protective effect on cardiovascular disease and now cancer.
Harvard researchers are currently enrolling patients for the randomized Vitamin D and Omega-3 Trial (also called VITAL), which will assess the impact of fish oil supplements and vitamin D on cancer, heart disease and stroke.
The researchers plan to enroll 20,000 U.S. men aged 60 years and older and women aged 65 years and older who do not have a history of these diseases and have never taken supplements.
Dr. Gu and her colleagues studied a cohort of 2148 elderly subjects 65 years and older living in New York City. All subjects were healthy and free of dementia at study entry. Their dietary habits were obtained via questionnaire, and they were prospectively evaluated with the same standardized neurologic and neuropsychological measures approximately every 1.5 years for an average of 4 years.
The researchers used reduced rank regression to calculate dietary patterns according to their effect on 7 nutrients previously shown in the literature to be related to Alzheimer's disease: saturated fatty acids, monounsaturated fatty acids, ω-3 polyunsaturated fatty acids, ω-6 polyunsaturated fatty acids, vitamin E, vitamin B12, and folate.
During the follow-up, 253 individuals developed Alzheimer's disease. The study found that one dietary pattern — characterized by higher intakes of salad dressing, nuts, fish, tomatoes, poultry, cruciferous vegetables, fruits, and dark and green leafy vegetables and a lower intake of high-fat dairy products, red meat, organ meat, and butter — was significantly associated with a reduced risk for Alzheimer's disease.
Compared with subjects in the lowest tertile of adherence to this pattern, the Alzheimer's disease hazard ratio (95% confidence interval) for subjects in the highest tertile was 0.62 (0.43 – 0.89) after multivariable adjustment (P for trend = .01).
The study also found that subjects who were older, less educated, and current smokers tended to be less adherent to the protective diet. Hispanic individuals adhered less than white and black individuals (P = .02), and women tended to adhere more than men (P = .05).
“The dietary pattern that was most protective against Alzheimer's reflected a diet rich in ω-3 and ω-6 polyunsaturated fatty acids, vitamin E, and folate but poor in saturated fatty acids and vitamin B12,” commented Dr. Gu. “The combination of nutrients in this dietary pattern reflects multiple pathways in the development of Alzheimer's disease.
“For example, vitamin B12 and folate are homocysteine-related vitamins that may have an impact on the disease through their ability to lower circulating homocysteine levels,” she said. “Vitamin E is a strong antioxidant, and the fatty acids may be linked to dementia and cognitive function through atherosclerosis, thrombosis, or inflammation. Fatty acids may also affect brain development and membrane functioning.”
She added that the study has several limitations. “We used a single measurement of the diet, and this might not have captured the long-term dietary habits of the subjects. We also excluded subjects from the final analysis because they were lost to follow-up, and this might have introduced selection bias. We also can't completely rule out the possibility that the reduced risk associated with this protective diet was due to residual confounding.”
Further studies are planned, Dr. Gu said. “We cannot say based on this study alone that this type of dietary pattern prevents Alzheimer's disease, but many studies have consistently shown that fruits and vegetables and unsaturated fatty acids are associated with a lower risk. We want to repeat these findings in different populations and see if they can be confirmed in other studies.”
Commenting on this study for Medscape Neurology, David Knopman, MD, professor of neurology at the Mayo Clinic and a member of the Mayo Clinic Alzheimer's Disease Research Center in Rochester, Minnesota, said that, despite the study authors' best efforts, it is still not clear whether diet alone makes a difference.
“Dietary habits, which often are lifelong, are certainly part of the array of health behaviors that contribute to better cognitive health in late life. However, diet and other health behaviors are intertwined. Because a healthy diet contributes to better cardiac health, lower weight, lower blood pressure and a lower risk for diabetes, there are many reasons to view the dietary habits described by Dr. Gu and colleagues as beneficial.”
The study was supported by federal National Institute on Aging grants. Dr. Gu and Dr. Knopman have disclosed no relevant financial relationships.
Arch Neurol. Published online April 12, 2010.
Trans fats are made through hydrogenation, which involves bubbling hydrogen through hot vegetable oil, changing the arrangement of double bonds in the essential fatty acids in the oil and “saturating” the “unsaturated” carbon chain with hydrogen. Because double bonds are rigid, altering them can straighten or twist fat molecules into new configurations that give the fats their special qualities, such as the lower melting point of margarine that makes it creamy at room temperature.
Kummerow, 94, has spent nearly six decades studying lipid biochemistry, and is a long-time advocate for a ban on trans fats in food.
While the body can use trans fats as a source of energy for maintenance and growth, Kummerow said, trans fats interfere with the body's ability to perform certain tasks critical to good health. Because these effects are less obvious, many researchers have missed the underlying pathologies that result from a diet that includes trans fats, he said.
Trans fats displace – and cannot replace – the essential fatty acids linoleic acid (omega-6) and linolenic acid (omega-3), which the body needs for a variety of functions, including blood flow regulation. Studies have shown that trans fats also increase low-density lipoproteins (LDLs) in the blood, a factor which some believe contributes to heart disease.
Trans fats are associated with increased inflammation in the arteries. And trans fats have been found to change the composition of cell membranes, making them more leaky to calcium. Inflammation, high LDL cholesterol and calcified arteries are the signature ingredients of atherosclerosis.
Trans fats also were shown to interfere with an enzyme that converts the essential fatty acid linoleic acid into arachidonic acid, which is needed for the production of prostacyclin (a blood-flow enhancer) and thromboxane (which regulates the formation of blood clots needed for wound healing). While some in the food oil industry believed this problem could be overcome simply by adding more linoleic acid to partially hydrogenated fats, in 2007 Kummerow's team reported that extra linoleic acid did not overcome the problem.
“Trans fats inhibited the synthesis of arachidonic acid from linoleic acid, even when there was plenty of linoleic acid available,” he said.
The new study reports that in addition to interfering with the production of arachidonic acid from linoleic acid, trans fats also reduce the amount of prostacyclin needed to keep blood flowing. Thus blood clots may more easily develop, and sudden death is possible.
According to the American Heart Association, each year more than 330,000 people in the U.S. die from coronary heart disease before reaching a hospital or while in an emergency room. Most of those deaths are the result of sudden cardiac arrest, the Heart Association reports.
“This is the first time that trans fatty acids have been shown to interfere with yet another part of the blood-flow process,” Kummerow said. This study adds another piece of evidence to a long list that points to trans fats as significant contributors to heart disease, he said.
Kummerow believes the U.S. Food and Drug Administration's new requirement (begun in 2006) that trans fats be included on food labels is inadequate and misleading. Anything less than one-half gram of trans fats per serving can be listed as zero grams, Kummerow said, so people are often getting the mistaken impression that their food is trans fat-free.
“Go to the grocery store and compare the labels on the margarines,” he said. “Some of them say zero trans fat. That's not true. Anything with partially hydrogenated oils in it contains trans fat.”
“Partially hydrogenated fats can be made trans fat-free,” Kummerow said. “The industry would be helped by an FDA ban on trans fat that would save labeling costs, medical costs and lives.”
Increased intakes of omega-3 fatty acids may decrease the risk of heart disease and heart attack in people with low fish intakes, says a new study from The Netherlands. Daily intakes of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) of about 240 milligrams was associated with a 50 per cent reduction in the risk of coronary heart disease (CHD), compared with intakes of about 40 milligrams, according to findings published in the Journal of Nutrition. Furthermore, the highest average intake of DHA and EPA was associated with a 38 per cent reduction in the heart attack, said researchers from Wageningen University following a study with over 21,000 people with low fish intakes.
The heart health benefits of consuming oily fish, and the omega-3 fatty acids they contain, are well-documented, being first reported in the early 1970s by Jorn Dyerberg and his co-workers in The Lancet and The American Journal of Clinical Nutrition. To date, the polyunsaturated fatty acids (PUFAs) have been linked to improvements in blood lipid levels, a reduced tendency of thrombosis, blood pressure and heart rate improvements, and improved vascular function.
Omega-3 fatty acids, most notably DHA and EPA, have been linked to a wide-range of health benefits, including reduced risk of cardiovascular disease (CVD) and certain cancers, good development of a baby during pregnancy, joint health, and improved behaviour and mood.
Intakes of EPA plus DHA, and fish were assessed in 21,342 people aged between 20 and 65. Fish intakes ranged from 1.1 to 17.3 grams per day. Over the course of an average of 11.3 years, the researchers documented 647 deaths, of which 82 were linked to coronary heart disease, with 64 of these being heart attack.
According to the results, the highest average intake of EPA plus DHA (234 milligrams per day) was associated with a 51 per cent reduction in the risk of fatal CHD, compared to the lowest average intake (40 mg per day).
“In conclusion, in populations with a low fish consumption, EPA+DHA and fish may lower fatal CHD and [heart attack] risk in a dose-responsive manner,” wrote the researchers.
Source: Journal of Nutrition
“Marine (n-3) Fatty Acids, Fish Consumption, and the 10-Year Risk of Fatal and Nonfatal Coronary Heart Disease in a Large Population of Dutch Adults with a Low Fish Intake”
Authors: J. de Goede, J.M. Geleijnse, J.M. A. Boer, D. Kromhout, W. M.M. Verschuren