Conjugated linoleic acid has shown very promising results as an anti-obesity agent in animal studies. Now a new study in humans, published in the International Journal of Obesity [Volume 25, Issue 8, August 2001], sheds some more light on the subject. “This is the first published paper investigating the effects of CLA in a group of obese men with pronounced abdominal obesity,” says principal investigator Ulf Risérus, M.Med., a Ph.D. student at the Faculty of Medicine, Uppsala University.

Twenty-four men saw the study through; 14 were randomly assigned to CLA, 10 served as the control. In the course of this month-long study, the 14 men (who had a body mass index classified as excessively obese) on 4.2 g CLA/day, lost a mean 0.6 cm in sagittal abdominal diameter (SAD). The drop in SAD was significant—meaning that it is unlikely that it was an accidental result—compared to that in the placebo group (no measurable change). The CLA group also experienced a mean decrease in waist circumference of 1.4 cm; the placebo group’s mean decrease (0.7cm) was not significant.

The men had other cardiovascular risk factors, including high blood lipids, high blood sugar and high blood pressure, placing them “on the edge of developing type II diabetes,” says Risérus.

“The indication that CLA might reduce body fat, especially abdominal fat in obese humans, is in agreement with a recent Norwegian study and unpublished results from our group,” says Risérus.

“The significant effect on abdominal fat was rather surprising, considering the short treatment period,” says Risérus. “If this reduction of body fat could be confirmed in other studies, it might be possible that a CLA treatment for longer duration could have a more pronounced effect on body fat, and might affect cardiovascular risk factors related to abdominal obesity.”

Risérus suggests that CLA could actually have a more powerful effect than his study indicates. There are several CLA isomers, which animal studies show have differing biological effects, he explains, and “we are now trying to isolate the one that could be the most beneficial.” Also, Risérus suggests that CLA might be useful in preventing the yo-yo effect.

CLA may have other benefits, says Richard L. Atkinson, professor of medicine and nutritional sciences at the University of Wisconsin. “In animals, and no doubt in humans, it has really interesting effects on the immune system, on cancer, and on some of the risk factors for heart disease.”

Sixty-one percent of Americans are considered to be overweight, and thus at increased risk for coronary heart disease, stroke, high blood pressure, type II diabetes, osteoarthritis and certain cancers.

The U.S. Food and Drug Administration (FDA) recently approved food labeling that makes health claims about soy protein in regards to offering protection against heart disease. The new regulation stipulates that, in order to make such a claim, food products must contain at least 6.25 grams of soy protein. That is based on the fact that the federal agency deems 25 grams per day of soy protein effective to potentially lower heart disease risk when combined with a low-fat diet.

Now, in addition to the Food and Drug Administration’s stamp of approval, the American Heart Association is formally endorsing the same claim, following a rigorous review of 38 clinical studies that showed that soy protein in the place of animal-source protein decreased low-density lipoproteins (LDL) or “bad” cholesterol by up to 8%. This new recommendation is part of the “American Heart Association’s AHA Dietary Guidelines, Revisions 2000,” which were released in October. The recommendation states that eating 25 to 50 grams of soy protein per day can aid in reducing LDL cholesterol levels by 4% to 8%. More specifically, the advisory reports, the higher people’s baseline cholesterol levels, the more pronounced soy’s lipid-lowering effect. Results from the 38 clinical studies collectively indicated that daily soy consumption led to a 9.3% drop in total cholesterol levels, a 12.9% reduction in LDL cholesterol, and a 10.5% decrease in triglycerides.

Among the studies reviewed, findings from Wake Forest University showed that the higher the concentration of isoflavone, the more effectively soy protein could decrease cholesterol levels [Arch Intern Med 1999 Sep 27;159(17):2070-2076]. The nine-week study put 156 healthy adults with cholesterol levels greater or equal to 140 milligrams per decliter (mg/dL) of blood, who were already on a standard cholesterol-controlling diet, on a soy protein diet containing one of four amounts of isoflavones (3-62 milligrams) or a milk protein placebo. Those who consumed the most isoflavones saw a 6% drop in LDL and a 4% decrease in total cholesterol. Subjects with the highest LDL levels (164 milligrams per deciliter mg/dl) who consumed 62 milligrams daily showed a 10% drop in LDL and a 9% decrease in total cholesterol.

A six-month study of post-menopausal women who consumed 40 grams per day of soy protein containing either 56 or 90 milligrams of isoflavones or casein (a milk protein placebo) showed an 8.2% drop in non-HDL cholesterol and a 4.4% increase in high-density lipoproteins (HDL) or “good” cholesterol, compared to control subjects [Am J Clin Nutr 1998;68:545-551]. Similarly, another study of hypercholesterolemic men showed that six weeks of soy consumption resulted in significantly greater reductions in non-HDL cholesterol compared to casein control group subjects [Am J Clin Nutr 2000;71:1077-1089]. Lipid-lowering effects ranged from a 1.5% to 4.5% drop in non-HDL cholesterol with positive effects being proportional to consuming 20, 30, 40 or 50 grams per day of soy protein.

Epidemiological data has already noted that Asian populations, which are known to consume as much as 55 grams per day of soy protein, have a lower incidence of cardiovascular disease than people who consume a typical Western diet and less than 5 grams per day of soy protein. The advisory also underlines the fact that scientific evidence supports the benefits of soy consumption specifically in conjunction with a diet low in saturated fat and cholesterol. The American Heart Association’s Nutrition Committee is also confident, after analyzing the many study findings, that soy protein does not have a cholesterol-lowering effect in adults with low to normal levels, which removes any fear of soy possibly decreasing levels to a dangerous point.

-Angela Pirisi

If research on mice holds up, DHEA may be an important new therapy for allergies and asthma. Researchers in Taiwan have uncovered mechanisms that explain how the hormone may affect allergic reactions. The research correlates with studies showing that adults with asthma have below-normal levels of DHEA.

DHEA (dehydroepiandrosterone) is the most abundant adrenal hormone in the body. Known for its control over the immune system, DHEA has been used to reverse age-related immune decline. DHEA can actually alter the biochemistry of the immune system, and make it more balanced. In asthma, DHEA suppresses biochemicals that provoke the closing of air tubes and fluid build-up. In mice exposed to house dust mites, DHEA reduced the allergic response and counteracted inflammation. The hyper-immune response characteristic of asthma was dampened down to become more like the response an animal without asthma would have to the same allergen. It appears that one of the functions of DHEA is to counteract glucocorticoids and keep the body’s responses to potential allergens on an even keel.

The authors of the study note that people who develop asthma as adults do so around age 40—the same time when DHEA levels naturally drop. It has been shown that older women who have asthma have lower levels of DHEA (and the sex hormones it converts to) than women without asthma.

In a study on men and women, 40% with asthma had as low levels of DHEA as people with medical conditions that cause abnormally low adrenal function. Clearly, a lack of DHEA is associated with asthma—at least in adults. No correlation between DHEA levels and asthma has been found in children.