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June 2008 Issue

College of Nursing associate professor Bonnie Brehm, PhD, (left), researches nutrition and obesity.
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UC Study Finds Popular Diets Might Not Be the Best Prescription for Long-Term Health

By Jill Hafner
Published June 2008

It’s still too early to tell if popular diets that focus on eliminating some essential nutrients while loading up on others will lead to long-term health benefits, according to UC researchers.

Bonnie Brehm, PhD, professor in the College of Nursing, says diet plans, such as the Atkins, (low-carbohydrate, high-fat) and Ornish (low-fat, high-carbohydrate) diets, have stirred a debate about the health effects of macronutrient distribution in the diet.

In fact, diets that include extreme ranges of macronutrients—carbohydrate, protein or fat—might not be what the doctor orders to manage weight and diabetes, and improve cardiovascular health.

“With the rise of obesity and diabetes, there is concern about whether popular diets are the best prescriptions for optimal health,” says Brehm. “There’s an intense debate about the ideal combination of carbohydrate, protein and fat for effectively managing obesity and its metabolic consequences such as diabetes, and for improving body composition and overall health.

Brehm, and co-author David D’Alessio, MD, professor of medicine at UC, published a literary review of the benefits of diets with varying fat and carbohydrate content in the March 2008 edition of Nature Clinical Practice.

In studies published over the last 20 years, Brehm and D’Alessio found that while low-carb, fad diets may help shed pounds and lower cardiovascular risks in the short term,

longer studies are needed to fully determine if these diets are really effective and safe—

and whether they warrant nutritional recommendations from health providers.

“The studies we examined provided additional, but not yet sufficient, evidence for modification of current nutritional guidelines, which suggest how much fat, protein and carbohydrate a person should consume to lose weight or improve their overall health,” Brehm says. “Despite a recent flurry of research, many fundamental questions related to dietary macronutrients and their effects on energy balance and metabolism remain unanswered.”

Macronutrients—protein, fat and carbohydrate—are nutrients the body needs in large quantities to provide energy for normal functions.

Brehm and D’Alessio focused their review on diets either low in carbohydrate or high in monounsaturated fat or the “good fats” generally known to reduce “bad” cholesterol levels in the blood and lower the risks of heart disease and stroke.

Brehm says that while each diet claims to offer a distinct health benefit over another, some may come with associated risks, which might not be worth taking in the long run.

“We found evidence that low-carbohydrate diets lead to weight loss in 12-month studies,” says Brehm, “but these same studies showed that these diets don’t affect everyone’s metabolism the same way and there’s potential for increased LDL-cholesterol or the ‘bad’ cholesterol.

“The unceasing demand by patients and health care providers for effective weight-loss methods has led to the use of a wide number of unproven strategies,” she adds. “A year might seem long for those conducting or participating in a study, but it comprises only a short time in the life of an overweight person. In essence, the long-term benefits remain unknown.”

Until more long-term research is conducted, Brehm recommends sticking with the diet recommendations of expert bodies such as the Institute of Medicine, American Heart Association and American Diabetes Association. These, she says, are based on clinical expertise and scientific data.

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