A silent problem that I have been observing in my practice for almost two decades.
During almost twenty years of clinical work I have seen a pattern that repeats itself with alarming frequency: people with digestive, intestinal and microbiota problems who, paradoxically, were not suffering from a lack of fiber... but from an excess .
And I'm not talking about an isolated case.
I'm talking about dozens and dozens of patients, over two decades, with symptoms ranging from unbearable gas to intestinal pain, including severe constipation, diarrhea, inflammation, dysbiosis, and even clear signs of intestinal hyperpermeability.
The trend of "microbiota," prebiotics, probiotics, and hyper-healthy diets has created a false sense that the more fiber you consume, the better you'll function . But physiology doesn't agree. Neither does biochemistry. And your gut, even less so.
The digestive system is wise. It's designed to function in balance , not in excess. When we talk about fiber, the appropriate dose is usually between 20 and 30 grams per day for a healthy adult. But today it's not uncommon to find someone consuming 50, 60, or even 80 grams daily , from whole grains, bran, excessive amounts of legumes, hard vegetables, fruits with peels, "superfoods," and trendy fiber supplements.
And I want to make this clear:
This excess is causing more constipation than I've ever seen from a fiber deficiency.
When "healthy" becomes toxic: the dark side of excess fiber
1. More fiber doesn't speed up transit: it blocks it
The idea that “more fiber = more bowel movements” is as popular as it is wrong. Fiber has two sides:
- If there is little water, the fiber absorbs and compacts , creating a literal "plug" inside the intestine.
- If traffic is already slow to begin with, it makes it even slower .
- If the gut microbiota is not balanced, it ferments excessively , producing gas, bloating, and pain.
Many patients who came to see me were taking more than 40–50g of fiber daily … and were more constipated than ever.
2. Excess fiber irritates the intestinal mucosa
Insoluble fiber (the “roughest”) can act like sandpaper if consumed in disproportionate amounts.
That sustained irritation can:
- Inflammation of the intestinal wall
- To cause micro-lesions
- Increase intestinal hyperreactivity
- Altering the state of the microbiota
- Generate visceral hypersensitivity
Over time, chronic irritation opens the door to bigger problems.
3. Excess fiber feeds some bacteria… and throws others out of balance
Fermentable fiber (soluble fiber) is very beneficial in moderation. But when consumed in excess:
- Certain fermenting bacteria grow excessively
- Others run out of resources and decrease.
- Diversity is disrupted
- Dysbiosis patterns appear
- They increase gas, bloating, and distension.
Dysbiosis, when maintained over time, is a direct precursor to metabolic, digestive, and even immunological pathology.
4. Absorption problems: too much fiber “drags away” nutrients
Especially minerals such as:
- Zinc
- Magnesium
- Iron
- Calcium
I have seen nutritional deficiencies in people who ate "wonderfully"... but with a diet so high in fiber that the intestine could not absorb it properly.
5. Intestinal hyperpermeability: the next step in the chain
The combination of “excess fiber + irritation + dysbiosis + inflammation” inevitably leads to:
- Increased permeability
- Immune activation
- Release of inflammatory cytokines
- Skin problems
- Fatigue
- Mood disorder
- Even worsening autoimmune response in predisposed individuals
This is not theory: it is real clinical observations made during almost twenty years of practice.
Quantity matters. Quality matters, too.
Fiber is necessary, yes. But not all fiber is the same, and not every amount is suitable for everyone.
Soluble fiber (the kind that gels)
Helps to:
- Feeding beneficial microbiota
- Improve stool consistency
- Control glucose
- Lower cholesterol
Balanced sources:
- Oatmeal
- Apple
- Carrot
- Chia (in moderate amounts)
- Legumes (in reasonable portions)
- Psyllium (always individually)
Insoluble fiber (the “brush” or rough)
It helps with transit in the right amount, but in excess it irritates.
Sources:
- Wheat bran
- Whole grains
- Fruit and vegetable peels
- Highly fibrous vegetables such as broccoli, cauliflower, artichoke
- Nuts and seeds
The most common mistake I see is abusing both without control, thinking that "more is healthier".
How much fiber do we really need?
- Healthy adult: 20–30 g/day
- Athletes with high metabolic demand: 25–35 g/day
- People with dysbiosis or SIBO: often less is better
- People with irritable bowel syndrome: fiber intake must be adjusted to the millimeter.
Exceeding 40 g/day without a clinical reason is directly counterproductive.
The problem with excess isn't the one-off day: it's the chronic accumulation.
What I have seen in consultations are not problems resulting from a day of eating too much salad.
These are people who have followed fashion trends for months or years :
- Whole grains at every meal
- Bran added to yogurts
- Chia seeds in absurd quantities
- Tough vegetables twice a day
- Eat legumes daily “because they are good for the gut microbiota”
- Fiber supplements without clinical indication
That cocktail has created:
- Chronic constipation
- Constant gases
- Inflammation
- Abdominal pain
- Poor absorption
- Postprandial fatigue
- Secondary intolerances
- And in many cases, dysbiosis and intestinal hyperpermeability
All because of an excess of a nutrient that, in balance, is wonderful.
Conclusion: fiber is medicine… but in overdose it becomes poison
After almost two decades of clinical experience, I can say it without fear:
Excess fiber is creating more constipation, more inflammation, and more bowel problems than a fiber deficiency.
You don't need to turn your food into a mixture of bran, seeds, and tough vegetables.
You don't need to obsess over "feeding your microbiota" at all costs.
You don't need to follow trends without understanding how your gut works.
You need balance, individualization, and basic physiology .
Because in nutrition—as in almost everything—it is not true that more is better.
It's better to do what your body can handle.