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United States Department of Agriculture

Agricultural Research Service

Susan K. Raatz

Nutrition Scientist

Susan Raatz

SUSAN RAATZ, PhD

Research Nutritionist

Biography

Dr. Raatz joined the Grand Forks Human Nutrition Research Center in November, 2009. She came to Grand Forks from Minneapolis, MN, where she was an Associate Professor of Medicine in the Division of Endocrinology and Diabetes and the Bionutrition Manager of the General Clinical Research Center. Dr. Raatz completed a BS in Dietetics at Northern Michigan University , Marquette, MI, a MS in Foods and Nutrition at Eastern Michigan University, a MPH in Epidemiology and a Ph.D. in Human and Clinical Nutrition at The University of Minnesota, Minneapolis, MN.

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Research Interests

Dr. Raatz' research focuses on the evaluation of the role of dietary macronutrient distribution in the promotion of optimal health and the prevention of chronic diseases. She primarily works with the utilization of whole foods diets to modify energy distribution from macronutrient substrates. Her work is focused primarily on macronutrient (carbohydrate, protein and fat) modification for metabolic control, body weight management, and the prevention of chronic diseases.

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Research Accomplishments

Demonstrated that a low-fat diet results in elevated circulating levels of omega-3 fatty acids in healthy men and women. Conducted a 12 week, randomized, crossover designed, controlled feeding trial in healthy men and women fed either a low-fat (20% of calories) vs. a high-fat (45% of calories) diet containing constant proportions of fatty acids. Found that consumption of the low-fat diet increased the circulating levels of total omega-3 fatty acids, EPA, DHA, phospholipid fatty acids and cholesterol esters. The change in plasma fatty acids appeared to be related to decreased competition for the enzymatic elongation and desaturation of n-3 and n-6 fatty acids, as well as to the reduced intake of linoleic acid on the low fat diet.

Conducted a randomized clinical trial testing the hypothesis that a low-calorie diet designed with a low glycemic index and low glycemic load would support in greater sustained weight loss than standard, low-calorie diets. The project was a parallel-designed, randomized 12-week controlled feeding trial with a 24 week follow-up phase. It involved 29 obese (BMI>30) subjects randomly assigned to one of three diets (high glycemic index, low glycemic index, low fat). Subjects were assessed for changes in body weight, body composition, and insulin sensitivity. Results demonstrated that diets with a low glycemic index/glycemic load do not provide any added benefit to energy restriction in promoting weight loss in obese individuals.

Was co-investigator in a major project investigating the role diet in type 2 diabetes. This was a multi-center, controlled feeding trial to determine the roles of dietary carbohydrate and fat contents in diabetic management. It involved a total of 42 subjects with type 2 diabetes recruited through four medical research centers into a randomized, crossover trial comparing the outcomes of a high-carbohydrate vs. high-monounsaturated fatty acid diet. The results revealed that the high-carbohydrate diet produced increases in VLDL-cholesterol, serum triglycerides, fasting serum glucose and serum insulin.

Demonstrated that a low-fat, high-omega-3 fatty acid diet reduced hormonal risk factors for breast cancer in post-menopausal women. Conducted a randomized, crossover designed, controlled feeding trial in which 18 women were assigned to high-fat (45% of calories), low-fat (20% of calories), or low-fat high-omega-3 (23% of calories, with 3% of calories as omega-3 fatty acids) diets for eight weeks. The outcome measures included plasma and urinary sex hormones, and plasma eicosanoids and fatty acids. Results demonstrated that a low-fat, high-omega-3 diet reduced several breast cancer risk factors including total and free estrogen in plasma.

Participated in a multi-center study of weight management for reducing diabetes risk - the multi-center, Look Ahead study, a 12-year, randomized, controlled trial with 5,145 overweight/obese individuals with type 2 diabetes. Subjects were randomly assigned to either a) intensive lifestyle intervention for weight reduction (ILI; intensive counseling regarding weight loss and physical activity) or b) diabetes support and education (DSE). Results demonstrated that ILI was superior to DSE, resulting in greater clinically significant weight loss, with improved diabetes control and reduced cardiovascular disease risk factors.

Co-investigator in a series of two clinical trials that produced the first evidence that neural redox control affects cognition. The first trial involved 10 human subjects in whom concentrations of the two most concentrated chemical antioxidants in the central nervous system, ascorbic acid and reduced glutathione (GSH) were quantified from double-edited 1H-MRS spectra measured from the occipital cortex prior to and throughout 24 hrs after bolus intravenous delivery of 3 g vitamin C. In the second trial, 55 subjects,18-24 or 70+ yrs, were evaluated for serum ascorbic acid using standard chemical methods, for brain ascorbic acid and GSH using the 1H-MRS spectral method, and for cognitive abilities using a series of 5 standardized questionnaires. Results indicate that elevated serum ascorbic acid and brain GSH improved cognitive function, particularly in the elderly. These data were ground-breaking in that they showed Vitamin C to play a hitherto undescribed role in cognitive function. They also pointed to this role involving the maintenance of GSH in the reduced form, which constitutes the primary antioxidant in the brain.

Conducted an experimental test of the hypothesis that high-protein weight loss diets can support smaller losses of lean body mass than diets containing normal protein levels. Conducted a randomized, crossover designed, controlled feeding trial in which 18 mid-life adults were assigned to control (15% of calories as protein), high mixed protein (30% of calories), or high whey-protein (30% of calories, with half coming from whey protein) diets for 8 wks. The outcomes included body composition by densitometry, resting metabolic rate, weight change, insulin sensitivity measures (glucose, insulin) , blood pressure, and measures of the Renin Angiotensin System (aldosterone, plasma rennin activity, angiotensin II). Results showed that subjects fed high-protein diets failed to demonstrate the decline in resting energy expenditure typical of weight loss (which reduces the weight-loss efficacy of caloric restriction). They also demonstrated that high-protein diets enhance satiety and preserve lean mass typically seen in weight reduction.

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Last Modified: 8/18/2014
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