***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Background : There is a need for objective and universally applicable biomarkers for the intake of foods believed to affect human health . Objective : The purpose of this feeding study was to test whether plasma concentrations of carotenoids could be used to distinguish recommended consumption of mixed fruits and vegetables ( five a day ) from the current national intake of fruits and vegetables ( two a day ) . Design : A strict crossover design was chosen to correct for observed interindividual variations in carotenoid response . A total of 40 healthy subjects were included in the study . After 1 week run-in period with no fruits and vegetables in the diet , one group was given two portions ( 300 g ) of fruits and vegetables daily , while another group was given five portions ( 750 g ) for 14 days . Following a 2 week wash-out period and 1 week run-in , the regimens were switched between the groups . Fruits and vegetables were combined to match a typical Norwegian diet . Results : Enhanced intake from two to five portions of mixed fruits and vegetables  increased plasma concentrations of α-carotene ( P=0.033 ) and lutein ( P=0.051 ) in a crossover analysis . Analysis of data in the parallel part of the study revealed differences between the high and low intake for plasma concentrations of α-carotene ( P=0.013 ) and β-carotene ( P=0.016 ) . A trend was also evident for plasma concentrations of lycopene ( P=0.057 ) and lutein ( P=0.076 ) in the parallel analysis . No effect of high vs low intake of fruits and vegetables was observed for plasma concentrations of β-cryptoxanthin , zeaxanthin , cholesterol and triacylglycerols . Conclusion : The study indicates that plasma concentration of α-carotene , β-carotene and lutein may be used to assess changes of fruit and vegetable intake corresponding to an increase from the present national intake in Norway to the recommended amount of five portions of fruits and vegetables daily . Sponsorship : Norwegian Research Council , National Nutrition Council , Throne Holst Foundation for Nutrition Research and Freia Chokoladefabriks Medisinske Fond In several epidemiological studies , high intakes of fruits and vegetables have been associated with a lower incidence of cancer . Theoretically , intake of antioxidants by consumption of fruits and vegetables should protect against reactive oxygen species and decrease the formation of oxidative DNA damage . We set up a parallel 24-day dietary placebo-controlled intervention study in which 43 subjects were r and omized into three groups receiving an antioxidant-free basal diet and 600 g of fruits and vegetables , or a supplement containing the corresponding amounts of vitamins and minerals , or placebo .  Blood and urine sample s were collected before , once a week , and 4 weeks after the intervention period . The level of str and breaks , endonuclease III sites , formamidopyrimidine sites , and sensitivity to hydrogen peroxide was assessed in mononuclear blood cells by the comet assay . Excretion of 7-hydro-8-oxo-2'-deoxyguanine was measured in urine . The expressions of oxoguanine glycosylase 1 and excision repair cross complementing 1 DNA repair genes , determined by real-time reverse transcription-PCR of mRNAs , were investigated in leukocytes . Consumption of fruits and vegetables or vitamins and minerals had no effect on oxidative DNA damage measured in mononuclear cell DNA or urine . Hydrogen peroxide sensitivity , detected by the comet assay , did not differ between the groups . Expression of excision repair cross complementing 1 and oxoguanine glycosylase 1 in leukocytes was not related to the diet consumed . Our results show that after 24 days of complete depletion of fruits and vegetables , or daily ingestion of 600 g of fruit and vegetables , or the corresponding amount of vitamins and minerals , the level of oxidative DNA damage was unchanged . This suggests that the inherent antioxidant defense mechanisms are sufficient to protect circulating mononuclear blood cells from reactive oxygen species Background — Observational evidence has consistently linked increased fruit and vegetable consumption with reduced cardiovascular morbidity ; however , there is little direct trial evidence to support the concept that fruit and vegetable consumption improves vascular function . This study assessed the dose-dependent effects of a fruit and vegetable intervention on arterial health in subjects with hypertension . Methods and Results — After a 4-week run-in period during which fruit and vegetable intake was limited to 1 portion per day , participants were r and omized to consume either 1 , 3 , or 6 portions daily for the next 8 weeks . Endothelium-dependent and -independent arterial vasodilator responses were assessed by venous occlusion plethysmography in the brachial circulation before and after intervention . Compliance was monitored with serial contemporaneous 4-day food records and by measuring concentrations of circulating dietary biomarkers . A total of 117 volunteers completed the 12-week study . Participants in the 1- , 3- , and 6-portions/d groups reported consuming on average 1.1 , 3.2 , and 5.6 portions of fruit and vegetables , respectively , and serum concentrations of lutein and & bgr;-cryptoxanthin increased across the groups in a dose-dependent manner . For each 1-portion increase in reported fruit and vegetable consumption , there was a 6.2 % improvement in forearm blood flow responses to intra-arterial administration of the endothelium-dependent vasodilator acetylcholine ( P=0.03 ) . There was no association between increased fruit and vegetable consumption and vasodilator responses to sodium nitroprusside , an endothelium-independent vasodilator . Conclusions — The present study illustrates that among hypertensive volunteers , increased fruit and vegetable consumption produces significant improvements in an established marker of endothelial function and cardiovascular prognosis Paraoxonase-1 ( PON1 ) , a HDL-associated enzyme , may protect against the development of atherosclerosis . Serum PON1 activity and PON1-mediated capacity of HDL to prevent lipoprotein oxidation are modulated by two common polymorphisms at positions 192 ( Gln-->Arg ) and 55 ( Leu-->Met ) of the PON1 gene . We studied the effect of dietary modifications on PON1 activity and the role of PON1 gene polymorphisms in the response . A controlled , crossover dietary intervention of two 5-wk periods was conducted in 37 healthy , nonsmoking women . The two study diets were either low or high in vegetables , and thus in natural antioxidants , with some differences in fatty acid contents . The mean plasma total ( -8 % , P < 0.001 ) , LDL ( -7 % , P < 0.01 ) and HDL ( -7 % , P < 0.001 % ) cholesterol , and apolipoprotein A-I ( -8 % , P < 0.001 ) concentrations were lower after the high vegetable diet period than after the low vegetable diet period . Also , the serum PON1 activity was lower ( P < 0.05 ) after the high vegetable compared with the low vegetable diet period . The reduction of PON1 activity correlated with the reduction in HDL cholesterol ( r = 0.35 , P < 0.05 ) . High baseline PON1 activity was related to the presence of the PON1(192Arg ) allele ( P < 0.001 ) and PON1(55Leu/Leu ) genotype ( P < 0.001 ) . The reduction of PON1 activity due to the high vegetable diet was greatest among the women with the PON1(192Arg ) allele ( P < 0.05 ) and PON1(55Leu/Leu ) genotype ( P < 0.05 ) . In conclusion , a diet high in vegetables , berries and fruit reduces PON1 activity , and the response is modulated by the genetic variance of PON1 Observational epidemiologic studies have shown that a high consumption of fruits and vegetables is associated with a decreased risk of chronic diseases . Little is known about the bioavailability of constituents from vegetables and fruits and the effect of these constituents on markers for disease risk . Currently , the recommendation is to increase intake of a mix of fruits and vegetables ( " five a day " ) . We investigated the effect of this recommendation on plasma carotenoids , vitamins and homocysteine concentrations in a 4-wk dietary controlled , parallel intervention study . Male and female volunteers ( n = 47 ) were allocated r and omly to either a daily 500-g fruit and vegetable ( " high " ) diet or a 100-g fruit and vegetable ( " low " ) diet . Analyzed total carotenoid , vitamin C and folate concentrations of the daily high diet were 13.3 mg , 173 mg and 228.1 microg , respectively . The daily low diet contained 2.9 mg carotenoids , 65 mg vitamin C and 131.1 microg folate . Differences in final plasma levels between the high and low group were as follows : lutein , 46 % [ 95 % confidence interval ( CI ) 28 - 64 ] ; beta-cryptoxanthin , 128 % ( 98 - 159 ) ; lycopene , 22 % ( 8 - 37 ) ; alpha-carotene , 121 % ( 94 - 149 ) ; beta-carotene , 45 % ( 28 - 62 ) ; and vitamin C , 64 % ( 51 - 77 ) ( P < 0.05 ) . The high group had an 11 % ( -18 to -4 ) lower final plasma homocysteine and a 15 % ( 0.8 - 30 ) higher plasma folate concentration compared with the low group ( P < 0.05 ) . This is the first trial to show that a mix of fruits and vegetables , with a moderate folate content , decreases plasma homocysteine concentrations in humans Normal healthy volunteers were studied after they ingested various beta-carotene doses .  Daily administration of 15 or 45 mg beta-carotene result ed in significant increase in plasma beta-carotene levels . The extent of increase and the pattern of plasma beta-carotene levels showed substantial interindividual variation . Absorption of beta-carotene was affected by dietary fat concentration . Individuals placed on a high-fat diet showed significant increases in plasma beta-carotene as compared with those placed on a low-fat diet . Pharmacological doses of beta-carotene ( 45 and 90 mg ) were used in intermittent schedules ( 5 - 6 d intervals ) without altering the steady state of beta-carotene plasma levels . Yellowing of the skin occasionally occurred during daily dosing with 45 mg beta-carotene without evidence of toxicity . The observed individual variation in bioavailability of beta-carotene raises questions regarding clinical use of this micronutrient . It appears that determination of target plasma beta-carotene concentrations is essential for effective use of this compound in prevention or treatment BACKGROUND Fruit and vegetables contain both nutritive and nonnutritive factors that might contribute to redox ( antioxidant and prooxidant ) actions . OBJECTIVE We investigated the relative influence of nutritive and nonnutritive factors in fruit and vegetables on oxidative damage and enzymatic defense . DESIGN A 25-d intervention study with complete control of dietary intake was performed in 43 healthy male and female nonsmokers who were r and omly assigned to 1 of 3 groups . In addition to a basic diet devoid of fruit and vegetables , the fruit and vegetables ( Fruveg ) group received 600 g fruit and vegetables/d ; the placebo group received a placebo pill , and the supplement group received a vitamin pill design ed to contain vitamins and minerals corresponding to those in 600 g fruit and vegetables . Biomarkers of oxidative damage to protein and lipids and of antioxidant nutrients and defense enzymes were determined before and during intervention . RESULTS Plasma lipid oxidation lag times increased during intervention in the Fruveg and supplement groups , and the increase was significantly higher in the former . Plasma protein carbonyl formation at lysine residues also increased in both of these groups . Glutathione peroxidase activity increased in the Fruveg group only . Other markers of oxidative damage , oxidative capacity , or antioxidant defense were largely unaffected by the intervention . CONCLUSIONS Fruit and vegetables increase erythrocyte glutathione peroxidase activity and resistance of plasma lipoproteins to oxidation more efficiently than do the vitamins and minerals that fruit and vegetables are known to contain . Plasma protein carbonyl formation at lysine residues increases because of the vitamins and minerals in fruit and vegetables BACKGROUND Health benefits associated with diets rich in vegetables and fruit ( VF ) are often attributed to the antioxidant activity of their constituent phytochemicals . However , in vivo evidence that VF actually reduce markers of oxidative stress is limited . OBJECTIVE An 8-wk dietary intervention was conducted to test the hypothesis that increased VF consumption decreases oxidative stress . Urinary excretion of 8-isoprostane F2alpha ( 8-iso-PGF2alpha ) was used as an index of whole-body lipid peroxidation . DESIGN The diets evaluated had comparable amounts of all macronutrients but varied in their content of VF . After a 2-wk low-VF ( 3.0 serv 
    Output:
    
Therefore , until further evidence identifies a particular biomarker to be superior , group-level compliance to fruit and vegetable interventions can be indicated equally well by vitamin C or a range of carotenoids .
High heterogeneity and a lack of dose-response suggest that individual-level biomarker responses to fruit and vegetables are highly variable