A group of researchers recently conducted a study on the relationship between access to vending machines in the high school environment and children's body mass index (BMI) and quality of diet. This research, conducted in Maine, represents one of the first and only studies on school vending machines' impact on the diet quality and BMI percentiles of high school students. The study was funded by the Centers for Disease Control and Prevention (CDC).
The research was presented at the 2005 annual meeting of NAASO, the Obesity Society, located in Silver Spring, Md. This is considered a leading scientific society dedicated to the study of obesity and committed to encouraging research on the causes and treatment of obesity and to keeping the medical community and public informed of new advances. The annual meeting was held in October 2005, in Vancouver, Canada.
An abstract of the study, titled "Frequency of school vending machine purchases, BMI and diet quality," appeared in a recent NAASO publication.
Automatic Merchandiser sought permission from the study's authors to provide a summary in the interest of providing readers some idea of how access to vending machines affects students' diet quality and BMI percentiles from a scientific standpoint. The vending industry has been criticized in recent years for contributing to rising childhood obesity, resulting in legislative proposals to restrict vending machines in schools.
While rising obesity has alarmed many public officials and a portion of the public at large, some observers have noted a lack of scientific understanding of the causes of obesity. Automatic Merchandiser is committed to providing its readers credible research on the role vending plays in contributing to childhood obesity.
The abstract noted that the purpose of the study was to examine the differences in the frequency of vending purchases and the BMI percentile and diet quality in high school students.
BMI is a measure of weight for height and is gender and age specific. Some school districts have begun using BMI assessment as part of their efforts to monitor students' health.
To determine BMI percentile in the study, height was measured twice to the nearest 0.25 cm using a stadiometer, the standard tool for measuring height. Weight was measured twice to nearest 0.1 kg using a calibrated digital scale. CDC growth charts were used to calculate age and gender specific BMI percentile.
To determine diet quality, researchers used the self-administered "Youth Food Frequency Questionnaire" to assess calories per day, total fat, saturated fat, total carbohydrates and sucrose.
The abstract noted there is concern that school vending machines offering low nutritional value items may contribute to weight gain and poor dietary intake in youth. The abstract also noted that a 2003 study found that 35 percent of items in vending machines in secondary schools met the "low-fat" criteria of less than or equal to 5.5 grams of fat per serving.
The study examined the differences between the frequency of vending purchases and percentile of body mass index and diet quality.
Subjects included 552 students (225 girls, 327 boys) with a mean age of 15.8, plus or minus 0.9 years, from seven public high schools in Maine.
A total of 74 vending machines — 55 beverage and 19 snack — were in the schools. Out of these 74 machines, 57 machines — 44 beverage and 13 snack — were accessible to students. Subjects self-reported frequency of vending purchased in the past 30 days.
The beverages in the 44 glassfront beverage machines accessible to students consisted of 1,065 items. Beverage machines carried the following product mix:
- Sweetened beverages other than regular soda, 43.2 percent
- Water, 40.4 percent
- Regular soda, 7.7 percent
- 100 percent juice, 4.8 percent
- Diet soda, 1.8 percent
- Milk, 2 percent
Forty-six percent of all beverages met a low-fat, low-sugar criteria.
Seven of the machines were restricted access.
The 13 snack vending machines accessible to students carried a total of 480 items. Snack machines carried the following product mix:
- Salty snacks, 39 percent
- Cookies, 26 percent
- Candy, 25 percent
- Other, 7.7 percent
- Ice cream, 2.5 percent
Twenty-three percent of all snack items met a low-fat criteria of less than or equal to 30 percent of total calories from fat and low sugar, less than 35 percent of sugar by weight.
Seven of the snack machines were restricted access.
Subjects were categorized into four groups based on self report of frequency of vending purchases:
- 35.5 percent: zero items or only water;
- 29 percent: 1 to 3 items;
- 18.5 percent: 4 to 6 items; and
- 17 percent: more than 7 items.
The greatest number of subjects reported purchasing water, followed by sweetened beverages other than soda, regular soda, salty snacks, 100 percent juice, candy, cookies, diet soda, other products and ice cream, as indicated in the chart above.
Preliminary analyses found consistent results for BMI percentile and diet quality between gender and age groups.
A later analysis showed no differences in BMI percentile between the groups. There were differences found in calories between groups.
Frequency of purchase and body mass index
The results suggest that frequency of purchases from school vending machines was not associated with BMI, however; greater frequency of purchases was associated with a poorer diet quality. Students reporting a greater frequency of vending purchases had a greater caloric intake and poorer absolute dietary intake as compared to a lower frequency of purchases. This trend was also observed with the relative dietary intake of total fat and sucrose.
Other factors such as type of vending machines available or access to machines during the school day need to be considered, the authors noted.
No association was found between the number of unrestricted vending machines per student and frequency of vending purchases.
The researchers noted that in considering differences among the "frequency of purchase" groups, other factors, such as physical activity, intake of fruits and vegetables or availability of foods from other school food venues, should be considered. Longer term studies are needed to determine the effect that frequency of purchases from school vending machines has on BMI percentile in high school students.
Contributing authors included: Janet Whatley Blum, College of Nursing and Health Professions, University of Southern Maine; Anne-Marie Davee, Muskie School of Public Service, University of Southern Maine; Rachel Devore, College of Nursing and Health Professions, University of Southern Maine; Paul Jenkins, Bassett Research Institute, Cooperstown, N.Y.; Christina Beaudoin, College of Nursing and Health Professions, University of Southern Maine; Janet Leiter, Bureau of Health, Maine Department of Health and Human Services; Lori Kaley, Muskie School of Public Service, University of Southern Maine; and Debra Wigand, Bureau of Health and Human Services.
For information about NAASO, call 301-563-6526 or go to: http://www.naaso.org.