Eating a Mediterranean-style diet may help people with type 2 diabetes keep their disease under control without drugs better than following a typical low-fat diet.A new study from Italy shows that people with type 2 diabetes who ate a Mediterranean diet rich in vegetables and whole grains with at least 30% of daily calories from fat (mostly olive oil) were better able to manage their disease without diabetes medications than those who ate a low-fat diet with no more than 30% of calories from fat (with less than 10% coming from saturated fat choices).
After four years, researchers found that 44% of people on the Mediterranean diet ended up requiring diabetes medications to control their blood sugars compared with 70% of those who followed the low-fat diet.
It’s one of the longest-term studies of its kind, and researchers, including Katherine Esposito, MD, of the Second University of Naples, say the results “reinforce the message that benefits of lifestyle interventions should not be overlooked.”
Best Diet for Diabetes Control
In the study, researchers randomly assigned 215 overweight people recently diagnosed with type 2 diabetes who had never been treated with diabetes medications to either a Mediterranean-style diet or a low-fat diet.
The Mediterranean diet was rich in vegetables and whole grains and low in red meat, which was replaced with fish or poultry. Overall, the diet consisted of no more than 50% of daily calories from carbohydrates and no less than 30% of calories from fat.
The low-fat diet was based on American Heart Association guidelines and was rich in whole grains and limited in sweets with no more than 30% of calories from fat and 10% from saturated fats, such as animal fats.
After four years of follow-up, the Mediterranean diet group had better glycemic (blood sugar) control and were less likely to require diabetes medications to bring their blood sugar within healthy levels.
In addition, people who followed the Mediterranean diet group also experienced improvement in other heart disease risk factors. Interestingly, weight loss was relatively comparable between the two groups by the end of the trial, suggesting that attributes of the Mediterranean diet beyond weight loss affect blood sugar control.
SOURCES: Esposito, K. Annals of Internal Medicine, Sept. 1, 2009; vol 151: pp 306-315. News release, American College of Physicians.
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
Over the past several decades, the food industry has reduced the amount of saturated fat in many products, and the public has reduced the amount of saturated fat in their diet. However, there has been a wide variation in the types of nutrients that have replaced this saturated fat. For example, in many products saturated fats were replaced with trans fats, which have since been determined to be detrimental; and in the overall American diet saturated fat was generally replaced with increased consumption of refined carbohydrates and grains.
“The specific replacement nutrient for saturated fat may be very important,” said lead author Dariush Mozaffarian, assistant professor in the department of epidemiology at HSPH and the department of medicine at Harvard Medical School. “Our findings suggest that polyunsaturated fats would be a preferred replacement for saturated fats for better heart health.”
Results from prior individual randomized controlled trials of saturated fat reduction and heart disease events were very mixed, with most showing no significant effects. Other trials focused only on blood cholesterol levels, which are an indirect marker of risk. Large observational studies have also generally shown no relationship between saturated fat consumption and risk of heart disease events; for example, earlier this month in the American Journal of Clinical Nutrition, researchers from HSPH and Children's Hospital Oakland Research Institute performed a pooled meta-analysis of prior observational studies and found no evidence that overall consumption of saturated fat was related to risk of coronary heart disease or stroke events.
Some of these mixed findings may relate to absence of prior focus on the specific replacement nutrient for saturated fat; in other words, was saturated fat replaced primarily with carbohydrate, monounsaturated fats such as in olive oil, or polyunsaturated fats such as in most vegetable oils?
Mozaffarian and his HSPH colleagues, Renata Micha and Sarah Wallace, performed a systematic review and meta-analysis of all randomized controlled trials through June 2009 in which participants specifically increased their polyunsaturated fat consumption as a replacement for saturated fat and in which coronary heart disease events were documented. Eight trials met the inclusion criteria, totaling 13,614 participants with 1,042 coronary heart disease events.
The meta-analysis of the trials showed that increasing polyunsaturated fat consumption as a replacement for saturated fat reduced the risk of coronary heart disease events by 19%. For every 5% increase (measured as total energy) in polyunsaturated fat consumption, coronary heart disease risk was reduced by 10%. This is now just the second dietary intervention–consuming long-chain omega-3 fatty acids is the first — to show a reduction in coronary heart disease events in randomized controlled trials.
Currently, the Institute of Medicine guidelines recommend that a range of 5%-10% energy consumption come from polyunsaturated fats. In addition, some scientists and organizations have recently suggested that consumption of polyunsaturated fats (largely “omega-6” fatty acids) should actually be reduced due to theoretical concerns that such consumption could increase coronary heart disease risk.
The results from this study suggest that polyunsaturated fats from vegetable oils may be an optimal replacement for saturated fats, an important finding for dietary guidelines and for when food manufacturers and restaurants are making decisions on how to reduce saturated fat in their products. The findings also suggest that an upper limit of 10% energy consumption from polyunsaturated fats may be too low, as the participants in these trials who reduced their risk were consuming about 15% energy from polyunsaturated fats.
Support for this study was provided by the National Heart, Lung, and Blood Institute, NIH and a Searle Scholar Award from the Searle Funds at the Chicago Community Trust.
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.”
Eating a diet of plenty of oily fish daily can protect women against infertility, says a new study. Researchers have carried out the study of 70,000 nurses and found those who ate the most tuna, salmon, mackerel and other fish high in omega-3 fatty acids were nearly 22 per cent less likely to develop endometriosis which is known to causes infertility.
However, the study found that those whose diets were heavily laden with harmful transfats – chemically altered vegetable oils – found in thousands of products from cakes and biscuits to pies and chips were 48 per cent more at risk of developing endometriosis. The condition arises when cells normally found in the womb lining attach themselves to other parts of the pelvic area, causing inflammation and often leading to infertility.
The study, the largest to have investigated the link between diet and endometriosis, followed the nurses for 12 years from 1989. It found while the total amount of fat consumed did not matter, the type did.
Gynaecologist Dr Stacey Missmer, of Harvard Medical School, Boston, said her findings, not only suggest that diet may be important in the development of endometriosis but also provide more evidence for eliminating trans fats, which are used to bulk up foods and increase their shelf life.
“Millions of women worldwide suffer from endometriosis. Many have been searching for something they can do for themselves, or their daughters, to reduce the risk of developing the disease. These findings suggest dietary changes may be something they can do. The results need to be confirmed by further research, but this study gives us a strong indication that we are on the right track in identifying food rich in omega-3 oils as protective for endometriosis and trans fats as detrimental,” she said.
The study is published in the 'Human Reproduction' journal.