In overweight type 2 diabetics, a low-carbohydrate Mediterranean diet improved HDL cholesterol levels and glucose control better than either the standard Mediterranean diet or American Diabetes Association diet, according to Israeli researchers reporting earlier this year.
Prior studies suggest that diets rich in monounsaturated fatty acids (olive oil, for example) elevate HDL cholesterol and reduce LDL cholestrol and triglycerides in type 2 diabetics.
Low-carb diets improve blood sugar levels and reduce excess body weight in type 2 diabetics, leading to the ADA’s allowance in 2008 of a low-carbohydrate diet as an alternative to standard diabetic diets.
Many—probably most—type 2 diabetics have insulin resistance: the body’s cells that can remove sugar from the bloodstream are not very sensitive to the effect of insulin driving sugar into those cells. They “resist” insulin’s effect. Consumption of monounsaturated fatty acids improves insulin sensitivity. In other words, insulin is better able to push blood sugar into cells, removing it from the bloodstream.
Previous studies have shown that both low-carb diets and the Mediterranean diet reduce after-meal elevations in blood sugar, which likely lowers levels of triglycerides and LDL cholesterol.
How Was the Study Done?
The goal was to compare effects of three diets in overweight type 2 diabetics in Israel over the course of one year. Study participants totalled 259. Average age was 56, average weight 86 kg (189 lb), average hemoglobin A1c 8.3%, and average fasting plasma glucose (sugar) was 10.3 mmol/L (185 mg/dl). [Many diabetics in the U.S. fit this profile.] People taking insulin were excluded from the study, as were those with proliferative diabetic retinopathy—no reasons given.
Participants were randomly assigned to one of three diets, so there were about 85 in each group. [Over the course of one year, people dropped out of the study for various reasons, leaving each group with about 60 subjects.]
Here are the diets:
- 2003 ADA (American Diabetes Association) diet: 50-55% of total caloric intake from carbohydrate (mixed glycemic index carbs), 30% from fat, 20% from protein
- Traditional Mediterranean (TM): 50-55% low-glycemic-index carbs, 30% fat—high in monounsaturated fat, 15-20% protein
- Low-carb Mediterranean (LCM) : 35% low-glycemic-index carbs, 45% fat—high in monounsaturated fat, 15-20% protein
Patients were followed-up by the same dietitian every two weeks for one year. All were advised to do aerobic exercise for 30-45 minutes at least three days a week.
Olive oil is traditionally the predominant form of fat in the Mediterranean diet and is a particularly rich source of monounsaturated fat. At no point in this report was olive oil mentioned, nor any other source of monounsaturated fat. Until I hear otherwise, I will assume that olive oil was the major source of monounsaturated fat in the TM and LCM diets.
All diets were designed to provide 20 calories per kilogram of body weight.
In all three diets, saturated fat provided 7% of total calories. Monounsaturated fatty acids provided 23% of total calories in the LCM, and 10% in the other two diets. Polyunsaturated fatty acids provided 15% of calories in the LCM, and 12% in the other two diets. The ADA diet provided 15 grams of fiber, the TM had 30 g, and the LCM had 45 g.
Adherence to the assigned diet was assessed with a “food frequency questionnaire” administered at six months.
What Did the Researchers Find?
Average reported energy intake was similar in all three groups: 2,222 calories per day.
Monounsaturated fat intake differences were statistically significant: 14.6, 12.8, and 12.6% for the LCM, TM, and ADA diets, respectively. Polyunsaturated fat intake differences were statistically significant: 12.9, 11.5, and 11.2% for the LCM, TM, and ADA diets, respectively.
Percentage of energy from carbs was highest for the ADA diet (45.4%), intermediate for the TM diet (45.2%), and lowest for the LCM diet (41.9%).
At the end of 12 months, all three groups lost about the same amount of weight (8-9 kg or 18-20 lb), body mass index, and waist circumference.
Hemoglobin A1c fell in all three groups, but was significantly greater for the LCM group than for the ADA diet (6.3% absolute value vs 6.7%).
Triglycerides fell in all three groups, but was significantly greater for the LCM diet compared to the ADA diet.
The LCM group achieved a significant increase (12%) in HDL cholesterol compared to the ADA diet, but not different from the TM group.
LDL cholesterol fell in all three groups, and the LCM group’s drop (25%) was clearly superior to that of the ADA diet (14%) but about the same as the TM diet (21%).
Conclusions of the Investigators
We found that an intensive community-based dietary intervention reduced cardiovascular risk factors in overweight patients with [type 2 diabetes] for all three diets. The LCM group had improved cardiovascular risk factors compared to either the ADA or the TM groups.
Only the LCM improved HDL levels and was superior to both the ADA and TM in improving glycaemic control.
It would appear that the low carbohydrate Mediterranean diet should be recommended for overweight diabetic patients.
There’s no way the average diabetic could replicate this low-carb Mediterranean diet without working closely with a dietitian or nutritionist.
Any superiority of this low-carb Mediterranean diet may have as much to do with the increased monounsaturated fat intake as with the reduced carb consumption. Monounsaturated fatty acid consumption is thought to improve insulin sensitivity.
NutritionData’s Nutrient Search Tool can give you a list of foods high in monounsaturated fat.
The Mediterranean diet and low-carb diets independently have been shown to lower after-meal glucose levels, which probably lowers LDL cholesterol and triglycerides.
I’m disappointed the dietitians were not able to achieve a lower level of carbohydrate consumption in the low-carb Mediterranean diet group. I suspect if they had, improvements in glucose control and lipids would have been even better. But proof awaits another day.
We saw last year an article in the Annals of Internal Medicine that showed a dramatic reduction in the need for glucose-lowering drugs in type 2 diabetics following a different low-carb Mediterranean diet over four years, compared to a low-fat American Heart Association diet. These two studies convince me a low-carb Mediterranean diet has real life-preserving and life-enhancing potential.
Diabetics looking for a low-carb Mediterranean diet today have several options:
If you’re aware of any other low-carb, explicitly Mediterranean-style diets, please share in the Comments section.
Steve Parker, M.D.
Elhayany, A., Lustman, A., Abel, R., Attal-Singer, J., and Vinker, S. A low carbohydrate Mediterranean diet improves cardiovascular risk factors and diabetes control among overweight patients with type 2 dabetes mellitus: a 1-year prospective randomized intervention study. Diabetes, Obesity and Metabolism, 12 (2010): 204-209.
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.