Bonnie Beezhold, a graduate student in the laboratory of Dr. Carol Johnston, presented the most recent study, on the impact of vitamin C depletion on a short-term diet, on April 3 at Experimental Biology 2006 in San Francisco. The presentation was part of the scientific program of the American Society for Nutrition, Inc. (ASN).
Before beginning a controlled four-week, low-fat diet, 20 obese men and women were randomized by gender and body weight into either a Vitamin C group, taking a 500 mg vitamin C capsule daily, or a control group, taking a capsule, identical in appearance to the vitamin, containing a placebo. Neither participants nor researchers knew who was receiving which capsule until the study was over. All participants consumed a low-fat diet that the researchers adjusted individually to promote slow weight loss (about two pounds per week). The diet contained 67 percent of the USRDA (recommended daily allowance) for vitamin C (40 mg/d).
At the beginning of the clinical trial, participants with the lowest concentrations of vitamin C in their blood had the highest body fat mass and tended not to oxidize fat well compared to their less obese counterparts. As the participants moved through the four week diet, with a steady amount of vitamin C being consumed, blood vitamin C concentrations increased 30 percent in those taking vitamins and fell 27 percent in the control group whose only vitamin C intake was the 67 percent of the USRDA contained in the food. As vitamin C blood concentrations fell, so did the participants' ability to oxidize fat (an 11 percent reduction).
Contact: Sarah Goodwin
Federation of American Societies for Experimental Biology