Table 1

Characteristics of RCTs investigating the effect of tree nuts on criteria of the MetS

Study (year) (reference)	Participants	Mean age (SD or range), years	Mean body weight or BMI (SD or range)*	Setting	Design	Feeding control	Nut type	Nuts dose (g/day)†	Comparator	Diet‡	Energy balance	Follow-up	MQS§	Funding sources¶
Sabate et al (1993)30
Walnut	18 (18 M)	30	73	OP, USA	Cross-over	Met	Walnut	84		55:31:14	Isocaloric	4 weeks	6	Agency
Control	18 (18 M)	30	73	OP, USA	Cross-over	Met			NCEP step 1 diet	56:30:14	Isocaloric	4 weeks	6	Agency
Chisholm et al (1998)13
Walnut	16 HLP	45 (6.8)	28.4 (4.3)	OP, New Zealand	Cross-over	DA	Walnut	78		40:38:17	Isocaloric	4 weeks	4	Agency
Control	16 HLP	45 (6.8)	28.4 (4.3)	OP, New Zealand	Cross-over	DA			Low-fat diet	46:30:19	Isocaloric	4 weeks	4	Agency
Spiller et al (1998)31
Almond	30 HLP	53 (10)	66 (13)	OP, Italy	Parallel	Supp	Almond	100		45:39:16	Isocaloric	4 weeks	6	Agency
Control	30 HLP	53 (10)	66 (13)	OP, Italy	Parallel	Supp			Matched macronutrient diet	47:36:17	Isocaloric	4 weeks	6	Agency
Curb et al (2000)10
Macadamia	30 (15 M, 15 W)	35.25 (18–53)	23 (19.1–28.3)	OP, USA	Cross-over	Met	Macadamia	46		48:35:17	Isocaloric	4 weeks	4	Agency–industry
Control									AHA	54:30:16
Control									AAD	48:35:17
Morgan and Clayshulte (2000)32
Pecan	19 (4 M, 15 W)	37 (12)	24 (5)	OP, USA	Parallel	Supp	Pecan	68		45:43:12	Isocaloric	8 weeks	6	Agency
Control	19 (4 M, 15 W)	45 (10)	24 (4)	OP, USA	Parallel	Supp			Self-selected diet	46:36:18	Isocaloric	8 weeks	6	Agency
Zambon et al (2000)33
Walnut	49 HC (26 M, 23 W)	56 (11)	70.6 (12.1)	OP, Spain	Cross-over	Supp	Walnut	48.5		48:34:18	Isocaloric	6 weeks	6	Agency
Control	49 HC (26 M, 23 W)	56 (11)	70.6 (12.1)	OP, Spain					Mediterranean diet	50:31:19	Isocaloric	6 weeks	6	Agency
Rajaram et al (2001)14
Pecan	23 (14 M, 9 W)	25–55	74.4 (16.7)	OP, USA	Cross-over	Met	Pecan	72		47:40:13	Isocaloric	4 weeks	8	Agency
Control	23 (14 M, 9 W)	25–55	74.4 (16.7)	OP, USA	Cross-over	Met			NCEP step 1 diet	57:28:15	Isocaloric	4 weeks	8	Agency
Iwamoto et al (2002)34
Walnut	40 (20 M, 20 W)	23.8 (3.1)**	22.2 (0.5)	OP, Japan	Cross-over	Met	Walnut	52††		60:26:14	Isocaloric	4 weeks	8	Agency
Control	40 (20 M, 20 W)	23.6 (4.6)**	20.7 (0.5)	OP, Japan	Cross-over	Met			Average Japanese diet	62:24:14	Isocaloric	4 weeks	8	Agency
Jenkins et al (2002)15
Almond	27 HLP (15 M, 12 W)	64 (9)	71.2 (2.5)	OP, Canada	Cross-over	Supp	Almond	73		47:36:17	Isocaloric	4 weeks	6	Agency
Control	27 HLP (15 M, 12 W)	64 (9)	71.0 (2.4)	OP, Canada	Cross-over	Supp		73	NCEP step 2 diet + muffin	57:26:18	Isocaloric	4 weeks	6	Agency
Lovejoy et al (2002)35
High-fat almond	30 DM2 (13 M, 17 W)	53.8 (10.4)	33.0 (5.5)	OP, USA	Cross-over	Met	Almond	85††		48:37:15	Isocaloric	4 weeks	5	Agency
Low-fat almond							Almond	85††		60:25:15
High-fat control									High-fat diet	48:37:15
Low-fat control									Low-fat diet	60:25:15
Sabate et al (2003)36
High almond	25 NL-HC (14 M, 11 W)	41 (13)	NA	OP, USA	Cross-over	Met	Almond	83		46:39:14	Isocaloric	4 weeks	5	Agency–industry
Low almond							Almond	42		35:51:14
Control									NCEP step 1 diet	56:30:14
Wien et al (2003)8
Almond	65 OW/DM2 (28 M, 37 W)	53 (2)	113 (5)	OP, USA	Parallel	Supp	Almond	84		53:18:29	Isocaloric	24 weeks	8	Agency
Control	65 OW/DM2 (28 M, 37 W)	57 (2)	114 (5)	OP, USA	Parallel	Supp			CHO-LCD	32:39:29	Isocaloric	24 weeks	8	Agency
Tapsell et al (2004)37
Walnut	37 DM2	57.7 (9)	87.6 (12.8)	OP, Australia	Parallel	Supp	Walnut	30		44:32:22	Isocaloric	6 months	6	Agency
Control	37 DM2	59.3 (7.1)	81.9 (11.2)	OP, Australia	Parallel	Supp			Modified fat	41:33:23	Isocaloric	6 months	6	Agency
Tamizifar et al (2005)38
Almond	30 HC (17 M, 13 W)	56 (6.1)	63 (8.9)	OP, Iran	Cross-over	Supp	Almond	25		47:37:17	Isocaloric	4 weeks	5	NA
Control	30 HC (17 M, 13 W)	56 (6.1)	63 (8.9)	OP, Iran	Cross-over	Supp			NCEP step 1 diet	45:29:15	Isocaloric	4 weeks	5	NA
Kocyigit et al (2006)16
Pistachio	44 (24 M, 20 W)	32.8 (6.7)	24.2 (6.1)	OP, Turkey	Parallel	DA	Pistachio	69		NA	Isocaloric	3 weeks	8	Agency
Control	44 (24 M, 20 W)	32.8 (6.7)	24.6 (5.6)	OP, Turkey	Parallel	DA			Regular diet		Isocaloric	3 weeks	8	Agency
Kurlandsky and Stoke (2006)39
Almond	47 (47 W)	41.8 (11.7)	25.3 (3.5)	OP, USA	Parallel	Supp	Almond	60		51:34:15	Isocaloric	6 weeks	5	Agency–industry
Almond + dark chocolate		46.2 (7.8)	27.2 (4.2)				Almond	60		46:39:15
Dark chocolate		36.5 (11.9)	23.9 (3.3)						NCEP ATP III diet + chocolate	55:30:15
Control		51.3 (6.3)	26.1 (4.1)						NCEP ATP III diet	57:27:16
Schutte et al (2006)60‡‡
Walnut	62 MetS	45.5	35.9	OP, South Africa	Parallel	Met	Walnut	85.5		47:36:17	Isocaloric	8 weeks	7	Agency–industry
Cashew		45.7	34.7				Cashew	85.5		47:36:17
Control		44.4	35.5						Control diet	50:33:18
Mukuddem-Petersen et al (2007)40
Walnut	64 MetS	45 (10)	107	OP, South Africa	Parallel	Met	Walnut	85.5††		49:35:16	Isocaloric	8 weeks	7	Agency–industry
Cashew			99				Cashew	85.5††		44:37:19
Control			106						Habitual diet	47:33:20
Sheridan et al (2007)17
Pistachio	15 HC	60 (11.2)	175 (26)	OP, USA	Cross-over	Supp	Pistachio	35		52:31:17	Isocaloric	4 weeks	6	Agency
Control	15 HC	60 (11.2)	175 (26)	OP, USA	Cross-over	Supp			Regular diet	53:31:16	Isocaloric	4 weeks	6	Agency
Gebauer et al (2008)41
1 Pistachio	28 HLP (10 M, 18 W)	48 (7.9)	76.6 (13.2)	OP, USA	Cross-over	Met	Pistachio	37		53:34:16	Isocaloric	4 weeks	5	Agency
2 Pistachio							Pistachio	74		57:29:16
Control									NCEP step 1 diet	62:25:15
Griel et al (2008)42
Macadamia	25 HC	50.2 (8.4)	26.3 (3.3)	OP, USA	Cross-over	Met	Macadamia	42.5§§		50:33:19	Isocaloric	5 weeks	8	Agency–industry
Control	25 HC	50.2 (8.4)	26.3 (3.3)	OP, USA	Cross-over	Met		42.5§§	AAD	52:33:17	Isocaloric	5 weeks	8	Agency–industry
Jenkins et al (2008)61‡‡
Almond	27 HLP (15 M, 12 W)	64 (9)	71.2 (2.5)	OP, Canada	Cross-over	Supp	Almond	73		47:36:17	Isocaloric	4 weeks	6	Agency
Control	27 HLP (15 M, 12 W)	64 (9)	71.0 (2.4)	OP, Canada	Cross-over	Supp		73	NCEP step 2 diet + muffin	57:26:18	Isocaloric	4 weeks	6	Agency
Rajaram et al (2009)43
Walnut	25 NL-HLP (14 M, 11 W)	23–65	71.9 (15.5)	OP, USA	Cross-over	Met	Walnut	42.5		60:31:15	Isocaloric	4 weeks	5	Agency
Control	25 NL-HLP (14 M, 11 W)	23–65	71.7 (15.5)	OP, USA	Cross-over	Met			AAD	57:30:14	Isocaloric	4 weeks	5	Agency
Tapsell et al (2009)44
Walnut	35 DM2¶¶	54 (8.7)	92.3 (15.7)	OP, Australia	Parallel	Supp	Walnut	30		42:29:24	Isocaloric	12 months	7	Agency
Control	35 DM2¶¶	54 (8.7)	93.4 (3)	OP, Australia	Parallel	Supp			Low-fat diet	41:34:20	Isocaloric	12 months	7	Agency
Li et al (2010)11
Almond	52 OW¶¶	45.4 (2.0)	86 (26.8)	OP, USA	Parallel	Supp	Pistachio	53		55:30:15	Hypocaloric	12 weeks	7	Agency
Control	52 OW¶¶	47.3 (2.3)	85.5 (40.2)	OP, USA	Parallel	Supp			Pretzel	65:20:15	Hypocaloric	12 weeks	7	Agency
Ma et al (2010)45
Walnut	22 DM2¶¶	58.1 (9.2)	89 (15.5)	OP, USA	Cross-over	Supp	Walnut	56		39:44:17	Isocaloric	8 weeks	5	NA
Control	22 DM2¶¶	58.1 (9.2)	89 (15.5)	OP, USA	Cross-over	Supp			Ad libitum diet	43:38:19	Isocaloric	8 weeks	5	NA
Torabian et al (2010)12
Walnut	87 (38 M, 49 W)	54 (10.2)	75.6 (13.2)	OP, USA	Cross-over	Supp	Walnut	46		NA	Isocaloric	6 months	6	Agency
Control	87 (38 M, 49 W)	54 (10.2)	75.6 (13.2)	OP, USA	Cross-over	Supp			Habitual diet		Isocaloric	6 months	6	Agency
Wien et al (2010)46
Almond	65 PD (17 M, 48 W)	53 (9)	82.9 (14.4)	OP, USA	Parallel	Supp	Almond	58		42:39:19	Isocaloric	16 weeks	9	Agency
Control	65 PD (17 M, 48 W)	54 (11)	80.5 (14.4)	OP, USA	Parallel	Supp			AAD	48:30:21	Isocaloric	16 weeks	9	Agency
Wu et al (2010)47
Walnut	189 MetS	48.2 (8.4)	72.2 (11.4)	OP, USA	Parallel	Supp	Walnut	30		48:37:15	Isocaloric	12 weeks	9	Agency
Control	189 MetS	48.6 (8)	70.6 (10.9)	OP, USA	Parallel	Supp			AHA	51:34:15	Isocaloric	12 weeks	9	Agency
Casas-Agustench et al (2011)48	50 MetS (28 M, 22 W)			OP, Spain	Parallel	Supp
Mixed nuts		52.9 (8.4)	31.6 (2.8)				Mixed nuts	30		41:36:19	Isocaloric	12 weeks	6	Agency
Control		50.6 (8.4)	30.0 (3.3)						Prudent diet	42:36:19	Isocaloric	12 weeks	6	Agency
Cohen and Johnston (2011)19
Almond	13 DM2 (7 M, 6 W)	66 (11.9)	96.1 (40.4)	OP, USA	Parallel	Supp	Almond	28		NA	Isocaloric	12 weeks	7	Agency
Control	13 DM2 (7 M, 6 W)	66 (11.9)	105.1 (32.1)	OP, USA	Parallel	Supp			Cheese sticks	NA	Isocaloric	12 weeks	7	Agency
Jenkins et al (2011)20
Mixed nuts	79 DM2 (52 M, 27 W)	63 (9)	80 (15)	OP, Canada	Parallel	Supp	Mixed nuts	75††		41:41:18	Isocaloric	12 weeks	8	Agency
Control	79 DM2 (52 M, 27 W)	61 (10)	83 (15)	OP, Canada	Parallel	Supp		75††	NCEP step 2 diet + muffin	46:35:19	Isocaloric	12 weeks	8	Agency
Li et al (2011)21
Almond	20 DM2 (9 M, 11 W)	58 (8.9)	26 (3.1)	OP, Taiwan	Cross-over	Met	Almond	56		47:37:17	Isocaloric	4 weeks	5	Agency
Control	20 DM2 (9 M, 11 W)	58 (8.9)	26 (3.1)	OP, Taiwan	Cross-over	Met			NCEP step 2 diet	57:27:17	Isocaloric	4 weeks	5	Agency
Tey et al (2011)49
Hazelnut	61	38.9 (14.3)	72 (11.1)	OP, New Zealand	Parallel	Supp	Hazelnut	42		45:39:16***	Isocaloric	12 weeks	9	Agency
Control	61	36.1 (15.2)	67.3 (9.5)	OP, New Zealand	Parallel	Supp			Regular diet	50:33:17	Isocaloric	12 weeks	9	Agency
Damavandi (2012)18
Cashew	43 DM2 (9 M, 34 W)	51 (7.9)	72.1 (13.1)	OP, Iran	Parallel	Supp	Cashew	30		53:32:16	Isocaloric	8 weeks	3	NA
Control	43 DM2 (9 M, 34 W)	56 (5.7)	71.9 (9.7)	OP, Iran	Parallel	Supp			Regular diet	57:27:16	Isocaloric	8 weeks		NA
Foster et al (2012)50
Almond	123 OW (11 M, 112 W)	47 (12)	94 (13.1)	OP, USA	Parallel	Supp	Almond	56		NA	Hypocaloric	18 months	9	Agency
Control	123 OW (11 M, 112 W)	46.7 (13)	91.5 (11.9)	OP, USA	Parallel	Supp			Nut-free diet		Hypocaloric	18 months	9	Agency
Katz et al (2012)51
Walnut	40 OW¶¶	57.4 (11.9)	33.2 (4.4)	OP, USA	Cross-over	Supp	Walnut	56		41:41:17	Isocaloric	8 weeks	7	Industry
Control	40 OW¶¶	57.4 (11.9)	33.2 (4.4)	OP, USA	Cross-over	Supp			Ad libitum diet	45:34:20	Isocaloric	8 weeks	7	Industry
Wang et al (2012)22
Pistachios	86 MetS	51.9 (8.8)	28.1 (3.2)	OP, China		Supp	Pistachio	42		NA	Isocaloric	12 weeks	5	Industry
High pistachios		51.8 (9.4)	28 (4.5)				Pistachio	70
Control		50.7 (9.9)	28 (4.4)						AHA step 1 diet
West et al (2012)62‡‡
1 Pistachio	28 HLP (10 M, 18 W)	48 (7.9)	76.6 (13.2)	OP, USA	Cross-over	Met	Pistachio	37		53:34:16	Isocaloric	4 weeks	5	Agency
2 Pistachio							Pistachio	74		57:29:16
Control									NCEP step 1 diet	62:25:15
Anderson et al (2013)52
Pistachio	22 OW	55 (2)	90 (3.6)	OP, USA	Parallel	NA	Pistachio	35.4		NA	NA	6 weeks	5	NA
Control	22 OW	55 (2)	90 (3.6)	OP, USA	Parallel	NA			NA	NA	NA	6 weeks	5	NA
Berryman et al (2013)53
Almond	53 HC	NA	NA	OP, USA	Cross-over	NA	Almond	42.5		51:33:16	Isocaloric	6 weeks	NA	NA
Control				OP, USA	Cross-over				Muffin	59:26:15	Isocaloric	6 weeks	NA	NA
Damavandi et al (2013)54
Hazelnut	48 DM2¶¶	55.7 (7.7)	72.1 (10.3)	OP, Iran	Parallel	Supp	Hazelnut	29		55:31:16	Isocaloric	8 weeks	6	None
Control	48 DM2¶¶	55.7 (7.7)	72 (9.6)	OP, Iran	Parallel	Supp			Self-selected diet	60:25:17	Isocaloric	8 weeks
Holligan et al (2013)63‡‡
1 Pistachio	28 HLP (10 M, 18 W)	48 (7.9)	76.6 (13.2)	OP, USA	Cross-over	Met	Pistachio	37		53:34:16	Isocaloric	4 weeks	NA	Agency
2 Pistachio							Pistachio	74		57:29:16
Control									NCEP step 1 diet	62:25:15
Sauder et al (2013)55
Pistachio	30 DM2 (15 M, 15 W)¶¶	56.1 (1.4)	31.2 (1.1)	OP, USA	Cross-over	Met	Pistachio	73.4		51:33:17	Isocaloric	4 weeks	NA	Industry
Control	30 DM2 (15 M, 15 W)¶¶	56.1 (1.4)	31.2 (1.1)	OP, USA	Cross-over	Met			Low-fat diet	55:27:18	Isocaloric	4 weeks	NA	Industry
Somerset et al (2013)9
Macadamia	64 OW (10 M, 54 W)	43.7 (8.4)	95 (14.7)	OP, Australia	Parallel	DA	Macadamia	46		36:38:21	Isocaloric	10 weeks	9	Agency
Control	64 OW (10 M, 54 W)	43.2 (10.9)	99.6 (15.2)	OP, Australia	Parallel				Regular diet	41:38:17	Isocaloric	10 weeks	9	Agency
Tan and Mattes (2013)56
Almond (breakfast)	137 OW (48 M, 89 W)	32.9 (11.5)	80.5 (15)	OP, USA	Parallel	Supp	Almond	43		50:16:15	Isocaloric	4 weeks	5	Industry
Almond (morning snack)		27.8 (10.7)	83.2 (21.1)				Almond	43		51:15:14
Almond (lunch)		29.3 (13.5)	84.8 (13.7)				Almond	43		48:16:17
Almond (afternoon snack)		29 (11.9)	81.8 (14.6)				Almond	43		49:15:16
Control		28.7 (9.6)	77.2 (16.8)						Regular diet	48:15:16
Tey et al (2013)57
Hazelnut 30 g	107 OW (46 M, 61W)	43.8 (13.5)	86.2 (11.8)	OP, New Zealand	Parallel	Supp	Hazelnut	30		42:39:17	Isocaloric	12 weeks	6	Agency
Hazelnut 60 g		42.8 (10.6)	92 (19.6)				Hazelnut	60		38:42:16
Control		41.1 (13.1)	88.7 (16.7)						Usual diet	47:33:17
Gulati et al (2014)58
Pistachio	68 MetS (37 M, 31 W)	41.6 (8.4)	81.6 (12.9)	OP, India	Parallel	DA	Pistachio	50§§		51:29:20	Isocaloric	24 weeks	4	Industry
Control	68 MetS (37 M, 31 W)	43.3 (8.1)	80.3 (10.3)	OP, India	Parallel	DA			Standard diabetic diet	60:25:15	Isocaloric	24 weeks	4	Industry
Wu et al (2014)59
Walnut	40 (10 M, 30 W)	60 (1)	24.9 (0.6)	OP, Germany	Cross-over	Supp	Walnut	43		50:35:15	Isocaloric	8 weeks	7	Industry
Control	40 (10 M, 30 W)	60 (1)	24.9 (0.6)	OP, Germany	Cross-over	Supp			Western-type diet	50:35:15	Isocaloric	8 weeks	7	Industry

*Body weight is reported in kg and BMI is reported in kg/m². BMI is reported only when no data on weight were available.
†Nut dose is given based on g/day, 1 oz=28 g.
‡Energy from carbohydrate:fat:protein.
§Trials with scores ≥8 were considered to be of high quality.
¶Agency funding is that from government, university or not-for-profit health agency sources.
**Mean age was given separately for men and women.
††Medians were calculated from the ranges reported: Iwamoto et al34 range 50–54 g/day; Jenkins et al20 range 50–75 g/day; Lovejoy et al35 range 57–113 g/day; Mukuddem-Petersen et al40 range 63–108 g/day; Torabian et al12 range 28–64 g/day; Zambon et al33 range 41–56 g/day.
‡‡Companion reports: Jenkins et al61 for Jenkins et al15; Schutte et al60 for Mukuddem-Petersen et al40; West et al62 and Holligan et al63 for Gebauer et al41.
¶¶Baseline characteristics were based on the number of randomised participants for Li et al11 n=70; Ma et al45 n=24; Zambon et al33 n=55; Katz et al51 n=46; Sauder et al55 n=30; Gulati et al58 n=68 for recruited participants for Tapsell et al44 (n=50), and for age for Damavandi et al54 (n=50).
§§Based on 2100 kcal for Griel et al42 and based on 1400 kcal (∼60 kg) for Gulati et al58.
***Values for carbohydrates are reported as geometric means.
AAD, Average American Diet; AHA, American Heart Association; BMI, body mass index; CHO-LCD, self-selected complex carbohydrate diet; DA, dietary advice; DM2, type 2 diabetes mellitus; HC, hypercholesterolaemic; HLP, hyperlipidaemic; M, men; Met, metabolic; MetS, metabolic syndrome; MQS, Heyland Methodological Quality Score; NA, not available; NCEP, National Cholesterol Education Program; NL-HC, normal to hypercholesterolaemic; NL-HLP, normal to mildly hyperlipidaemic; PD, prediabetes; OP, out-patient; OW, overweight; RCT, randomised controlled trial; SUPP, supplement; W, women.