From March 2019 to the end of February 2021, 267 participants in total were randomized (Fig. 1). Due to the COVID-19 pandemic, the study was temporarily interrupted due to safety concerns about continued in-person intervention delivery. Study leadership withdrew 20 recently randomized participants who had not yet reached 3 months of follow-up (that is, the time point at which data required for the primary endpoint were collected). We prespecified that these participants would be excluded from all subsequent analyses. The overall cohort, including for assessment of the primary endpoint, consisted of 247 participants. For subsequent prespecified COVID-19 analyses, the prepandemic subgroup consisted of 109 participants.

Due to the COVID-19 pandemic, recruitment and all in-person study visits were stopped on 13 March 2020. Under safety precautions, recruitment and study visits were resumed in June 2020.

In the overall cohort, 91% of participants provided 3-month dietary intake data. In Strategies 1 and 2, 96% of participants attended one or more intervention visits, with 80% attending all six scheduled intervention visits. To understand the disruption due to the pandemic, study conduct is also reported separately for the prepandemic and pandemic cohorts (Supplementary Tables 8 and 9). In the prepandemic cohort (n = 109), intervention visit completion was 97.8% (264 of 270 total visits) in Strategy 1 and 98.4% (248 of 252 total visits) in Strategy 2. In the pandemic cohort (n = 138), intervention visit completion dropped to 84.5% (279 of 330 total visits) in Strategy 1 and to 81.1% (287 of 354) in Strategy 2. Prepandemic, dietary data and biometrics collection at 3 months was 100.0% (109 of 109) and 100.0% (109 of 109), respectively. In the pandemic cohort, dietary data and biometrics collection at 3 months dropped to 84.1% (116 of 138) and 79.0% (109 of 138), respectively.

At baseline in the overall cohort, median age was 58 years, 69% of which were female and 21% self-identified as black or African American. In addition, 64.8% were married or living with a partner, 53.4% were employed full-time and 63.6% had at least a bachelor’s degree. Mean systolic blood pressure (SBP) was 129.3 (standard deviation (s.d.), 16.7) and hypertensive medication use was 72.9%. Obesity was present in 63.6%. Median non-high-density lipoprotein cholesterol (non-HDL-C) was 111 (min, 36; max, 216) and hypercholesterolemia medication use was 41.7%. Baseline characteristics were balanced across the groups (Table 1).

The baseline mean DASH score was 45.4 (10.4), indicating that participants had on average approximately 50% adherence to the DASH dietary pattern goals. From baseline to 3 months, there were mean increases in DASH score of 5.8 (95% CI (2.5, 9.2), P = 0.0006), 8.6 (95% CI (6.4, 10.8), P < 0.0001) and 12.4 (95% CI (10.3, 14.6), P < 0.0001) for control, Strategy 1 and Strategy 2 groups, respectively (Table 2). From baseline to 3 months, the combined Strategies 1 and 2 showed a DASH score increased by 10.5 (95% CI (9.0, 12.1), P < 0.0001). The combined Strategies 1 and 2 resulted in a significant increase in DASH score by 4.7 (95% CI (0.9, 8.5), P = 0.02) compared with control (enhanced medical nutrition therapy) (Table 3). At 6 months (3 months post intervention), there were persistent increases in DASH score of 4.4 (95% CI (0.6, 8.1), P = 0.02), 6.6 (95% CI (4.0, 9.2), P < 0.0001) and 8.4 (95% CI (5.9, 11.0), P < 0.0001) for control, Strategy 1,and Strategy 2 groups, respectively (Table 2). At 6 months, the combined Strategies 1 and 2 had a persistently increased DASH score of 7.5 (95% CI (5.7, 9.3), P < 0.0001). However, the combined Strategies 1 and 2 no longer demonstrated a difference in DASH score (3.1, 95% CI (−1.0, 7.3), P = 0.14) compared with the enhanced control group (Table 3).

Individualized nutrition education, enhanced with online shopping technologies and training (Strategy 2), significantly increased DASH score by 3.8 (95% CI (0.8, 6.9), P = 0.01) compared with education without online enhancement (Strategy 1), from baseline to 3 months (Table 3). This increase was at least partially due to an increase in daily mean servings of fruits in Strategy 2 versus 1 (P < 0.05) (Table 4). From baseline to 6 months, Strategy 2 resulted in no difference in DASH score (1.8, 95% CI (− 1.9, 5.5), P = 0.34) compared with Strategy 1 (Table 3).

From baseline to 3 months, SBP, diastolic blood pressure (DBP) and body mass index (BMI) did not decrease in the control group (Supplementary Table 14). From baseline to 3 months, SBP decreased in Strategy 1 and Strategy 2 groups by −6.6 (−9.8, −3.4) and −5.7 (−8.7, −2.8) mmHg, respectively. DBP decreased in Strategy 1 and Strategy 2 groups by −2.4 (−4.2, −0.6) and −2.0 (−3.9, −0.1) mmHg, respectively. BMI decreased in Strategy 1 and Strategy 2 groups by −0.4 (−0.7, −0.2) and −0.8 (−1.0, −0.5) kg m–2, respectively. In between-group comparisons, however, no differences were found.

From baseline to 6 months, SBP decreased in control, Strategy 1 and Strategy 2 groups by −5.4 (−10.7, −0.1), −5.2 (−8.8, −1.6) and −4.2 (−7.8, −0.5) mmHg, respectively (Supplementary Table 15). DBP decreased in control and Strategy 1 groups by −3.7 (−7.1, −0.3) and −4.4 (−6.7, −2.2) mmHg, respectively, but did not decrease in the Strategy 2 group. BMI decreased in Strategy 1 and Strategy 2 groups by −0.6 (−0.9, −0.3) and −0.7 (−1.1, −0.4) kg m–2, respectively. In between-group comparisons, however, no differences were found.

From baseline to either 3 months (Supplementary Table 16) or 6 months (Supplementary Table 17), non-HDL-C, total cholesterol and triglycerides (TG) were not reduced by the combined Strategies 1 and 2 versus the enhanced control.

In the prepandemic cohort, from baseline to 3 months, the combined Strategies 1 and 2 increased the DASH score by 8.3 (95% CI (3.4, 13.3), P = 0.001) compared with the enhanced control (Supplementary Table 18). From baseline to 6 months, the combined Strategies 1 and 2 did not result in a significant difference in DASH score: 5.1 (95% CI (−0.8, 11.1), P = 0.09) compared with control (Supplementary Table 19).

Strategy 2 resulted in no significant difference in DASH score, at 3.1 (95% CI (−1.3, 7.6), P = 0.017), from baseline to 3 months compared with Strategy 1 (Supplementary Table 18). From baseline to 6 months, the increase in DASH score was nonsignificant at 1.2 (95% CI (−4.2, 6.6), P = 0.67) when comparing Strategy 2 with Strategy 1 (Supplementary Table 19).

From baseline to 3 months, there were no reductions in SBP, DBP, BMI, non-HDL-C, total cholesterol or TG comparing the combined Strategies 1 and 2 versus the enhanced control (Supplementary Table 18).

A prespecified exploratory subgroup analysis evaluating absolute mean DASH score difference for selected subgroups within Strategies 1 and 2 versus control was performed. Greater improvements in DASH diet adherence were associated with older age (51–75 versus 21–50 years), white race (white versus nonwhite) and baseline hypertension (with versus without) (Supplementary Table 20; interaction terms, P ≤ 0.01). There was no difference by gender (men versus women).