Environmental Factor, March 2011, National Institute of Environmental Health Sciences
New insights into fitness versus fatness and diabetes risk
By Melissa Kerr
Cannon was making his first trip to NIEHS. He told the audience, "This is not high science. This is old-fashioned clinical research, sort of gumshoe clinical research." (Photo courtesy of Steve McCaw)
A new exercise program at the NIH in Bethesda, Md., encourages employees to participate in more heart-healthy behavior and has the added advantage of helping researchers learn more about diabetes and obesity. National Heart, Lung, and Blood Institute (NHLBI) investigator Richard Cannon, M.D.(http://www.nhlbi.nih.gov/research/intramural/researchers/pi/cannon-richard) , explained in an NIEHS Clinical Director's Lecture Series presentation Feb. 7 that data from the NHLBI Keep the Beat worksite wellness program is leading to new insights into how diabetes and obesity affect the body.
"This is a relatively new field for me, diabetes in the workforce," Cannon explained. "This is of public health importance because the prevalence of obesity is high and is increasing."
Cannon has been on the staff of NHLBI since 1979. He is currently clinical director in the Institute's Division of Intramural Research, and head of the Clinical Cardiology Section in the Cardiology Branch. Colleague Darryl Zeldin, M.D., NIEHS acting clinical director, hosted Cannon's talk on "Diabetes Risk in the Workforce: NHLBI's Keep the Beat Program."
Promoting health at the job site
Cannon and his team used Keep the Beat enrollment data in research on insulin sensitivity in non-diabetic overweight and obese subjects. Cannon worked closely with scientists at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), as the team evaluated 141 middle-aged overweight and obese women, 89 African-American and 52 white.
During their exercise program, subjects were tested for exercise oxygen consumption and carbon dioxide release, adipose tissue or body fat by Dexa scanning, and insulin sensitivity, among other measures of cardiac health. They will be tested again at the conclusion of their six-month program.
Fit versus fat
Cannon's research focused specifically on truncal fat, because it seems to have the strongest correlation to insulin sensitivity. Truncal fat, he said, is responsible for adipokines, signaling proteins that help to regulate insulin transport. The greater the truncal fat, Cannon explained, the higher a person's resistance to insulin. However, "Fitness does matter," Cannon insists, especially in African-American overweight and obese women. "There clearly is a relationship between cardiac respiratory fitness and insulin sensitivity that is independent of truncal fat."
Cannon was particularly interested in results that indicated previously unrecognized differences between white women and African-American women. He found a significant difference of 20 percent in oxygen consumption and treadmill exercise duration between African American women and white women. "Although black women have greater muscle mass than white women, for any given muscle mass measure, African-Americans have worse exercise performance than whites," he said. In reviewing the data, he found an interesting deviation from the conventional wisdom that more muscle equates with better health. He found instead that in obese black women, the greater the muscle mass, the more resistant the muscle is to insulin. This was not the case in white obese women.
However, despite their poorer exercise performance, African-American women show a positive relationship between lean mass and insulin resistance, while white women do not.
Cannon said that he plans to continue this line of investigation into patterns of insulin sensitivity and racial differences in the impact of obesity on health. "There are some interesting questions with regards to genetic determinants of insulin sensitivity that hopefully we'll address in future research," he said, "maybe in collaboration with some people here [at NIEHS]."
(Melissa Kerr studies chemistry at North Carolina Central University. She is currently an intern in the NIEHS Office of Communications and Public Liaison.)