What happens when you have not enough fiber?: The hidden health risks

October 10, 2025 •

3 min read

According to the Centers for Disease Control and Prevention, most Americans consume only about half the recommended daily amount of fiber. This widespread deficiency can have significant and often overlooked consequences for your health, raising the question: what happens when you have not enough fiber?

Quick Summary

Inadequate fiber intake can lead to a host of problems, including digestive troubles like constipation and hemorrhoids, an increased risk of cardiovascular disease, unstable blood sugar levels, and difficulty managing weight. A low-fiber diet also negatively impacts your gut microbiome, can cause chronic inflammation, and may contribute to fatigue and mood swings over time.

Key Points

Digestive issues: Inadequate fiber is a primary cause of constipation, hemorrhoids, and diverticulitis due to a lack of bulk in stool.
Increased heart disease risk: Low fiber intake, particularly soluble fiber, is linked to higher LDL cholesterol levels and an increased risk of cardiovascular disease.
Unstable blood sugar: Fiber deficiency can lead to rapid blood sugar spikes and crashes, increasing the risk of type 2 diabetes and causing fatigue.
Weight management struggles: A low-fiber diet doesn't provide the same feeling of fullness, which can lead to overeating, snacking, and difficulty controlling weight.
Poor gut health and inflammation: Without fiber to feed beneficial gut bacteria, the microbiome becomes imbalanced (dysbiosis), which can lead to chronic inflammation and a weaker immune system.
Wider health impacts: Fatigue, mood swings, and even poor skin health are all symptoms that can be traced back to a lack of dietary fiber.

Dietary fiber, often called roughage, is a crucial component of a healthy diet found primarily in plant foods. Unlike other carbohydrates, it is not broken down and absorbed by your body. Instead, it passes through your digestive system, performing a range of vital functions. When your intake is consistently low, your body can suffer from several negative health consequences, both short-term and long-term. Understanding the full spectrum of these effects is the first step toward improving your nutritional habits.

The Immediate Impact on Your Digestive System

Insufficient fiber significantly affects your digestive system. Fiber adds bulk and moisture to stool, making it easier to pass through the intestines. A lack of fiber can lead to several uncomfortable conditions:

Constipation: This is the most common symptom, characterized by infrequent and difficult-to-pass bowel movements.
Hemorrhoids: Chronic straining from constipation can cause painful, swollen veins in the anus or rectum.
Diverticular Disease: A low-fiber diet is linked to developing pouches in the colon (diverticula) which can become inflamed (diverticulitis).

Long-Term Effects on Overall Health

A long-term lack of fiber can increase the risk of several chronic diseases.

Cardiovascular Health

A strong link exists between fiber intake and reduced cardiovascular disease risk. Soluble fiber helps lower LDL cholesterol by binding to it in the digestive tract. A low-fiber diet is also associated with higher-risk coronary plaques.

Blood Sugar Regulation

Fiber is crucial for managing blood glucose. Soluble fiber slows sugar absorption, preventing spikes and crashes. Consistent low fiber can lead to insulin resistance and increase the risk of type 2 diabetes.

Weight Management Difficulties

Fiber aids weight management by promoting fullness and slowing digestion. Low fiber can lead to feeling hungry sooner, increased snacking, and potential weight gain.

Compromised Gut Microbiome

Beneficial gut bacteria rely on fiber for fuel. Insufficient fiber can lead to an imbalance (dysbiosis), causing inflammation. Studies also suggest a fiber-free diet can weaken the gut barrier.

Low-Fiber Diet vs. High-Fiber Diet: A Comparison


Feature	Low-Fiber Diet	High-Fiber Diet
Bowel Movements	Irregular, often constipated, and hard to pass stools.	Regular, soft, and easy to pass stools.
Digestion Speed	Rapid gastric emptying, quick passage through the intestines.	Slowed digestion and absorption of nutrients.
Satiety	Feeling hungry sooner after meals, increased snacking.	Feeling fuller for longer, better appetite control.
Blood Sugar	Fluctuates rapidly, with frequent spikes and crashes.	Steady blood sugar levels, preventing large swings.
Cholesterol Levels	Tend to be higher, especially LDL (bad) cholesterol.	Help to lower LDL cholesterol by binding to bile acids.
Gut Microbiome	Diminished diversity, with fewer beneficial bacteria.	Thriving and diverse microbiome, producing beneficial short-chain fatty acids.
Energy Levels	Often characterized by midday energy crashes and fatigue.	Sustained, consistent energy throughout the day.
Disease Risk	Increased risk of heart disease, diabetes, and certain cancers.	Lowered risk of heart disease, diabetes, obesity, and some cancers.

How to Increase Your Fiber Intake

Increasing fiber intake is achievable with simple dietary adjustments:

Prioritize Whole Grains: Choose whole-wheat products, brown rice, or quinoa.
Eat More Fruits and Vegetables: Consume fruits with skin and add vegetables to meals.
Incorporate Legumes: Add beans, lentils, or chickpeas to various dishes.
Add Nuts and Seeds: Include seeds or a handful of nuts in your diet.
Increase Fluid Intake: Drink plenty of water when increasing fiber to prevent constipation.

Conclusion

A low-fiber diet has significant health consequences beyond digestive issues. It increases the risk of heart disease, type 2 diabetes, obesity, and poor gut health. By consciously adding more fiber-rich foods like fruits, vegetables, whole grains, and legumes to your diet, you can improve digestive health, stabilize blood sugar, and reduce the risk of chronic diseases, contributing to better overall well-being. For more information on fiber and heart health, refer to resources like Harvard Health.

Frequently Asked Questions

The recommended daily fiber intake for adults varies by age and gender. Generally, it's about 25 grams per day for women and 38 grams for men, though most people consume significantly less.

Common signs include constipation, feeling hungry soon after meals, fatigue and energy crashes, persistent bloating, and high cholesterol levels. Paying attention to your bowel regularity and how satisfied you feel after eating are key indicators.

Yes, a lack of fiber, especially soluble fiber, can lead to higher cholesterol levels. Soluble fiber binds to cholesterol in the digestive system and helps remove it from your body, thereby lowering LDL (bad) cholesterol.

Yes, it can. Fiber helps you feel full and satisfied for longer, which reduces overall calorie intake. A low-fiber diet digests more quickly, leaving you feeling hungry sooner and more likely to overeat, leading to weight gain.

Long-term risks include an increased risk of cardiovascular disease, type 2 diabetes, obesity, and certain types of cancer, particularly colorectal cancer.

Soluble fiber dissolves in water to form a gel-like substance that can lower cholesterol and regulate blood sugar. Insoluble fiber adds bulk to your stool and helps move waste through your digestive tract, promoting regularity.

Yes. A sudden and large increase in fiber intake, without enough water, can cause bloating, gas, and stomach cramps. It's best to increase your fiber intake gradually and ensure you drink plenty of fluids.

Yes. The gut-brain axis connects your gut health to your mental state. An imbalanced gut microbiome due to a lack of fiber can affect mood-regulating neurotransmitters, potentially contributing to mood swings, anxiety, and depression.

Good sources of fiber include whole grains, fruits (especially with the skin), vegetables, legumes like beans and lentils, and nuts and seeds.