Low-carb diets like Atkins and South Beach have, in some studies, shown counterintuitive effects on the heart, garnering them support from an unlikely corner: cardiology. The debate over how low-carb diets stack up against the low-fat diets long recommended by heart experts has proved to be both lively and enduring.
Is there a way to stop the obesity juggernaut? Drs Roger Blumenthal, Bob Eckel, and Christopher Gardner gathered to discuss their thoughts on obesity and suggest options for permanent weight loss in obese patients.
Obesity experts say physicians and drug regulators need to sit up and take notice: the pharmacy shelves are all but bare of weight-loss drugs. Some say soaring BMIs mean certain risks should be deemed acceptableeven in "healthy" obese subjectsto prevent progression to more serious disease down the road. But it's a tough sell.
The Atkins diet is always the subject of controversy when it comes to scientific claims. The latest assertion by one proponent is that it can help treat diabetes, mostly because people can lose weight easily while on this diet. But others argue that there are better options to lose weight and that Atkins is far too restrictive to stay on long term. And perhaps most important, they question the safety of this diet.
A new study examining whether use of the Mediterranean diet prevented the onset of diabetes in individuals at high cardiovascular risk found that it did, halving the incidence over four years compared with a low-fat diet. Importantly, this benefit was seen without any weight loss, a finding an ADA spokesperson said is "very exciting."
Improvements in carotid disease severity, as measured by conventional ultrasound but also a three-dimensional volumetric ultrasound technique, were independent of whether patients followed a low-fat, "low-carb," or Mediterranean diet in an imaging substudy of a randomized trial.
The one-year randomized study is the first to compare the low-carb diet with a low-fat strategy in combination with a diet drug. While lipid changes were similar, diastolic and systolic BP improved more with low-carb.
UPDATED //A small study in only 24 patients and lasting just eight weeks has once again thrust low-carb diets into the spotlight, with the finding that this diet adversely affected a little-known measure of arterial stiffness, the aortic-augmentation index, which could have implications for long-term vascular health.
Weight loss was similar, but serum lipid levels were better after one month on a low-carb, plant-based diet vs a high-carb, lacto-ovo vegetarian diet, in a small study of overweight adults with hyperlipidemia.
One of the longest diet studies to compare different heart-healthy diets emphasizing different macronutrient levels has shown that what matters is reducing calorie intake over the long term and getting regular support or counseling. (Sacks FM et al. N Engl J Med 2009; 360:859-873.)
Researchers say almost all of the obese diabetics randomized to a diet of <20 g carbs per day lost weight, improved their HDL, and reduced or eliminated their diabetes meds. Others highlight the high dropout rate and, with the researchers, call for fat-vs-carb trials. (Westman EC et al. Nutr Metab; published online before print December 19, 2008.)
After six months eating foods with a low-glycemic index, diabetic patients had significantly better glycemic control and increased HDL-cholesterol levels when compared with individuals eating a high-cereal-fiber diet, report researchers. (Jenkins DJ et al. JAMA 2008; 300:2742-2753.)
While all three groups in the DIRECT study lost weight, the greatest weight loss was in the low-carb and Mediterranean-diet groups. Investigators and others say it is time to rethink the low-fat paradigm. (Shai I et al. N Engl J Med 2008; 359:229-241.)
A study comparing the metabolic effects of two diets, one a low-carbohydrate, high-fat, Atkins-like diet and the other a more traditional high-carbohydrate, low-fat diet, showed that both diets had similar improvements on a number of metabolic risk markers, although the traditional diet had more favorable effects on LDL-cholesterol levels. (Tay J et al. J Am Coll Cardiol 2008; 51:59-67.)
Individual differences in insulin secretion may explain why some individuals respond well to either low-fat or low-glycemic-load diets, while others do not, hinting that a simple oral glucose-tolerance test might help physicians and dieticians choose weight-loss strategies for obese subjects. (Ebbeling CB et al. JAMA 2007; 297:2092-2101.)
Dieters and their physicians can be reassured that slashing carbs may be a safe option for losing weight: results from the A TO Z trial found that premenopausal women randomized to the Atkins diet lost statistically more weight than women on the Zone diet. All four diets may be reasonable options for modest weight reduction, authors say. (Gardner CD et al. JAMA 2007; 297:969-977.)
New observations from the Nurses' Health Study may help allay fears that people who eat higher amounts of protein and fat while cutting back on carbs are not trading hopes of a slimmer waistline for increased coronary heart disease risk. In fact, diets lower in carbohydrates and higher in fats from vegetable sources were associated with a reduced risk for CAD. (Halton TL et al. N Engl J Med 2006; 355:1991-2002.)
In addition to food advice, the 2006 revision also includes guidance on tobacco exposure, socioeconomic status, and environmental factors. Aspects of the new guidelines offer a glimpse into the progress of nutritional science, but at least one expert believes the approach ignores data that challenge the conventional low-fat diet. (Lichtenstein A et al. Circulation; published online before print June 19, 2006.)
Both low-carb and low-fat diets promoted weight loss, but only the latter reduced total LDL-C levels. On the other hand, the low-carb diets improved triglyceride and HDL-C profiles. Although the outcomes-oriented evidence base favors low-fat diets, the real message may be more complicated. (Nordmann AJ et al. Arch Intern Med 2006; 166:285-293.)
A comparison of the Atkins, Ornish, Weight Watchers, and Zone diets showed weight reduction over one year to be comparable between the four strategies and that adherence to diet was the only strong predictor of weight loss in overweight subjects. Cardiac risk factor changes were also comparable, authors say. (Dansinger ML et al. JAMA 2005; 293:43-53.)
For the first time, the Lancet is weighing in on the Atkins diet craze with a review calling for longer-term, larger studies of the popular low-carb, high-fat, high-protein diet. (Astrup A et al. Lancet 2004; 364:897-99.)
Updated with correction / with slides / Two new studies of carbohydrate-reduced diets make it more difficult than ever to "dismiss" the possibility that these diets can help overweight subjects, experts say. Only one of the two studies found weight loss to be greater in the low-carb group than in the low-fat dieters, while both documented positive changes in lipid profiles. (Stern L et al; Yancy WS et al. Ann Intern Med 2004; 140: 778-85; 769-77.)