A low-carbohydrate Mediterranean diet dramatically reduced the need for diabetic drug therapy, compared to a low-fat American Heart Association diet. The Italian researchers also report that the Mediterranean dieters also lost more weight over the first two years of the study.
Investigators suggest that the benefit of the Mediterranean-style diet is due to greater weight loss, olive oil (monunsaturated fats increase insulin sensitivity), and increased adiponectin levels.
The American Diabetes Association recommends both low-carbohydrate and low-fat diets for overweight diabetics. The investigators wondered which of the two might be better, as judged by the need to institute drug therapy in newly diagnosed people with diabetes.
Newly diagnosed type 2 diabetics who had never been treated with diabetes drugs were recruited into the study, which was done in Naples, Italy. At the outset, the 215 study participants were 30 to 75 years of age, had body mass index over 25 (average 29.5), had average hemoglobin A1c levels of 7.73, and average glucose levels of 170 mg/dl.
Participants were randomly assigned to one of two diets:
- Low-carb Mediterranean diet (“MED diet”, hereafter): rich in vegetables and whole grains, low in red meat (replaced with poultry and fish), no more than 50% of calories from complex carbohydrates, no less than 30% of calories from fat (main source of added fat was 30 to 50 g of olive oil daily). [No mention of fruits or wine. BTW, the traditional Mediterranean diet derives 50-60% of energy from carbohydrates.]
- Low-fat diet based on American Heart Association guidelines: rich in whole grains, restricted additional fats/sweets/high-fat snacks, no more than 30% of calories from fat, no more than 10% of calories from saturated fats.
Both diet groups were instructed to limit daily energy intake to 1500 (women) or 1800 (men) calories.
All participants were advised to increase physical activity, mainly walking for at least 30 minutes a day.
Drug therapy was initiated when hemoglobin A1c levels persisted above 7% despite diet and exercise.
The study lasted four years.
By the end of 18 months, twice as many low-fat dieters required diabetes drug therapy compared to the MED dieters—24% versus 12%.
By the end of four years, seven of every 10 low-fat dieters were on drug therapy compared to four of every 10 MED dieters.
The MED dieters lost 2 kg (4.4 lb) more weight by the end of one year, compared to the low-fat group. The groups were no different in net weight loss when measured at four years: down 3–4 kg (7–9 lb).
Compared to the low-fat group, the MED diet cohort achieved significantly lower levels of fasting glucose and hemoglobin A1c throughout the four years.
The MED diet group saw greater increases in insulin sensitivity, i.e., they had less insulin resistance.
The MED group had significantly greater increases in HDL cholesterol and decreases in trigylcerides throughout the study. Total cholesterol decreased more in the MED dieters, but after the first two years the difference from the low-fat group was not significantly different.
The Mediterranean group’s intake of carbohydrates was 8-9% lower than baseline, monounsaturated fat was 5.5% higher than baseline, and polyunsaturated fat was 2.5% higher than baseline. Compared with their baseline, the low-fat group didn’t make much change in these nutrient groups. These numbers hold up for all four years of the study.
The MED diet here includes “no more than 50% of calories from complex carbohydrates.” The authors don’t define complex carbs. Simple carbohydrates are monosaccharides and disaccharides. Complex carbs are oligosaccharides and polysaccharides. Another definition of complex carbs is “fruits, vegetables, and whole grains,” which I think is definition of complex carbs applicable to this study.
The editors of the Annals of Internal Medicine conclude that:
A low-carbohydrate, Mediterranean-style diet seems to be preferable to a low-fat diet for glycemic control in patients with newly diagnosed type 2 diabetes.
I’m sure the American Diabetes Association will take heed of this study when they next revise their diet guidelines. If I were newly diagnosed with type 2 diabetes, I wouldn’t wait until then.
This study dovetails nicely with others that show prevention of type 2 diabetes with the Mediterranean diet, reversal of metabolic syndrome—a risk factor for diabetes—with the Mediterranean diet (supplemented with nuts), and prevention of type 2 diabetes and pre-diabetes in people who have had a heart attack.
For instruction on how to lose weight with a Mediterranean-style diet, click here (it’s not the low-carb diet used in the study at hand).
For general information on Mediterranean eating, visit Oldways.
Steve Parker, M.D.
Reference: Esposito, Katherine, et al. Effects of a Mediterranean-style diet on the need for antihyperglycemic drug therapy in patients with newly diagnosed type 2 diabetes. Annals of Internal Medicine, 151 (2009): 306-314.