Natural dairy and beef fats have been unfairly attacked as unhealthy when in fact they're often health promoting, says Helen Bishop MacDonald.
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Helen Bishop MacDonald
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While the promise of CLA continues to grow, a key challenge lies not in science but in the narrow public perception regarding ruminant fats, says nutritionist and author Helen Bishop MacDonald.
"Since CLA became known to the scientific and health community my concern has been that even if CLA were absolutely proven to prevent cancer, which it may very well, we would have a difficult time getting health professionals and consumers on board," says MacDonald. This is because of the mindset about ruminant fats, which she says can be summed up in two words: "They're bad!"
But the battle of perception need not be lost, says MacDonald, who offered insight into the ruminant fats debate in a keynote presentation at the CLA Summit 2007. There's a growing body of evidence that ruminant fats have been unfairly maligned and in fact are often health promoting. CLA is a leading example of a good fat found naturally in dairy and beef products that has been linked to considerable potential for human health benefits.
That's why a key benefit of CLA research is its role in providing knowledge to help rehabilitate the image of animal fats, she says. "CLA can play a major role in reshaping the negative image of animal fats. It's a great example that many of these fats are not harmful but in fact are healthful."
Among the myths that have persisted around ruminant fats is the notion that these fats cause heart disease, notes MacDonald. But close examination of the research reveals substantial evidence to the contrary. She cited numerous studies supporting her conviction that animal fats don't cause heart disease and more typically either have no negative effect or are associated with health promotion.
"We need to pay attention to the fact that we may have been barking up the wrong tree by targeting animal fats," says MacDonald.
In fact, the targeting of animal fats may very well be a "red herring" that has distracted attention from much more likely causes of health concern, she says. One major concern is man made hydrogenated fats, which contain trans fats. Another concern is excess intake of linoleic acid.
It's important not to confuse linoleic acid with conjugated linoleic acid (CLA), since these are two different fatty acids. Linoleic acid is a type of omega-6 fatty acid that is an essential fatty acid beneficial to human health. However, emerging studies indicate that when linoleic acid is consumed at very high levels this can upset the desired healthy ratio of omega-6 to omega-3 fatty acids. The greatest source of linoleic acid in the human diet is vegetable oils.
"In the early 1900s if your great, great grandmother was going to make a cake, she didn't use vegetable oils; she used butter," says MacDonald. "If she were going to make a pie she used lard. Our intake of trans fats and linoleic acid has gone up considerably since that time."
Ruminant fats contain trans fats but a growing body of research indicates these natural forms are not harmful and may be beneficial, she says. The real culprits are man-made trans fats, which have been shown to raise bad cholesterol and lower good cholesterol.
Regarding disruption to the omega-6 to omega-3 ratio, studies have indicated this imbalance may enhance carcinogen induced mammary and pancreatic cancer in rodents and may also enhance colon cancer in rodents. One study noted that linoleic acid is the only fatty acid to exhibit an unequivocal cancer enhancing effect.
"About sixty years ago the ratio of omega-6 to omega-3 was about two to one. Today the ratio is 25 to 1 and we've seen cancer rates increase."
By comparison, research exonerating animal fats continues to grow, says MacDonald. Among the most recent research are studies indicating that ruminant fats, including saturated and trans fats, have no adverse affect on lipid profile and may have a beneficial effect on the size of low-density lipoproteins (LDL "bad" cholesterol).
"LDL particle size is now getting to be one of the big issues in research on heart disease. This is one example of more and more findings that show animal fats have gotten a bad rap."
CLA shows significant promise to decrease body fat and increase lean muscle mass says Dr. Corey Scott.
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Dr. Corey E. Scott
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A rapid increase in scientific publications on CLA worldwide over the past decade is yielding growing promise for this unique fatty acid as a tool to aid in fat loss in humans, says Dr. Corey Scott of Lipid Nutrition, B.V.
"There is a growing body of evidence indicating that CLA can play a role in decreasing body fat and increasing lean muscle mass," says Scott, who delivered a presentation at the CLA Summit 2007 titled "New studies of CLA on the effects on regional fat mass and glucose metabolism in humans."
Much of the promise centres on two CLA isomers – CLA 9,11 and CLA 10,12. "Studies indicate that CLA 10,12 targets fat mass and CLA 9,11 can increase lean tissue," says Scott.
There are now approximately over 60 publications of human studies investigating CLA, based on over 40 trials involving more than 2,100 subjects. Close examination of trends in these studies reveals a clear pattern of evidence indicating CLA affects body fat mass and lean body mass, says Scott.
In its own research, Lipid Nutrition, B.V., which markets lipid products, has examined CLA efficacy in target populations, monitoring changes in key areas of regional fat mass including the arms, waist / hips and legs. The company has also investigated the safety of CLA by examining its effects on a variety of important body composition parameters.
One recent Lipid Nutrition study was based on a trial that examined effects of a CLA mix on regional fat mass in healthy overweight and obese men and women over a period of six months. After six months, results showed subjects had an average reduction in body fat mass of 2 kg or 5.6 percent and an average increase in lean body mass of 0.4 kg or 1.2 percent.
Overall, the trial showed a trend for CLA to reduce weight, body mass index and waist and hip circumference; and concluded that CLA reduces fat mass region specifically; CLA increases lean body mass; and that all blood lipid and inflammatory safety parameters remained within the normal range. "The trial showed clear benefits to the CLA supplementation," says Scott. "It also showed that the CLA mixture used is safe in healthy overweight and obese subjects."
Scott also provided an overview of new research related to CLA and insulin sensitivity. He noted that previous studies suggest that individual isomers of CLA may have an effect on glucose metabolism in certain populations, but commercially available 50:50 CLA mixtures of the key CLA isomers CLA 9,11 and CLA 10,12 have shown no negative effect.
A recent Lipid Nutrition study evaluating human subjects over a period of six months showed that the company's commercially available mixture of CLA at 3.4 g / day has no negative effects on either glucose metabolism or insulin resistance in healthy overweight and obese subjects. Insulin sensitivity was also unaffected.
Understanding the mechanisms and implications of how CLA reduces fat is key to harvesting benefits for humans, says Dr. Martha Belury.
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Dr. Martha Belury
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How does CLA fight fat and what are the implications?
A leading researcher examining this question is Dr. Martha Belury of Ohio State University. At the CLA Summit 2007, she provided a window on the latest knowledge, as part of a presentation on "The role of adipokines in effects of CLA on insulin resistance."
Delivering an overview of key research findings, including from several from her own studies, Belury recapped the strong promise CLA has shown as a fat reducer. She also provided insights into the mechanisms and consequences of this activity.
"We now know that CLA does reduce fat in multiple animal models, including some studies in humans," says Belury.
Research shows the specific isomer CLA 10,12 is the type responsible for fat reducing effects, says Belury. Mice are most pronounced in their responses to CLA 10,12; rats typically show some body fat reduction though not as significant; and human studies, though limited in number and scope, have shown links between CLA 10,12 and fat reduction.
Ongoing research is aimed toward understanding the mechanisms of CLA as a fat fighter, says Belury. "It appears CLA is working in part through either indirect or direct effects on inflammation and metabolism. Indications are some of those effects are in adipose (fat) tissues and those effects also then indirectly effect surrounding tissues. CLA's influence on gene expression also likely plays a role."
A key research focus is examining the role of proteins and hormones produced by fat cells. One of area of progress is learning more about CLA's effect on leptin – a peptide hormone produced by fat cells that plays a role in body weight regulation by acting on the hypothalamus to suppress appetite and burn fat stored in adipose tissue. A second protein secreted from adipose, known as adiponectin, is also severely reduced in mice fed CLA 10, 12. The loss of adiponectin further exacerbates insulin resistance and inflammation in mice fed CLA 10,12. Future studied aimed to sustain adiponectin levels while still reducing adipose mass are underway in Belury's lab.
Another important aspect pursued by Belury and colleagues is the effect of CLA on lipodystrophy, a problem known to occur under several conditions of disease and drug treatment of disease. Lipodystrophy occurs when adipose tissue builds up in areas it normally shouldn't, such as in the liver and other major organs.
In studies with mice, CLA 9,11 has been shown to have an anti-inflammatory effect that may mitigate lipodystrophy, while CLA 10,12 has been shown to move fat away from adipose tissue and into these abnormal areas.
"It may be that we need to look at ratios of CLA 9,11 and CLA 10,12 other than 1:1, to find the combination that results in the best effect," says Belury. "There may be other effective approaches to combine CLA 10,12 with anti-inflammatories."
A key aspect of the lipodystrophy research along with the broader research effort related to CLA effects is the examination of the role of adipokines - the proteins secreted by fat cells. A major focus of the adipokines research is its role in the effects of CLA on insulin resistance.
Belury citied findings from other researchers showing CLA 9,11 significantly reduces insulin resistance, while results with CLA 10,12 are mixed.
The knowledge harvested from ongoing research into adipokines will provide a base of information from which strategies for best use of CLA may be developed.
Related to the CLA insulin resistance research, Belury and colleagues are pursuing a new study to examine the effects of CLA supplementation on people with type II diabetes.
Early studies shed light on promise and challenges, says Dr. Roger McLeod
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Dr. Roger McLeod
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With approximately $4.3 billion per year spent on obesity and obesity related diseases in Canada alone, it's easy to see why investigating the promise of CLA to help battle the obesity epidemic is one of the most important areas of CLA research.
In Canada, a leading researcher in this area is Dr. Roger McLeod of Dalhousie University, whose major research interest is the role of obesity in chronic diseases and specifically in heart disease. At the CLA Summit 2007, McLeod presented an overview of recent studies by his laboratory that provide "Insights into CLA action from animal and cell culture models."
Obesity rates in North America have shot upward over the past decade, creating an economic burden measured in multi-billions annually, notes McLeod. "Obviously, obesity is a very important problem. But it's also a very complex problem, particularly in terms of understanding the connection between obesity and atherosclerosis."
The American Heart Association has indicated that obesity is one of the major modifiable risk factors for cardiovascular disease, he observes. At the same time, CLA has been promoted in advertisements as an effective weight loss supplement.
To better understand the promise of CLA for reducing obesity and atherosclerosis, McLeod recently pursued animal studies and two cell culture studies.
In the first animal study, McLeod used a hamster model to examine the effects of CLA on atherosclerosis and on lipoproteins, which include both good cholesterol (high density lipoproteins) and bad cholesterol (low density lipoproteins). The hamster was chosen as a model because on a human diet it develops a human-like profile for blood cholesterol. The hamster it also susceptible to early atherosclerotic lesions, and it has a liver protein called apoB100, which is the same as in humans.
The hamster study looked at the effects of adding CLA to the diet of hamsters already on a high fat, high cholesterol diet. It looked at the impact of isomer CLA 9,11, isomer CLA 10,12 and a mixed treatment that included both of these isomers.
The main statistically significant finding of the study was that hamsters on the CLA 10,12 diet had a significant increase in good cholesterol.
In another aspect of the hamster study, McLeod examined the effect of the different treatments on atherosclerotic plaques. This research showed a reduction in atherosclerotic lesions associated with both CLA 9,11 and CLA 10,12. However, due to variability among individual animals these findings did not meet the threshold of statistical significance.
"Part of the problem with the hamster as a model is that these animals are not genetically homogenous," says McLeod. "They have significant individual variability in response to diet. As a result, while both CLA isomers seem to be effective at reducing the early lesions found in the hamster, we don't have enough numbers yet to say that unequivocally."
To provide additional perspective using a different model, McLeod next evaluated CLA effects in a study using the Apo-E deficient mouse. These mice are genetically homogenous and develop very severe atherosclerotic lesions when placed on a high fat, high cholesterol diet.
This study found no significant effect of CLA on the severe atherosclerotic lesions. CLA 9,11 and the mixed isomer preparation showed no effect on blood cholesterol, blood triglycerides or liver mass. Results with CLA 10,12 showed an increase in blood cholesterol, blood triglycerides and an almost three-fold increase in liver mass due almost exclusively to the accumulation of triglycerides within the liver.
Next McLeod wanted to further examine the direct effect of CLA on adipocytes (fat cells). The literature had shown mixed isomer CLA causing a reduction of up to 60 percent body mass in several mice strains, with CLA 10,12 primarily responsible for these effects Limited human studies have shown modest or no weight loss. To shed light on the weight loss effects, McLeod pursued cell culture studies to examine how CLA may interfere with fat tissue formation.
These studies found that supplementation with CLA 10,12 leads to loss of fat cell function and that may be accomplished in part through the role of this CLA isomer as an antagonist of 'PPAR gamma' – a gene that influences fat formation. It also found negative effects of CLA associated with this loss of fat cell function.
"If we are going to lose fat we would like to lose it with an increase in adipocyte function, not a loss," says McLeod. The study indicated that reduction of the hormone adiponectin may be an early marker of adipose tissue dysfunction. "It's very important to monitor what is happening to adiponectin as we move into next phase of investigating CLA."
Reprintable with credit. Individual articles in the Report on CLA Summit 2007 are available for reprint, with acknowledgement of the source: The CLA Network. For broader reprint requests or reprint assistance contact the CLA Network at CLAnetwork@gov.ab.ca.
