Impact of providing walnut samples in a lifestyle intervention for weight loss: a secondary analysis of the HealthTrack trial

Figures & data

Figure 1. Participant flow in the HealthTrack randomized controlled trial *n = 1 was randomized to I but provided with walnuts, therefore was treated as IW for this analysis.

Table 1. Baseline characteristics of participants in the HealthTrack study.

	Control group	Intervention group	Intervention + walnut group
n	126	124	127^
Age (years)*	43.80 ± 7.46	43.79 ± 7.97	42.10 ± 8.69
Gender (% female)	73%	73%	75%
Body weight (kg)*	91.84 ± 14.69	91.86 ± 15.22	91.38 ± 15.51
BMI (kg/m^2)*	32.49 ± 4.12	32.59 ± 4.25	32.63 ± 4.28
kJ intake†	9400 (7840–11 574)	8666 (7176–11 004)	8810 (7445–10 783)
Fish and seafood products and dishes (kJ) †	122 (5–287)	166 (17–328)	128 (0–271)
Fruit products and dishes (kJ) †	364 (164–602)	315 (160–584)	286 (135–490)
Vegetable products and dishes (kJ) †	520 (353–848)	519 (348–762)	540 (387–831)
Discretionary foods and beverages (kJ) †	2543 (1814–3931)	2465 (1493–4020)	2685 (1799–3898)
MET-mins/week†‡	876 (396–1523)	921 (392–1552)	1040 (568–2328)
DASS-21†	13 (6–19)	11 (7–19)	11 (7–18)
SF-12 Physical component score†§	49 (43–54)	50 (45–54)	51 (45–55)
SF-12 Mental component score†	49 (41–53)	48 (38–55)	48 (39–54)

^n = 1 participant randomized to I was provided with walnuts, they were treated as IW for this per-protocol analysis

*Values are mean ± standard deviation

†Values are median (interquartile range)

‡Baseline sample size: control (n = 124), intervention (n = 122), intervention + walnut (n = 125)

§ Baseline sample size: control (n = 126), intervention (n = 123), intervention + walnut (n = 126)

Table 2. Median (IQR) total nut and walnut intake per day (grams) as reported in diet history interviews.

		Control		Intervention		Intervention + walnuts
Variable	n	Value	n	Value	n	value	p-value (between groups)†
Total nut intake, median (IQR), grams/day
Baseline	126	7.1 (0.0–20.6)	124	6.1 (0.0–15.0)	127	4.9 (0.0–17.9)^x	0.662
Three months	93	6.8 (0.0–20.6)^a	96	2.7 (0.0–8.9)^a	104	30.0 (25.7–31.3)^b, y	0.000
12 months	60	8.6 (2.2–17.9)^a	43	7.1 (0.0–15.0)^a	72	23.4 (8.6–30.0)^b, z	0.000
p-value (time)‡		0.385		0.191		0.000
Walnut intake, median (IQR), grams/day
Baseline	126	0.0 (0.0–0.0)	124	0.0 (0.0–0.0)	127	0.0 (0.0–0.0)^x	0.389
Three months	93	0.0 (0.0–0.0)^a	96	0.0 (0.0–0.0)^a	104	30.0 (22.0–30.0)^b, y	0.000
12 months	60	0.0 (0.0–0.0)^a	43	0.0 (0.0–0.0)^a	72	17.1 (4.3–30.0)^b, z	0.000
p-value (time)‡		0.209		0.761		0.000

Superscripts indicate significant differences between groups (a, b) and within groups (x, y, z) after Bonferonni adjustment

† Kruskal-Wallis test

‡ Friedman test

Table 3. Median (interquartile range) change over three months between study groups.

Variable	Control group (n = 93)	Intervention group (n = 96)	Intervention + walnut group (n = 74)*	P-value
Body weight (kg)	−1.60 (−2.50 – −0.10)^a	−2.00 (−4.00 – −0.35)^a, b	−2.45 (−5.23 – −0.48)^b	0.011
Energy (kJ)	−1752 (−3469 – −45)	−2047 (−3769 – −640)	−1591 (−2637 – −641)	0.295
Fish and seafood products and dishes (kJ)	3 (−87 – 166)	2 (−70 – 177)	87 (−27 – 232)	0.162
Fruit products and dishes (kJ)	52 (−93 – 238)^a	125 (−180 – 382)^a, b	196 (−29 – 355)^b	0.042
Vegetable products and dishes (kJ)	19 (−310 – 275)	24 (−159 – 268)	56 (−231 – 383)	0.544
Discretionary foods and beverages (kJ)	−758 (−1982 – −159)^a	−1155 (−2654 – −346)^a, b	−1457 (−2441 – −606)^b	0.020
MET-mins/week†	489 (−196.5 – 1457)	401 (−150 – 1257)	1095 (198 – 1846)	0.083
DASS-21‡	−1 (−5–2)	−1 (−6 – 2)	−1 (−6 – 1)	0.667
SF12 Physical component summary§	1 (−2 – 5)	0 (−3 – 3)	2 (−2 – 6)	0.639
SF12 Mental component summary§	2 (−1 – 7)	1 (−4 – 7)	2 (−2 – 8)	0.094

Superscripts indicate significant differences between groups (a, b) after Bonferroni adjustment

*Analysis restricted to Intervention + walnut participants who consumed at least 80% of the provided walnuts

† Available sample size: control (n = 90), intervention (n = 91), intervention + walnut (n = 71)

‡ Available sample size: control (n = 92), intervention (n = 93), intervention + walnut (n = 74)

§ Available sample size: control (n = 91), intervention (n = 94), intervention + walnut (n = 72)

Table 4. Median (interquartile range) change over 12 months between study groups.

Variable	Control group (n = 60)	Intervention group (n = 43)	Intervention + walnut group (n = 23)*	P-value
Body weight (kg)	−1.10 (−4.18 – 0.50)^a	−2.40 (−7.70 – 0.90)^a, b	−4.60 (−10.70 – −1.20)^b	0.026
Energy (kJ)	−1508 (−3115 – 137)	−1710 (−3279 – −210)	−561 (−1988 – 651)	0.111
Fish and seafood products and dishes (kJ)	0 (−158 – 83)	0 (−92 – 96)	0 (−156 – 433)	0.759
Fruit products and dishes (kJ)	12 (−223 – 126)	22 (−327 – 209)	71 (−101 – 304)	0.526
Vegetable products and dishes (kJ)	−10 (−257 – 251)	−19 (−250 – 203)	−38 (−526 – 330)	1.000
Discretionary foods and beverages (kJ)	−647 (−2392 – 212)	−943 (−2025 – −56)	−608 (−1358 – 270)	0.624
MET-mins/week†	840 (−80 – 2247)	548 (−68 – 1643)	948 (−238 – 3095)	0.696
DASS-21‡	−2 (−5 – 1)	−1 (−6 – 4)	−1 (−6 – 2)	0.869
SF12 Physical component summary§	3 (−1 – 8)	2 (−1 – 5)	2 (−2 – 9)	0.526
SF12 Mental component summary§	3 (−3 – 7)	2 (−3 – 6)	1 (−1 – 7)	0.862

Superscripts indicate significant differences between groups (a, b) after Bonferroni adjustment

*Analysis restricted to Intervention + walnut participants who consumed at least 80% of the provided walnuts

† Available sample size: control (n = 55), intervention (n = 38), intervention + walnut (n = 22)

‡ Available sample size: control (n = 46), intervention (n = 33), intervention + walnut (n = 20)

§ Available sample size: control (n = 59), intervention (n = 41), intervention + walnut (n = 23)