Research: Yo-Yo Diets Increase Risk of Cancer
12-27-2007 12:10 PM
Research: Yo-Yo Diets Increase Risk of Cancer
ScienceDaily (Dec. 24, 2004) — BETHESDA, Md. (Dec. 17, 2004) – Perhaps Ukrainian opposition leader Viktor Yushchenko should try an "Olestra diet" to rid his body of dioxin.
It wouldn't be the first time that the "fake fat" product was used as an emergency agent to flush out dioxin, one of a group of chlorinated hydrocarbons that are toxic, lipophilic (attracted to fat) – and persistent in the environment and animal tissues. About five years ago, two Austrian women suffering from dioxin poisoning were given olestra snacks, which resulted in removal of dioxin at 10 times the normal rate, according to some reports.
In an as-yet-unpublished study, researchers at the University of Cincinnati School of Medicine, along with Trevor Redgrave at the University of Western Australia, treated a patient with PCB toxicity over a two-year period with olestra in the form of fat-free Pringles. The patients chloracne disappeared and the PCB level in fat tissue dropped dramatically.
The same University of Cincinnati School of Medicine team is reporting new research that sheds light into how diet affects retention and re-distribution through the weight gain-loss-regain cycle of chlorinated hydrocarbons, which include DDT, PCBs and dioxins. They also looked at the effects of the additive olestra, which is made by Procter & Gamble, on this redistribution and perhaps more importantly, on excretion of toxins from the body.
Indeed, "combined dietary olestra and caloric restriction caused a 30-fold increase in the rate of excretion" of a test toxin, while the toxin's distribution "into the brain resulting from the restricted diet was reduced by 50% by dietary olestra," the study found.
The study, "Effects of yo-yo diet, caloric restriction, and olestra on tissue distribution of hexachlorobenzene," was conducted by Ronald J. Jandacek, Nicole Anderson, Min Liu, Shuqin Zheng, Qing Yang and Patrick Tso of the Department of Pathology and Laboratory Medicine, University of Cincinnati School of Medicine, Cincinnati, Ohio. The research appears in the online edition of the American Journal of Physiology-Gastrointestinal and Liver Physiology, published by the American Physiological Society.
They're everywhere, and with long half-lives
Toxic lipophilic substances like PCBs and dioxins are so widespread globally, and are known to ascend the food chain, that virtually "all people tested have measurable levels of some of these compounds," the Jandacek et al. report notes. Because the compounds and many of their metabolites are lipophilic (attracted to fat) they are stored in adipose (fat) tissue where they remain stable, usually without adverse affect in moderate amounts for their long half-lives.
Jandacek and his colleagues designed a multi-branch, multi-endpoint study that showed with weight loss (with and without olestra) toxins redistribute around the body, but with differing affinity to various organs.
Method and results: brain, adipose and liver tissue differences
The Cincinnati researchers used 14C-hexachlorobenzene (14C-HCB), a radioactively-marked toxin that is only partly metabolized by mice, to measure how its distribution changed in various organs during the weight gain-loss yo-yo process.
They found that continued "weight loss resulted in a three-fold increase of 14C amount and concentration in the brain. After weight regain, 14C in the brain decreased but then increased again after a second weight loss." In adipose tissue, weight loss resulted in an increase in the concentration of 14C without changing the total amount in the fat tissue. "Weight loss and regain resulted in an increase of 14C in the liver that reflected an increase of fat in the liver," Jandacek et al. reported.
At this point, the regimen of weight gain and loss was repeated in mice gavaged (direct-fed to the stomach) with 14C-HCB, with one group receiving the "non-absorbable fat, olestra" in their diet. The results were striking: "Combined dietary olestra and caloric restriction caused a 30-fold increase in the rate of excretion of 14C, relative to an ad lib diet or a reduced caloric (diet) alone. The distribution of 14C into the brain resulting from the restricted diet was reduced by 50% by dietary olestra," Jandacek et al. reported.
The results of the current study have indicated several avenues to pursue, among them being:
* Plasma HCB increased with prolonged caloric restriction, indicating the need for future studies into the possible role of carriers of HCB.
* HCB was cleared more rapidly from chylomicrons than triacylglycerol, "suggesting an affinity of organochlorines for the fatty acids generated during fat metabolism."
* "How plasma carriers facilitate HCB entry into the brain is an interesting question with potential physiological implications."
* Jandacek's laboratory is currently studying the relationship of fasting and refeeding to liver lipid deposition.
* The exact role of olestra and its mechanism of action in the excretion process.
* Whether and how different organochlorine compounds (PCBs, dioxins, etc.) undergo redistribution in yo-yo diet situations.
* Testing a lipase inhibitor such as orlistat (Xenical, Roche) "will also result in partial blockage of the enterohepatic circulation of lipophiles by providing an undigested intestinal triacylglycerol phase that will solubilize these compounds."
Source and funding
The study, "Effects of yo-yo diet, caloric restriction, and Olestra on tissue distribution of hexachlorobenzene," by Jandacek et al. appears online in the American Journal of Physiology-Gastrointestinal and Liver Physiology, published by the American Physiological Society.
Research was supported by grants from the U.S. Department of Agriculture Cooperative State Research Education and Extension Service and the National Institutes of Health.
The American Physiological Society was founded in 1887 to foster basic and applied bioscience. The Bethesda, Maryland-based society has more than 10,000 members and publishes 14 peer-reviewed journals containing almost 4,000 articles annually.
APS provides a wide range of research, educational and career support and programming to further the contributions of physiology to understanding the mechanisms of diseased and healthy states. In May, APS received the Presidential Award for Excellence in Science, Mathematics and Engineering Mentoring (PAESMEM).
12-28-2007 11:38 AM
Not only that, they wreck your metabolism which impairs your body's ability to burn fat and digest food properly.
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