Low-carb diet better with vegetables, study says

To test the diets, the researchers followed more than 85,000 women enrolled in the Nurses' Health Study and more than 44,000 men in the Health Professionals’ Follow-up Study. Participants answered periodic questionnaires on the food they ate, how active they were, how much they weighed, and whether they smoked, among other variables.

After 20 years for the men and 26 years for the women, more than 20,000 people had died. To see if there might be a connection between diet and death, the researchers divided the participants into 10 groups based on their carb intake and looked specifically at deaths caused by cardiovascular disease or cancer.

The observational study cannot establish cause and effect, but it did find a correlation between people on low-carb, high animal-source diets and mortality, especially from cancer, compared with high-carb diets. People eating low-carb, high plant-source diets had a lower mortality rate than people eating high-carb diets, especially from cardiovascular disease. The association remained after body mass index, smoking, and other factors were taken into account.

An editorial appearing with the article says the study cannot provide a definitive answer.

“No one can legitimately claim that a low-carbohydrate diet is either harmful or safe with any degree of certainty until a large-scale, randomized study with meaningful clinical endpoints is done,” Dr. William S. Yancy Jr. and colleagues from the Veterans Affairs Medical Center and Duke University Medical Center wrote.

Fung said she and her co-authors agree that randomized clinical trials are the gold standard for medical research, but she also argues that observational studies complement clinical trials because they are more likely to gather information over the long haul. In the large randomized clinical trial called the Women’s Health Initiative, for example, participants had trouble staying on low-fat diets, so they ended up eating diets so similar to women in the comparison group that the results cannot be considered conclusive, she said.

If ordinary people are wondering what to do while waiting for a definitive answer, Fung has some guidance based not just on her study, but on many other diet studies.

“Everything seems to be pointing toward the direction that plant- based diets are more beneficial in helping people live longer and healthier lives,” she said. "When we think, 'What am I going to have for dinner?' we think of meat first. Can we change that to, 'What is the vegetable?' first?"