BOSTON — Proponents of the Atkins low-carbohydrate/high-saturated-fat diet say that you can have your steak and eat it, too, and still lose weight.
But the adverse metabolic consequences are too heavy a price to pay, Australian investigators reported at a symposium sponsored by the International Atherosclerosis Society.
After 1 year, overweight and obese patients randomly assigned to the Atkins diet or to a low-saturated-fat, high-carbohydrate diet lost similar amounts of weight. But patients on the Atkins diet had a deterioration in flow-mediated arterial dilatation, a marker for cardiovascular disease, and higher levels of LDL cholesterol than at baseline, reported Dr. Peter Clifton of the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Adelaide, South Australia.
“What I really want to know is, does the early elevation of HDL, which has been shown convincingly [with the Atkins diet], and lowering of triglycerides plus the lowering of blood pressure and glucose outweigh the rise in LDL cholesterol that you see in some individuals in some studies?” he said.
“Of course, there are no Atkins end point studies, which is a bit disappointing since there are a fair number of advocates of the Atkins diet,” he added.
Dr. Clifton and his colleagues analyzed the effects of two diets on flow-mediated dilatation (FMD), a measurement of the ability of blood vessels to dilate in response to increases in blood flow. FMD is reduced in both cardiovascular disease and diabetes, but whether it improves with significant weight loss is unclear; if so, it might be related to either decreases in glucose or in LDL, Dr. Clifton said.
The study's aim was to evaluate the effects on markers of endothelial dysfunction and cardiovascular disease risk of a very-low-carbohydrate/high-saturated-fat diet, and an isocaloric high-carbohydrate/low-saturated fat diet.
The outcomes were FMD and markers of endothelial dysfunction, including cellular adhesion molecules, inhibitors and promoters of fibrinolysis, adiponectin, glucose, insulin, C-reactive protein (CRP), lipids, and apolipoprotein B.
The study involved 70 men and women aged 16-60 years with body mass index between 27 and 40 kg/m
The Atkins diet consisted of 35% protein, 61% fat (20% saturated fat), and 4% carbohydrates. The low-fat diet was composed of 30% fat (less than 8% saturated), 46% carbohydrates, and 24% protein.
“We managed to keep people on the Atkins diet for a year without too many complaints, and certainly they had no constipation or halitosis,” Dr. Clifton said. These effects often result from the ketogenic state induced by the Atkins diet.
After 1 year, the 33 patients on the Atkins diet lost slightly more weight on average (14.5 kg) than did the 36 patients on the low-fat diet (11.5 kg), but this difference was not significant. Body fat decreased by a mean 11.3 kg among the Atkins dieters, and by 9.4 kg among the low-fat dieters, a difference that was not significant. Loss of muscle mass was significantly greater among those on the meat-heavy diet, at a mean of 3.2 vs. 2.3 kg for the low-fat, high-carb diet.
There was no diet-specific effect on blood pressure, glucose, insulin, or CRP, but the Atkins diet was superior to the low-fat diet at decreasing triglycerides and increasing HDL. The Atkins diet also was associated with increases in LDL levels. In addition, apolipoprotein B, a marker for cardiovascular disease, increased with the Atkins diet and declined with the low-fat diet, although this difference was not significant.
Overall, 49 patients (26 on the Atkins diet, 23 on the low-fat diet) underwent FMD assessment. Endothelial function decreased by almost half from baseline among patients on the Atkins diet, compared with no change among patients on the low-fat diet. Pulse-wave velocity, a measure of arterial stiffness, improved significantly over baseline in both groups, with no diet-specific effect; another measure of stiffness, augmentation index, did not change in either group.
“So overall, FMD deteriorated after 12 months on a high-saturated-fat Atkins diet, despite their fantastic weight loss and improvement in all those other things,” Dr. Clifton said. “Solely because the LDL increased, it outweighed all the other measures of weight loss. The other measures of endothelial function that we took actually improved except ICAM-1 on the Atkins diet, so there seems to be a separation of endothelial functions as expressed by nitric oxide and these other endothelial markers.
“This really calls into question that fantastic elevation of HDL [with the Atkins diet] as being a good thing or having anything much to do with cardiovascular health,” he added, noting that when changes in HDL in clinical trials are adjusted for LDL changes, any potential relationship of HDL to cardiovascular disease outcomes disappears.