Wheat bread: what switching to whole grain changes

Whole grain wheat bread has a measurable effect in trials, and it is small. In a randomized double-blind trial of 50 Japanese adults with a BMI of 23 or more, eating whole grain instead of refined wheat bread for 12 weeks reduced visceral fat area by 4 cm2, while the refined bread group showed no significant change. That is one trial and a small absolute change. Whole grain wheat bread also holds its own as a comparator. In 194 adults at risk of diabetes eating at least three slices a day for 16 weeks, oat beta-glucan bread did no better than whole grain wheat bread on HbA1c (difference -0.01 percent, 95% CI -0.03 to 0.06). A US medium slice of whole wheat bread weighs 1.3 oz (36 g) and carries about 2.2 g fiber and 155 mg sodium, recalculated from the 100 g values. UK whole wheat bread averages 217 calories, 9.4 g protein and 7.0 g fiber per 3.5 oz (100 g). We found no meta-analysis of whole wheat bread itself.

The numbers, per 3.5 oz (100 g)

How much is actually in it

• UK whole wheat bread averages 217 calories, 9.4 g protein, 7.0 g fiber and 400 mg sodium per 3.5 oz (100 g). — CoFID 2021 Bread, whole wheat, average (11-981) (n = 1 record) Evidence E source
  Per 100 g: 217 calories, protein 9.4 g, AOAC fiber 7.0 g, sodium 400 mg, iron 2.40 mg, selenium 7 ug, folate 40 ug

What a real portion looks like

• A medium slice of US whole wheat bread weighs 1.3 oz (36 g) and carries about 2.2 g fiber, 155 mg sodium and 9 ug selenium. — USDA FNDDS Bread, whole wheat (51300110, fdc_id 2707709) (n = 7 measures) Evidence E source
  Per 100 g: fiber 6 g, sodium 430 mg, selenium 25.8 ug; medium slice 36 g; thin slice 24 g; thick slice 43 g

What your body absorbs

• About 90% of the lysine in whole wheat bread was metabolically available in 5 young men, but the bread still runs short of lysine. — 5 healthy young males, repeated-measures indicator amino acid oxidation study (n = 5) Evidence B source
  Lysine metabolic availability 90%
• Adding phytic acid to white wheat bread cut magnesium absorption from 32.5% to 13.0% in healthy adults. — Two stable-isotope studies with 8-9 healthy adults each, 200 g wheat bread test meals (n = 8-9 per study) Evidence B source
  Fractional Mg absorption 32.5% to 13.0% with 1.49 mmol phytate; 32.2% to 24.0% with 0.75 mmol
• Drinking a polyphenol-rich herbal tea with iron-fortified wheat bread cut iron absorption by 65-72% in young Senegalese children. — 17 Senegalese mother-child pairs, fortified wheat bread with tea or water (n = 17 pairs) Evidence B source
  Iron absorption down 56% (mothers, FeSO4) and 65-72% (children) with tea; ferrous fumarate RBV 51-64% in children
• Eating 5.3 oz (150 g) of strawberry puree with white wheat bread improved its glycemic profile by 36% in healthy women. — Healthy women (n = 13-20 per study), bread with 50 g available starch plus 150 g berry puree (n = 13-20) Evidence B source
  Strawberries improved glycemic profile 36%; berry mix 38% with wheat bread; lower insulin response

What cooking and storage change

• Bioprocessing the bran before baking made phenolic acids from 11 oz (300 g) of whole wheat bread 2 to 3 times more bioavailable in 8 men. — 8 healthy men, 300 g whole wheat bread with native or bioprocessed bran, crossover (n = 8) Evidence B source
  Ferulic, vanillic, sinapic and 3,4-dimethoxybenzoic acid bioavailability 2- to 3-fold higher
• Bread baked from high-amylose wheat flour lowered post-breakfast glucose by 27-39% versus regular wheat bread in 20 overweight adults. — 20 overweight adults (BMI 30), crossover breakfasts of 85% or 70% high-amylose flour vs conventional bread (n = 20) Evidence B source
  Glucose response 27% and 39% lower; insulin after next lunch 28% lower with 85% bread
• Toasting whole wheat bread drives off water, so per 3.5 oz (100 g) it rises from 217 to 255 calories and from 7.0 to 8.2 g fiber. — CoFID 2021 Bread, whole wheat, toasted (11-982) vs average (11-981) (n = 2 records) Evidence E source
  Water 41.2 to 31.1 g; energy 217 to 255 calories; fiber 7.0 to 8.2 g; thiamin 0.25 mg in both

What it does to your health

• Swapping refined for whole grain wheat bread for 12 weeks trimmed visceral fat area by 4 cm2 in 50 Japanese adults with BMI 23 or more. — 50 Japanese adults with BMI >= 23, whole grain vs refined wheat bread, 12 weeks (n = 50) Evidence B source
  Visceral fat area -4 cm2 (p < 0.05) in whole grain group; no change with refined

Safety, limits and interactions

• In one woman with wheat-dependent exercise-induced anaphylaxis, 2.3 oz (64 g) of bread before exercise triggered hives while 45 g did not. — One 24-year-old woman with wheat and gluten IgE (n = 1) Evidence D source
  Reaction with 64 g bread plus exercise, none with 45 g or bread alone
• A survey of 274 Portuguese breads found widespread low-level ochratoxin A, with wheat bread the main exposure source because people eat most of it. — 274 commercial bread samples, Portugal, winter 2007 (n = 274) Evidence C source
  Low-level contamination in all regions and types; higher in maize and whole-grain breads

What people believe that the data does not support

• In 194 adults at risk of diabetes, 16 weeks of oat beta-glucan bread did no better than whole-grain wheat bread on HbA1c (difference -0.01%). — 194 adults aged 58, BMI 32, HbA1c 5.6%, at least 3 slices a day, 16 weeks, three countries (n = 194) Evidence B source
  HbA1c difference -0.01% (95% CI -0.03 to 0.06); LDL -4.3 mg/dL (95% CI -10 to 1.9; metric: -0.11 mmol/L, -0.27 to 0.05)
• WHO notes that flour fortified with folic acid was linked to 68% fewer neural tube defects in one non-randomized trial of 8037 births. — Women of reproductive age and pregnant women; one non-randomized trial, 8037 births (n = 8037 births) Evidence E source
  Total neural tube defects RR 0.32 (95% CI 0.21 to 0.48), low-certainty evidence

Who this works differently for

• In 20 adults with type 2 diabetes, 100% wheat bread raised 4-hour glucose more than breads with 50% high-amylose barley flour, which cut it by 34%. — 20 adults with type 2 diabetes, four test breads in random order (n = 20) Evidence B source
  4-h glucose iAUC 34% lower with 50% amylose-only barley bread and 11% lower with 75% hulless barley vs 100% wheat
• In people with IBS, sourdough-fermented wheat bread and pasta with under half the usual gluten lowered pain scores over 2 weeks versus normal-gluten versions. — Adults with irritable bowel syndrome, 2-week crossover periods after a gluten-free run-in Evidence B source
  Visual analog scale lower (p = 0.042); IBS severity score, anxiety and quality of life unchanged

The bottom line

Some of what whole wheat bread carries is hard to absorb. When phytic acid was added to white wheat bread, magnesium absorption fell from 32.5 to 13.0 percent in 8 to 9 healthy adults, in a study that added the phytate to white bread. Lysine goes the other way. In 5 young men about 90 percent of the lysine in whole wheat bread was available to the body, yet the bread stays short of lysine because it holds so little. In Senegal, drinking a polyphenol-rich herbal tea with iron-fortified wheat bread cut iron absorption by 56 percent in mothers and 65 to 72 percent in children, across 17 mother and child pairs and one kind of tea. Toasting drives off water, so per 3.5 oz (100 g) UK toasted whole wheat rises from 217 to 255 calories and from 7.0 to 8.2 g fiber, with nothing added. Special flours move blood sugar. High amylose wheat flour bread lowered post-breakfast glucose by 27 and 39 percent against ordinary bread in 20 overweight adults, in a one-meal test with a flour that is not widely sold. In 20 adults with type 2 diabetes, bread made with 50 percent of a high amylose barley flour cut 4-hour glucose by 34 percent against 100 percent wheat bread, and that barley is not on the market. Eating 5.3 oz (150 g) of strawberry puree with white wheat bread improved its glycemic profile by 36 percent in healthy women over 2 hours. Bioprocessing the bran before baking made its phenolic acids 2 to 3 times more bioavailable in 8 men after a single 11 oz (300 g) serving. For people with irritable bowel syndrome, sourdough-fermented wheat bread and pasta with under half the usual gluten lowered pain scores over 2 weeks against normal gluten versions (p = 0.042). Severity, anxiety and quality of life scores did not change. Wheat bread contains gluten, and this page has no card on celiac disease or on how common wheat allergy is. The one allergy card is a single case. In one woman with wheat-dependent exercise-induced anaphylaxis, 2.3 oz (64 g) of bread before exercise brought on hives, while 45 g did not and bread alone never did. A survey of 274 Portuguese breads in 2007 found low level ochratoxin A in all regions and types, especially maize and whole grain breads, with wheat bread still the largest source of exposure. In pregnancy, WHO reports one non-randomized trial of 8037 births in which wheat flour fortified with folic acid was associated with 68 percent fewer neural tube defects (RR 0.32), low certainty evidence about the flour.

Compared with other foods

Sources

1. whb-daily-r3-14 · food composition dataset
   Bread, wholemeal, average (11-981): Energy 217 kcal | Protein 9.4 g | AOAC fibre 7.0 g | Sodium 400 mg | Iron 2.40 mg | Selenium 7 ug | Folate 40 ug
   CoFID 2021 (Public Health England, OGL v3.0), code 11-981 Bread, wholemeal, average · checked 2026-09-29
2. whb-daily-r3-16 · reference dataset
   Bread, whole wheat, FNDDS 51300110, fdc_id 2707709: 1 small or thin slice 24 g | 1 medium or regular slice 36 g | 1 large or thick slice 43 g || Fiber, total dietary 6 g | Sodium 430 mg | Selenium 25.8 ug per 100 g
   USDA FNDDS (FoodData Central survey), Bread, whole wheat, food code 51300110, fdc_id 2707709 · checked 2026-09-29
3. whb-daily-r3-01 · randomized controlled trial
   Five healthy young males (≤30 y, BMI <25 kg/m2) were studied in a repeated-measures design using the indicator amino acid oxidation (IAAO) method ... The MA of lysine from whole wheat bread was 90%. CONCLUSIONS: Lysine has a high MA but it is still limiting in whole wheat bread due to its low concentration.
   J Nutr, 2025 · checked 2026-09-29
4. whb-daily-r3-02 · randomized controlled trial
   The addition of phytic acid lowered fractional apparent magnesium absorption from 32.5 +/- 6.9% (no added phytic acid) to 13.0 +/- 6.9% (1.49 mmol added phytic acid; P < 0.0005) and from 32.2 +/- 12.0% (no added phytic acid) to 24.0 +/- 12.9% (0.75 mmol added phytic acid; P < 0.01).
   Am J Clin Nutr, 2004 · checked 2026-09-29
5. whb-daily-r3-03 · randomized controlled trial
   In mothers, the presence of TK decreased FAFe by 56% (P < 0.05) and 50% (P = 0.077) and in children by 65 and 72% (both, P < 0.0001), in the meals with 58FeSO4 and 57FeFum, respectively.
   Eur J Clin Nutr, 2020 · checked 2026-09-29
6. whb-daily-r3-04 · randomized controlled trial
   Only strawberries (36%) and the berry mixture (with WB, 38%; with RB, 19%) significantly improved the glycemic profile of the breads.
   J Nutr, 2013 · checked 2026-09-29
7. whb-daily-r3-05 · randomized controlled trial
   8 healthy men consumed 300 g of whole wheat bread containing native bran (control bread) or bioprocessed bran (bioprocessed bread) in a cross-over design. ... The bioavailabilities of ferulic acid, vanillic acid, sinapic acid, and 3,4-dimethoxybenzoic acid from the bioprocessed bread were 2- to 3-fold those from the control bread.
   J Nutr, 2011 · checked 2026-09-29
8. whb-daily-r3-06 · randomized controlled trial
   Postprandial plasma glucose responses were 27% and 39% lower after breakfasts with 85%- and 70%-HAF breads than control bread (P = 0.026 and P = 0.003, respectively), with no difference after lunch.
   J Nutr, 2023 · checked 2026-09-29
9. whb-daily-r3-15 · food composition dataset
   Bread, wholemeal, toasted (11-982): Water 31.1 g | Energy 255 kcal | AOAC fibre 8.2 g | Protein 11.2 g | Thiamin 0.25 mg | Sodium 470 mg
   CoFID 2021 (Public Health England, OGL v3.0), code 11-982 Bread, wholemeal, toasted · checked 2026-09-29
10. whb-daily-r3-07 · randomized controlled trial
    A randomized double-blind placebo-controlled intervention study was conducted in 50 Japanese subjects with body mass index (BMI) ≥ 23 kg/m2. ... The WW group showed decrease (-4 cm2) in visceral fat area (VFA) (p < 0.05), whereas the RW group showed no significant changes.
    Plant Foods Hum Nutr, 2018 · checked 2026-09-29
11. whb-daily-r3-11 · case report
    Exercise following ingestion of 64 g, but not 45 g, of bread induced generalized urticaria. ... Ingestion of bread or udon alone failed to elicit any allergic reaction.
    Br J Dermatol, 1998 · checked 2026-09-29
12. whb-daily-r3-12 · contaminant survey
    analysis for ochratoxin A content on 274 samples of commercialized bread in the Portuguese market, during the winter 2007. ... A wide-ranging low level contamination was observed in all regions and types of bread products analyzed, especially in the Porto and Coimbra regions, and in the maize and whole-grain or fiber-enriched bread. Nevertheless, the exposure through contaminated wheat bread continues to be the most significant
    Food Chem Toxicol, 2010 · checked 2026-09-29
13. whb-daily-r3-08 · randomized controlled trial
    A 16-wk randomized, double-blind dietary intervention was conducted in 194 adults ... After 16 wk, there was no significant between-group difference in HbA1c [Δ = -0.01%, 95% confidence interval (CI): -0.03, 0.06; P = 0.49].
    Am J Clin Nutr, 2025 · checked 2026-09-29
14. whb-daily-r3-13 · guideline
    In one non-randomized controlled trial of women of reproductive age and pregnant women, wheat flour fortified with folic acid and other micronutrients was associated with significantly lower occurrence of total neural tube defects, spina bifida, and encephalocele compared to unfortified flour (total neural tube defects: risk ratio [RR] 0.32, 95% CI 0.21 to 0.48; 8037 births; low-certainty evidence) (32).
    WHO, Guideline: Fortification of Wheat Flour with Vitamins and Minerals as a Public Health Strategy, 2022 · checked 2026-09-29
15. whb-daily-r3-09 · randomized controlled trial
    Twenty adults with T2D were randomly allocated to one of four breads at four separate visits. ... Bread made from 50% AmOn lowered the 4 h postprandial glucose by 34%, 27%, 23% (P < 0.05) compared with 100% wheat, 50% or 75% hulless barley, respectively.
    Eur J Clin Nutr, 2024 · checked 2026-09-29
16. whb-daily-r3-10 · randomized controlled trial
    Fungal proteases and selected sourdough lactic acid bacteria were used to produce wheat bread and pasta with a reduced-gluten content (<50% of traditional products). ... Compared to normal-gluten content, the administration of a reduced-gluten content diet resulted in a decrease of the Visual Analogue Scale score (p = 0.042), while no differences were found in the IBS-Severity Score, Hospital Anxiety and Depression Scale, and IBS-Quality of Life.
    Nutrients, 2018 · checked 2026-09-29