Low-carb dieters knew it all along
Obesity rates are rising, but science has barely weighed in on the best way for people to shed fat. That state of affairs is starting to change, and doctors are getting a surprise or two.
Last week, the popular carb-slashing Atkins diet received a dollop of endorsement from two new studies after years of being pooh-poohed by health specialists. The studies, published Tuesday in the journal Annals of Internal Medicine, showed that the meat- and fat-rich regimen caused faster weight loss in the short term than a conventional low-fat diet.
More important -- because many had feared that the diet, even if slimming, might unfavorably affect cholesterol levels and be bad for the heart -- the low-carb regimen also seemed to improve the dieters’ blood fat profiles.
But Atkins, like every other diet, is no miraculous fat-melter. The longer of the two studies suggested that a low-carb regimen might be harder to maintain beyond six months compared with a low-fat approach: By the end of the year, the low-fat dieters had caught up and lost the same -- very modest -- amount of heft.
In addition, even though on average people on low-carb diets didn’t experience rises in their so-called “bad” (or LDL) cholesterol levels, about 30% of individuals did.
Even with these caveats, “we can no longer dismiss very-low-carbohydrate diets,” said Dr. Walter Willett, a nutritional epidemiologist at the Harvard School of Public Health, in a written editorial accompanying the papers. To maximize the diets’ healthfulness, he added, people should avoid going hog wild on fatty bacon and red meat -- opting instead to eat healthy oils (monounsaturated and polyunsaturated fats) and get protein from fish, beans, nuts and chicken.
The weight-loss regimen popularized by the late Dr. Robert Atkins -- rich in meat, eggs and cheese but almost bereft of grains, potatoes and fruit -- is highly popular but had not been tested in a scientifically rigorous way until last year, when two studies reported that very obese and moderately obese people lost more weight initially on the Atkins diet than on a conventional diet.
The studies published last week bolster and extend these findings.
Conducted at the Philadelphia Veterans Affairs Medical Center, the first study enrolled 132 severely obese adults who had an average weight of 288 pounds. Many of the patients in the study had diabetes or other risk factors for coronary artery disease.
Roughly half of them were instructed to pursue a low-fat diet in which they were to eat 500 fewer calories a day. The others followed a regimen in which they were to limit their carbohydrate intake to less than 30 grams daily but were not instructed to count calories or fat. Both groups were counseled on the diets each week.
The scientists reported last year that at six months, the low-carbohydrate group had lost an average of about 13 pounds, compared with four pounds for the low-fat group.
On Tuesday, the scientists reported that after one year, individuals on the Atkins-style diet largely kept the weight off but did not continue to lose more weight. The low-fat group continued to lose weight slowly over the course of the year.
Total weight loss for both groups over the year was slight: an average of 11 to 19 pounds for the low-carb group and seven to 19 pounds for the low-fat group.
In addition, the study found that diabetic patients improved control over their blood sugar levels using the low-carb approach.
The second investigation was funded by the Robert C. Atkins Foundation, although the foundation did not take part in the study or its analysis. Conducted at Duke University Medical Center in Durham, N.C., it enrolled 120 moderately obese adults who had high blood cholesterol levels.
At six months, participants who followed a low-carb approach had lost an average of 26 pounds, compared with 14 pounds for the low-fat group.
Weight loss wasn’t the only effect of these diets. Both studies found that levels of triglycerides -- blood fats that are risk factors for heart disease -- fell further in the low-carb group than in the low-fat group. Levels of HDL, or “good,” cholesterol also appeared to improve more in the low-carb group.
Still, experts said more studies were needed to ensure that the HDL lipid change was favorable and that the higher amounts of fat consumed on an Atkins-style diet would not increase a dieter’s risk for heart disease. The American Heart Assn. issued a statement expressing concern about the safety of the diet given its richness in saturated fats -- and noting that at one year, in any case, the results for the diets were a wash.
To be safe, people on an Atkins-style diet should have their blood lipids monitored regularly in case their “bad” cholesterol goes up, said Dr. William Yancy, assistant professor of medicine at Duke and lead author of the study there.
If a low-carb diet sheds more fat in the short term -- why does it? Atkins always held that the secret of his diet was “ketosis,” a body state in which fat would be burned more efficiently. But the key may be rather less magical, said Dr. Frederick Samaha, chief of cardiology at the Philadelphia Veterans Affairs Medical Center and coauthor of the Philadelphia study.
Low-carbohydrate diets are richer in protein and fat, which have the effect of making a person feel full more rapidly. That means they’ll eat fewer calories.
Not only that, but people following an Atkins-style diet have many more food restrictions, which could also slash the number of calories they consume.
These very restrictions could make it harder to stay with the diet over the longer haul -- and might easily be the reason why patients on low-carb diets eventually stopped losing weight, while low-fat dieters continued to lose, Samaha said.
“I think it’s partly the monotony -- but also, the low-carb diet really forces people to prepare their own foods -- to go out and buy fish and chicken and meat,” he said. “Whereas for low-fat diets there’s a lot of really good, readily available food to grab off the shelf.”
The current flood of low-carb snacks in the marketplace might either help the diet or undermine it, Samaha said, making it easier to stick to the diet but also increasing opportunities for unfettered snacking.
