Developed and validated the tetrapolar bioelectrical impedance method for assessing human body composition. Models for predicting fat-free mass based upon conductance measurements of the body were developed and cross-validated in adults. The error of estimating fat-free mass was within the limits of the reference method of assessing body composition. The predictive accuracy was better than that found by standard caliper procedures. Based on these results, this method is currently used in the National Health and Nutrition Examination Survey to determine the body composition of the U.S. population. Other studies resulted in the development and validation of models using impedance measurements to estimate total body water and extracellular water in healthy adults, to assess fluid changes in surgical patients, obese women undergoing weight loss, and women during pregnancy and lactation. Provided the first evidence that dietary copper in amounts consumed by a majority of American adults raises blood pressure during low level work. Young women fed marginal dietary copper had markedly increased diastolic and systolic blood pressures during mild intensity exercise similar to lifting grocery bags or shoveling snow. This finding indicates that copper plays a key role in regulating blood pressure in humans.
Demonstrated that iron deficiency without overt anemia in humans is associated with impairments in energy metabolism. A reduced thermogenic response during acute cold exposure and a blunted rate of oxygen utilization during progressive exercise to exhaustion were observed in young women who were iron-deficient but not anemic by a combination of reduced iron intake, phlebotomy and menstruation. The inability to produce heat in the cold and the reduced rate of oxygen uptake during work were associated with an increase in anaerobic metabolism. Thus, iron-dependent factors other than oxygen-carrying capacity can influence body energy metabolism.
Demonstrated that dietary stearic acid promotes iron utilization. Studies of iron-deficient dogs revealed that 59Fe absorption and red blood cell regeneration were increased significantly after ingestion of stearic acid compared to that after safflower oil. Studies of intestinal mucosal kinetics in canines indicated that the mechanism behind these effects was an increased transfer of iron from the intestinal cell into the blood. Cells in culture, made iron-deficient by using a novel serum-free media, demonstrated increased iron uptake and translocation when incubated in media containing stearic and palmitic fatty acids as compared to safflower oil. These findings suggest that stearic acid may be the factor in meat that facilitates the utilization of non-heme iron.
Identified altered energy efficiency during moderate intensity work in women fed a low magnesium diet (150 mg/d). Postmenopausal women exhibited a 10% increase in oxygen utilization with an increase of 9 beats per minute during submaximal ergocycle exercise when they performed the same amount of work as when they consumed a diet adequate (350 mg/d) of magnesium. These findings indicate that adequate dietary magnesium is needed for optimal use of energy to perform daily activities.
Determined that women consuming diets low in magnesium, but similar to amounts ingested by many American women, had depleted muscle and red blood cell magnesium concentrations and lost magnesium from their bodies. This deficiency resulted in increased oxygen needs to perform low level exercise, which has been shown previously in competitive athletes. This finding provides the first confirmation of the new recommendation for dietary magnesium for women.
Determined a new role of zinc in support of energy use during exercise. Physically active men consuming diets low in zinc had significantly decreased activity of carbonic anhydrase that was associated with increased ventilation, reduced carbon dioxide exhalation and oxygen use during exercise. Studies in rats fed graded dietary zinc and exercise-trained confirmed these findings and showed for the first time that skeletal muscle carbonic anhydrase activity and protein were decreased with low dietary zinc. These observations provide novel evidence that zinc supports cardiorespiratory function during exercise in humans. |