Relative to current public health recommendations, the majority of Americans consume inadequate amounts of vegetables (minimum of 4 servings) in their diet [7, 31, 32]. Consistent with this report, our subjects' average daily intake of vegetables did not meet recommendations (for either DASH or 2005 Dietary Guidelines) at any time during this study despite DASH diet education. Importantly, the dietary intake of vegetables apart from the juice was similar among the three groups. However, the incorporation of the vegetable juice significantly increased the total daily intake of vegetables to an average of 4.3 and 6.5 servings of vegetables in the 8 and 16 fluid ounce groups, respectively. The DASH diet instruction emphasized inclusion of vegetables, and did not instruct subjects to consume vegetable juice in place of mealtime vegetable servings. These results support the concept that the daily consumption of a vegetable juice is a feasible way for an individual to help meet their dietary recommendation for vegetable intake. During the study we obtained information from participants related to their perceptions on including vegetable juice into their diets. The majority of those drinking the juice self-reported that they enjoyed the taste, felt they were doing something good by drinking it, were satisfied they had a diet that provided the right vitamins and minerals, and were satisfied with the ease of getting vegetables in their diet.
The data from the current study were obtained from a population of healthy, well-educated adults in California. Similar to what is found in various sectors of the U.S. population [33–35], the majority of people enrolled into this study did not consume the recommended daily servings of vegetables. Indeed, reported intakes at the 12-week point in the control group were lower than those reported in these previous national surveys. In a study of African American men, Wolf et al. found that they were not aware of, nor meeting, dietary recommendations due to a lack of knowledge and perceived barriers . Similarly, McGee et al.  found that individuals in the lower Mississippi delta felt that they lacked knowledge and skills to prepare meals with healthful food choices. However, our subject population was provided with education on developing meals plans and tips for making healthy eating easier. This dietary education, coupled with the high education level of the individuals enrolled in the current study, should have resulted in their meeting DASH recommendations. Based on our data, we suggest that behavior change for an extended time period, even for highly educated individuals, is difficult. Studies suggest that beneficial changes in behavior for even motivated individuals require intensive, extended behavioral counseling, relapse prevention training, incentives, self efficacy and social support [36, 37]. Results from a meta analysis conducted to evaluate the overall effectiveness of behavioral interventions to promote dietary change in fruit and vegetable intake were not conclusive .
Our results confirm that dietary training alone is not enough to elicit change; this finding underscores the need for new modalities to encourage beneficial dietary modification. Guenther et al.  and Casagrande et al.  emphasize the need for broadening interventions beyond increasing individual awareness of the value of vegetables and education toward altering eating behavior. While several studies have shown successful improvements in vegetable consumption through various dietary behavior change programs [37, 39], others have not reported these benefits [40, 41]. More effective intervention possibilities may include increasing access to vegetables . The need for lower calorie, nutrient dense, convenient , inexpensive  methods to increase vegetable consumption are important for future public health campaigns. Our data suggests that vegetable juice may serve as a portable and convenient method to aid individuals in meeting dietary vegetable recommendations.
Although vegetable consumption was enhanced in those consuming juice, no significant changes were observed over the 12-week test period for any of the measured vascular health parameters listed in Table 1. The vegetable juice in the study provided a one to one ratio of sodium to potassium and thus it is important to note that blood pressure measurements did not change in any of the groups over the 12 week period. The group blood pressure results obtained in the current study are consistent with previous reports that show total dietary mineral intake is a consideration relative to blood pressure [44–46]. To further probe this issue, we analyzed the data from the subset of individuals whose initial blood pressures were over 120/80 mm Hg (pre-hypertensive but less than hypertensive range). In the vegetable juice group, this subgroup showed a significant decrease in blood pressure over the 12 week intervention period (the number of pre-hypertensive subjects in the no vegetable juice group was too low (N = 7) to allow for meaningful statistical comparisons for this specific subgroup). While preliminary in nature, our finding that the consumption of the vegetable juice was associated with a reduction in blood pressure in pre-hypertensive subjects is consistent with the putative positive vascular health effects of diets rich in vegetables, which are good sources of dietary potassium. This differential blood pressure response between normotensive and pre-hypertensive individuals has been seen in other intervention studies [47, 48].
Svendsen et al.  reported improvements in blood pressure following an intervention promoting very high levels of vegetable and fruit intake. Those improvements were seen in a more compromised population exhibiting a higher baseline body mass index and included some individuals with cardiovascular risk factors such as hypertension and diabetes mellitus, smokers, and those with a prior cardiovascular event .
In several papers, the concept has been raised that vegetables or their respective extracts can result in an improvement in the oxidant defense system, with a consequential reduction in tissue oxidative damage [50–52]. While the measurements are controversial , numerous investigators have used plasma TBARS as a general indicator for oxidative damage [54, 55]. For the above reason, this measurement was included in the current study. However, consistent with our expectation, the consumption of the vegetable juice product did not result in significant changes in this parameter. We think it is important to note, however, that the above finding does not rule out the possibility that the vegetable juice intervention could have improved select parameters of the oxidative defense system. For example, it is possible that phytochemicals present in vegetable juice could reduce the extent of the oxidation of select targets, such as low density lipoproteins (LDL)  and deoxyribonucleic acid (DNA) [56, 57]. However, it is likely that these phytochemicals are acting, in part, through mechanisms that are independent of the direct antioxidant properties of the phytochemicals. For example, it has been suggested that certain phytochemicals can inhibit enzymes that produce reactive oxygen and nitrogen species [58, 59]. Additional research similar to that conducted by Valtueña et al. , correlating the intake of adequate vegetables, containing dietary antioxidants, to functional antioxidant and oxidative stress parameters is needed.
An important consideration for our study is that the subject selection does not reflect the general population because it was a fairly homogenous, highly educated, Caucasian, healthy population with very high adherence and willingness to volunteer for a study that included drinking vegetable juice. The current findings need to be replicated in a larger, more diverse population group, and ideally it needs to be conducted over a longer period of time.