many us americans consume diets that are overly high in energy and in constituents associated with disease risk , particularly saturated fat ( sfa ) , cholesterol and sodium and low in protective components such as fiber or -carotene . poorly balanced diets contribute to overweight , cardiovascular disease , type 2 diabetes and other conditions . in clinical research studies , individuals who adopt diets emphasizing vegetables , fruits , whole grains and legumes report significant reductions in the intake of fat and cholesterol and increases in fiber , -carotene , magnesium , potassium and vitamin k intake . plant - based diets are associated with improvements in body weight , plasma lipid concentrations , glycemic control and blood pressure and may assist in the management of prostate cancer . we tested a program designed to translate a plant - based dietary intervention from the research environment to the workplace . an initial controlled study at two corporate sites of the government employees insurance company , a large us insurer , showed that providing instruction in the use of plant - based diets tended to cause weight loss , improvements in plasma lipid concentrations and , for those with diabetes , improved blood glucose control . a subsequent trial at 10 corporate government employees insurance company sites in diverse regions of the united states showed similar results . as plant - based diets may alter a wide range of macronutrient and micronutrient intakes affecting health in many ways , we sought to assess the nutrient changes associated with the intervention diet in the latter study . we hypothesized that a plant - based dietary intervention would reduce the intake of energy , sfa and cholesterol and increase the intake of fiber , -carotene , vitamin c and potassium . the study design and major physiological results have been described elsewhere . briefly , the overall study tested the hypothesis that a program including a low - fat vegan diet taught through group sessions at worksites in widely divergent areas of the united states would elicit improvements in body weight and other health indicators . the study was intended to translate the findings of intervention trials into a simple program that could be implemented for large groups of individuals at work . it was designed not to test individual program components ( for example , a diet or a group of classes ) but rather to assess the effect of the intervention program as a whole , similar to the design of the diabetes prevention program , which tested the combined effects of diet and exercise interventions in individuals at risk for diabetes . individuals aged 18 years or above with a body mass index of 25  kg / m or a previous diagnosis of type 2 diabetes were recruited through employee notices at 10 government employees insurance company corporate offices in the united states : tucson , arizona ; san diego , california ; lakeland , florida ; macon , georgia ; chevy chase , maryland ; buffalo , new york ; woodbury , new york ; dallas , texas ; fredericksburg , virginia ; and virginia beach , virginia . exclusion criteria were current alcohol or drug abuse , pregnancy , history of severe mental illness , unstable medical status , current adherence to a low - fat vegetarian diet , participation in the previous government employees insurance company study and inability to attend weekly meetings . those who appeared to satisfy the participation criteria were scheduled for individual interviews to review the study procedures and confirm eligibility . the study was approved by an external institutional review board ( independent review consulting , whose name was later changed to ethical and independent review services , corte madera , ca , usa . ) . each pair of sites represented a cluster , and , using a random - number table , the sites within each pair were randomly assigned to the intervention ( fives sites ) or control ( five sites ) groups . as the assignment was done by site rather than by individual , this method was used because of the likelihood that the intervention , which would be strongly apparent in the work environment , would tend to influence the behavior of individuals throughout the worksite , including those not assigned to the intervention group . at intervention sites , participants were asked to follow a low - fat vegan diet and attend weekly group meetings . individuals at control sites were given no dietary guidance and were not asked to make any dietary changes . they were given monetary compensation in the form of gift certificates to retail stores ( whole foods market or target ) , totaling $ 50 for completion of all baseline and week-18 assessments . the rationale for compensation of control - group participants was that , unlike the intervention group , they received no other benefit from the study and had no contact with the investigators , aside from the assessments . all participants in both groups were asked to avoid changing exercise patterns during the study period . participants at intervention sites were asked to avoid animal products ( that is , meat , poultry , fish , dairy products and eggs ) and to base their diets on whole grains , vegetables , legumes and fruits . they were also encouraged to minimize added oils and to favor foods with a low glycemic index , such as beans , fruit , pasta , rye and pumpernickel bread ( rather than typical wheat breads ) , and oatmeal or bran cereal ( rather than typical cold cereals ) . intervention - group participants were also asked to take a daily supplement of vitamin b12 , such as a multiple vitamin . at intervention sites with cafeterias , food service managers were asked to include low - fat plant - based menu options , such as oatmeal , minestrone or lentil soup , veggie burgers and portobello sandwiches , among the daily offerings . whether and how to implement such menu additions were left to their discretion , and their progress in doing so was not formally assessed . they were provided group support in the form of weekly lunch - hour classes at the worksite led by a registered dietitian , physician and/or a cooking instructor , following an established curriculum for the duration of the study . classes included sessions on replacements for animal products , healthful snacking , dining out , travel , shopping and cooking , as well as nutrition - related health topics such as weight loss , diabetes , heart disease and cancer . participants were offered additional support through an interactive online message board on which they could ask or respond to questions . all instructors received training in study procedures and best practices for facilitating group discussion and used identical instruction materials ( a standardized curriculum , handouts , videos , instructions for cooking , and so on ) . the following measures were assessed at baseline and week 18 : a diet recall was used to assess nutrient intake over two 24-h periods at baseline and two 24-h periods at 18 weeks , using an online ( automated self - administered 24-h recall , asa-24 ) program developed by the national cancer institute ( bethesda , md , usa ) . the format and design of the asa-24 are based on the interviewer - administered automated multiple pass method 24-h recall developed by the us department of agriculture . the online program has the advantages of ease of use and scoring and face validity ; however , although the automated multiple pass method is a validated instrument , validation trials of asa-24 remained in progress at the time of this study . subjects were advised of vegan items that asa-24 does include , such as vegan burger , seitan and tofu , and of common vegan items that are not on asa-24 , such as quinoa and tempeh . subjects were instructed not to skip any entries even if exact matches were not found in asa-24 . instead , they were coached on how to find a suitable alterative , such as substituting brown rice for quinoa or vegetarian sub for vegan sandwich . registered dietitians cross - checked data on asa-24 by taking participant nutrient data and entering them into the usda nutrient database to make sure nutrient intake numbers were relevant to asa-24 . numbers that appeared erroneous were excluded , such as an intake of 500 calories reported for an entire day . macronutrient intakes were reported as percentages of total energy intake , and fiber and micronutrients were reported as quantities per 1000  kcal . as animal products are the only significant source of dietary cholesterol , cholesterol intake reported at 18 weeks served as a rough gauge of adherence to the intervention diet . the numbers of group participants whose cholesterol intake was 50  mg / day ( the amount of cholesterol in 2 ounces of typical meats or cheeses ) and 75  mg / day ( the amount of cholesterol found in 3 ounces of typical meats or cheeses ) were calculated from 18-week diet recalls . the number of group participants whose fat intake was below 25 and 35% of the total calorie intake was also calculated . all participants were asked to continue their pre - existing medication regimens unless otherwise instructed by their personal physicians . student 's t - tests and -tests were used to assess whether any demographic or clinical measures between groups at baseline were unbalanced . nutrient data were examined for extreme values , and distributions of variables were examined for skewness using a normality plot and the shapiro  wilk test . statistical analyses of nutrient intake were performed on an intention - to - treat basis , including all participants who completed an initial diet recall , with the post - intervention values for dropouts set to the pre - intervention values . a second analysis was limited to participants who completed diet recalls at baseline and 18 weeks . the significance of within - group changes in dietary variables was determined using paired t - tests . a general linear model univariate analysis ( analysis of covariance ) was used to estimate the treatment effect and determine whether the changes in nutrient intake of the intervention and control groups during the 18-week trial were significantly different from each other . diet group was included as a fixed factor in these models , with the baseline value of each nutrient as a covariate . in addition , the geographic site was added to the model as a random effect to account for within - site correlation in outcomes . as the number of sites was small , the significance of and confidence intervals for treatment effect were computed using the kenward participants at intervention sites were asked to avoid animal products ( that is , meat , poultry , fish , dairy products and eggs ) and to base their diets on whole grains , vegetables , legumes and fruits . they were also encouraged to minimize added oils and to favor foods with a low glycemic index , such as beans , fruit , pasta , rye and pumpernickel bread ( rather than typical wheat breads ) , and oatmeal or bran cereal ( rather than typical cold cereals ) . intervention - group participants were also asked to take a daily supplement of vitamin b12 , such as a multiple vitamin . at intervention sites with cafeterias , food service managers were asked to include low - fat plant - based menu options , such as oatmeal , minestrone or lentil soup , veggie burgers and portobello sandwiches , among the daily offerings . whether and how to implement such menu additions were left to their discretion , and their progress in doing so was not formally assessed . they were provided group support in the form of weekly lunch - hour classes at the worksite led by a registered dietitian , physician and/or a cooking instructor , following an established curriculum for the duration of the study . classes included sessions on replacements for animal products , healthful snacking , dining out , travel , shopping and cooking , as well as nutrition - related health topics such as weight loss , diabetes , heart disease and cancer . participants were offered additional support through an interactive online message board on which they could ask or respond to questions . all instructors received training in study procedures and best practices for facilitating group discussion and used identical instruction materials ( a standardized curriculum , handouts , videos , instructions for cooking , and so on ) . the following measures were assessed at baseline and week 18 : a diet recall was used to assess nutrient intake over two 24-h periods at baseline and two 24-h periods at 18 weeks , using an online ( automated self - administered 24-h recall , asa-24 ) program developed by the national cancer institute ( bethesda , md , usa ) . the format and design of the asa-24 are based on the interviewer - administered automated multiple pass method 24-h recall developed by the us department of agriculture . the online program has the advantages of ease of use and scoring and face validity ; however , although the automated multiple pass method is a validated instrument , validation trials of asa-24 remained in progress at the time of this study . subjects were advised of vegan items that asa-24 does include , such as vegan burger , seitan and tofu , and of common vegan items that are not on asa-24 , such as quinoa and tempeh . subjects were instructed not to skip any entries even if exact matches were not found in asa-24 . instead , they were coached on how to find a suitable alterative , such as substituting brown rice for quinoa or vegetarian sub for vegan sandwich . registered dietitians cross - checked data on asa-24 by taking participant nutrient data and entering them into the usda nutrient database to make sure nutrient intake numbers were relevant to asa-24 . numbers that appeared erroneous were excluded , such as an intake of 500 calories reported for an entire day . macronutrient intakes were reported as percentages of total energy intake , and fiber and micronutrients were reported as quantities per 1000  kcal . as animal products are the only significant source of dietary cholesterol , cholesterol intake reported at 18 weeks served as a rough gauge of adherence to the intervention diet . the numbers of group participants whose cholesterol intake was 50  mg / day ( the amount of cholesterol in 2 ounces of typical meats or cheeses ) and 75  mg / day ( the amount of cholesterol found in 3 ounces of typical meats or cheeses ) were calculated from 18-week diet recalls . the number of group participants whose fat intake was below 25 and 35% of the total calorie intake was also calculated . all participants were asked to continue their pre - existing medication regimens unless otherwise instructed by their personal physicians . student 's t - tests and -tests were used to assess whether any demographic or clinical measures between groups at baseline were unbalanced . nutrient data were examined for extreme values , and distributions of variables were examined for skewness using a normality plot and the shapiro  wilk test . statistical analyses of nutrient intake were performed on an intention - to - treat basis , including all participants who completed an initial diet recall , with the post - intervention values for dropouts set to the pre - intervention values . a second analysis was limited to participants who completed diet recalls at baseline and 18 weeks . the significance of within - group changes in dietary variables was determined using paired t - tests . a general linear model univariate analysis ( analysis of covariance ) was used to estimate the treatment effect and determine whether the changes in nutrient intake of the intervention and control groups during the 18-week trial were significantly different from each other . diet group was included as a fixed factor in these models , with the baseline value of each nutrient as a covariate . in addition , the geographic site was added to the model as a random effect to account for within - site correlation in outcomes . as the number of sites was small , the significance of and confidence intervals for treatment effect were computed using the kenward the intervention sites were in tucson , macon , chevy chase , buffalo and lakeland . the control sites were in san diego , fredericksburg , woodbury , dallas and virginia beach . of 319 volunteers screened for eligibility , 292 ( 142 at intervention sites and 150 at control sites ) met the participation criteria and were enrolled in the overall clinical trial . of this group , 271 ( 130 at intervention sites and 141 at control sites ) completed usable baseline diet recalls and constituted the baseline sample for the current inquiry . at 18 weeks , 183 ( 78 in the intervention group and 105 in the control group ) completed diet recalls and were considered study completers for purposes of the nutrient analysis . there were no significant demographic differences between the intervention and control groups at baseline , except for a somewhat greater percentage of women at control sites ( table 1 ) . among completers , the intervention - group and control - group completers differed only with regard to gender ( 76% women in the intervention group , 88% women in the control group , p=0.04 ) . compared with noncompleters , study completers were older ( 45.5 versus 41.6 years , p=0.008 ) and had a lower mean baseline body mass index ( 34.3 versus 37.3  kg / m , p=0.006 ) . the median percentage of group sessions attended per participant ( among the completers at intervention sites ) ranged from 33% in macon to 75% in chevy chase , with an overall median of 50% . among study completers , cholesterol intake at 18 weeks was 75  mg / day for 85% ( 66/78 ) of intervention - group participants and 21% ( 22/105 ) of control - group participants ( p<0.001 ) . cholesterol intake was 50  mg / day for 74% ( 58/78 ) of intervention - group participants but only 13% ( 14/105 ) of control - group participants ( p<0.001 ) . total fat intake was 35% of the total calorie intake for 86% ( 67/78 ) of intervention - group participants compared with 40% ( 42/105 ) of the control - group participants ( p<0.001 ) . fat intake was 25% for 49% ( 38/78 ) of intervention - group participants and for 8% ( 8/105 ) of control - group participants ( p<0.001 ) . sfa intake was 10% of total calorie intake for 88% ( 69/78 ) of intervention - group participants and 38% ( 40/105 ) of control - group participants ( p<0.001 ) . sfa intake was 5% of total calorie intake for 51% ( 40/78 ) of intervention - group participants but only for 5% ( 5/105 ) of control - group participants ( p<0.001 ) . at baseline , there were significant differences between participants in the two study arms with respect to the percentage of energy from fat ( p=0.04 ) and vitamin b12 per 1000  kcal ( p=0.05 ) . during the 18-week intervention , both groups reduced the reported energy intake but the between - group difference was not significant ( table 2 ) . comparing nutrient intake changes over time between the two groups in the intention - to - treat analysis , adjusting for baseline values and accounting for within - site correlations in outcome , the intervention group significantly reduced the mean reported intake of fat , particularly of sfa but also of monounsaturated fat ( table 2 ) . the intervention group also increased the reported intake of -carotene , vitamin c , magnesium and potassium . the calcium intakes of both groups were below the recommended levels at baseline , and calcium intake fell further in the intervention group . limiting the analysis to study completers , results were similar to those in the intention - to - treat analysis ( table 3 ) . overall reported energy intake fell in both groups . compared with changes in the control group , the intervention group reduced the reported intake of fat ( total , monounsaturated fat and sfa ) , protein and cholesterol and increased carbohydrate and fiber intake . in addition , retinol intake fell , which was compensated for by an increase in -carotene . reported intakes of vitamin k , vitamin b6 , folate , vitamin c , iron , magnesium and potassium increased , whereas calcium intake decreased . among study completers , cholesterol intake at 18 weeks was 75  mg / day for 85% ( 66/78 ) of intervention - group participants and 21% ( 22/105 ) of control - group participants ( p<0.001 ) . cholesterol intake was 50  mg / day for 74% ( 58/78 ) of intervention - group participants but only 13% ( 14/105 ) of control - group participants ( p<0.001 ) . total fat intake was 35% of the total calorie intake for 86% ( 67/78 ) of intervention - group participants compared with 40% ( 42/105 ) of the control - group participants ( p<0.001 ) . fat intake was 25% for 49% ( 38/78 ) of intervention - group participants and for 8% ( 8/105 ) of control - group participants ( p<0.001 ) . sfa intake was 10% of total calorie intake for 88% ( 69/78 ) of intervention - group participants and 38% ( 40/105 ) of control - group participants ( p<0.001 ) . sfa intake was 5% of total calorie intake for 51% ( 40/78 ) of intervention - group participants but only for 5% ( 5/105 ) of control - group participants ( p<0.001 ) . at baseline , there were significant differences between participants in the two study arms with respect to the percentage of energy from fat ( p=0.04 ) and vitamin b12 per 1000  kcal ( p=0.05 ) . during the 18-week intervention , both groups reduced the reported energy intake but the between - group difference was not significant ( table 2 ) . comparing nutrient intake changes over time between the two groups in the intention - to - treat analysis , adjusting for baseline values and accounting for within - site correlations in outcome , the intervention group significantly reduced the mean reported intake of fat , particularly of sfa but also of monounsaturated fat ( table 2 ) . the intervention group also increased the reported intake of -carotene , vitamin c , magnesium and potassium . the calcium intakes of both groups were below the recommended levels at baseline , and calcium intake fell further in the intervention group . limiting the analysis to study completers , results were similar to those in the intention - to - treat analysis ( table 3 ) . overall reported energy intake fell in both groups . compared with changes in the control group , the intervention group reduced the reported intake of fat ( total , monounsaturated fat and sfa ) , protein and cholesterol and increased carbohydrate and fiber intake . in addition , retinol intake fell , which was compensated for by an increase in -carotene . reported intakes of vitamin k , vitamin b6 , folate , vitamin c , iron , magnesium and potassium increased , whereas calcium intake decreased . these changes were similar to those previously reported in clinical research settings , suggesting that these research findings effectively translated into an intervention implemented at worksites in widely divergent areas of the united states . part of this reduction may be because of underreporting , which is common in clinical trials of non - institutionalized participants . another possible explanation is that because asa-24 does not contain common vegan food items , subjects may have omitted these foods , resulting in lower energy intake reports . however , it is likely that the reduced energy intake of the intervention group is , at least in part , on account of increased fiber intake and reduced fat intake , both of which would tend to reduce the energy density of the diet . in turn , a reduction in energy intake favors weight loss , which has been observed in prior studies using low - fat , plant - based diets and was observed in the current study . reductions in reported energy intake and weight loss commonly occur with plant - based diets , even in the absence of specific limitations on energy intake or specific guidance regarding portion control . diets high in fiber may also facilitate removal of cholesterol , with favorable effects for individuals at risk of cardiovascular disease . in a 5-year study of patients with heart disease , a low - fat vegetarian diet as a part of a program of lifestyle changes has been shown to reverse atherosclerosis and reduce the risk of cardiac events . reported protein intake decreased in the intervention group , but the percentage of energy from protein remained within the range recommended by the institute of medicine . among micronutrients , the intervention group increased the reported intake of -carotene , vitamin c , magnesium and potassium . calcium intake was below the levels recommended by the institute of medicine at baseline and again at 18 weeks , and was dropped in the intervention group . in estimating calcium requirements , committees have used varying methods to calculate skeletal accretion and turnover rates , resulting in a considerable worldwide debate about whether currently recommended intakes of calcium are adequate to maximize peak bone mass and to minimize bone loss and fracture risk in later life . however , this may indicate the need for further instruction on plant - based sources of calcium , such as green leafy vegetables and legumes . reported iron intake increased in the intervention group , reflecting the increased intake of plant - based sources of iron . the 18-week nutrient intake data indicate that some intervention group participants continued to include some animal products in their diets and consumed more fat than had been recommended . nonetheless , the two groups diverged markedly in their reported dietary behavior , suggesting that the intervention elicits significant changes even for those participants who do not fully adhere to the prescribed guidelines . as previously reported , these nutrient changes are reflected in improvements in body weight , plasma lipid concentrations , and , for those with diabetes , improvements in glycemic control . the tendency of plant - based diets to favorably influence nutrient intake and clinical measures related to disease risk raises the question of their sustainability over the long term . a university of pittsburgh survey of young women who had tried both vegetarian and various calorie - restricted diets found that the mean duration of adherence to vegetarian diets was at least 2 years , compared with only 4 months for calorie - restricted diets . in the course of dietary intervention trials , adherence , attrition and eating behavior have been studied , and vegetarian and vegan regimens appear to be generally similar to other therapeutic diets within these parameters . strengths of the study include participation by individuals from divergent geographical areas , whose tastes and dietary habits and whose access to healthful foods likely varied as well ; the use of a dietary intervention that can be reproduced in other corporate locations ; and sufficient statistical power to demonstrate significant changes . its duration was limited to 18 weeks , primarily on account of the challenges of retaining untreated control - group participants over a longer period of time . had the study design included an active comparison program within the control group , it may have permitted sufficient engagement for a longer study , although such a design would have eliminated the possibility of comparisons with an untreated control . although there appeared to be a reasonable balance among those variables that were reported , we can not assume balance on other unreported or unmeasured variables . possible reasons for a failure to complete nutrient records include limited access to the internet and difficulties in navigating through the asa-24 online diet recall program . in summary , the present study demonstrated that a simple nutrition education program using modest group support at the place of employment yields significant improvements in nutrient intakes . the worksite is a potentially important venue for nutrition teaching and lifestyle modification and merits increased attention . in interventions using plant - based diets , planning for adequate intake of vitamin b12 and calcium future studies should focus on the longer - term nutrient changes associated with worksite dietary intervention programs .