Effect of food prices on dietary intakes in US Food Stamp Program eligible populations

Presenter: Qi (Harry) Zhang, Old Dominion University

Abstract

Background:

The Food Stamp Program (FSP) in the U.S. is designed to provide a nutritional safety net for low-income groups: 67.3% of 62 million eligible individuals participated in FSP in 2006. Studies suggest that FSP participantion is associated with higher obesity risk. However, little is known about how FSP participation may affect participants’ dietary intake and whether food prices affect potential differences between FSP participants’ and eligible non-participants’ dietary intakes.

Objective:

To examine the independent and joint effects of food prices and FSP participation on dietary intake among FSP eligible adults.

Methods:

Data: The National Health and Nutritional Examination Survey III (NHANES 1988-1994) was linked with the American Chamber of Commerce Researchers’ Association (ACCRA) food price data by state and county. Participants’ dietary intakes were assessed using 24-hour recalls. Dietary intakes were assessed as to whether they met related age-sex specific dietary recommendations.

Outcomes: Dietary intakes such as total energy intake (TEI), fat (grams and percent energy from fat), fiber, calcium, and vitamins.

Exposure Variables: FSP participation, nutrient-specific food price indices, and interaction terms between these two variables. FSP eligibility is defined as <=130% of federal poverty line. For each nutrient, we constructed the nutrient-specific food price (NSFP) index. NSFP was a weighted price index of a basket of foods providing that nutrient. The price weights were based on the Consumer Expenditure Survey (CES).

Covariates: Age, gender, race/ethnicity, and income.

Statistical Methods: We conducted multivariate linear regression analyses for continuous outcome variables, and logistic regression analyses for dichtomous outcomes (eg, whether the intake met dietary recommendations).

Results:

We included 1,980 adults who were at least 18 years old and eligible for FSP. Mean Body Mass Index (kg/m2) and obesity prevalence in FSP participants were greater than those in eligible non-participants ( 28.0 and 30.1% vs. 26.3 and 22.2%, p<0.05). FSP participation was positively related to TEI (kcal) (β=133.5 kcal, p=0.04), fat intake (gm) (β=5.1 p=0.04), but were less likely to meet recommended amount of intake for vitamin C (Odds Ratio (OR)=0.6, 95%CI: 0.41-0.93) and vitamin A (OR=0.5, 95%CI: 0.29-0.83). Food prices had significant impact on dietary intakes. Higher NSFP were associated with lower TEI (β= -10.0, p=0.03), fat intake (β= -0.34, p=0.003), lower percent energy from fat (β= -0.09, p=0.01), and were less likely to meet recommendations for calcium (OR=0.9, 95%CI: 0.96-1.00). FSP participation modified the association between food prices and some nutrient intakes. The interaction term between food prices and FSP participation was significant for TEI (β= 13.0; p=0.06), fat intake (β= 0.3, p=0.08), and meeting recommendations for calcium (OR=1.03: 95%CI: 1.00-1.05).

Conclusion:

FSP participation contributed to increased intakes of energy and fat, but FSP participants were at higher risks of not meeting dietary recommendations for some vitamins. Higher food prices were associated with lower energy and fat intake among FSP eligible populations, while FSP participation can offset these price effects. Our findings suggest that increasing fat-related food prices, such as “fat tax”, can help reduce unhealthy eating among low-income populations, but its impact could be compromised by the current FSP.