THE PHYSICIAN AND SPORTSMEDICINE - VOL 31 - NO. 6 - JUNE 2003
Diet Wars: Low-Carb vs Low-Fat
New Studies Shed Light
Debate on the key to effective, long-term weight loss has pitted proponents of low-carbohydrate, high-protein diets against those who back low-fat diets. New research findings on the safety and efficacy of the diets and the accidental death of one of the low-carbohydrate diet proponents, Robert Atkins, MD, have renewed the focus on the diet debate.
A recent meta-analysis1 in the Journal of the American Medical Association (JAMA) that examined the results of low-carbohydrate diet studies did not settle the debate, but it did shed some light on efficacy and safety concerns. The authors analyzed 107 studies that detailed 94 dietary interventions. They found that patients on low-carbohydrate diets did not lose more weight than patients on higher-carbohydrate diets. They determined that overall calorie reduction along with longer duration correlated to weight loss with both types of diets. Carbohydrate intake, however, did not relate to weight loss. Lower-carbohydrate diets did not have adverse effects on serum lipid levels, fasting serum glucose levels, or blood pressure. However, because few studies reported these outcomes, the meta-analysis lacked the statistical power to detect small changes. The authors concluded that there is insufficient evidence to recommend for or against low-carbohydrate diets, particularly in patients older than 50, for use longer than 90 days, or for diets that contain less than 20 g per day of carbohydrate.
A study2 published after the meta-analysis was completed echoed the safety findings of the JAMA study and was notable because the researchers followed the study participants (53 healthy, obese women) for 6 months, making it the longest randomized, controlled trial of a low-carbohydrate diet to date. This study, however, found that women on the low-carbohydrate diet lost significantly more weight than those on the low-fat diet. The authors found that the low-carbohydrate group spontaneously restricted their food intake, suggesting the higher-protein diet may have been more satiating.
Though the study supports greater weight-loss benefits of low-carbohydrate diets, the authors pointed out several safety concerns. They note that the effects of the diet on serum lipids and other health parameters should be studied for longer than 6 months. They note that a low-carbohydrate diet may have harmful effects in patients who have hyperlipidemia, diabetes, or other metabolic disorders. They also point out the low intake of calcium and fiber in the low-carbohydrate group.
Nancy Clark, MS, RD, nutritionist at SportsMedicine Associates in Brookline, Massachusetts, says the recent studies won't change her recommendations to active patients. The studies don't address health issues such as cancer, and Clark says a plethora of research has documented the health benefits of fruits, vegetables, healthy oils, and nuts. Extra protein in the diet displaces carbohydrates, which are needed to replace glycogen stores. "Physiologically, your body can handle the extra protein, but can you optimally fuel your muscles with too few carbs?"
Athletes should consume slightly more protein than the general population, Clark says. The recommended intake for protein is 1.0 to 1.5 g/kg body weight per day for most athletes and .8 g/kg body weight per day for the general population.
Clark's advice for active people who want to lose weight is to consume a well-balanced breakfast and lunch, and then eat fewer calories at night to create a calorie deficit.
No one diet works for everyone, Clark says, and those who struggle with their weight should meet with a registered dietitian for a nutrition check-up. "Another approach would be to modify one of the high-protein diets to be a healthier high-protein diet with the addition of leaner meats, vegetables, and fruit," she says.
Guidance From Physicians
Phillip Zinni III, DO, ATC/L, corporate medical director for E & J Gallo Winery in Modesto, California, says he fields a lot of questions from patients about high-protein diets, particularly the Atkins diet. Though Zinni says his own bias leans toward the Mediterranean diet, he says he encourages most who ask about low-carbohydrate diets to give them a try. He worries that if he discourages them from trying the diets, "they're either going to write me off or do it anyway. They need my support, and I try to educate them."
When Zinni's patients say they're going to start a low-carbohydrate diet, he obtains baseline kidney and liver function tests along with basic blood chemistries. He advises them to return in 6 weeks, or earlier if weight loss is rapid, for follow-up evaluation. He advises patients who have hypertension or advanced diabetes to avoid such diets, and he urges those who have a history of gout or kidney stones to drink lots of water and proceed with caution.
L. Tyler Wadsworth, MD, medical director of the St John's Mercy Sports and Therapy Center in St Louis, says his patients on low-carbohydrate diets lose weight, but he worries about the long-term effects of missing fiber and other nutrients that have been shown to prevent cancer and heart disease. However, Wadsworth says he's impressed by the safety findings that recent studies have shown.
Some of Wadsworth's patients who are involved in vigorous activities such as tennis have reported that the low-carbohydrate diets have hurt their performance. "They might say, for example, that they don't have the energy for that second set of doubles," he adds. He advises his active patients to at least, for glycogen replacement purposes, replace the calories they burn during exercise with a comparable amount of carbohydrates.
When patients ask his diet advice, Wadsworth refers them to a nutritionist with whom he works closely. He also stresses the importance of adding exercise to their lifestyle. "People want to be healthier, and there's no dietary substitute for physical activity," he says.
Runners: Let Thirst Guide Hydration
In a major policy shift, USA Track & Field, the national governing body for track and field and race walking, in early May issued new hydration recommendations for distance runners. The changes, aimed at preventing exertional hyponatremia, advise runners to drink only when they're thirsty.
Previous recommendations urged runners to "stay ahead" of their thirst and to drink as much as possible to avoid dehydration. The new policy, available on the USA Track & Field Web site, emphasizes that each runner's hydration needs are different, and that runners should determine their own sweat rate during training.
The new recommendations follow a 2002 advisory statement from the International Marathon Medical Director's Association (IMMDA), a consulting committee of the Association of International Marathons (AIMS). The IMMDA-AIMS advisory summarized the most recent findings on heat stress and issued five new guidelines for preventing and diagnosing heat illness.
Researchers Link Concussions to Depression
A study of retired National Football League (NFL) players has found an association between multiple mild traumatic brain injuries and depression. The study, released in April at the American Association of Neurological Surgeons annual meeting in San Diego, also found a link between concussion frequency and depression risk.
The study was based on a general health questionnaire, completed by 2,488 retired NFL players, that was designed by the Center for the Study of Retired Athletes, based at the University of North Carolina in Chapel Hill. Among the group, 263 (11%) had been diagnosed as having clinical depression. The study also found that players who had more than 5 concussions had nearly a threefold risk of depression, and those who had 3 to 4 concussions had a twofold depression risk.
Researchers also attempted to confirm earlier findings that concussions increase the risk of Alzheimer's disease; however, they found no significant association between the two.