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With fad diets like Atkins and South Beach making the best-seller lists,the weight loss industry is capitalizing on the feeding frenzy of anincreasingly desperate public. But whether their promises of success aremasked in clinical studies or simply claim miracle results, the public iseating it up.
"These products would not sell, infomercials would not be around, ifwe had cures for obesity," said Gary Foster, MD, of the University ofPennsylvania School of Medicine, at a panel discussion on controversies inobesity treatment at the recent Endocrinology Society annual meeting in NewOrleans.
One matter that is the subject of considerable debate is the issue of whichis more beneficial for reducing weight and avoiding the consequences ofobesity—a low-carb/high-protein diet or a low-calorie/low-fat diet.
"We need to be open to alternatives, but they have to besystematically evaluated," said Foster. "Just because it is new,doesn't mean it is better. And it does have to go through the rigor ofrandomized controlled trials." The clinical evidence supporting the dietdu jour is sparse indeed. Clinical data to support various diets are based onsmall groups of patients in short follow-up studies, according to Foster. Itis important for physicians to emphasize for patients the context of themedical evidence; in many respects, the jury is still out.
TO CARB OR NOT TO CARB
"All of the hype you see about low-carbohydrate diets comes from thedata in less than 100 patients studied at 1 year," emphasized Foster."These studies say that there is no statistically significant differencebetween these two approaches at one year."
Such a study design is inadequate to answer the low-calorie versus low-carbdiet debate. "This idea about whether it is calories or carbohydrates orfat or protein cannot be answered in an outpatient clinical trial,"Foster said.
The few randomized controlled trials available do consistently show that,at 6-month follow-up, a low-carbohydrate approach induces about twice theweight loss of a low-calorie approach, according to Foster. There are alsoconsistently greater reductions in triglycerides, but no effects on totalcholesterol or LDL. Half of the studies show improvements in HDL with thelow-carbohydrate approach.
However, the differences appear to pan out in studies with longerfollow-up, Foster said. At 1-year follow-up, the difference in weight lossbetween low-carb/high-protein and low-calorie/low-fat diets do not reachstatistical significance. Both approaches show lower LDL levels after 1 year,while the low-carb approach is associated with greater reduction intriglycerides and increased HDLlevels.
RANDOMIZED CONTROLLED STUDIES
Foster's group reported 1-year data from a multicenter comparison of theAtkins and low-calorie/low-fat diets in a small sample of 63 patients who werecandidates for gastric bypass surgery. Forty percent of the patients in aseries reported by Foster and colleagues had type 2 diabetes and 40% hadmetabolic syndrome.
Analysis showed more weight loss, greater reduction in triglycerides, andlower blood glucose with the low-carbohydrate diet at 6 months compared to thelow-calorie diet. At 1 year, differences in weight loss and blood glucoselevels between the groups vanished.
Findings from the study indicate greater improvement in insulin sensitivityfor nondiabetic patients using the low-carbohydrate approach than for thoseusing the low-fat approach, Foster said. There was a 28% decrease intriglycerides for those on the Atkins diet, but no change among patients onthe conventional diet. There was a 20% increase in HDL at 6 months, and 17% at1 year.
Patients on the Atkins diet had lower blood insulin levels at 6 months, butno differences from the low-calorie/low-fat diet were evident at 1 year.Foster explained that his data suggest that it is weight loss itself, and notthe nutritional composition of a diet, that affects insulin sensitivity."Whether you lose weight by a low-fat or low-carbohydrate diet, yourinsulin sensitivity is improved significantly," he said.
A randomized controlled study comparing a low (15%) carbohydrate and alow-fat, moderate (45%) carbohydrate diet showed twice the weight loss at 6months with the low-carb approach in 42 morbidly obese subjects. Althoughpatients had significantly lower triglycerides, no significant differenceswere noted for total cholesterol, LDL, HDL, or blood glucose, according toFoster.
Six-month data from a study of 120 primarily female subjects who weregenerally overweight and dyslipidemic revealed that the low-carbohydrateapproach demonstrated greater weight loss, lower triglycerides, and higherlevels of HDL than other diets.
IT'S NOT A CONTEST
The question is not, "Which diet is the best?" but morespecifically, "Which diets work best for which people andwhen?"
"We can't close our eyes to the data out there, something isdefinitely going on," said Holly Wyatt, MD, of the University ofColorado. "We just don't know and can't determine what is responsiblefor the effect of weight loss."
Arne Astrup of the Institute of Human Nutrition at RVA University inCopenhagen, Denmark, discussed studies comparing a moderate-fat diet deriving40% of calories from fat and a low-fat diet. The proportion of subjects losing10% or more of initial body weight was higher in the low-fat diet group thanin the moderate-fat group (18% versus 12%), suggesting that calorierestriction is more important than the level of dietary fat for weight loss.There were more pronounced reductions in total cholesterol, LDL, andtriglycerides and a significantly higher dropout rate in patients on thelow-fat diet, he added.
None of these findings conclusive; however, each gives a new and morespecific hypothesis for future studies of safety and efficacy, according toAstrup.
Despite a number of clinical studies, satisfactory answers for achievingand maintaining weight loss are still elusive, according to Stanley Kornenman,MD, of the University of California Los Angeles School of Medicine.
Foster still believes the answer is in the calories—but that countingcarbohydrates may actually be an easier way of cutting calories than trying tocount calories directly. "When you tell people to count carbohydratesthey actually consume fewer calories than they do when you tell them to countcalories," he explained.
Counting calories directly can become difficult when guidelines requiredifferentiating calories from fat, animal fat from plant fats, and complexfrom whole carbohydrates. "That requires a lot of cognitivegymnastics," said Foster.
By contrast, a low-carbohydrate approach involves eliminating wholecategories of food. "What may be advantageous about this[low-carbohydrate] approach, right or wrong, is its simplicity."
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