Americans have been debating the risks and benefits of different diets, specifically low-fat versus low-carbohydrate diets, even decades before the Atkins Diet and the South Beach Diet swept the nation.
Now, a new study has answers to an old question: Is a low-carbohydrate diet bad for the heart?
No, suggests new research published in today's issue of the New England Journal of Medicine, and it's not any worse than a diet high in carbs.
The study, which involved more than 82,000 women from across the country over 20 years, confirms what previous research has suggested: Low-carbohydrate diets do not increase heart-disease risk.
Even though low-carb dieters might tend to eat more fats and other heart-unhealthy foods, over time their risk of coronary heart disease (CHD) did not exceed that of their counterparts who instead consumed a low-fat, low-cholesterol diet.
The study's researchers say the results suggest that low-carb diets are at least on equal footing with other forms of dieting when it comes to heart health.
"This study suggests that neither a low-fat dietary pattern nor a typical low-carbohydrate dietary pattern is ideal with regards to risk of CHD. Both have similar risks," said study researcher Tom Halton, a former doctoral student in the Department of Nutrition at the Harvard School of Public Health in Boston.
"However, if a diet moderately lower in carbohydrates is followed, with a focus on vegetable sources of fat and protein, there may be a benefit for heart disease," Halton said.
Backing the findings are data from three trials published in 2003, which showed that low-carb diets do not increase cardiovascular risk factors.
In those studies, the Atkins Diet, a bellwether regimen on the low-carb scene, was compared to a different diet emphasizing a low intake of fat and cholesterol.
The results? Those on the Atkins Diet actually had greater improvements in insulin sensitivity, HDL (good) cholesterol and triglyceride levels than did the low-fat, low-cal dieters.
The findings, however, come with a caveat common to many of the other studies on high-protein, low-carb diets. In short, don't go crazy on the red meat.
"This study doesn't mean that you should load your plate with steak and bacon," said the study's senior author Frank Hu, associate professor of nutrition and epidemiology at Harvard School of Public Health.
"The quality of fat and carbohydrate is more important than quantity. A heart-healthy diet should embrace healthy types of fat and carbohydrates," Hu said.
Some experts remain skeptical of the study.
"This is an observational study, not a randomized trial," said Dr. Neal D. Barnard, president of the Physicians Committee for Responsible Medicine in Washington, D.C.
"We already have randomized trials of low-carb diets, and they clearly show that approximately one in three low-carb diets has a significant increase in LDL [bad] cholesterol. Such findings are far more relevant than observational studies to the question of what effects do low-carb diets have," Barnard said.
Adding to the skepticism of some experts are the limitations of the study -- specifically, that it only looked at female nurses, and that the self-reporting method used could be considered unreliable.
"A strong limitation of this study is that since the subjects were nurses who may make more informed food choices that other women, the results may not be applicable generally," said Carla Wolper of the Obesity Research Center at St. Luke's Hospital in New York.
"In other words, these nurses may have chosen healthier forms of protein [fish, leaner meats, skim milk and lower-fat cheeses]. Thus, even with increased protein intake, they may not have increased intake of saturated fats so damaging to coronary health."
Wolper says the study, which defies conventional wisdom on the consumption of high-protein (and often high-fat) foods, could be puzzling to average consumers who are just hoping to eat healthier.
"As for patients, they are confused, and this study will confuse even more," she said. "If you include obesity in the picture, with all its inherent health risks, and then add a poor diet, heart disease increases. Americans are already overweight or obese, and choosing a high-fat diet will increase coronary risk."
Is the Low-Carb Diet Dead?
The discussion could be a moot point, however. Many experts believe the era of the low-carb diet may be on its way out.
"If the low-carb diet isn't dead, it's more or less on life support," said Keith-Thomas Ayoob, associate professor at the Department of Pediatrics at Albert Einstein College of Medicine in New York.
"No one sticks to them anyway. Healthy eating is about balance -- balance between what we need and what we can't manage to live without. Fail to recognize that, and that consumers are not robots who are going to eat the same way for 20 years, and we're just doing nutrition theory and hypotheticals."
The issue of sustainability is echoed by other experts in the field, many of whom say low-carb diets are just too difficult for most people to stick to.
"Most people cannot sustain a very low-carb diet in the long term," said Joanne Shearer, team leader of food and nutrition services at Avera Heart Hospital of South Dakota in Sioux Falls, S.D. "I recently gave a presentation where I asked a group of 40 nurses if they had tried a low-carb diet, and several hands went up. When I asked if anyone was currently following the diet, not one person raised their hand."
The salad days of the low-carb diet could also be shortened by what appears to be the next trend: a focus on low-glycemic foods.
"People's interest in low-carb diets has definitely waned," said Mary Beth Kavanagh, instructor at the Department of Nutrition at Case Western Reserve University in Cleveland. "There is great interest in glycemic index and glycemic load of diets and the effect on weight loss, cardiovascular disease risk, and glycemic control in diabetics."
In the confusion over what to eat, many experts say that the best course of action is a tried-and-true mantra: moderation, moderation, moderation.
"Better studies have said time and again to limit saturated fat," Ayoob said. "That's what I tell my patients and what I'll continue to tell them."
"The message should be carefully evaluated in reference to saturated fat," said Jana Klauer, a physician specializing in nutrition and exercise in New York. "What the study does say is: All carbohydrates are not the same. Those that spike blood sugar are not good for your heart. High amounts of protein will not hurt you. Vegetable protein and fat lower risk for heart disease."
"I recommend high amounts of protein to my patients but advise them to focus on lean meats, take the skin off chicken, and eat good amounts of fish."