January 15, 2003
Dogs on fatty diet may give clues to human disease development
WEST LAFAYETTE, Ind. Coonhound puppies on diets containing the type of fat found in deep-fried foods are furthering understanding of how these fats contribute to aging and development of human diseases such as atherosclerosis and cancer, according to Purdue University scientists.
One group of dogs fed a highly-oxidized lipid diet and another group fed one with a moderate level of this fat type, both had reduced growth, bone formation and immune function, said John Turek, Purdue professor of basic sciences. This was the first study in dogs to assess the effects of oxidized lipids on growth, antioxidant status, bone development and immune function.
"We know that eating diets high in oxidized fat contributes to atherosclerosis and other diseases in people," said Turek, a School of Veterinary Medicine cellular biologist. "But we don't know the long-term effects of foods high in oxidized lipids fed during the growth stage. Will organ and tissue growth be compromised? Will children develop geriatric diseases at an earlier point in their lives?"
Turek, along with Department of Food Science professor Bruce Watkins and their colleagues, report the research in the January issue of The Journal of Nutritional Biochemistry
Results showing that dogs on a moderate oxidized fat diet also exhibited some of the same effects as those eating meals containing high oxidized lipids were unexpected, Turek said. This finding has major significance for studies on overall health in both people and animals.
Watkins, of the School of Agriculture, said fats, oils and processed foods without added antioxidants can contain oxidized lipids. In addition, frying food adds more of this type of fat.
"Increasingly restaurants prepare convenience foods by frying, and more meals are eaten out at fast-food establishments," said Watkins, a nutritional biochemist. "Consequently, the level of oxidized fat in Americans' diets has escalated alarmingly in recent years."
The process that forms oxidized lipids also occurs in the body's metabolic processes. Free radicals, a component of lipid oxidation, damages proteins, other lipids, DNA and cells, thereby causing disease. For this reason it's important to eat foods, such as fresh fruits and vegetables, which are low in oxidized lipids and high in antioxidants, Watkins said.
Though researchers have linked oxidized fat to several human diseases, most of the research was done in rodents. Young, growing dogs might give a better picture of how oxidized lipids affect humans, especially children during critical stages of development and growth, the scientists said. In the early months of life, dogs grow rapidly, adding considerable bone and lean body mass, which is more comparable to humans in rapid growth phases, such as puberty.
In the puppies, researchers found that those consuming highly oxidized fat gained less weight and had less body fat than their kennelmates that ate moderate- and low-oxidized fat diets, Turek said. The coonhounds on the diet high in oxidized fat also had decreased immune function and less vitamin E, an antioxidant that helps counteract the effects of free radicals. In addition, bone formation rate was reduced.
"Our study shows the need to control the amount of oxidized fats in food for both humans and companion animals so that we can ensure proper growth and optimum health," Turek said.
The 24 dogs, all 2 months old, were divided into three groups: One group ate a low-oxidized fat diet, one a diet with a moderate level of oxidized fat, and one a high oxidized fat diet. They were all kept on their assigned feeding regimen for 16 weeks. Other than the oxidation level of the fat, their diets were identical and contained all the other nutrients necessary for a healthy dog.
The oxidized lipid research is one of the ongoing projects by members of the Center for Enhancing Foods to Protect Health, of which Watkins is director. The center is a collaboration between Purdue and the Indiana University School of Medicine.
The other researchers on this study were: research assistant Ingrid Schoenlein, Department of Basic Medical Sciences, Purdue School of Veterinary Medicine; Kenneth Allen, Department of Food Science and Human Nutrition, Colorado State University; Michael Hayek, Research and Development Division, The Iams Company, Lewisburg, Ohio; and C. Gregory Aldrich, formerly with Iams.
The Iams Company Research and Development Fund funded the research.
Writer: Susan A. Steeves, (765) 496-7481, firstname.lastname@example.org
Sources: John Turek, (765) 494-5854, email@example.com
Bruce Watkins, (765) 494-5802, Watkins@foodsci.purdue.edu
Ag Communications: (765) 494-2722; Beth Forbes, firstname.lastname@example.org; http://www.agriculture.purdue.edu/AgComm/public/agnews/
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A publication-quality photograph is available at ftp://ftp.purdue.edu/pub/uns/turek.lipids.jpeg.
Oxidized Lipid Depresses Canine Growth,
John Turek, Bruce Watkins, Ingrid Schoenlein, Kenneth Allen, Michael Hayek, and Gregory Aldrich
Dietary oxidized lipids can increase oxidative stress and potentially contribute to a variety of disease syndromes. This research describes the first use of a canine model to assess the effects of dietary oxidized lipids on growth, antioxidant status, and some immune functions. Three groups of eight, two-month old coonhound puppies were pair fed diets for 16 weeks. The control diet contained < 50 ppm aldehydes, and two additional diets contained thermally oxidized lipids targeted to contain 100 ppm aldehydes (medium-oxidation_ and 500 ppm aldehydes (high-oxidation). Dogs fed the high-oxidation diet weighted less than those from the medium-oxidation (P<0.05) and control groups (P<0.001) at the end of the study. Oxidized lipids reduced serum vitamin E levels, total body fat content, and bone appositional rate. At different time points of the study, peripheral blood neutrophils and monocytes from dogs fed the HO diet had reduced oxidative burst capacity and produced less superoxide and hydrogen peroxide when stimulated with phorbol esters compared to the control group. Lymphocyte blastogenesis in response to concanavalin A was suppressed by dietary oxidized lipid. This study indicates that dietary oxidized lipids negatively affect the growth, antioxidant status, and some immune functions of dogs. Importantly, some effects are evident at 100 ppm aldehydes in the diet, which is a moderate level of oxidation. The rapid growth and weight gain of the dog during the first six months of life may also provide a better model for assessing the risks of dietary oxidized lipid in children and adolescents than previously used rodent models.