Vegetarian and Weight-Loss Diets among Young Adults Cheryl F. Smith, Lora E. Burke, and Rena R. Wing

Abstract F. SMITH, CHERYL, LORA E. BURKE, AND RENA R. WING. Vegetarian and weight-loss diets among young adults. Obes Res. 2000;8:123–129. Objective: Young adults frequently experiment with vegetarian and weight-loss diets. Comparisons of their experiences on these two different diets may help in the development of approaches to improve long-term adherence to weight-loss regimens. In the current study vegetarian and weight-loss diets were compared on how long and how strictly they were followed, and reasons why they were initiated and discontinued. Research Methods and Procedures: From 428 college students surveyed, four groups were delineated: 1) 59 participants had been following a vegetarian diet but not a weightloss diet (Vegetarian), 2) 117 participants had tried a weight-loss diet but not a vegetarian diet (Weight Loss), 3) 133 participants had followed both a vegetarian and a weight-loss diet (Both), and 4) 119 participants had not tried either diet (Neither). Results: Differences were examined by comparing the Vegetarian and Weight-Loss groups as well as by comparing the two diets within the Both group. Duration of the vegetarian diet was much greater than the weight-loss diet; most participants in the Vegetarian group (62%) remained on their diet for more than 1 year, whereas the majority of the Weight-Loss participants (61%) followed their diet for 1 to 3 months. Similar results were found when comparing the two diets within the Both group. How strictly the two diets were followed, however, did not differ. Analyses revealed that reasons for discontinuing a diet varied; participants were more likely to cite boredom as a reason for discontinuing a weight-loss diet than a vegetarian diet (53% vs. 5% between groups and

Submitted for publication May 4, 1999. Accepted for publication in final form August 17, 1999. University of Pittsburgh Medical Center, Western Psychiatric Institute and Clinic, Pittsburgh, Pennsylvania. Address correspondence to Cheryl F. Smith, Ph.D., Western Psychiatric Institute and Clinic, 3811 O’Hara Street, Pittsburgh, PA 15213. E-mail: [email protected] Copyright © 2000 NAASO.

30% vs. 10% within the Both group). Discussion: The longer duration of the vegetarian diet relative to the weight-loss diet warrants further investigation. Results could possibly be applied to behavioral weight-loss treatment to improve long-term maintenance. Key words: vegetarianism, eating patterns, weight control, undergraduates

Introduction Although behavioral weight control programs have proven effective in helping individuals lose weight, longterm results have not been as favorable (1,2). Data indicate that much of the lost weight is regained within 1 to 3 years following completion of treatment (3,4). Thus, it appears that the behavioral changes in eating and exercise resulting in weight loss are only temporary. Approximately 40% of women and 19% of men aged 18 to 29 report that they are trying to lose weight (5). Thus, the prevalence of dieting among young adults is similar to that of all adults. The most common weight-loss practices used by women in this age group are consuming fewer calories (83%), increasing physical activity (74%), and counting calories (26%), with similar results for men, 74%, 73%, and 13%, respectively (6). However, epidemiological data suggest that the average duration of a weight-loss diet is only 4 to 6 weeks (7), and only 12.6% of men and women aged 18 to 29 stay on a diet for longer than 1 year (5). Thus, it appears that even though dieting is prevalent among young adults, most diets are very short-lived. Since permanent alterations in activity level and eating habits are needed for maintenance of weight loss, it may be helpful to examine populations in which comparable lifestyle changes are thought to be adopted and maintained over long periods. One such population may be vegetarians. The prevalence of vegetarianism among young adults has increased over the past several years (8). According to the few studies that have been conducted, motives for adopting a vegetarian diet include religious beliefs, health, animal welfare, and environmental reasons (9 –11). Vegetarians have been shown to eat a diet that is lower in dietary fat (9) and OBESITY RESEARCH Vol. 8 No. 2 March 2000

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to eat more carbohydrates and consume less alcohol than nonvegetarians (9,12). They have also been found to have lower body weights than nonvegetarians with a recent study finding body mass increases with consumption of animal fat (12). Furthermore, vegetarians have been found to be at decreased risk for medical conditions such as cardiovascular disease (13) compared to nonvegetarians. Differences between vegetarians and nonvegetarians on other health behaviors such as smoking and exercise are not as clear (12). Even so, it appears that vegetarianism is “a way of life” that is associated with improved health and lower body weight. These characteristics make vegetarians a potentially interesting group to study with regard to maintenance of dietary behavior change. Understanding further why they choose their diet and how long they remain on it may have implications for weight-loss intervention and maintenance. This study was designed to determine if individuals remain on vegetarian diets longer than weight-loss diets. Such results may have implications for overweight and obese populations, given that vegetarianism is associated with improved health status (e.g., lower body weight, decreased risk of disease) and that innovative approaches to improving weight-loss maintenance are needed. In addition to duration, vegetarian and weight-loss diets were compared on how strictly the diets are followed and reasons why they are discontinued.

Research Methods and Procedures Participants were 428 undergraduate students recruited from psychology, physical education, and nursing courses at a large university. The sample was predominantly female (70%) and white (85%) with a mean age of 21 years and a body mass index (BMI) of 23 kg/m2 (See Table 1). Evaluation During their respective class periods participants completed a 3-part questionnaire evaluating their experiences with vegetarian and weight-loss diets. The first part contained eight questions concerning vegetarian eating patterns. Participants were given definitions of semivegetarian, vegetarian, and vegan diets (14) and then asked if they had ever adopted any of these diets. If they answered “yes” to any of the vegetarian diets, they then responded to a series of questions evaluating the type of their most recent (or current) vegetarian diet, how strictly they followed the diet (1 ⫽ not strictly at all; 5 ⫽ extremely strictly), how long they followed the diet, reasons for adopting the diet, and reasons for abandoning the diet (if applicable). A second section of the questionnaire focused on experience with weight-loss diets. Those who had tried a weight-loss diet answered questions regarding how strictly they followed their most recent (or current) diet, the duration of the diet, reasons for attempting weight loss, and reasons for discontinuing the diet (if applicable). A final section contained 124

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questions about demographic information (age, gender, ethnicity). Self-reported height and weight were also obtained to calculate the BMI. Most participants completed the entire questionnaire in less than 10 minutes. Statistical Analyses Data are means ⫾ SD unless otherwise noted. Participant characteristics of the four groups were compared using chi-square statistic for gender and ethnicity groups and one-way ANOVA followed by Tukey’s post hoc test (if indicated) for age and BMI. Within-group comparisons utilized the Wilcoxon signed ranks test for related samples to evaluate duration categories (ordinal data) and a t test for correlated samples to evaluate differences in strictness ratings. Comparisons between the Vegetarian and Weight groups were made using the chi-square statistic or ANOVA where appropriate. All analyses were performed with SPSS 8.0 for Windows (15).

Results Among the 428 undergraduates surveyed, 192 (45%) reported that at some point in their lives they had tried a vegetarian diet, and over half of the subjects (n ⫽ 250; 58%) reported that they had been on a weight-loss diet. Four independent groups were formed from the overall sample: 1) Vegetarian: 59 participants who had been on a vegetarian diet, but not on a weight-loss diet, 2) Weight Loss: 117 participants who had tried a weight-loss diet, but not a vegetarian diet, 3) Both: 133 participants who indicated that they had followed both a vegetarian and a weight-loss diet at some point in their lives, and (4) Neither: 119 participants who had tried neither diet. Descriptive statistics for these groups are shown in Table 1. There were no significant differences in age or ethnic composition across groups (p values ⬎ 0.05). There were significantly fewer female participants in the Neither group than in the other three groups, ␹2 (3, 419) ⫽ 67.3, p ⬍ 0.001. Gender differences for the main variables of the study (i.e., reasons for discontinuing a diet, strictness and duration of diet) were examined, and only two significant differences were identified. These results are presented later. Given that there were only two significant gender differences, gender was collapsed within the groups for the following analyses. The mean BMI of participants in the Vegetarian group was significantly lower than the Weight-Loss and Both groups. In addition, the Weight-Loss group’s BMI was greater than the Neither group’s BMI (p values ⬍ 0.01, see Table 1). When participants who were currently on one of the diets were excluded from this analysis, these differences persisted and the difference between the Both and Neither groups also became significant (BMI, 23.6 ⫾ 3.9 vs. 22.4 ⫾ 2.4, respectively; p ⬍ 0.05). Of the 59 Vegetarian participants, 40 had been on a semivegetarian diet (no red meat), 13 had been on a vege-

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Table 1. Participant characteristics*

Age (years) Female Ethnicity White Black Asian American Hispanic Other BMI Vegetarian diet Semivegetarian Vegetarian Vegan

All (n ⴝ 428)

Vegetarian (n ⴝ 59)

Weight Loss (n ⴝ 117)

21.0 ⫾ 4.3 70 (298)

20.7 ⫾ 4.0 73 (43)a

85.3 (365) 5.8 (25) 1.4 (6) 0.7 (3) 3.9 (17) 23.0 ⫾ 3.6

83.1 (49) 6.8 (4) 1.7 (1)

N/A

5.2 (3) 21.0 ⫾ 2.2a 68 (40) 22 (13) 10 (6)

Both (n ⴝ 133)

Neither (n ⴝ 119)

21.4 ⫾ 4.3 79 (92)a

21.3 ⫾ 4.3 85 (113)a

20.4 ⫾ 3.4 42 (50)b

85.5 (100) 5.1 (6) 1.7 (2) 1.7 (2) 3.4 (4) 24.1 ⫾ 4.0b

85.7 (114) 4.5 (6) 0.8 (1) 0.8 (1) 4.6 (6) 23.5 ⫾ 3.7bc

86.4 (102) 7.6 (9) 1.7 (2)

N/A

65 (86) 26 (35) 9 (12)

3.3 (4) 22.4 ⫾ 2.9ac N/A

* Means ⫾ SD or percentages (n) within a row with different superscripts (a– c) are significantly different (p ⬍ 0.01).

tarian diet (no red meat, poultry, or fish), and 6 had been on a vegan diet (no meat, poultry, or fish, as well as eggs and dairy products, e.g., cheese and milk) (see Table 1). The main reasons cited for adopting a vegetarian diet were “health” (64%) and “disgust with appearance of food” (42%). Other reasons endorsed included “animal welfare” (28%), “personal appearance reasons” (25%), and “weight loss” (24%). Participants in the Both group (n ⫽ 133) were similar to the Vegetarian group in that the most common reason for adopting their most recent (or current) vegetarian diet was “health” (70%) followed by “weight loss” (59%), “disgust with appearance of food” (36%), and “personal appearance” (36%). The Weight-Loss participants cited “physical appearance” (90%) followed by “health reasons” (32.5%) and “special event, e.g., wedding” (26%) as the main motives for going on a weight reduction diet. The Both group was similar to the Weight-Loss group in that “physical appearance” and “health” were also the two most common reasons for going on a weight-loss diet, 93% and 55%, respectively. The primary aim of this study was to compare three aspects of vegetarian and weight-loss diets, including how strictly the diets are followed, how long individuals remain on the diets, and reasons for discontinuing the diets. These comparisons were made in two ways: 1) by comparing the Vegetarian group to the Weight-Loss group, and 2) by comparing the two diets within the Both group. Strictness of Diets There was no difference between the Vegetarian and Weight-Loss groups on how strictly (on a 1 to 5 scale)

participants followed their most recent (or current) diet, 3.2 ⫾ 1.2 vs. 3.1 ⫾ 0.8, respectively (p ⬎ 0.05). Similarly, among the Both group the vegetarian and weight-loss diets were followed with comparable strictness, 3.3 ⫾ 1.2 and 3.5 ⫾ 1.0, respectively (p ⬎ 0.05). Men within the Weight-Loss group indicated that they followed their diet more strictly than did women (p ⬍ 0.05). Duration of Diets Five categories of duration were created to compare the lengths of the two diets (1 to 3 months, 4 to 6 months, 7 to 9 months, 10 to 12 months, and 12⫹ months). Figure 1 shows the percentages of Vegetarian and Weight-Loss participants in each of these categories. Most Vegetarian participants (62%) remained on their diet for longer than 12 months, whereas the majority of Weight-Loss participants (61%) remained on their diet for 1 to 3 months. A chi-square test performed on these categories for these two groups was significant, ␹2 (4, 168) ⫽ 51.3, p ⬍ 0.001. In addition, the median time spent following a weight-loss diet was 3 months compared to 24 months for a vegetarian diet. When participants who were currently on a vegetarian or weight-loss diet were excluded from this analysis, the same pattern of results emerged with most (57%) Vegetarian participants remaining on their diet longer than 12 months compared to most (63%) Weight-Loss participants staying on their diet for less than 3 months (p ⬍ 0.001). Within the Both group, the five duration categories of weight-loss and vegetarian diets were compared using the signed-rank test for related samples. A significant difference in the frequency distribution was found between diets (p ⬍ OBESITY RESEARCH Vol. 8 No. 2 March 2000

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Figure 1. Participants who had followed either a vegetarian or weight-loss diet by duration of diet, ␹2 (4, 168) ⫽ 51.3, p ⬍ 0.001. (Data were missing for the duration of four vegetarian diets and four weight-loss diets.)

Figure 2. Participants who had followed both a vegetarian and a weight-loss diet by duration of each diet, signed-rank test, p ⬍ 0.01. (Data were missing for the duration of 10 vegetarian diets and 8 weight-loss diets.)

0.01). As can be seen in Figure 2, participants remained on the vegetarian diet longer than the weight-loss diet. The median time spent following a weight-loss diet was 4 months compared to 24 on a vegetarian diet. When participants who were currently on one of the diets were omitted from this analysis, the results were essentially the same (p ⬍ 0.01).

“missed eating certain food” as a reason for discontinuing a diet in the Weight-Loss group, ␹2 (1, 116) ⫽ 6.1 p ⬍ 0.05. Over half of the participants in the Both group (59%) reported that they eventually resumed eating red meat or other animal products, and most (87%) reported that they eventually stopped their weight-loss diet. For statistical analyses purposes, only the participants who reported that they had discontinued both diets were examined (n ⫽ 73). Signed-rank tests revealed that “lost interest/bored” and “did not lose weight” were more likely to be reasons to stop a weight-loss diet as opposed to a vegetarian diet (p values ⬍ 0.001) (see Table 2). One could argue that participants did not remain on a weight-loss diet very long because they were normal weight. To address this issue, a subset of 35 overweight participants in the Both group (BMI ⬎ 25 kg/m2) was examined. Results for these subjects were similar to those of the total sample: overweight subjects remained on a weightloss diet for a much briefer period (median ⫽ 5 months) compared to a vegetarian diet (median ⫽ 24). Given that there were only three subjects in the Vegetarian group with a BMI ⬎ 25 kg/m2, a similar comparison between this group and the Weight-Loss group was not conducted. It is also possible that engaging in vegetarianism for religious reasons may affect duration of the diet. However, when participants who went on a vegetarian diet for religious reasons were omitted, the findings were not significantly altered. In fact, results revealed that these participants did not necessarily remain on the diet for longer than 1 year. Finally, it is possible that those who discontinued their diet did so because they achieved their desired weight. However, when participants who had discontinued their weight-loss diet because they “achieved desired weight loss” (36%) were excluded from analysis, the reasons for stopping the

Reasons for Discontinuing the Diets Table 2 shows reasons for discontinuing the diets and the percentages of participants who endorsed each. Six reasons that were possible choices for both diets were compared. (The reason “did not get adequate nutrients” was a choice for only the vegetarian diet, whereas the reason “achieved desired weight loss” was a choice for only the weight-loss diet.) Among the 64% (38 of 59) of the Vegetarian participants who had resumed eating meat and other animal products, the main reasons cited for stopping the vegetarian diet were “missed eating (meat)” (42%) and “inconvenience” (21%). Approximately 24% of participants indicated that they discontinued their vegetarian diet because they “did not get adequate nutrients.” “Other” reasons were cited by 29%. Almost all of the Weight-Loss participants (90%) reported that they had eventually stopped following a weight-loss diet. Most frequently cited was “lost interest/ bored” (53%) and “missing certain foods” (48%). Chisquare tests revealed that Weight-Loss participants were more likely to stop their diet due to “lost interest/bored” than Vegetarian participants, ␹2 (1, 143) ⫽ 26.7, p ⬍ 0.001. Other significant differences were found between the two groups on the reasons, “did not lose weight” and “other,” ␹2 (1, 143) ⫽ 8.4, p ⬍ 0.01 and ␹2 (1, 143) ⫽ 6.3, p ⬍ 0.05, respectively. In addition, more women than men endorsed 126

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Table 2. Reasons for discontinuing diets Between-group comparisons

Missed eating “meat” or “certain foods” Lost interest/bored Did not lose weight Did not feel healthier Inconvenient or time-consuming Other Did not get adequate nutrients Achieved desired weight loss

Comparisons within the Roth group

Vegetarian (n ⴝ 38)

Weight Loss (n ⴝ 105)

Vegetarian diet (n ⴝ 73)

Weight Loss diet (n ⴝ 73)

42.1%* 5.3 2.6 2.6 21.1 28.9 23.7 N/A

47.6% 53.3† 23.8† 8.6 16.2 11.4† N/A 35.6

54.8% 9.6 5.5 8.2 21.9 28.8 31.5 N/A

45.2% 30.1† 23.3† 12.3 17.8 27.4 N/A 31.5

* Percentages represent the participants who endorsed each reason. † A significant chi-square test (p ⬍ 0.05) for between-group comparisons or a significant signed-ranks test (p ⬍ 0.001) for within-group comparisons of “Yes” vs. “No” responses for each reason. Percentages may exceed 100% because participants endorsed as many reasons that applied.

diet remained similar (“lost interest/bored” 60%, “missed certain foods” 55%, “did not lose weight” 34%, “did not feel healthier” 10%, “inconvenient or time-consuming” 18%, and “other” 16%).

Discussion Many of the young adults in the current study (45%) reported trying a vegetarian diet. This was expected given reports of the rising prevalence of vegetarianism (8). Even though BMI values across the groups were relatively low, participants who had only tried a vegetarian diet had significantly lower BMIs than those who tried a weight-loss diet or both diets. Further analysis of this difference indicated that this finding was not due to the inclusion of current dieters. This finding supports earlier reports of lower body weights in vegetarians (12). Whether weight loss is a result of following a vegetarian diet or individuals with lower body weights select vegetarian diets remains to be determined. Reasons for adopting a meatless diet, including health, disgust with appearance of food, and animal welfare, were also similar to those that have been reported previously (9,11). Interestingly, many participants (24% of the Vegetarian group and 59% of the Both group) endorsed “weight loss” as a reason for adopting a vegetarian diet. It could be a reflection of the sample used, given that college-age individuals, particularly females, report a high frequency of dieting (5). Thus, they may view any change in dietary habits as an attempt to lose weight, even though it may not be their primary reason to become vegetarian. Interestingly, a recent study reported a similar finding in that 25% of young women on a vegetarian diet endorsed “weight loss”

as a reason for choosing the diet (16). Using vegetarianism as a means to control weight deserves further attention. Primary motivations for weight loss cited in the current study, i.e., physical appearance and health, were consistent with previous research (17). One might argue that participants with different reasons for attempting weight loss may have different experiences on a diet (e.g., longer duration). However, due to the fact that 90% of the Weight-Loss participants and 93% of the Both group reported going on a weight-loss diet for “physical appearance” reasons, such differences between “health” and “physical appearance” motivations could not be examined. Future research could explore this possibility by recruiting individuals who endorse only one of these two main reasons for weight loss. This study provided support for the belief that individuals remain on vegetarian diets longer than weight-loss diets. One may assert that the participants in the Both group described the same diet for both the weight-loss and vegetarian sections of the questionnaire, because there was no mechanism to ensure that they were describing different diets. However, given the difference in reported duration of each diet, it appears that many participants were describing two separate diets. Notably, participants in the Both group reported staying on their vegetarian diet longer than their weight-loss diet, providing evidence that the findings were not due to mere personal characteristics. In addition, excluding participants who were currently on one of the diets did not alter the results. Thus, perhaps there is something about the vegetarian diet per se that is associated with longer duration. OBESITY RESEARCH Vol. 8 No. 2 March 2000

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Participants reported following both diets moderately strictly, indicating that individuals do not necessarily adhere to one diet more stringently than the other. Thus, it does not appear that participants remained on a vegetarian diet longer, because it was more structured (or more flexible) than a weight-loss diet. That participants were more likely to abandon a weight-loss diet due to “not losing weight” is an understandable difference between the diets, given that 100% of the participants who had tried a weight-loss diet desired weight loss, whereas only 24% to 59% of participants who had tried a vegetarian diet (Vegetarian and Both groups, respectively) expected to lose weight. More interesting is the finding that participants were more likely to discontinue a weight-loss diet due to “lost interest/bored.” This is curious since there does not seem to be anything inherently more interesting about a vegetarian diet compared to a weight-loss diet. Perhaps since most (65% to 68%) of the vegetarians in the current study were actually just avoiding red meat, they were less likely to become bored with their diet. Alternatively, this finding could reflect an attitude change that occurs while on a weight-loss diet. Regardless, this result raises the question of whether long-term adherence to weight-loss diets would be improved by efforts to make weight-loss diets more interesting, e.g., by providing recipes, encouraging a wider variety of physical activities. Another option may be to focus on modifying the cognitions that are associated with weight-loss dieting and feelings of boredom. Further research on what makes weight-loss diets boring or disinteresting is needed to understand the significance of this difference and how it should be addressed. In contrast, it is also important to explore reasons why people are able to remain on vegetarian diets. A strength of this study is that the main findings were consistent when the two diets were examined using between and within group comparisons. Another strength is that evidence was provided to dispel some possible explanations for some of the findings. An analysis using a subset of overweight participants revealed duration results consistent with the initial findings using the larger sample. Thus, it is unlikely that weight-loss diets were briefer due to the fact that most of the participants were not overweight. It is also unlikely that the duration results were significantly affected by data from participants who went on a vegetarian diets for religious reasons, because the findings were not altered when these particular subjects were excluded. Furthermore, results concerning the reasons for discontinuing the diets were not significantly altered when analyses were rerun after excluding participants who stopped dieting because they reached their desired weight. A limitation of this study is that self-reported weight measurement was used, which has been found to be slightly less accurate than an actual 128

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measurement (18). The study also would have been strengthened if data were collected on how much weight was lost on the diets and how long the weight loss was maintained. In summary, the results of this study suggest that young adults maintain vegetarian diets longer than weight-loss diets. Reasons for improved adherence for the vegetarian diet deserve further examination. If certain factors such as motivations for adopting and/or abandoning the diets are found to significantly increase maintenance or adherence to a diet, the results could be applied to behavioral weight-loss programs to improve long term weight-loss maintenance. Additionally, given vegetarianism’s attractiveness and increased adherence in young (normal weight) adults, exploring it as a viable option for prevention of overweight and obesity may be a worthwhile venture.

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12. Appleby PN, Thorogood M, Mann JL, Key TJ. Low body mass index in non-meat eaters: the possible roles of animal fat, dietary fibre and alcohol. Int J Obes. 1998;22: 454 – 60. 13. Dwyer JT. Health aspects of vegetarian diets. Am J Clin Nutr. 1988;48:712s–38s. 14. Donovan UM, Gibson RS. Dietary intakes of adolescent females consuming vegetarian, semi-vegetarian, and omnivorous diets. J Adolesc Health. 1996;18:292–300. 15. SPSS-PC for Windows. SPSS, Chicago, IL, 1997.

16. Gilbody SM, Kirk SF, Hill AJ. Vegetarianism in young women: another means of weight control. Int J Eating Disord. 1999;26:87–90. 17. Striegel-Moore RH, Wilfley DH, Caldwell MB, Needham ML, Brownell KD. Weight-related attitudes and behaviors of women who diet to lose weight: a comparison of black and white dieters. Obes Res. 1996;4:109 –16. 18. Jeffery RW. Bias in reported body weight as a function of education, occupation, health, and weight concern. Addict Behav. 1996;21:217–22.

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