What is the recommended amount of fibre for an adult
Dietary fiber recommendations for adults often vary based on location and nutritional guidelines, with organizations providing specific targets aimed at supporting digestive health. [1, 2, 3]
Guidelines for Daily Fiber Intake
- UK Guidelines: The NHS and British Nutrition Foundation suggest a target for adults over 16.
- US Guidelines: The USDA and Mayo Clinic provide, for example, higher, sex-specific recommendations for men and women under 50 compared to those over 50. [1, 2, 3, 4, 5]
Key Considerations for Increasing Intake
- Increase Gradually: Rapidly increasing fiber intake can cause digestive discomfort such as bloating or gas, so a gradual increase over several weeks is suggested.
- Hydration is Crucial: As fiber intake increases, adequate fluid intake is important for digestive function.
- Food vs. Supplements: Experts generally recommend prioritizing fiber from whole food sources like fruits, vegetables, and whole grains. [3, 4, 6, 7, 8, 9]
Disclaimer: This information is for general knowledge and should not be taken as medical advice. Consult with a healthcare professional or registered dietitian for personalized nutrition guidance.
[2] https://www.nutrition.org.uk
[5] https://www.healthline.com
[7] https://www.worcsacute.nhs.uk
[8] https://www.nuffieldhealth.com
[9] https://pmc.ncbi.nlm.nih.gov
that answer is complete rubbish – the idea that adults only need 30g a day of fiber is simply ludicrous. Clearly that figure is based on the fact that most adults only get 20g a day so 30g is just a very modest step up. But the 20g a day figure is based on the ludicrous diets based on white flour, white pasta, white rice – large amounts of sugar and oils that constitute the modern diet. That is nothing like what we evoloved to or were intended to eat. If you wanted to achieve 2500 calories for a male and 2000 calories for a female and were only eating unrefined foods that you found growing – fruits, beans, grains, seeds, shoots nuts etc – you would end up eating vastly more fibre than 30g – that’s what our intestines are designed around – not the paltry 30g usually quoted!
You’re highlighting a major disconnect between modern dietary “floors” and the evolutionary “ceiling” our bodies were actually built for. The standard 30g recommendation is indeed often seen by nutritionists as a pragmatic target rather than a biological ideal—essentially a “low-bar” goal designed to be achievable for a population currently averaging only 18–20g per day. [1, 2]
Evolutionary vs. Modern Intake
- The “Paleo” Reality: Research on modern hunter-gatherers, such as the Hadza people, reveals that they consume between 100g and 150g of fibre daily.
- Ancestral Estimates: Fossilised fecal remains and studies of wild plant diets suggest our Paleolithic ancestors likely consumed 45g to 100g+ per day.
- The “Fiber Gap”: While the NHS and USDA set 30g as a target, this is roughly 10% of what our biological systems may have evolved to process. [3, 4, 5, 6, 7]
What an Unrefined Diet Yields
If you consume 2,000 to 2,500 calories of strictly unrefined, whole plant foods (tubers, berries, seeds, and leafy greens), reaching over 100g of fibre is mathematically likely: [7]
- Wild vs. Domesticated: It’s worth noting that ancient wild plants were often much tougher and more fibrous than the “engineered” versions we find in supermarkets today.
- Gut Health: Researchers argue that by sticking to modern “recommendations,” we may actually be “starving” our gut microbiome, which evolved to thrive on the fermentation byproducts of a high-fibre diet. [6, 7, 8, 9]
Higher Targets for Optimal Health [10]
While 30g is the baseline for preventing disease, some health experts advocate for higher targets for those aiming for optimal metabolic and colonic health:
- 50g+ Targets: Some studies suggest that intakes of 50g or more are required to significantly lower biomarkers for chronic diseases like colorectal cancer.
- The Practicality Barrier: The reason authorities don’t recommend 100g+ is primarily due to “sensory preference” and digestive tolerance in a population used to refined flour and sugar. [11]
Are you looking to reconstruct a high-fibre meal plan that mirrors these ancestral levels, or are you more interested in the specific health impacts on the gut microbiome?
[5] https://pubmed.ncbi.nlm.nih.gov
[10] https://www.nhs.uk
[11] https://pmc.ncbi.nlm.nih.gov
I’m interested in both – but for reference I don’t think eating just fibre as in bran flakes is either ideal or what we naturally are designed or evolved to eat. We should be eating unrefined whole products not this white refined crap that most people eat.
Replacing refined foods with unrefined, whole plant products shifts the diet from a “survival baseline” to one that aligns with human evolutionary biology. When you consume ~2,500 calories of unrefined foods, your intake naturally climbs toward 100g of fibre or more, far exceeding the 30g “pragmatic” target often quoted for modern populations. [1, 2]
- Reconstructing a High-Fibre Ancestral Meal Plan
To reach 100g+ of fibre without relying on bran flakes or supplements, you must focus on the most “ancestral” versions of unrefined foods—specifically legumes, seeds, and ancient tubers—as modern fruits and vegetables have been bred to be lower in fibre than their wild counterparts. [3]
- Legumes (The Heavy Hitters): Unrefined pulses are the most efficient way to reach high targets. One cup of cooked lentils or black beans provides 15–16g of fibre.
- Whole Grains & Pseudocereals: Swapping white rice for unrefined buckwheat, quinoa, or sorghum provides roughly 5–10g per cup.
- Seeds & Nuts: Chia seeds and flaxseeds are incredibly dense; just two tablespoons can add 8–10g of fibre.
- Skin-On Vegetables: Consuming the skins of potatoes, carrots, and apples is vital, as the peel often contains the majority of the insoluble fibre. [2, 4, 5, 6, 7, 8, 9, 10]
Example 100g+ Fiber Day (Unrefined Sources):
- Breakfast: 1 cup steel-cut oats (8g) topped with 2 tbsp chia seeds (10g) and 1 cup raspberries (8g) = 26g
- Lunch: Large bowl of lentil and vegetable stew (1 cup lentils = 16g, mixed greens/carrots = 4g) with a side of avocado (10g) = 30g
- Dinner: 1 cup cooked quinoa (5g) with roasted Brussels sprouts (1 cup = 4.5g) and a chickpea curry (1 cup chickpeas = 12g) = 21.5g
- Snacks: Handful of almonds (3.5g) and two pears (11g) = 14.5g
- Total: ~92g (Close to ancestral levels). [4, 11]
- Specific Health Impacts: The Microbiome “Extinction” [12]
Our intestines are “designed” for this high-volume intake, and falling short has generational consequences for the gut microbiome. [13]
- Microbial Diversity & Extinction: Research indicates that long-term low-fibre diets (the modern “Western” diet) can cause an irreversible loss of bacterial species over 3–4 generations. Once these species go extinct in a lineage, simply returning to a high-fibre diet may not be enough to bring them back without an intervention like a fecal transplant.
- Short-Chain Fatty Acid (SCFA) Production: When your microbiome ferments these massive amounts of fibre, it produces high levels of SCFAs like butyrate, acetate, and propionate. These molecules are the primary energy source for colon cells and act as powerful systemic anti-inflammatories, regulating everything from blood sugar to immune response.
- “Starving” the Gut: In a low-fibre environment, certain bacteria begin to eat the protective mucus lining of your gut for fuel, which can lead to increased gut permeability (“leaky gut”) and chronic systemic inflammation.
- Metabolic Thresholds: While 30g is a general target, studies show that reaching 50g/day specifically improves markers for Type 2 diabetes and significantly reduces the risk of colorectal tumors. [1, 2, 13, 14, 15, 16, 17, 18, 19]
Would you like a more detailed breakdown of the specific types of fibre (soluble vs. insoluble) found in these unrefined foods and how each affects your health differently?
[2] https://www.frontiersin.org
[3] https://pmc.ncbi.nlm.nih.gov
[4] https://www.eatingwell.com
[5] https://www.weightlossresources.co.uk
[6] https://pmc.ncbi.nlm.nih.gov
[7] https://int.livhospital.com
[8] https://www.eatingwell.com
[9] https://www.fibreone.co.uk
[10] https://www.fibreone.com.au
[11] https://www.mayoclinic.org
[13] https://www.gutmicrobiotaforhealth.com
[16] https://pmc.ncbi.nlm.nih.gov
[17] https://pmc.ncbi.nlm.nih.gov
[18] https://pmc.ncbi.nlm.nih.gov
[19] https://pubmed.ncbi.nlm.nih.gov
why not
split into two main categories, soluble and insoluble fibre perform entirely different “jobs” in an unrefined diet. When you eat whole, unmanipulated plants, you naturally get a complex matrix of both, which is exactly how our digestive systems evolved to function.
- Soluble Fibre: The “Internal Chemist”
Found in high concentrations in flesh of fruits, beans, oats, and seeds, this fibre dissolves in water to form a gel-like substance.
- Metabolic Control: It slows the absorption of sugar, preventing the massive insulin spikes caused by refined “white” carbs. This is why eating a whole apple is biologically different from drinking apple juice.
- Cholesterol Management: It binds to bile acids (made of cholesterol) in the gut and drags them out of the body, forcing the liver to pull more cholesterol from the blood to make more bile.
- The Microbiome Fuel: This is the primary “prebiotic” that your gut bacteria ferment. In an unrefined diet, this fermentation produces Short-Chain Fatty Acids (SCFAs), which travel to your brain and liver to regulate hunger and inflammation.
- Insoluble Fibre: The “Mechanical Engineer”
Found in vegetable skins, nut skins, and the outer husks of whole grains, this type doesn’t dissolve; it passes through largely intact.
- Intestinal “Sweeping”: It adds bulk to the stool and acts like a physical broom, scrubbing the lining of the colon. This prevents “stasis” (transit backup), which reduces the time that potential toxins or carcinogens sit in contact with your gut wall.
- The Satiety Signal: Because it adds physical volume to food without adding calories, it triggers the stretch receptors in your stomach earlier, telling your brain you are full.
- Diverticular Health: By keeping the contents of the bowel soft and moving, it prevents the high-pressure strain that causes “pockets” (diverticula) to form in the intestinal wall—a common “disease of civilisation” caused by low-fibre, refined diets.
The Synergistic Effect
In nature, you almost never find one without the other. For example:
- An unrefined lentil: The tough outer skin provides insoluble fibre for transit, while the starchy interior provides soluble fibre for your bacteria.
- A whole pear: The skin provides the “scrubbing” insoluble fibre, while the pectin in the fruit provides the “gel” soluble fibre.
When you strip these away to make white flour or fruit juice, you lose the mechanical protection and the chemical regulation, leaving the gut vulnerable to inflammation and the microbiome “starving.”
Would you like to look at specific unrefined food swaps that maximise both types of fibre, or perhaps explore how resistant starch (another “ancestral” carbohydrate) fits into this picture?
I’ve already swapped pretty much everything for higher fibre versions but my readers may be interested to know – I’m personally also interested in the idea of “resistant starch” – a term that I haven’t heard of before.
Resistant starch is a unique form of carbohydrate that functions more like a high-performance fibre than a standard energy source. Unlike typical starches, it resists digestion in the small intestine, arriving intact in the large intestine to serve as a specialized fuel for your gut microbiome. [1, 2, 3, 4]
In an unrefined, ancestral diet, this was a constant staple. Modern processing has largely stripped it away, converting what was once “resistant” into highly digestible, high-glycemic sugar. [5]
The Four Natural Types of Resistance
To understand how to get it from unrefined sources, it helps to see the different ways nature “armours” starch:
- Type 1 (Physically Trapped): Found in whole seeds, grains, and legumes. The starch is physically locked behind tough cell walls that human enzymes can’t penetrate, so it only releases its benefits once it reaches your colon.
- Type 2 (Crystalline): Found in raw potatoes and green (unripe) bananas. These starches are packed into such a tight crystalline structure that enzymes simply can’t “grip” them to break them down.
- Type 3 (The “Retrograded” Trick): This occurs when you cook a starchy food and then cool it down. The cooling process causes the starch chains to realign into a new, rigid structure that remains resistant even if you reheat the food gently later.
- Type 5 (Fat-Bound): Occurs naturally when amylose bonds with lipids (fats) in certain whole foods, making the starch much harder to hydrolyse. [3, 6, 7, 8, 9, 10, 11, 12, 13]
Impact on Gut Biology
When this starch reaches your large intestine, it triggers a cascade of biological benefits that standard “white” carbs don’t:
- Feeding the “Specialists”: It specifically fuels beneficial bacteria like Bifidobacterium adolescentis and Ruminococcus bromii, which are often depleted in modern guts.
- The Butyrate Factory: The fermentation of resistant starch is one of the most efficient ways to produce butyrate, the preferred “fuel” for the cells lining your colon. High butyrate levels are strongly linked to lower inflammation and a reduced risk of colorectal cancer.
- Restoring the Barrier: Research shows that a high intake of resistant starch can actually help seal a “leaky gut” by strengthening the tight junction proteins in the intestinal wall, preventing toxins from leaking into the bloodstream. [2, 14, 15]
Maximising it with Unrefined Swaps [16]
For your readers, the most effective way to “hack” their starch without eating refined products is:
- The “Cook-Cool-Reheat” Method: Cook brown rice, whole-wheat pasta, or skin-on potatoes, then refrigerate them for 24 hours before eating. This “retrograded” starch can lower the glycemic response of the meal by up to 20–25%.
- Green Banana Flour: Adding a tablespoon of green banana or plantain flour to unheated smoothies provides a massive dose of Type 2 resistant starch.
- Overnight Oats: Soaking raw rolled oats overnight in liquid instead of boiling them into porridge preserves the natural Type 1 and Type 2 starch that heat would otherwise destroy. [6, 17, 18, 19]
Would you be interested in a comparison of resistant starch levels in specific ancestral staples, such as different types of beans or ancient grains?
[2] https://www.healthline.com
[4] https://hopkinsdiabetesinfo.org
[5] https://resistantstarchresearch.com
[6] https://www.healthline.com
[7] https://pmc.ncbi.nlm.nih.gov
[8] https://ift.onlinelibrary.wiley.com
[9] https://www.healthline.com
[11] https://www.diabetesvic.org.au
[12] https://www.uhhospitals.org
[13] https://hopkinsdiabetesinfo.org
[14] https://www.sciencedirect.com
[16] https://www.uclahealth.org
[18] https://www.eng.cam.ac.uk
[19] https://www.verywellhealth.com
ah – very interesting – so refried brown rice may fall into that category as would maybe hummus made with cooked cooled and frozen chick-peas?
Yes, you’ve hit on exactly how to “engineer” your food to be more ancestral. Both of those examples are perfect illustrations of Type 3 (Retrograded) Resistant Starch in action.
- The “Fried Rice” Hack
When you cook brown rice and then let it cool (ideally for 12–24 hours in the fridge), the starch molecules undergo a process called retrogradation. They physically rearrange into a tight, crystalline structure that your digestive enzymes can’t easily break down.
- The Reheating Benefit: Even when you “refry” the rice, much of that newly formed resistant starch stays intact.
- The Result: You get the same calories on the plate, but fewer of them are absorbed as glucose in the small intestine. Instead, they travel to the colon to feed your bacteria. Using brown rice is key here because you keep the Type 1 fibre-rich bran intact as well.
- Hummus and Legumes
Legumes (chickpeas, lentils, beans) are already the kings of resistant starch, but the cook-cool-freeze cycle you mentioned supercharges them.
- The Freezing Effect: Freezing actually promotes even more retrogradation than just refrigerating. Making hummus from chickpeas that have been cooked, cooled, and frozen/thawed creates a “bacterial feast.”
- Blending vs. Whole: While blending chickpeas into hummus breaks down some of the physical “armor” (Type 1 starch), the chemical “cooling” (Type 3 starch) remains. This makes hummus a much more metabolic-friendly “dip” than anything made with refined flour.
Why This Matters for Your Readers
In a modern diet, we usually eat “hot and fresh” starch (mashed potatoes, hot white rice, fresh bread), which hits the bloodstream like a bag of sugar. By simply changing the temperature history of the food:
- You lower the Glycaemic Index (GI) of the meal.
- You increase the Satiety (how full you feel).
- You essentially turn a “carb” into a “fibre.”
It’s a way of making “domesticated” crops behave more like the tough, slow-digesting wild plants our ancestors ate.
Would you like to see a list of the best “high-resistance” legumes to use for this cook-cool method, or perhaps some other ancestral food prep techniques like fermentation?
yes both things are of interst to me and my readers
When you shift from a modern, refined diet to one based on unrefined, whole plant foods, you are not just getting more “traditional” fibre; you are significantly increasing your intake of resistant starch (RS). In unrefined legumes and grains, this starch behaves as a “stealth fibre” that bypasses the small intestine entirely to serve as a critical fuel for your gut microbiome. [1, 2, 3]
- High-Resistance Legumes for the Cook-Cool Method [4]
While all legumes are naturally high in RS, specific varieties and preparation methods significantly influence the final amount that reaches your colon. [5, 6]
- Top High-Resistance Legumes:
- Pinto Beans: Found to be one of the best sources of RS after standard boiling.
- Black Beans & Kidney Beans: Contain high levels of amylose (up to 40% of their starch), which is highly resistant to digestion.
- Adzuki & Fava Beans: Fava beans are among the highest-recorded sources, with up to 7–12g of RS per 100g.
- Lentils: Known for maintaining a stable RS content (~5% dry weight) even after conventional boiling.
- The “Retrogradation” Bonus:
- Cooling Advantage: Cooling cooked legumes for 24 hours at 4°C can increase RS levels by approximately 30%.
- Refried/Canned Stability: Interestingly, canned whole beans and canned refried beans often contain similar or even higher RS levels (5-6% dry weight) compared to freshly boiled beans due to the cooling and processing cycles they undergo. [1, 5, 7, 8, 9, 10, 11]
- Ancestral Food Prep: Fermentation as a Fibre Booster
Beyond simple cooling, ancestral preparation techniques like fermentation actively transform the structure of carbohydrates, increasing their resistance to human enzymes. [12, 13]
- Sourdough vs. Commercial Yeast: Research indicates that sourdough fermentation significantly increases RS content compared to standard yeast methods. This is due to the synergistic action of lactic acid bacteria (LAB) and wild yeasts that break down rigid fibre matrices and synthesize new microbial polysaccharides.
- Traditional Maize & Grain Porridges: In many African cultures, eating stale maize porridge (cooled overnight) is a staple practice. This “stale” porridge has significantly higher RS and produces nearly double the amount of butyrate (a key anti-inflammatory fatty acid) compared to fresh porridge.
- Germination (Sprouting): Steaming mung beans after germination can boost RS content to over 27% when followed by refrigeration, compared to only ~17% in freshly prepared germinated beans. [11, 14, 15, 16, 17, 18]
- Impact on Gut Biology: The “Butyrate Factory”
When these resistant starches and unrefined fibres reach the colon, they are fermented by specialized bacteria like Ruminococcus bromii. This process produces Short-Chain Fatty Acids (SCFAs), which have systemic benefits: [19, 20, 21]
- Intestinal Integrity: Butyrate is the primary energy source for colon cells, helping to maintain the gut barrier and potentially preventing colorectal cancer.
- Metabolic Regulation: Propionate travels to the liver, where it may inhibit cholesterol synthesis and help regulate glucose homeostasis.
- pH Balance: Fermentation lowers the pH of the colon, creating an acidic environment that inhibits pathogens while improving the absorption of minerals like calcium and iron. [12, 19, 22, 23]
Would you like a specific high-fibre, high-RS daily meal plan that incorporates these cooling and fermentation techniques?
[1] https://www.sciencedirect.com
[2] https://pmc.ncbi.nlm.nih.gov
[3] https://www.healthline.com
[4] https://www.elizabethrider.com
[5] https://nutritionsource.hsph.harvard.edu
[6] https://countrylifefoods.com
[7] https://www.verywellhealth.com
[8] https://wholeisticliving.com
[9] https://goldenmarathontours.co.th
[10] https://pmc.ncbi.nlm.nih.gov
[11] https://pmc.ncbi.nlm.nih.gov
[12] https://www.sciencedirect.com
[13] https://link.springer.com
[14] https://pmc.ncbi.nlm.nih.gov
[15] https://link.springer.com
[16] https://www.intechopen.com
[17] https://pubmed.ncbi.nlm.nih.gov
[18] https://www.sciencedirect.com
[19] https://www.sciencedirect.com
[20] https://www.sciencedirect.com
[21] https://pubmed.ncbi.nlm.nih.gov
[22] https://onlinelibrary.wiley.com
[23] https://www.mdpi.com