L ONGITUDINAL S TUDIES

9.4.1 L ONGITUDINAL S TUDIES

In comparison to cross-sectional studies, longitudinal studies are considered more compelling in pointing to causal relationships between dietary intake and adiposity, because they examine change over time. Thirteen longitudinal studies that examined the relationship between carbohydrates and adiposity were identified in the literature published within the last decade (Table 9.1). Of these 13 studies, 2 examined associations in adults, 46,47 1 followed adolescents into adulthood from age 13 to 28

years, 48 and the other 10 studied children of various ages. 49–58 Of the 11 studies that reported on the association between total carbohydrates and weight change, 2 found a significant negative association between total

Carbohydrates and Obesity

carbohydrate intake and adiposity, 51,54 1 found a significant negative association only with regard to subscapular skinfolds, 53 and the other 8 found no significant association. 46,48,49,52,55–58 In a well-controlled study, Eck et al. 51 followed 187 white children ages 3 to 4 years in Tennessee for 1 year. They found that children at risk for overweight (as defined by parental weight status) gained marginally but significantly more weight than their low-risk counterparts and ate a relatively

larger percentage of calories from carbohydrates. Lee 54 followed 5-year-old white girls for 2 years and found that larger absolute intakes of carbohydrates were associated with lower BMI; however, few control variables were included in the analysis. All of the longer-term studies (from 4 to 15 years in length) 48,49,52,55–57 and the two studies conducted among adults 46,49 failed to find an association

between carbohydrate intake and adiposity. Robertson et al. 49 took a slightly different approach by examining the association between adiposity take-off (defined as a 1.5 or greater standard deviation increase in skinfolds over a 1-year period) and carbohydrate intake in children ages 3 through 7, but also found no significant association.

The relation of dietary fiber intake to adiposity was reported in two longitudinal studies. 47,50 The CARDIA study 47 followed black and white adults in five U.S.

cities for 10 years and showed a significant negative relationship between fiber intake and change in BMI after controlling for a number of possible confounders.

The Growing Up Today study 50 followed a large cohort of children ages 9 to 14 for 1 year and showed no significant relationship between fiber intake and change

in BMI. Although several potential covariates were controlled for, there was no reported control for socioeconomic status or physical activity, two factors that can impact overweight risk.

Sucrose intake was not found to be associated with weight change in adults in the one study that examined this relationship. 46 In the CARDIA study, 47 however, the glycemic index (defined as low fiber and low fat) was significantly and positively associated with increases in BMI among whites.

Given that none of the adult studies found a significant association between total carbohydrates and adiposity, it appears that carbohydrate intake may have a limited

influence on adiposity in adults. However, due to the limited number of longitudinal studies conducted among adults, it is not possible to draw firm conclusions. Likewise, among children it appears that the percent of calorie intake from total carbohydrates has a limited influence on weight change in free-living populations; less than half of the studies found a significant relationship between these two variables. However, these studies suffered from several methodological limitations, including relatively small sample sizes and a limited number of control variables, as well as being conducted among primarily white populations. Furthermore, dietary intake data for children are notoriously inaccurate due to the difficulty children have in recalling or recording their intake and the incomplete knowledge parents have of their chil- dren’s intake. Unfortunately, there have also been too few longitudinal studies conducted to draw conclusions about the impact of sugar or fiber intake on weight changes, although fiber appears to be protective against weight gain. Further study is merited.

TABLE 9.1 334 Summary of Longitudinal Studies That Examined the Relationship between Carbohydrate Intake and Adiposity

(in Descending Order by Sample Size, Adults First)

Association with Adiposity a Study

Study Characteristics

Time Frame

Subjects

Total CHO b Fiber Sugars

– Parker (1997), 46 Pawtucket Heart Health Study,

Ludwig (1999), 47 CARDIA, 5 U.S. cities

10 years

2909 adults, black and white, ages 18–30

0 0 New England

4 years, 1986–1987

176 men, 289 women

Sucrose c Kemper (1999), 48 Amsterdam Growth and Health

and 1991–92

15 years

83 males, 98 females, age 13, nonobese at start

Longitudinal Study Berkey (2000), 50 Growing Up Today, U.S.

1 year

6149 girls, 4620 boys, ages 9–14

Magarey (2001), 53 Adelaide Nutrition Study,

13 years

243 children, age 2 at start

Australia

BMI/TC skinfolds

– SS skinfolds

Alexy (1999), 58 DONALD Study, Germany

2 years

105 boys, 100 girls, age 3 at start

Lee (2001), 54 Pennsylvania

2 years

192 white girls, age 5 at start, and their mothers

– (g)

Eck (1992), 51 Tennessee

1 year

187 white children

Scaglioni (2000), 52 Italy

5 years, began 1991

67 girls, 80 boys, birth to 5 years

0 Functional F

Maffeis (1998), 56 Italy

4 years

112 white children, mean age = 8.7 at start

Rolland-Cachera (1995), 55 France

4 years

112 children, age 10 months at start

Carruth (2001), 57 Tennessee

6 years

53 white children, age 2 at start

Mean longitudinal intakes of

total CHO (g)

ood Carboh

Robertson (1999), 49 SCAN Study, Texas

Case-control, 4 years

15 subjects and 33 controls, ages 3–7, mixed race

Note : CHO = carbohydrate; BMI = body mass index; TC = triceps; SS = subscapular. a Association with adiposity: – indicates an inverse and significant association with adiposity; + indicates a direct and significant association with adiposity; 0 indicates the association was

ydrates

not significant; blank space indicates no association was reported. Findings were the same for all age, gender, and ethnic groups unless otherwise indicated.

c Definition of independent variable is indicated if different from that indicated in the column heading. All studies defined carbohydrate intake in terms of percent of total calories unless otherwise indicated by g (grams). d Outcome variable was adiposity take-off (increase of 1.5 standard deviations in skinfolds in 1 year).

Carbohydrates and Obesity