The aim of this study was to compare the variations in the concentrations of tocopherols and retinol in obese adults in the postprandial state after the intake of a Mediterranean or Western-style breakfast. The study was designed as a randomized, controlled intervention trial in the postprandial state, for which 24 male adults (12 obese and 12 of normalweight) were recruited. After a fat challenge, blood samples were collected at different times postprandially and α-tocopherol, γ-tocopherol and retinol concentrations were determined in serum by HPLC. The Mediterranean-style meal produced a greater increase in serum α-tocopherol levels in both obese and normal-weight subjects, compared to the Western-style meal, indicating that the composition of the food affects the concentration of tocopherols in the postprandial state. However, the serum concentrations of γ-tocopherol and retinol remained unmodified. In conclusion, the presence of α-tocopherol in the meal could contribute to the protection of the Mediterranean-style meal against atherosclerosis in the postprandial state.
Obesity is considered one of the main public health concerns in Western countries as it gives rise to other conditions, such as diabetes or cardiovascular disease. Obesity has also been associated with systemic inflammation and increased oxidative stress, which lead to decreased α-tocopherol bioavailability, increasing the requirements for this vitamin in obese individuals (Traber
There is also considerable evidence that vitamin A homeostasis is involved in regulating body fat and blood glucose levels. It appears that altered levels of circulating retinol have a relevant role in the modulation of endocrine hormones and gene transcription associated to lipid and glucose metabolism (Mody
This study was designed to determine whether plasma concentrations of retinol and tocopherols (α-tocopherol and γ-tocopherol) are altered in the postprandial state in obese individuals and whether a Mediterranean-type breakfast can contribute to restoring such concentrations.
Twenty-four adult male subjects (22-56 years-old), without a history of digestive or metabolic disorders, were recruited for the study by placing announcements in online social networks and among acquaintances of the research team in the city of Seville (Spain). Sample size was calculated by power analysis, considering a type 1 error (α) = 0.05 and a power (1-β) = 0.9 and the resulting minimum number was 10 individuals per group. Subjects were classified as normal-weight or obese using BMI cut-off points according to age and sex. Twelve adults were obese (BMI > 30 Kg/m2) and 12 normal-weight (BMI = 20-25 Kg/m2). A written consent form, which was approved by the Institutional Committee on Human Research of HHUU Virgen del Rocío (Seville, Spain), was obtained from the participants. The consent form and the protocol were in accordance with the institutional and national ethical standards for human experimentation and the Helsinki declaration of 1975 (revised in 2000). The study was registered in clinicaltrials.gov (NCT01518803).
The study was designed as crossed-over to test the effect of two variables, obesity and meal composition, on α-tocopherol, γ-tocopherol and retinol serum postprandial concentrations. Participants were asked to have a low-fat dinner the evening prior to the postprandial assay and to abstain from alcohol drinking and smoking for 24 h. After an overnight fast (12 h), a cubital vein was catheterized and a baseline blood sample was taken immediately before consumption of the first test meal, which was consumed in less than 15 minutes. Blood samples were collected at baseline (0h) and at 2h and 4h after the intake of the meals. During the course of the experiment, the subjects were allowed to drink water and to undertake only light activities. The subjects consumed a Mediterranean breakfast consisting of 3 slices of brown bread (71 g), 200 mL of skimmed milk, 250 mL of orange juice and 20 g of mashed tomato and 57 g of olive oil. The composition of the meal was selected to reflect the habitual breakfast consumption in southern Spain. Olive oil was kindly supplied by Oleicola El Tejar, S.A. (El Tejar, Cordoba, Spain). The Western breakfast consisted of 55 g of butter, three slices of brown bread and a glass of skimmmed milk (200 ml) with cocoa powder (20 g). The main composition of the meals is indicated in
Nutrient compositions of the experimental meals.
Western breakfast | Mediterranean breakfast | |
---|---|---|
Energy (kJ) | 1963 | 2022 |
Protein (g) | 14 | 15 |
Carbohydrates (g) | 53 | 62 |
Sucrose (g) | 26 | 26 |
Fats (g) | 53 | 57 |
SFA (g) | 32 | 8 |
MUFA (g) | 15 | 44 |
PUFA (g) | 2 | 5 |
Fiber (g) | 6.4 | 7.0 |
Cholesterol (mg) | 104 | 0 |
Tocopherols (mg) | 1.70 | 45.85 |
SFA, saturated fatty acids; MUFA, monounsaturated fatty acids; PUFA, polyunsaturated fatty acids.
α-Tocopherol and retinol equivalent compositions of the experimental meals.
Western breakfast | Mediterranean breakfast | Western breakfast | Mediterranean breakfast | |
---|---|---|---|---|
α-Tocopherol (mg) | Retinol (μg) | |||
Brown bread | 0.47 | 0.47 | ND | ND |
Skimmed milk | 0.02 | 0.02 | ND | ND |
Orange juice | - | 0.43 | - | 182.5 |
Tomato | - | 0.18 | - | 16.4 |
Olive oil | - | 44.75 | - | 19.4 |
Cocoa powder | 0.11 | - | 0.2 | - |
Butter | 1.10 | - | 430.7 | - |
Total | 1.70 | 45.85 | 430.9 | 218.3 |
ND: not detected. - : ingredient not present in the meal.
Serum glucose, cholesterol and triglycerides were determined by enzymatic colorimetric methods on a Roche/Hitachi System analyzer (Roche Diagnostic, Mannheim, Germany). Serum HDL-cholesterol was measured by a direct enzymatic method (HDL-C-plus 2nd generation, Roche Diagnostics, Mannheim, Germany) on a Roche/Hitachi System analyzer (Roche Diagnostic) and LDL cholesterol was estimated by the Friedewald equation (Friedewald
Liposoluble vitamins were extracted from 500 μL of serum as follows: 500 μL of ethanol and 1mL of hexane were added sequentially. The mixture was centrifuged (3500 rpm, 15 ºC for 10 min) and the supernatant was collected. Hexane was evaporated under a stream of nitrogen and the vitamins were re-dissolved in choloroform/methanol (2:1, v/v) for injection into the the HPLC system. This system consisted of a reversed-phase column (Novapack) and an elution system composed of methanol/acetonitrile (chloroform (9:78:13, v/v/v) which run isocratically. A photodiode array detector (PAD 996, Waters) was used for α-tocopherol, γ-tocopherol and retinol detection at 290 nm (α-tocopherol and γ-tocopherol) and 325 nm (retinol), respectively. These compounds were identified using commercial standards and quantified by means of external standard.
The results were expressed as mean ± SEM. Data analyses were performed with the GraphPad Prism® 5 statistical package (GraphPad Software Inc., San Diego, CA). The baseline statistical significance of anthropometric measurements, serum biochemical determinations and serum α-tocopherol, γ-tocopherol and retinol concentrations between obese subjects and their normalweight counterparts were assessed with the Student’s t test. The same comparisons were made for the incremental AUC (iAUC) values which were calculated from the postprandial curves. A 2x2 ANCOVA test was applied on iAUC values using the meals (Mediterranean and Western) and body size as the independent variables. For those comparisons which resulted in significantly different, a Student’s t test was used to compare the iAUC values. Differences were considered statistically significant at p < 0.05.
Anthropometric characteristics and baseline serum concentrations of lipids, glucose, insulin and liposoluble vitamins.
Normal-weight | Obese | p | |
---|---|---|---|
Age (y) | 27.3 ± 2.9 | 35.8 ± 3.5 | 0.075 |
Weight (kg) | 74.9 ± 2.3 | 112.9 ± 3.9 | <0.001 |
Height (cm) | 179.6 ± 2.0 | 180.8 ± 1.5 | 0.778 |
BMI (kg/cm2) | 23.2 ± 0.3 | 34.7 ± 1.4 | <0.001 |
Systolic Pressure (mmHg) | 110.9 ± 3.7 | 130.8 ± 2.2 | <0.001 |
Diastolic Pressure (mmHg) | 68.9 ± 2.1 | 74.5 ± 2.9 | 0.120 |
Glucose (mg/dL) | 73.7 ± 1.4 | 83.6 ± 2.4 | 0.002 |
Insulin (mU/ml) | 4.9 ± 0.8 | 12.6 ± 1.2 | <0.001 |
Triglycerides (mg/dl) | 78.7 ± 7.1 | 129.7 ± 17.4 | 0.013 |
Cholesterol (mg/dl) | 172.5 ± 9.4 | 202.9 ± 10.0 | 0.030 |
LDL-c (mg/dl) | 94.7 ± 5.6 | 158.7 ± 4.8 | <0.001 |
HDL-c (mg/dl) | 57.5 ± 2.8 | 45.9 ± 2.5 | 0.005 |
α-Tocopherol (μg/ml) | 9.87 ± 0.73 | 10.48 ±1.69 | 0.703 |
γ-tocopherol (μg/ml) | 0.17 ± 0.03 | 0.14 ± 0.02 | 0.414 |
Retinol (μg/ml) | 0.45 ± 0.04 | 0.73 ± 0.10 | 0.016 |
Data are expressed as mean ± SEM; n = 12. BMI: body mass index. LDL-c, low-density-lipoprotein cholesterol; HDL-c, high-density-lipoprotein cholesterol. Statistical differences were assessed by the Student’s t test.
The postprandial concentrations of the liposoluble vitamins analyzed are depicted in
Serum postprandial α-tocopherol, γ-tocopherol and retinol concentrations in the normal weight (1a, 1c and 1e) and obese (1b, 1d and 1f) groups in the postprandial state. Values corresponding to the Mediterranean meal are represented by circle dots, whereas values corresponding to the Western meal are represented by square dots. Data are shown as mean ± SEM. *: p < 0.05, **: p < 0.01, ***: p < 0.001.
As shown in
Impact of body size, type of breakfast and their interaction on the postprandial incremental area under the curve (iAUC) values of the study endpoints.
Body size | Breakfast | Body size x breakfast | |||||||
---|---|---|---|---|---|---|---|---|---|
F | p | Partial ETA square | F | p | Partial ETA square | F | p | Partial ETA square | |
α-Tocopherol | 0.105 | 0.747 | 0.003 | 7.252 | 0.011 | 0.164 | 0.429 | 0.517 | 0.011 |
γ-Tocopherol | 0.001 | 0.980 | 0.000 | 0.401 | 0.531 | 0.011 | 0.000 | 0.988 | 0.000 |
Retinol | 0.059 | 0.809 | 0.001 | 0.173 | 0.680 | 0.004 | 1.396 | 0.244 | 0.034 |
2x2 ANCOVA was applied on iAUC calculated from the postprandial profiles for each dependent variable, using body size (normal weight or obese) and breakfast (Mediterranean or Western) as independent variables. Partial ETA square was used to measure the effect size of the variable.
Incremental area under the curve (iAUC) values for serum postprandial α-tocopherol, γ-tocopherol and retinol concentrations in the normal weight (2a, 2c and 2e) and obese (2b, 2d and 2f) groups. Data are shown as mean ± SEM. *: p < 0.05.
We report here that a Mediterranean-style meal can increase postprandial serum α-tocopherol levels in both obese and normal weight subjects compared to a Western-style meal. The content of α-tocopherol was higher in the Mediterranean breakfast, mainly due to its content in olive oil (
Traber
In our study, significant differences in plasma α-tocopherol concentrations between meals were found only at 4 hours postprandially. At this time point, the size of triglyceride-rich lipoproteins (TRL), which are in fact the transporters of tocopherols and retinol, is key in atherogenesis (Amigo-Benavent
Therefore, we believe that postprandial α-tocopherol may play a protective role in serum against atherosclerosis and that the Mediterranean breakfast favors it positively. In this regard, Carnevale
Nielsen
We also were unable to find differences in serum postprandial retinol concentrations between the groups when the results were expressed as iAUC. Guerci
The 2x2 ANCOVA test employed in the present study showed that the type of breakfast affected the levels of α-tocopherol in plasma but no influence of body size on the postprandial levels of tocopherols and retinol. Although, as stated above, Bates
In conclusion, a Mediterranean-style breakfast increases serum α-tocopherol, but not γ-tocopherol or retinol content in both lean and obese individuals in the postprandial state compared to a Western-style meal. Interestingly, the highest α-tocopherol concentration was found 4h after the meal intake, a time point at which CMR are most atherogenic. The well-known antioxidant properties of α-tocopherol together with its reported abilities to down-regulate scavenger receptors in macrophages, could contribute to the protection of the Mediterranean-style meal against atherosclerosis in the postprandial state.
This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness under Grant AGL2011-23810.