How we calculate
The reference comes from Bulgaria's national nutrition norms, issued by the Ministry of Health: for people over 19 the adequate intake of fibre is 25 g a day. The European Food Safety Authority (EFSA) gives the same figure and considers 25 g a day enough for normal bowel function in adults.
The norms also give a range of 8.4–12.6 g of fibre for every 1,000 kcal you eat. At 2,000 kcal a day that's about 17–25 g, and at 2,500 kcal about 21–32 g. The calculator doesn't ask how many calories you eat, so it compares with 25 g.
The fibre in each food comes from the US Department of Agriculture's food composition database (FoodData Central). For beans, lentils, rice and pasta we use the values for the cooked food: they absorb water as they cook, so 100 g of cooked food has less fibre than 100 g of dry.
Portions are a guide. For fruit and vegetables we use the weight of a medium piece from the same database, for example 182 g for a medium apple. For most cooked foods we use a 150 g bowl, for pasta a 200 g plate, and for nuts a 30 g handful. If your portion was bigger or smaller, change the number of portions.
How much fibre a food contains also depends on how it is made and prepared, so the result is approximate and we show it in whole grams.
The levels are our choice, as in the water calculator: under half of the reference, up to 80% of it, up to the reference, and the reference or more. We set no upper limit, because the reference values give none for fibre. In a review of 185 observational studies and 58 clinical trials, the benefit seen in the observational data was greatest at 25–29 g of fibre a day.
The formula in short
- Fibre per portion = portion weight × fibre per 100 g ÷ 100, rounded to 0.1 g.
- For each food we multiply the number of portions by the fibre per portion.
- We add up all the foods and round to the nearest gram.
- Your share of the reference is the total divided by 25.
Example: 3 slices of white bread, 1 small bowl of cooked beans, 1 tomato and 1 apple. 3 × 0.8 + 9.5 + 1.5 + 4.4 = 17.8 g, or about 18 g. That's 72% of the reference, level “Below”. Swap the white bread for rye and you add 1.1 g a slice, or 3.3 g for all three, which takes you to about 21 g.
Easy swaps
One swap adds fibre without changing your whole menu.
- White bread → rye or wholemeal bread: +1.1 g per slice
- White rice → bulgur wheat: +6.3 g per bowl
- Pasta or spaghetti → wholewheat pasta: +4.2 g per plate
- A glass of orange juice → a whole orange: +2.6 g
How much fibre is in foods
Fibre per portion and per 100 g for every food in the calculator, from US Department of Agriculture data.
| Food | Fibre per portion | |
|---|---|---|
| Bread and grains | ||
| White bread1 slice (30 g) | 0.8 g | |
| Wheat bread (Bulgarian tipov)1 slice (30 g) | 1.2 g | |
| Wholemeal bread1 slice (32 g) | 1.9 g | |
| Rye bread1 slice (32 g) | 1.9 g | |
| Porridge oats1 bowl of porridge (40 g dry oats) | 4.0 g | |
| Muesli1 bowl (50 g) | 4.3 g | |
| Oat bran2 tablespoons (12 g) | 1.8 g | |
| White rice, cooked1 small bowl (150 g cooked) | 0.5 g | |
| Brown rice, cooked1 small bowl (150 g cooked) | 2.4 g | |
| Pasta or spaghetti, cooked1 plate (200 g cooked) | 3.6 g | |
| Wholewheat pasta, cooked1 plate (200 g cooked) | 7.8 g | |
| Bulgur wheat, cooked1 small bowl (150 g cooked) | 6.8 g | |
| Popcorn1 large bowl (30 g) | 3.0 g | |
| Pulses | ||
| Beans (white), cooked1 small bowl (150 g cooked) | 9.5 g | |
| Lentils, cooked1 small bowl (150 g cooked) | 11.9 g | |
| Chickpeas, cooked1 small bowl (150 g cooked) | 11.4 g | |
| Hummus2 tablespoons (30 g) | 1.7 g | |
| Green peas, cooked1 small bowl (150 g cooked) | 6.8 g | |
| Green beans, cooked1 small bowl (150 g cooked) | 4.8 g | |
| Vegetables | ||
| Tomato1 medium tomato (123 g) | 1.5 g | |
| Cucumber½ long cucumber (150 g) | 0.8 g | |
| Green pepper1 medium pepper (119 g) | 2.0 g | |
| Red pepper1 medium pepper (119 g) | 2.5 g | |
| Onion1 medium onion (110 g) | 1.9 g | |
| Carrot1 medium carrot (61 g) | 1.7 g | |
| Cabbage, raw1 side salad (150 g) | 3.8 g | |
| Sauerkraut1 small bowl (150 g) | 4.4 g | |
| Broccoli, cooked1 small bowl (150 g cooked) | 5.0 g | |
| Spinach, cooked1 small bowl (150 g cooked) | 3.6 g | |
| Courgette1 medium courgette (196 g) | 2.0 g | |
| Aubergine, cooked1 small bowl (100 g cooked) | 2.5 g | |
| Sweetcorn, cooked1 corn cob (103 g kernels) | 2.5 g | |
| Potatoes, boiled1 medium potato (167 g) | 3.0 g | |
| Chips (fries)1 portion (150 g) | 5.7 g | |
| Lettuce1 bowl of salad (70 g) | 0.9 g | |
| Fruit | ||
| Apple1 medium apple (182 g) | 4.4 g | |
| Pear1 medium pear (178 g) | 5.5 g | |
| Banana1 medium banana (118 g) | 3.1 g | |
| Orange1 orange (131 g) | 3.1 g | |
| Orange juice, fresh1 glass (about 250 ml) | 0.5 g | |
| Tangerine1 medium tangerine (88 g) | 1.6 g | |
| Kiwi1 kiwi (69 g) | 2.1 g | |
| Grapes1 small bowl (150 g) | 1.4 g | |
| Peach1 medium peach (150 g) | 2.3 g | |
| Plums1 small bowl (150 g) | 2.1 g | |
| Apricots3 apricots (105 g) | 2.1 g | |
| Cherries1 small bowl (150 g) | 3.2 g | |
| Strawberries1 small bowl (150 g) | 3.0 g | |
| Raspberries1 small bowl (125 g) | 8.1 g | |
| Watermelon1 slice (286 g) | 1.1 g | |
| Avocado½ avocado (100 g) | 6.7 g | |
| Prunes5 prunes (48 g) | 3.4 g | |
| Dried figs3 dried figs (25 g) | 2.5 g | |
| Nuts and seeds | ||
| Walnuts1 handful (30 g) | 2.0 g | |
| Almonds1 handful (30 g) | 3.8 g | |
| Hazelnuts1 handful (30 g) | 2.9 g | |
| Peanuts, roasted1 handful (30 g) | 2.5 g | |
| Sunflower seeds1 handful, shelled (30 g) | 2.7 g | |
| Pumpkin seeds1 handful, shelled (30 g) | 2.0 g | |
| Chia seeds1 tablespoon (10.5 g) | 3.6 g | |
| Flaxseed (linseed)1 tablespoon (10 g) | 2.8 g | |
| Tahini1 tablespoon (15 g) | 1.4 g | |
What does fibre do in the gut?
Fibre is carbohydrate that the small intestine can't absorb. It travels on to the large intestine, where gut microbes feed on it. There some of the fibre is fermented: the microbes break it down into short-chain fatty acids, mainly acetate, propionate and butyrate, and into gases such as hydrogen and carbon dioxide.
Butyrate is the main fuel for the cells lining the colon. Microbes make it together: some break down fibre such as inulin into acetate and lactate, and others, such as Roseburia and Faecalibacterium, turn these into butyrate.
Not all fibre ferments in the same way. Insoluble fibre such as cellulose barely ferments, but it speeds up the passage of food through the gut. Beta-glucans from oats and barley and pectin from apples dissolve in water and ferment easily, and so does inulin, found in onions, leeks, garlic, bananas and wheat. That is why a varied plant-based diet gives your microbes many different kinds of fibre.
What happens to fibre also depends on the microbes of the person eating it. In a review of 64 studies with 2,099 healthy adults, fibre, especially fructans and galacto-oligosaccharides, increased bifidobacteria and lactobacilli in the gut and slightly raised butyrate in stool, but it didn't change microbial diversity. In a small Stanford University study of 18 people on a high-fibre diet, the immune system responded in three different ways depending on how diverse their microbes were at the start.
This page shows how much fibre you eat; the gut microbiome test shows what your microbes do with it. Its “Short Chain Fatty Acid (SCFA) Production Potential” section shows your microbes' potential to make butyrate, acetate, propionate and 6 more of these acids from fibre, on a 3-zone scale compared with reference groups of healthy people from different parts of the world. “Carbohydrate Metabolism Potential” shows how many of your microbes break down carbohydrates and turn fibre into these acids. And “Gut Function” shows their potential linked to gut motility and to absorbing iron, zinc and calcium from plant foods.
“Foundation Microbiota” shows the share of 36 core species, including Faecalibacterium prausnitzii and three Roseburia species that produce butyrate, on a 7-zone scale. The Shannon index shows how diverse your microbes are, and “Health Indicators” shows whether microbes linked to inflammation dominate in your gut. The report's 12-week food plan runs in 3 phases: about 250 foods in 11 groups, including rye, oats, oat bran, lentils, chickpeas and psyllium husk, each labelled with how often to eat it in each phase. This is information about your microbes, not a diagnosis.
When to ask a doctor
- if your bowel habits have changed suddenly and the change doesn't go away;
- if you see blood in your stool or your stool is black;
- if you are losing weight without trying;
- if you often have tummy pain or feel bloated;
- if you have irritable bowel syndrome: fibre is then often reduced, and if it is increased, soluble fibre such as oats is preferred;
- if you have Crohn's disease or ulcerative colitis: in Crohn's disease the gut sometimes narrows and food passes through with more difficulty, so decide how much fibre to eat with your doctor.
This calculator gives a guide, not medical advice. It is meant for healthy adults and does not replace a conversation with your doctor or a dietitian.
Sources (17)
- [1]Bulgarian Ministry of Health. Ordinance No. 1 of 22 January 2018 on the physiological nutrition norms for the population (State Gazette No. 11/2018), Art. 6(8), Art. 11, Art. 12(3) and § 1(7): dietary fibre.
- [2]EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA), 2010. Scientific Opinion on Dietary Reference Values for carbohydrates and dietary fibre. EFSA Journal 8(3):1462.
- [3]U.S. Department of Agriculture, Agricultural Research Service. FoodData Central, 2019 (SR Legacy). Public domain (CC0 1.0).
- [4]Reynolds A, Mann J, Cummings J et al., 2019. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. The Lancet.
- [5]Holscher HD, 2017. Dietary fiber and prebiotics and the gastrointestinal microbiota. Gut Microbes.
- [6]So D, Whelan K, Rossi M et al., 2018. Dietary fiber intervention on gut microbiota composition in healthy adults: a systematic review and meta-analysis. American Journal of Clinical Nutrition.
- [7]Wastyk HC, Fragiadakis GK, Perelman D et al., 2021. Gut-microbiota-targeted diets modulate human immune status. Cell.
- [8]van der Schoot A, Drysdale C, Whelan K, Dimidi E, 2022. The Effect of Fiber Supplementation on Chronic Constipation in Adults: An Updated Systematic Review and Meta-Analysis of Randomized Controlled Trials. American Journal of Clinical Nutrition.
- [9]Dimidi E, van der Schoot A, Barrett K et al., 2025. British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults. Journal of Human Nutrition and Dietetics.
- [10]Bharucha AE, Pemberton JH, Locke GR 3rd, 2013. American Gastroenterological Association technical review on constipation. Gastroenterology.
- [11]NHS. How to get more fibre into your diet (reviewed 2 March 2026).
- [12]NHS. Constipation (reviewed 26 October 2023).
- [13]NHS. Symptoms of bowel cancer (reviewed 4 September 2026).
- [14]NHS. Irritable bowel syndrome (IBS): diet, lifestyle and medicines (reviewed 17 March 2025).
- [15]NHS. Crohn's disease (reviewed 14 April 2025).
- [16]NICE. Irritable bowel syndrome in adults: diagnosis and management. Clinical guideline CG61 (2008, updated 2017), recommendation 1.2.1.5.
- [17]Regulation (EC) No 1924/2006 on nutrition and health claims made on foods, Annex: “Source of fibre” and “High fibre” (consolidated text of 13 December 2014).
