Short and middle term effects of hypocaloric low carbohydrate diet vs hypocaloric Mediterranean diet on endothelial function in obese subjects

Adequate nutritional treatment is required to address the problem of increasing prevalence of obesity in Western countries. The Mediterranean diet style is now acknowledged to have large scientific evidences in terms of cardiovascular prevention. However, many popular diets are diffusing also as self-prescribed treatments. Among those, the efficacy of low-carbohydrate diets (also known as Atkins’ diet in its most popular variety) has been addressed by some investigations. It is generally concluded that the low-carbohydrate diet is able to induce a greater weight loss, at least in the middle term, and a better serum lipid profile than the conventional diet. In this longitudinal, randomised, open study we compared the effects on endothelial function of a hypocaloric low-carbohydrate diet (according to the Atkins’ diet; AD) versus a similarly hypocaloric Mediterranean diet (MD). Overweight-obese (range of BMI: 27-34.9 Kg/m2; range of age: 30-50 years) otherwise healthy, normal glucose tolerant women were enrolled and randomly assigned to one of the two dietary treatments until reaching the final number of 10 women for each group of treatment. So, twenty-five women were enrolled and five of them (3 in the MD group and 2 in the AD group) were subsequently excluded from the study due to intercurrent diseases (1 subject) or declaration of inadequate compliance (2 subjects) or f voluntary drop out (2 subjects). Measurements were performed before (T0), 5-7 days (T5) and 2 months (T60) after starting the diet treatment. Endothelial function was investigated at each time of the study by measuring the brachial artery flow-mediated dilation (FMD). Serum concentrations of insulin, adiponectin, interleukin 6 (IL-6), tumor necrosis factor α (TNF-α) and 8-iso-prostaglandin (8-iso-PG) F2α were also assessed at each time of the study. Urinary ketone bodies were observed at T5 only in AD group. Briefly, body weight was not significantly decreased at T5 in both groups; as expected, a higher body weight reduction was observed at T60 in AD group (change in body weight T60 – T0, mean ± sem, MD -4.9 ± 0.6 Kg vs AD -7.6 ± 0.8 Kg, p= 0.014). The FMD was significantly reduced at T5 in the AD group and increased at T60 until reaching the T0 values (T0: 12.2 ± 2.9; T5: 5.2 ± 0.8; T60: 11.0 ± 1.2 %; p< 0.05 T5 vs T0 and T60). On the contrary, the FMD increased significantly at T5 in the MD group and decreased until reaching values comparable to those of T0 at T60 (T0: 10.3 ± 2.3; T5: 14.5 ± 2.8; T60: 10.6 ± 1.9 %; p< 0.05 T5 vs T0 and T60). This trend of FMD change was observed in each subject. Insulin concentrations and HOMA-I decreased significantly at T5 and at T60 in both groups. Adiponectin and TNF-α concentrations remained unchanged in both groups throughout the study. Both IL-6 and 8-iso-PGF2α increased significantly at T5 in the AD group and decreased at T60 to values comparable to T0 (IL-6: T0 57.5 ± 9.0, T5 78.1 ± 10.9, T60 56.6 ± 6.8 pg/ml; T5 vs T0 p< 0,005, T5 vs T60 p< 0,02; 8-iso-PGF2α: T0 171.5 ± 30.6, T5 222.6 ± 35.1, T60 178.7 ± 25.8 pg/ml; T5 vs T0 p< 0,005, T5 vs T60 p< 0,02); no significant change was observed in the MD group. This study suggests that the hypocaloric low-carbohydrate diet induces a significant endothelial dysfunction in the short term (5-7 days) that is reverted in the middle term (2 months) as suggested by both the brachial artery FMD and serum markers of inflammation (IL-6) and oxidative stress (8-iso-PGF2α). On the contrary, the hypocaloric Mediterranean diet is able to improve the endothelial function at least in the short term. These effects are independent of body weight loss. Therefore, this study points out also the potential disadvantages of low-carbohydrate diets when prescribed (or self-prescribed) especially in subjects at high cardiovascular risk.