Table 2 The type and dose of whole grain intake and the relative risk of breast cancer in the included studies

Farvid et al., 2016 [15]

whole grain foods

Q1: 5.6; Q2: 14; Q3: 19.6; Q4: 28; Q5: 42

Q1: 1; Q2: 0.93 (0.83–1.03); Q3: 0.87 (0.77–0.97); Q4: 0.91 (0.81–1.02); Q5: 0.91 (0.81–1.03)

Mourouti et al., 2016 [16]

whole grain foods (including whole grain bread, whole grain cereals, oatmeal, whole wheat pasta, brown or wild rice)

No reported

Never/rarely: 1; 1–6 times/week: 0.68 (0.41, 1.09); > 7 times/week:0.49 (0.29, 0.82)

Tajaddini et al., 2015 [18]

whole-wheat bread (Sangak, Taftoon, Barbari, barley, corn flakes and sprouts)

< 1.0; 1.0–23.0; > 23.0

< 1.0 g/d: 1; 1.0–23.0 g/d: 1.39(0.68–2.83); > 23.0 g/d: 0.61(0.37–0.99)

Yun et al., 2010 [17]

mixed brown rice

0; 100; 350

0 g/d:1.0; 100 g/d: 0.90(0.47,1.71); 350 g/d: 0.42(0.20,0.87)

Per 100 g/d: 0.76(0.61,0.95)

Egeberg et al., 2009 [23]

whole grain products (rye bread, whole grain bread and oatmeal)

≤72; 72 to ≤112; 112 to ≤163; > 163

≤72 g/d: 1; 72 to ≤112 g/d: 0.98 (0.82–1.17);

112 to ≤163 g/d: 1.00 (0.85–1.19); > 163 g/d: 1.03 (0.85–1.24)

Per each additional 50 g/day: 1.01(0.96–1.07)

Sonestedt et al.,2008 [19]

high-fibre bread (≥ 6% of fibre for soft bread, ≥10% for crisp bread and ≥ 10% for biscuits and rusks)

Q1: 0; Q2:9; Q3:19; Q4: 34; Q5: 65

Q1: 1; Q2: 0.87 (0.67–1.13); Q3: 0.74 (0.56–0.97); Q4: 0.82 (0.63–1.07); Q5: 0.75 (0.57–0.98)

Adzersen et al., 2003 [20]

the whole-grain category all whole-grain bread and rice, rolled oats, muesli, and cornflakes.

Q1: < 18.3; Q2:18.3 ≤ 32.6; Q3: 32.6 ≤ 45.5;Q4:> 45.5

Q1: 1; Q2: 0.96 (0.61,1.52); Q3:0.76 (0.47–1.24); Q4:0.57 (0.34–0.95)

Nicodemus et al., 2001 [22]

whole grains

Q1:0–3.5; Q2: 4–7; Q3: 7.5–10.5; Q4:11–18.5; Q5:19–108.5 (servings/week)

Q1: 1; Q2: 0.95 (0.76–1.2); Q3: 1.04 (0.84–1.3); Q4: 1.19 (0.96–1.5); Q5: 1.21 (0.96–1.5)

Chatenoud et al., 1998 [21]

whole grain food (essentially bread or pasta)

No reported

Low (no or rare consumption): 1; Intermediate (1–3 days/week): 0.9(0.8–1.0);High (> 3 days/week): 0.9(0.8–1.0)

Levi et al., 1993 [25]

whole-grain bread and pasta

No reported

Low: 1; Intermediate: 0.77(0.41–1.44); High: 0.63(0.35–1.15)

LaVecchia et al., 1987 [24]

whole-grain bread or pasta

No reported

Never: 1; Occasionally: 0.75(0.57–0.96); Frequently: 0.90(0.69–1.17)