My research interests revolve around understanding the relationships between the foods we eat, metabolic health, and body weight. Current areas of investigation include evaluating the benefits of consuming important foods such as whole grains or dairy products on energy expenditure, substrate oxidation, satiety and chronic disease risk factors; determining optimal sources and amounts of different types of dietary carbohydrates that contribute to satiety, healthy eating behaviors, and reduce risk of chronic disease; and evaluating benefits of an active lifestyle in terms of preventing obesity and related chronic diseases.
•• Answers to the question of why some people lose more weight than others when dieting despite similar calorie intakes have been elusive. In collaboration with colleagues at the WHNRC, Dr. Keim identified critical factors associated with inter-individual variability in weight loss in response to controlled interventions. Following up on work done early in her career at ARS, where she identified associations between body fat loss, use of fat as preferred fuel, and exercise-induced lipolysis, Dr. Keim discovered more recently that body weight loss during a food-controlled trial was linked to executive function skills: participants with the best decision-making skills lost the most weight. A more in-depth analysis of clinical and metabolic determinants of weight loss demonstrated that physical activity levels, fat-burning capacity and metabolites indicative of mitochondrial oxidation were important variables associated with magnitude of weight change.
•• Considering the current obesity epidemic, it is of vital importance to understand how exercise impacts energy balance and metabolic health. Dr. Keim demonstrated that regular aerobic exercise did not consistently affect energy intake of moderately overweight women, contrary to conventional thinking. Instead, previously-learned eating behavior, based on the cognitive restraint construct, played a major role in determining energy intake and food choice. In a recent study, Dr. Keim found that regular physical activity prevented the accretion of android fat ("visceral" fat around the internal organs, typically associated with metabolic disease), and attenuated the drop in insulin sensitivity that is common in peri-menopausal women, providing the first evidence of these effects in a sub-population that is vulnerable to weight gain and the accompanying metabolic disturbances.
•• Restrained eating is a behavioral construct defined as a conscious effort to restrict food intake to reduce body weight or avoid weight gain. Dr. Keim used this construct to demonstrate that restrained eaters have different metabolic and physiologic responses to dietary interventions including increased insulin sensitivity, preferential use of carbohydrate for energy following standard mixed meals, and blunted satiety signals in response to food consumption when compared to unrestrained eaters. These distinct metabolic responses of restrained eaters may thwart their dietary efforts aimed at reducing weight and maintaining control of food intake.
•• Leptin is a fat cell-derived hormone critical to regulation of food intake (dampening) and energy expenditure (maintaining).Provided the first evidence in humans that leptin influences hunger during conditions of calorie restriction: during a long-term energy restriction, women who reported feeling most hungry had the largest relative decrease in circulating leptin levels.
•• One proposed barrier to healthy eating in low-income populations is the cost of nutrient-rich foods compared to energy-dense but nutrient-poor foods (i.e., "fast foods"). In collaboration with scientists at Univ. of Washington and Univ. of California Davis, found that the cost of diets of low-income women was higher for those women who chose diets of lower energy density and higher nutrient density. Further, the women who consumed a greater variety of vegetables on a weekly basis, a recommendation of the Dietary Guidelines, had better quality diets, but the cost of the diets was higher.
•• The health impacts of dietary sugar and, in particular, fructose and high fructose corn syrup have been widely-debated. Dr. Keim has been a long-standing member of a NIH-funded collaborative multi-disciplinary team who demonstrated that consumption of large amounts of beverages sweetened with fructose leads to metabolic dysfunctions including elevations in circulating triglycerides and LDL-cholesterol, stimulation of hepatic synthesis of lipids, accumulation of abdominal fat, and decreases in insulin sensitivity-all symptomatic of metabolic syndrome. Consumption of high levels of fructose also depressed metabolic rate and fat-burning for energy, which would substantially contribute to undesirable gain of weight and body fat with prolonged use.