This diet has had several incarnations over the years. Today it’s simply called the low-carbohydrate, high-protein diet: a plan that restricts bread, pasta, rice, potatoes, fruit, some vegetables and sweets and allows 30 to 50 percent of total calories from protein-rich beef, pork, chicken, fish and dairy products—without regard for fat content.

The diet has been touted as an effective and easy way to lose weight. But research in the past few years has found dieters on the plan have increased risks for cancer, heart disease and kidney disease. And a study published in June 2012 in the Journal of American Medical Association (JAMA) comparing the low-carbohydrate, high-protein diet to two others demonstrated what many experts say they’ve always promoted: a diet that includes a mix of carbohydrates, fats and protein is the best option for healthy weight loss.

“It’s what I’ve been advocating for a long time,” says Alison Massey, a registered dietician and diabetes educator with the Endocrinology Center at Mercy Medical Center in Baltimore. “Choosing a diet that includes high fiber, complex carbohydrates, some healthy fat and a moderate amount of lean protein is best not only for losing weight but for maintaining it, which is definitely challenging.”

A high-protein diet works in part because it leaves you satiated, or satisfied, so you don’t feel hungry. By restricting carbohydrates, the body goes into what is known as ketosis, where it burns its own fat for fuel instead of the carbohydrates it normally relies on. When fat stores become the primary energy-burning source, you lose weight. 

Mixed results

A high-protein diet might help you lose weight and might even improve some areas of your health. But it could also increase some health risks. In a study published in October 2011 in the JAMA, researchers at Brigham and Women’s Hospital at Harvard Medical School found that at six months, a high-protein, very low-carbohydrate diet showed better weight-loss results and also improved cholesterol levels when compared to a conventional low-fat diet. 

But the diet also could put you at greater risk for kidney and heart disease and cancer. A Brigham and Women’s study published in the February 2012 issue of the American Journal of Kidney Disease showed that while participants with healthy kidneys did not show any noticeable negative effects in kidney function, those with early symptoms of kidney disease experienced an accelerated loss of kidney function on the low-carb, high-protein diet. 

Cancer concerns were raised in a May 2011 study in the American Journal of Clinical Nutrition, which found that after a four-week weight-loss diet high in protein but reduced in total carbohydrates and fiber, participants had a “significant decrease” in cancer-protective metabolites and increased concentration of hazardous metabolites, which may increase risk for colonic disease. 

The heart may also suffer on this diet plan, according to recent research. A study of 43,000 Swedish women over 16 years published in June 2012 in the British Medical Journal found that women who consumed a diet consisting of high protein and low carbohydrates were at a 5 percent higher risk for cardiovascular disease. 

Keys to long-term success

If you want to lose weight, keep it off and stay healthy, a more moderate approach—a mix of protein and carbohydrates—could be the answer. 

A comparison of diets in the June 2012 issue of JAMA showed some eye-opening results. After first losing 10 to 15 percent of their body weight, participants went on three different diets for four weeks at a time in random order: 

• A low-fat diet of 60 percent carbohydrates, 20 percent fat and 20 percent protein;
• A low-carbohydrate diet of 10 percent carbohydrates, 60 percent fat and 30 percent protein;
• A low-glycemic index diet—known as the Mediterranean diet—of minimally processed grains, vegetables, healthy fats, legumes and fruits with 40 percent carbohydrates, 40 percent fat and 20 percent protein.

The study found that the low-carbohydrate diet showed the biggest increase in metabolism—the amount of energy burned, which means the highest number of calories. But the authors emphasized, “This diet increased participants’ cortisol levels, which can lead to insulin resistance and cardiovascular disease.” They also noted that the very low carbohydrate diet raised inflammatory levels, which may increase risk of cardiovascular disease. The lowest energy burn came from the low-fat diet, which also showed increases in triglycerides and lower levels of “good” cholesterol. 

In the middle was the low-glycemic index diet, which burned calories at a higher rate than the low-fat diet and did so with no negative health issues associated with the other two diets. “In addition to the benefits noted in this study, we believe the low-glycemic-index diets are easier to stick to on a day-to-day basis, compared to low-carb and low-fat diets, which many people find limiting,” said Cara Ebbeling, one of the study’s authors. “(It) doesn’t eliminate entire classes of food, likely making it easier to follow and more sustainable.”

That’s key, says Roberta Jenero, a registered dietician and founder of Figure Facts, which offers tools for reaching health and wellness goals. “We keep looking for a magic bullet, but it’s not going to happen,” she says. “When you’re following a low-glycemic index diet, you’re getting fiber, healthy fat from nuts, seeds and avocados, whole grains and complex carbohydrates.”