Whole-fat dairy products containing high levels of a natural fatty acid might help lower the risk of type 2 diabetes, according to a recent research by U.S. scientists. A diet rich in milk, cheese, yogurt and butter contains trans-palmitoleic acid which is known to shield against insulin resistance and diabetes. “Our results demonstrate an inverse relationship between levels of trans-palmitoleate and metabolic risk factors and diabetes incidence,” Dariush Mozaffarian, MD, DrPH, of the Harvard School of Public Health, and coauthors wrote in conclusion. “The small differences in trans-palmitoleate levels raise questions about whether this is the active compound or a marker for some other, unknown protective constituent of dairy or other ruminant foods.”
The study looked at 3,736 American seniors from Medicare eligibility lists aged 65 years or older. Physical tests, diagnostic testing, questionnaires on health status, and laboratory evaluation was conducted to evaluate the levels of 45 different fatty acids in the participants. They were further followed for 10 years with the help of annual clinic visits and interim telephone calls.
Trans-palmitoleate was responsible for an average of 0.18 percent of total fatty acid levels, with whole-fat dairy consumption accounting for the highest trans-palmitoleatele proportions. Participants who had consumed high levels of whole-fat dairy products revealed higher levels of trans-palmitoleate acid in their blood three years later, Dariush and his co-authors reported in the December issue of the journal ‘Annals of Internal Medicine.’ Further, participants with the highest levels of the acid circulating in their blood faced two-third the risk of suffering from type 2 diabetes as compared to the ones with the lowest levels. Such people also had lesser fat on their bodies, higher proportions of good cholesterol and lower levels of C-reactive protein.
“This is an extremely strong protective effect, stronger than other things we know can be beneficial against diabetes,” said Gökhan Hotamisligil, the study’s senior author and chair of the department of genetics and complex diseases at Harvard School of Public Health. “The next step is to move forward with an intervention trial to see if there is therapeutic value in people,” he added in a statement.
The research has been funded by the U.S. National Heart, Lung and Blood Institute, the U.S. National Institute of Diabetes and Digestive and Kidney Diseases, the National Institute of Health Office of Dietary Supplements and National Institute of Neurological Disorders and Stroke.
The study was conducted in mice, some of which were fed a normal diet of rodent chow and some a 16-week diet of fructose and sucrose-enriched drinking water and trans-fat solids. Their liver tissue was then analyzed for fat content, scar tissue formation (fibrosis), and the biological mechanism of damage. This was done by measuring reactive oxygen stress, inflammatory cell type and plasma levels of oxidative stress markers, which are known to play important roles in the development of obesity-related liver disease and its progression to end-stage liver disease.
The investigators found that mice fed the normal calorie chow diet remained lean and did not have fatty liver disease. Mice fed high calorie diets (trans-fat alone or a combination of trans-fat and high fructose) became obese and had fatty liver disease.
“Interestingly, it was only the group fed the combination of trans-fat and high fructose which developed the advanced fatty liver disease which had fibrosis,” says Dr. Kohli. “This same group also had increased oxidative stress in the liver, increased inflammatory cells, and increased levels of plasma oxidative stress markers.”
Dr. Kohli hopes to further investigate the mechanism of liver injury caused by high fructose and sucrose enriched drinking water and study a therapeutic intervention of antioxidant supplementation. Antioxidants are natural defenses against oxidative stress and may reverse or protect against advanced liver damage, according to Dr. Kohli.
The investigators also would like to use this model to better understand human fatty liver disease and perform clinical trials using novel therapeutic and monitoring tools.
“Our data suggest that supplementation with pharmaceuticals agents should be tested on our new model to establish whether one is able to reverse or protect against progressive liver scarring and damage,” says Dr. Kohli.
The study was supported by grants from the National Institutes of Health and the Children's Digestive Health and Nutrition Foundation.
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.