Researchers reporting in the July 17 issue of the New England Journal of Medicine published results of their two-year investigation into three popular diets: A low-carbohydrate diet (based on Atkins guidelines), a Mediterranean diet, and a low-fat diet (based on American Heart Association guidelines).The full study can be found at:
Weight Loss with a Low-Carbohydrate, Mediterranean, or Low-Fat Diet
Weight Loss
For weight loss, the low-carbohydrate and Mediterranean diets performed best, and were just about tied at 2 years:
- Low-carbohydrate Diet: 4.7 kg (approximately 10 pounds)
- Mediterranean Diet: 4.4 kg (approximately 10 pounds)
- American Heart Association (AHA) Diet: 2.9 kg (approximately 6 pounds)
Diabetes
There was an unexpected finding that applied specifically to participants with diabetes. Fasting blood glucose of people with diabetes who followed the Mediterranean dropped an average of 32.8 mg/dl; while the fasting glucose of diabetics in the other groups increased by 1.2 mg/dl in the low-carb group and 12.1 mg/dl in the AHA group.
People with diabetes who followed the Mediterranean diet also had the lowest fasting insulin and lowest insulin resistance (HOMA-IR).
Differences Between Diets
All participants reduced their intake from baseline and were eating about the same amount of calories, 1500/day for women and 1800/day for men, regardless of group assignment. Physical activity also increased from baseline but was not different between groups.
The low-fat AHA diet derived about 30% of its calories from fat and 50% from carbohydrate. "The participants were counseled to consume low-fat grains, vegetables, fruits, and legumes and to limit their consumption of additional fats, sweets, and high-fat snacks."
The Mediterranean diet derived about 33% of its calories from fat and 50% from carbohydrate. This group had the highest ratio of monounsaturated-to-saturated fat, probably owing to olive oil and nut consumption: "the main sources of added fat were 30 to 45 g of olive oil and a handful of nuts (five to seven nuts, <20 g) per day." It was a diet "rich in vegetables and low in red meat, with poultry and fish replacing beef and lamb." Members also consumed the greatest amount of dietary fiber.
The low-carbohydrate diet derived about 39% of its calories from fat and 40% from carbohydrate. Members consumed the least amount of carbohydrates (consuming about 120 g/day after the first 2 months and throughout) and the most amount of fat, protein, and cholesterol. It diverged from Atkins' protocol by advising vegetarian sources of fat and protein. This was the only diet that was unrestricted in calories. However, participants averaged about the same amount of calories as the other groups. Notably, even though limits were not placed on how much members of this group could eat, the low-carb group had the highest drop-out rate.
Conclusion
"Mediterranean and low-carbohydrate diets may be effective alternatives to low-fat diets. The more favorable effects on lipids (with the low-carbohydrate diet) and on glycemic control (with the Mediterranean diet) suggest that personal preferences and metabolic considerations might inform individualized tailoring of dietary interventions."
