Postprandial Effects of the Mediterranean Diet on Oxidant and Antioxidant Status in Elderly Men and Women

To the Editor: Aging is a natural and multifactorial process that occurs within an organism at genetic, molecular, cellular, organ, and system levels. Current knowledge points toward reactive oxygen species and oxidative stress as the primary determinants of aging. Although aging is inevitable, linked to the passage of time, nutritional intervention may influence the intrinsic rate of aging as well as the incidence of age-associated diseases. Prospective studies suggest that the adherence to a Mediterranean diet (with antioxidant components) is associated with lower mortality and prevents the onset and progression of coronary heart disease1 and other aging-related diseases.2, 3 The leading hypothesis on the mechanism of this association is a decrease of oxidative stress because of the antioxidant capacity of this diet.4 Classical studies aimed to analyze the influence of diet on oxidative stress in the fasting state, but the postprandial state represents the usual metabolic situation under which human beings behave throughout the day. It was recently demonstrated that a diet high in monounsaturated fatty acids (MUFAs) limits postprandial oxidative stress more than a diets low in fat and high in complex carbohydrates and saturated fatty acids (SFAs) in people with metabolic syndrome.5 Nevertheless, there is still a lack of data in this field, and the influence of dietary interventions on postprandial oxidative status remains an active field of research, especially relating to age and age-associated diseases. The purpose of this study was to determine whether diets with different fat quantity and quality affect oxidative stress during the postprandial state in older adults. Twenty participants (aged ≥65; 10 men, 10 women) were randomly assigned to receive, in a crossover design, three isocaloric diets for 4-week periods each: a Mediterranean diet (38% of energy as fat (24% MUFA (provided by virgin olive oil), 10% SFA, 4% polyunsaturated fatty acids (PUFAs)), a Western diet rich in SFAs (SFA diet; 38% of energy as fat (12% MUFA, 22% SFA, 4% PUFA)), or a low-fat, high-carbohydrate diet enriched in omega-3 PUFAs of vegetal origin (CHO-Ω3 diet) (28% of energy as fat (10% SFA, 12% MUFA, and 8% PUFA with 2%α-linolenic acid)). The Human Investigation Review Committee of the Reina Sofia University Hospital approved the study protocol, which was conducted as previously described according to institutional and Good Clinical Practice guidelines.6 Hydrogen peroxide (H2O2), lipid peroxide (LPOs), oxidized low-density lipoprotein cholesterol (oxLDL), protein carbonyl (PC), total nitrite, nitrotyrosine plasma levels, catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) activities and ischemic reactive hyperemia (IRH) were determined. All data were analyzed using SPSS 17.0 for Windows (SPSS, Inc., Chicago, IL). Analysis of variance (ANOVA) for repeated measures was performed, followed by Bonferroni correction for multiple comparisons. Differences were considered to be significant at P<.05. All data presented in text and tables are expressed as means±standard errors. Two hours after the intake of the Mediterranean diet, a greater postprandial increase in IRH was observed than with the other diets (P=.38) and a greater decrease in IRH after the CHO-Ω3 diet than the SFA diet (P=.043). A greater postprandial increase in IRH was observed 4 hours after the Mediterranean and CHO-Ω3 diets than the SFA diet (P=.045) (Figure 1A). Two hours after consumption of the Mediterranean diet, a greater postprandial decrease in plasma H2O2 levels was observed than with the other diets (P=.028). Four hours after consumption of the CHO-Ω3 diet, a greater increase in plasma H2O2 levels was observed than with the other diets (Figure 1B). The Mediterranean diet also led to lower postprandial SOD (P=.041) and GPx (P<.001) activities that the other diets (Figure 1C and D). Differences in (A) ischemic reactive hyperemia change, (B) hydrogen peroxide levels in plasma and antioxidant enzyme (C) superoxide dismutase activity and (D) glutathione peroxidase activity according to the type of fat consume during the postprandial phase. Differences in the parameter levels between Times 0 and 2 are shown as Δ2 h (value of Time 2 minus value of Time 0) and between Times 0 and 4 are shown as Δ4 h (value of Time 4 minus value of Time 0). Data were analyzed using analysis of variance for repeated measures. All values represent means (standard errors). Bars with different superscript letters depict statistically significantly differences (P<.05). p1: diet effect, p2: time effect, p3: diet × time interaction. The Mediterranean diet produced a greater postprandial decrease in plasma LPO and nitrotyrosine levels than the other diets and a greater postprandial decrease in plasma oxLDL levels than the CHO-Ω3 diet. The Mediterranean diet also led to lower CAT activity than the other diets. The SFA diet induced a greater postprandial decrease in plasma total nitrite levels than the other two diets (data not shown). These results support the hypothesis that the Mediterranean diet has a protective effect against free radical overgeneration through the lowering of postprandial oxidative stress in elderly men and women. These findings suggest that the study of the postprandial state may provide a starting point for prevention of the oxidative stress generated during the aging process by demonstrating the benefits of consumption of a Mediterranean diet. A specific dietary intervention might be a new, interesting, and promising challenge in the treatment (and mainly prevention) of processes that lead to a rise in oxidative stress, such as cardiovascular and neurodegenerative diseases and aging. Conflict of Interest: The authors have no conflicts of interest to disclose. Funding: Supported in part by research grants from the Ministerio de Ciencia e Innovación (AGL 2004-07907, AGL2006-01979, AGL2009-12270 to JL-M), (CB06/03/0047-CIBER Fisiopatologia de la Obesidad y Nutrition is an initiative of ISCIII to FP-J), Consejería de Innovación, Ciencia y Empresa, Junta de Andalucía (P06-CTS-01425 to JL-M); Consejería de Salud, Junta de Andalucía (06/128, 07/43, PI0193/2009 to JL-M, 06/129 to FP-J. Author Contributions: JLM designed the research and conducted research. JDL, PPM, and JLM provided materials and participants. JDL, NDC, AGR, FF, FR, CCT, and EMYS collected and assembled data. EMYS, IT, AGR, and ITC analyzed data. EMYS wrote the letter. JDL and FJT provided significant advice and support in reviewing the drafting of the paper. JLM and FPJ had primary responsibility for final content. All authors read an approved the final manuscript. Sponsor's Role: None.