Table 1

Characteristics of studies included

Author, year (ref.)CountrynEstimated sample sizeDefinition of GDMDuration of dietary interventionGestational age in weeks at enrollment (mean ± SD)Baseline BMI, kg/m2 (mean ± SD)Mean maternal age, years (mean ± SD)Dietary interventionDiet composition (mean ± SD)*
Low-GI diet
Grant, 2011 (26)Canada4750 to detect a 0.6 mmol/L difference in capillary glucose; n not achievedCanadian Diabetes Association (40)28 weeks until deliveryControl: 29 ± 2.35 Intervention: 29 ± 3.21Control: 26 ± 4.69 Intervention: 27 ± 4.58 (prepregnancy)Control: 34 ± 0.46 Intervention: 34 ± 5.16Low GI: Women were provided with a list of starch choices specific to either intervention (low GI) or controlControl: GI 58.0 ± 0.5 Intervention: GI 49.0 ± 0.8
Louie, 2011 (29)Australia99120 to detect a 260-g difference in birth weight (stopped early because of smaller than expected SD)Australasian Diabetes in Pregnancy Society criteria (41)Randomization until deliveryControl: 29.7 ± 3.5 Intervention: 29 ± 4.0Control: 24.1 ± 5.7 Intervention: 23.9 ± 4.4 (prepregnancy)Control: 32.4 ± 4.5 Intervention: 34 ± 4.1Low GI: Target GI ≤50 but otherwise similar composition to the control dietControl: energy 1,934 ± 465; carbohydrate 40.3 ± 8.3; protein 22.2 ± 7.5; fat 35.1 ± 16.9; GI 53.0 ± 6.5 Intervention: energy 1,836 ± 403; carbohydrate 38.7 ± 8.3; protein 23.4 ± 5.8; fat 34.9 ± 11.0; GI 47.0 ± 6.5
Ma, 2015 (30)China95Not reportedChinese Medical Association and American Diabetes Association (42)24–26 weeks until deliveryControl: 27.9 ± 1.1 Intervention: 27.5 ± 1.1Control: 21.15 ± 2.75 Intervention: 21.90 ± 3.14 (prepregnancy)Control: 30.0 ± 3.5 Intervention: 30.1 ± 3.8Low GI: Women provided with an exchange list for starch choices specific to either intervention (low GI) or controlControl: energy 2,030 ± 215; carbohydrate 49.8 ± 6.8; protein 18.8 ± 2.5; fat 31.8 ± 3.8; GI 53.8 ± 2.5 Intervention: energy 2,006 ± 215; carbohydrate 48.56 ± 7.0; protein 18.9 ± 2.9; fat 32.1 ± 4.1; GI 50.1 ± 2.2
Moses, 2009 (13)Australia63Not reportedAustralasian Diabetes in Pregnancy Society (41)28–32 weeks until deliveryControl: 29.9 ± 1.11 Intervention: 30.3 ± 1.11Control: 32.8 ± 7.92 Intervention: 32.0 ± 6.68 (at enrollment)Control: 31.3 ± 4.52 Intervention: 30.8 ± 3.90Low GI: Women asked to avoid specific high-GI foods and were provided with a booklet outlining carbohydrate choicesControl: energy 1,656 ± 433; carbohydrate 36.2 ± 8.2; protein 24.0 ± 4.4; fat 34.3 ± 9.9; GI 52.2 ± 6.0 Intervention: energy 1,713 ± 368; carbohydrate 36.7 ± 6.1; protein 23.9 ± 3.9; fat 33.4 ± 6.12; GI 48.0 ± 5.0
DASH diet
Asemi, 2013 (22)Iran3432 for “key variable serum HDL”50-g glucose challenge >140 mg/dL → 100 g OGTT; GDM if two or more of fasting >95 mg/dL, 1-h 180 mg/dL, 2-h 155 mg/dL, or 3-h 140 mg/dL4 weeksNot reportedControl: 31.4 ± 5.7 Intervention: 29.0 ± 3.2 (at enrollment)Control: 29.4 ± 6.2 Intervention: 30.7 ± 6.7DASH diet: diet rich in fruit, vegetables, whole grains, and low-fat dairy; low in saturated fats, cholesterol, refined grains, and sweetsControl: energy 2,392 ± 161; carbohydrate 54.0 ± 6.9; protein 17.6 ± 2.8; fat 29.3 ± 5.6 Intervention: energy 2,400 ± 25; carbohydrate 66.8 ± 2.2; protein 16.8 ± 1.2; fat 17.6 ± 0.9
Asemi, 2014 (23)Iran5242 to detect a 75-g difference in birth weightAs above4 weeksControl: 25.9 ± 1.4 Intervention: 25.8 ± 1.4Control: 31 ± 4.9 Intervention: 29.2 ± 3.5 (at enrollment)Control: 30.7 ± 6.3 Intervention: 31.9 ± 6.1DASH diet: as aboveControl: energy 2,352 ± 163; carbohydrate 54.2 ± 7.1; protein 18.2 ± 3.4; fat 28.5 ± 5.6 Intervention: energy 2,407 ± 30; carbohydrate 66.4 ± 2.04; protein 17.0 ± 1.3; fat 17.4 ± 1.0
Yao, 2015 (36)China3342 to detect a 75-g difference in birth weight; not achieved50-g glucose challenge → 100 g OGTT results with two or more of fasting >95 mg/dL, 1-h ≥180 mg/dL, 2-h ≥155 mg/dL, or 3-h ≥140 mg/dL4 weeksControl: 25.7 ± 1.3 Intervention: 26.9 ± 1.4Control: 30.9 ± 3.6 Intervention: 30.2 ± 4.1 (at enrollment)Control: 28.3 ± 5.1 Intervention: 30.7 ± 5.6DASH diet: same as aboveControl: energy 2,386 ± 174; carbohydrate 52.3 ± 7.2; protein 18.0 ± 3.3; fat 28.3 ± 5.1 Intervention: energy 2,408 ± 54; carbohydrate 66.7 ± 2.3; protein 16.9 ± 1.2; fat 17.17 ± 1.16
Low-carbohydrate diets
Cypryk, 2007 (25)Poland30Not reportedWorld Health Organization criteria2 weeks29.2 ± 5.4Not reported28.7 ± 3.7Low (intervention) vs. high (control) carbohydrate (45% vs. 60% of total energy, respectively)Control: carbohydrate 60; protein 25; fat 15 Intervention: carbohydrate 45; protein 25; fat 30
Hernandez, 2016 (12)U.S.12Pilot study to estimate SDCarpenter and Coustan criteria (43)30–31 weeks until deliveryControl§: 31.7 ± 2.45 Intervention: 31.2 ± 0.98Control: 34.3 ± 3.92 Intervention: 33.4 ± 3.43 (at enrollment)Control: 30 ± 2.45 Intervention: 28 ± 4.90Low carbohydrate (intervention) vs. higher-complex carbohydrate/ lower fat (control)Control: carbohydrate 60; protein 15; fat 25 Intervention: carbohydrate 40; protein 15; fat 45
Moreno-Castilla, 2013 (31)Spain152152 to detect a 22% difference in need for insulin2006 National Diabetes and Pregnancy Clinical Guidelines (44,45)≤35 weeks until deliveryControl: 30.1 ± 3.5 Intervention: 30.4 ± 3.0Control: 26.6 ± 5.5 Intervention: 25.4 ± 5.7 (prepregnancy)Control: 32.1 ± 4.4 Intervention: 30.4 ± 3.0Low carbohydrate (intervention) vs. control (40% vs. 55% of total diet energy as carbohydrate)Control: energy 1,800 minimum; carbohydrate 55; protein 20; fat 25 Intervention: energy 1,800 minimum; carbohydrate 40; protein 20; fat 40
Soy protein–enrichment diets
Jamilian, 2015 (27)Iran6856 (minimum clinical difference not reported)One-step 75 g OGTT, American Diabetes Association (46)6 weeksNot reportedControl: 28.4 ± 3.4 Intervention: 28.9 ± 5.0Control: 29.3 ± 4.2 Intervention: 28.2 ± 4.6Soy protein diet had the same amount of protein as control diet but the protein portion was made up of 35% animal protein, 35% soy protein, 30% other plant proteinsControl: energy 2,426 ± 191; carbohydrate 54.6 ± 7.1; protein 14.4 ± 1.7; fat 32.1 ± 5.4 Intervention: energy 2,308 ± 194; carbohydrate 54.6 ± 7.3; protein 15.0 ± 2.6; fat 30.3 ± 4.7
Sarathi, 2016 (14)India62Not reportedInternational Association of Diabetes and Pregnancy Study Groups criteria (47)From diagnosis until deliveryControl: 25.56 ± 1.69 Intervention: 25.19 ± 1.92Not reportedControl: 29.17 ± 3.38 Intervention: 29.43 ± 2.98Soy protein diet: 25% of cereal part of high-fiber complex carbohydrates replaced with soyControl: energy 1,600–2,000; minimum carbohydrate 175 g Intervention: energy 1,600–2,000; minimum carbohydrate 175 g
Fat-modification diets
Lauszus, 2001 (28)Denmark2720 to detect a difference in cholesterol of 0.65 mmol/L3-h 75 g OGTT with blood samples taken every 30 minutes, GDM if 2 or more glucoses >3 SD above the mean34 weeks until deliveryNot reportedControl: 32.2 ± 5.61 Intervention: 35.3 ± 8.65 (at enrollment)Control: 29 ± 3.74 Intervention: 31 ± 3.61High monounsaturated fatty acids: source was hybrid sunflower oil with high-content oleic acid and snacks of almonds and hazelnutsControl: energy 1,727; carbohydrate 50.0 ± 3.6; protein 19.0 ± 3.6; fat 30.0 ± 7.2 Intervention: energy 1,982; carbohydrate 46 ± 3.5; protein 16 ± 3.5; fat 37 ± 3.5
Wang, 2015 (35)China84Not reportedInternational Association of Diabetes and Pregnancy Study Groups criteria (47)∼27 weeks until deliveryControl: 27.3 ± 1.96 Intervention: 27.4 ± 1.52Control: 22.2 ± 3.6 Intervention: 21.4 ± 3.0 (prepregnancy)Control: 29.7 ± 4.64 Intervention: 30.3 ± 4.17Polyunsaturated fatty acid meals (50–54% carbohydrate, 31–35% fat with 45–40 g sunflower oil)Control: energy 1,978 ± 107; carbohydrate 55.4 ± 2.0; protein 17.9 ± 1.0; fat 26.7 ± 1.3 Intervention: energy 1,960 ± 90; carbohydrate 47.7 ± 0.7; protein 18.0 ± 0.7; fat 34.3 ± 0.2
Other diets
Bo, 2014 (24)Italy99 in diet study (total n = 200)200 to detect a 10% difference in fasting glucose (based on exercise portion of trial)75 g OGTT24–26 weeks until deliveryNot reportedControl: 26.8 ± 4.1 Intervention: 26.9 ± 4.6Control: 33.9 ± 5.3 Intervention: 35.1 ± 4.4Behavioral dietary recommendations: individual recommendations for helping dietary choicesControl: energy 2,116 ± 383; carbohydrate 46.9 ± 5.9; protein 15.6 ± 2.6; fat 37.4 ± 4.2 Intervention: energy 2,156 ± 286; carbohydrate 47.8 ± 4.9; protein 15.5 ± 2.4; fat 36.7 ± 3.9
Rae, 2000 (32)Australia124120 to detect a decrease in insulin use from 40% to 15% and a decrease in macrosomia from 25% to 5%OGTT fasting glucose >5.4 mmol/L and/or 2-h glucose >7.9 mmol/L (48)<36 weeks until deliveryControl: 28.3 ± 4.6 Intervention: 28.1 ± 5.8Control: 38.0 ± 0.7 Intervention: 37.9 ± 0.7 (at diagnosis)Control: 30.6 Intervention: 30.2 (SD not reported)Moderate energy restriction (1,590–1,776 kcal/day) vs. control (2,010–2,220 kcal/day)Control: energy 1,630 ± 339; carbohydrate 41.0 ± 4.6; protein 24.0 ± 2.3; fat 34.0 ± 5.3 Intervention: energy 1,566 ± 289; carbohydrate 42.0 ± 5.7; protein 25.0 ± 2.4; fat 31.0 ± 5.7
Reece, 1995 (33)U.S.50Post hoc calculationNot reported24–29 weeks until deliveryNot reportedNot reportedNot reportedFiber-enriched diet: fiber taken as fiber-rich foods (40 g/day) and a high-fiber drink (40 g/day)Control: carbohydrate 50; fat 30; fiber 20 g/day Intervention: carbohydrate 60; fat 20 with 80 g fiber/day
Valentini, 2012 (34)Italy20Not reported (pilot study)Fourth International Workshop Conference on Gestational Diabetes Mellitus (49)From diagnosis (screening at 24–28 weeks) until deliveryControl 27.1 ± 5.9 Intervention: 21.3 ± 6.8Control: 24.1 ± 4.7 Intervention: 25.7 ± 3.6 (prepregnancy)Control: 30.2 ± 4.7 Intervention: 28.9 ± 3.3Ethnic meal plan: foods commonly consumed per participant’s ethnicity with the same kcal and nutrient composition as the control dietControl: carbohydrate 53; protein 18; fat 28; fiber 26 g/day Intervention: carbohydrate 55; protein 17; fat 28; fiber 21 g/day
  • Unless otherwise stated, the units are kcal/day for energy, % for carbohydrate, protein, and fat. OGTT, oral glucose tolerance test.

  • *Reported actual dietary intake. When not reported, prescribed dietary intake is reported.

  • †Intervention is defined as dietary intervention different from the usual dietary intervention used in the control group.

  • ‡Indicates prescribed diet.

  • §The control and intervention groups were reversed for the purpose of meta-analysis so it could be included in the low-carbohydrate group.