Dietary compliance of walnut or no walnut intake in a 1‐year randomized intervention trial among free‐living elderly in the Walnuts and Healthy Aging Study (WAHA)

Abstract

BackgroundDietary compliance is difficult to measure in clinical trials with free‐living subjects. Measuring dietary compliance relies on self‐reported dietary intake and, when available, biological markers.ObjectiveIn the context of a large clinical trial, we assessed compliance of a prescribed dietary intervention for a year of daily ingestion of walnuts or abstaining from walnuts in free‐living elderly.DesignDietary compliance was measured within the context of the Walnuts and Healthy Aging Study (WAHA), a randomized clinical trial assessing the effect of daily ingestion of walnuts on age‐related health outcomes. A total of 365 free‐living healthy elderly subjects (237 women, 199 men), ages 63–79 years old, from one center at Loma Linda University were considered for this assessment. Within the context of their habitual lifestyle, the walnut group (120 participants) was prescribed to consume an allotted amount of walnuts based upon 15% of their energy intake (30–60 grams) and proscribed up to 2 servings/week (2 oz.) of other nuts. The control group (137 participants) was prescribed to consume their habitual diet without any walnuts and the same proscription of up to 2 servings/week (2 oz.) of other nuts. Compliance was measured using two methods of self‐reporting; responses on a 179‐item semi‐quantitative food frequency questionnaire, and approximately three unannounced 24‐hour dietary recalls given per subject, for a total of over 1,000 completed 24‐hour dietary recalls. A third measure of compliance was taken to evaluate changes in plasma α‐linolenic acid in red blood cells from baseline to one year.ResultsIn the completed 24‐hour dietary recalls, 99% of the walnut group self‐reported consumption of daily allotted walnuts and only 1% of the control group self‐reported any ingestion of walnuts. The food frequency questionnaire determined average intake of other nuts was 1.90 servings/week (53.9 grams or 1.90 oz.) for the control group and 1.85 servings/week (52.4 grams or 1.85 oz.) for the walnut group, respectively. Self‐reported walnut intake on the food frequency questionnaire demonstrated that 95% of participants in the walnut group ingested at least 1 oz. of walnuts per day, compared to 0.7% in the control group. Together, the two self‐reported measures of compliance had 95% degree of correspondence within and between the two groups. The self‐reported measures coincide with changes observed in plasma α‐linolenic acid from baseline to one year. At baseline, both groups had equivalent means for plasma α‐linolenic acid at 0.31 for the walnut group and 0.29 for the control group (P= 0.167), however by the end of the first year, the walnut group increased by 28%, while the control group simultaneously decreased by 17% (P< 0.001).ConclusionIn this elderly population, there was a high degree of congruence with the two methods of self‐reporting. Change observed in plasma α‐linolenic acid from baseline to one year was consistent with these self‐reported measures. Thus, simple self‐reported measures of dietary intake could suffice in long‐term clinical trials of nut intake.Support or Funding InformationCalifornia Walnut Commission