July 16, 2008 -- The debate about the best weight loss diet is on again, with all the usual contenders.
A low-fat diet is not the only safe and effective way to shed pounds, according to a new study that shows low-carbohydrate and Mediterranean diets also result in weight loss, and appear to also offer other health benefits.
"We saw a reduction in weight in all three diets," says Iris Shai, RD, PhD, the study's lead author and a researcher in nutrition and chronic diseases at Ben-Gurion University of the Negev, Beer-Sheva, Israel. "But we saw that other diet strategies, which are higher in fat proportions, like the Mediterranean diet, and the low-carb diet, even result in an increase in weight loss and improvement in blood lipids and blood glucose measurements."
Mediterranean and low-carb diets may be effective alternative diets to the low-fat plan, the researchers conclude. "There are some other diet strategies out there," Shai says.
The study is published in The New England Journal of Medicine.
Comparing Low-Fat, Low-Carb, and Mediterranean Diets
Shai and researchers from Harvard University and other institutions assigned 322 moderately obese men and women, average age 52 and with a body mass index (BMI) of 31, to one of three diets.
The low-fat diet was based on American Heart Association guidelines. In the group following this diet, women ate 1,500 calories a day and men ate 1,800 calories. They took in just 30% of calories from fat, including 10% saturated fat, and were limited to 300 milligrams of cholesterol a day. (A large egg has about 200 milligrams of cholesterol). They focused on eating low-fat grains, vegetables, legumes, and fruits -- and reduced intake of extra fats, sweets, and fatty snacks.
The Mediterranean diet was based on the writings of Walter Willett from Harvard Medical School. In the group following this diet, women consumed 1,500 calories a day and men consumed 1,800 calories. The goal was to eat no more than 35% of calories from fat, and the main sources of added fat were olive oil and a few nuts a day. The diet was rich in vegetables and low in red meat, with fish and chicken replacing beef and lamb.
The low-carb diet was based on the Atkins plan. In this group, calories weren't restricted. These participants were told to eat about 20 grams of carbs a day (about the amount in two slices of bread) for two months, and then increase it to no more than 120 grams a day. They focused on vegetarian sources of fat and protein and avoided foods with trans fat.
Study participants were from a workplace in Dimona, Israel, and ate their lunch, typically the big meal of the day in Israel, in the company cafeteria. Cooks at the company made sure the subjects had the food items they needed. Participants were weighed in every month and had other measurements, such as cholesterol and blood sugar taken four times during the two-year study, from 2005 to 2007.
The maximum weight loss occurred during the first six months; then dieters went on maintenance.
Weight Loss Comparisons
Overall, at the end of two years, the low-fat dieters lost an average of 6.5 pounds, while those on the Mediterranean diet lost 10 pounds and those on the low-carb plan lost 10.3.
Women tended to lose more on the Mediterranean diet. At the 24-month mark, women on the low-fat diet averaged a loss of less than a pound, while those on the low-carb plan lost about 5 pounds and those on the Mediterranean more than 13 pounds.
The drop-out rate in the study was much less than in other diet studies, Shai tells WebMD. At one year, less than 5% had dropped out, compared to up to 60% in other studies, she says. At two years, about 15% had dropped out.
Beyond the weight loss differences, the researchers found some additional health benefits with the low-carb and Mediterranean diet. "The low-carb diet improved HDL ["good" cholesterol] the most,'' she says. And in the 36 dieters with diabetes, those on the Mediterranean diet had better blood sugar and insulin measures.
Diet Debate: Which Is Best?
"I'm not saying the low-fat diet is not efficient," Shai tells WebMD. "I don't think we can say there is one diet that fits all."
Every diet seems to work, if you stay on it, for six months, she says. "After that comes the difficult part, not regaining."
The best advice? Choose a diet that you can follow. For instance, if you hate to count calories, you may be better suited to the low-carb plan than a low-fat, calorie-counting diet. "But once you choose one you should stick with it," she says.
Funding for the study came from multiple sources, including the Ben-Gurion University of the Negev's S. Daniel Abraham International Center for Health and Nutrition, the Dr. Robert C. and Veronica Atkins Research Foundation (set up after the death of low-carb diet founder Robert Atkins in 2003), and the Nuclear Research Center Negev.
Best Diet: Second Opinion
The study results don't surprise Lona Sandon, RD, a spokeswoman for the American Dietetic Association, and an assistant professor at University of Texas Southwestern Medical Center, Dallas.
"As shown in this study and many others that have come before it, any of the diet approaches will work short term, as the most amount of weight was lost in the first six months."
But the long-term question -- what works best for health and disease prevention -- is not yet settled, she says. "My first reaction to this data is, if I am needing to lose weight and decrease the risk of heart disease and diabetes, I would choose the Mediterranean diet approach."
Although the low-carb diet may be a quick fix, "the Mediterranean diet may prove to be the better long-term solution," she says.