Fiber is an important part of a healthy diet.
In fact, eating enough fiber is said to keep your gut healthy and protect against type 2 diabetes and weight gain (1).
It’s recommended that men aim for 38 grams of fiber per day, while women should aim for 25 grams (2).
However, not all dietary fiber is created equal, and different types have different health effects (3).
This article explores how dietary fiber works to protect your health and how much of it you should eat.

Different Types of Fiber

Dietary fiber is a group of carbs that humans can’t digest. It’s found in all plant foods, including fruits, vegetables, nuts, seeds and grains.
Because dietary fiber refers to a diverse group of different types of carbs, it can be categorized in various ways.
However, it’s usually grouped into one of the following categories, according to its solubility:
  • Insoluble fibers: These fibers don’t dissolve in water. They generally pass through your gut unchanged and add bulk to your stool.
  • Soluble fibers: These fibers absorb water in your gut to form a gel-like paste. This slows down the digestion of nutrients in your food.
Most foods contain both soluble and insoluble fibers, but usually have more of one type than the other.
In general, foods that contain mostly insoluble fibers include whole grains, wheat bran and some fruits (like avocados) and vegetables (such as celery and cauliflower).
Good sources of soluble fibers include oats, flaxseeds, beans and lentils, as well as some fruits (such as berries and bananas) and vegetables (like broccoli and carrots).
Bottom Line: Dietary fiber is usually classified as soluble or insoluble. It’s found in all plant foods, including fruits, vegetables, nuts and seeds.

Fiber Can Help Keep Your Gut Healthy

Grapes, Apples, Oranges and Vegetables
Eating fiber is said to help maintain regular bowel movements and relieve constipation.
Additionally, people with constipation who don’t eat much fiber can usually benefit from eating more (14).
In fact, one study found that as many as 77% of people with chronic constipation experienced relief by simply eating more fiber (5).
Furthermore, it’s thought that sufficient amounts of some types of fiber help promote the growth of “good” bacteria in your bowel (6).
For example, soluble fibers known as prebiotics feed your gut’s beneficial bacteria. By helping your good gut bacteria thrive, they can benefit your health (78).
They also increase the production of some important nutrients, including short-chain fatty acids like butyrate, which are thought to promote a healthy immune system and good gut barrier function (91011).
Having a strong gut barrier is important. It helps keep you healthy by preventing things like viruses and harmful bacteria from entering your body.
Some prebiotic foods include oats, bananas and berries.
However, it’s currently not fully known which types and amounts of fiber best promote the growth of good bacteria in your gut (12).
Bottom Line: Eating adequate amounts of dietary fiber can prevent constipation. Soluble, prebiotic fibers help maintain the balance of good bacteria in your gut.

Fiber Can Make You Feel Full and Help You Lose Weight

Bowl of Oats, Berries and Seeds
Including fiber-rich foods in your diet can help you lose weight.
In fact, observational studies show that people who eat lots of fiber tend to weigh less and have less body fat than those who don’t (1314).
This may be because high-fiber foods are both lower in calories and more filling than low-fiber foods. This means that high-fiber foods could help you eat less, without you even noticing (15).
This was reflected in one review of over 50 studies, which estimated that people who ate 14 grams more fiber per day automatically reduced their calorie intake by around 10% (16).
Interestingly, this effect was larger in people who were overweight or obese.
However, a recent review found that only around 39% of fibers helped reduce hunger. Of these, just 22% resulted in a reduction in the amount of food eaten at a meal (17).
Viscous, soluble fibers — which form a thicker, sticky gel in your gut when they absorb water — are the most effective at keeping you full (18).
Food sources of viscous, soluble fibers include flaxseeds, legumes and oats.
Emerging research is also investigating whether supplementing with specific types of fiber may help weight loss (19).
However, in general, fiber supplements haven’t always been found to be particularly useful (20).
One exception to this is a fiber supplement called glucomannan, which has been shown to help people lose a small amount of weight in the short term (21).
Nevertheless, it can’t be presumed that fiber supplements have the same health benefits as whole-food fibers. This is because whole-food fibers come with many other beneficial nutrients (22).
Bottom Line: Viscous, soluble fibers are thought to be the most helpful fibers for weight loss. If you don’t eat much fiber, increasing your intake by around 14 grams per day could help you lose weight.

Fiber Can Lower Blood Sugar Levels and Protect Against Type 2 Diabetes

Cooked Vegetables
Regularly eating the recommended amount of fiber is thought to help prevent and treat type 2 diabetes.
Observational studies have linked eating more fiber with a lower risk of developing type 2 diabetes (23242526).
One study followed over 75,000 people for 14 years and found that those who ate more than 15 grams of fiber per day had a significantly lower risk of developing diabetes (27).
Additionally, this risk was lowest in the group that ate the most insoluble fiber.
Another study found that people eating 3–5 servings of whole grains per day had a 26% lower risk of type 2 diabetes (28).
If you already have diabetes, it’s also thought that eating more fiber could help you control your blood sugar levels.
This is because soluble fibers slow down the digestion and absorption of sugars, resulting in a more gradual rise in blood sugar levels and fewer blood sugar spikes.
Studies show that increasing fiber intake, especially soluble fiber, can lower blood sugar levels and improve metabolic health in people with type 2 diabetes (2930).
Bottom Line: Regularly eating dietary fiber may help prevent type 2 diabetes. Eating fiber may also improve blood sugar control in people with type 2 diabetes.

Does Fiber Have Any Negative Effects?

Dried Fruit, Nuts and Seeds
While increasing the amount of fiber in your diet should benefit your health, doing so can sometimes cause problems.
If you aren’t used to eating a lot of fiber, suddenly increasing your intake by a large amount could result in digestive symptoms like bloating, pain and gas.
Moreover, if you are chronically constipated, you may find that increasing the amount of fiber you eat doesn’t help. It may be that reducing your fiber intake is the best way to improve your symptoms (31).
However, this is usually only the case if you have chronic constipation that isn’t caused by an inadequate fiber intake (5).
Also, those with irritable bowel syndrome (IBS) may find fiber-rich foods problematic.
This is because many high-fiber foods are also high in fermentable carbs known as FODMAPs. These are known to make IBS symptoms worse (3233).
Bottom Line: Eating too much fiber can be a problem, especially if you have a functional bowel problem like IBS.

So How Much Fiber Should You Eat?

Unfortunately, most people don’t eat much fiber. In the US, most people eat less than half of the recommended daily amount (34).
That said, the current evidence does not indicate which type or amount of fiber is optimal for your health.
Fiber from whole foods comes with many other healthy nutrients. So it may be that the type of fiber and where it comes from is more important than the total number of grams.
Therefore, for most people, eating enough fiber doesn’t require obsessing over each and every gram.
Simply aiming to include healthy high-fiber foods with most of your meals should be sufficient.
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Gluten intolerance is a fairly common problem.
It is characterized by adverse reactions to gluten, a protein found in wheat, barley and rye.
Celiac disease is the most severe form of gluten intolerance.
It is an autoimmune disease that affects about 1% of the population and may lead to damage in the digestive system (12).
However, 0.5–13% of people may also have non-celiac gluten sensitivity, a milder form of gluten intolerance that can still cause problems (34).
Both forms of gluten intolerance can cause widespread symptoms, many of which have nothing to do with digestion.
Here are the 14 main signs and symptoms of gluten intolerance.

1. Bloating

Bloating is when you feel as if your belly is swollen or full of gas after you’ve eaten. This can make you feel miserable (5).
Although bloating is very common and can have many explanations, it may also be a sign of gluten intolerance.
In fact, feeling bloated is one of the most common complaints of people who are sensitive or intolerant to gluten (67).
One study showed that 87% of people who had suspected non-celiac gluten sensitivity experienced bloating (8).
Bottom Line: Bloating is one of the most common symptoms of gluten intolerance. It involves the belly feeling swollen after eating.

2. Diarrhea, Constipation and Smelly Feces

Five Slices of White Bread
Occasionally getting diarrhea and constipation is normal, but it may be a cause for concern if it happens regularly.
These also happen to be a common symptom of gluten intolerance.
Individuals with celiac disease experience inflammation in the gut after eating gluten.
This damages the gut lining and leads to poor nutrient absorption, resulting in significant digestive discomfort and frequent diarrhea or constipation (9).
However, gluten may also cause digestive symptoms in some people who don’t have celiac disease (10111213).
More than 50% of gluten-sensitive individuals regularly experience diarrhea, while about 25% experience constipation (8).
Furthermore, individuals with celiac disease may experience pale and foul-smelling feces due to poor nutrient absorption.
Frequent diarrhea can cause some major health concerns, such as loss of electrolytes, dehydration and fatigue (14).
Bottom Line: Gluten-intolerant people commonly experience diarrhea or constipation. Celiac disease patients may also experience pale and foul-smelling feces.

3. Abdominal Pain

Abdominal pain is very common and can have numerous explanations.
However, it is also the single most common symptom of an intolerance to gluten (131516).
Up to 83% of those with gluten intolerance experience abdominal pain and discomfort after eating gluten (817).
Bottom Line: Abdominal pain is the most common symptom of gluten intolerance, experienced by up to 83% of gluten intolerant individuals.

4. Headaches

Brunette with a Headache Holding Her Hands to Her Temples
Many people experience headaches or migraines once in a while.
Migraines are a common condition, with 10–12% of the Western population experiencing them regularly (1819).
Interestingly, studies have shown that gluten-intolerant individuals may be more prone to migraines than others (2021).
If you have regular headaches or migraines without any apparent cause, you could be sensitive to gluten.
Bottom Line: Gluten-intolerant individuals seem to be more prone to migraines than healthy people.

5. Feeling Tired

Feeling tired is very common and usually not linked to any disease.
However, if you constantly feel very tired, then you should explore the possibility of an underlying cause.
Gluten-intolerant individuals are very prone to fatigue and tiredness, especially after eating foods that contain gluten (2223).
Studies have shown that 60–82% of gluten-intolerant individuals commonly experience tiredness and fatigue (823).
Furthermore, gluten intolerance can also cause iron-deficiency anemia, which in turn will cause more tiredness and lack of energy (24).
Bottom Line: Feeling extremely tired is another common symptom, affecting about 60–82% of gluten-intolerant individuals.

6. Skin Problems

Gluten Free Stamp on a Slice of Bread
Gluten intolerance can also affect your skin.
A blistering skin condition called dermatitis herpetiformis is the skin manifestation of celiac disease (25).
Everyone who has the disease is sensitive to gluten, but less than 10% of patients experience digestive symptoms that indicate celiac disease (25).
Furthermore, several other skin diseases have shown improvement while on a gluten-free diet. These include (26):
  • Psoriasis: An inflammatory disease of the skin characterized by scaling and reddening of the skin (272829).
  • Alopecia areata: An autoimmune disease that appears as non-scarring hair loss (283031).
  • Chronic urticaria: A skin condition characterized by recurrent, itchy, pink or red lesions with pale centers (3233).
Bottom Line: Dermatitis herpetiformis is the skin manifestation of celiac disease. Several other skin diseases may also improve with a gluten-free diet.

7. Depression

Depression affects about 6% of adults each year. The symptoms can be very disabling and involve feelings of hopelessness and sadness (34).
People with digestive issues seem to be more prone to both anxiety and depression, compared to healthy individuals (35).
This is especially common among people who have celiac disease (36373839).
There are a few theories about how gluten intolerance can drive depression. These include (40):
  • Abnormal serotonin levels: Serotonin is a neurotransmitter that allows cells to communicate. It is commonly known as one of the “happiness” hormones. Decreased amounts of it have been linked with depression (3741).
  • Gluten exorphins: These peptides are formed during the digestion of some of the gluten proteins. They may interfere with the central nervous system, which may raise the risk of depression (42).
  • Changes in the gut microbiota: Increased amounts of harmful bacteria and decreased amounts of beneficial bacteria may affect the central nervous system, increasing the risk of depression (43).
Several studies have shown that depressed individuals with self-reported gluten intolerance want to continue a gluten-free diet because they feel better, even though their digestive symptoms may not be resolved (4445).
That suggests that gluten exposure on its own may induce feelings of depression, irrelevant to digestive symptoms.
Bottom Line: Depression is more common among individuals with gluten intolerance.

8. Unexplained Weight Loss

Brunette Holding a Bag of Baguettes
An unexpected weight change is often a cause for concern.
Although it can stem from various reasons, unexplained weight loss is a common side effect of undiagnosed celiac disease (46).
In one study in celiac disease patients, two-thirds had lost weight in the six months leading up to their diagnosis (17).
The weight loss may be explained by a variety of digestive symptoms, coupled with poor nutrient absorption.
Bottom Line: Unexpected weight loss may be a sign of celiac disease, especially if coupled with other digestive symptoms.

9. Iron-Deficiency Anemia

Iron-deficiency anemia is the most common nutrient deficiency in the world and accounts for anemia in 5% and 2% of American women and men, respectively (47).
Iron deficiency causes symptoms such as low blood volume, fatigue, shortness of breath, dizziness, headaches, pale skin and weakness (48).
In celiac disease, nutrient absorption in the large intestine is impaired, resulting in a reduced amount of iron being absorbed from food (49).
Iron deficiency anemia may be among the first symptoms of celiac disease that your doctor notices (50).
Recent studies suggest that iron deficiency may be significant in both children and adults with celiac disease (5152).
Bottom Line: Celiac disease may cause poor absorption of iron from your diet, causing iron-deficiency anemia.

10. Anxiety

Bread Caution
Anxiety may affect 3–30% of people worldwide (53).
It involves feelings of worry, nervousness, unease and agitation. Furthermore, it often goes hand-in-hand with depression (54).
Individuals with gluten intolerance seem to be more prone to anxiety and panic disorders than healthy individuals (3955565758).
Additionally, a study showed that up to 40% of individuals with self-reported gluten sensitivity stated that they regularly experienced anxiety (8).
Bottom Line: Gluten-intolerant individuals seem to be more prone to anxiety than healthy individuals.

11. Autoimmune Disorders

Celiac disease is an autoimmune disease that causes your immune system to attack your digestive tract after you consume gluten (59).
Interestingly, having this autoimmune disease makes you more prone to other autoimmune diseases, such as autoimmune thyroid disease (6061).
Furthermore, autoimmune thyroid disorders may be a risk factor for developing emotional and depressive disorders (626364).
This also makes celiac disease more common in people that have other autoimmune diseases, such as type 1 diabetes, autoimmune liver diseases and inflammatory bowel disease (61).
However, non-celiac gluten sensitivity has not been associated with an increased risk of autoimmune disorders, malabsorption or nutritional deficiencies (6566).
Bottom Line: Individuals with autoimmune diseases like celiac disease are more likely to get other autoimmune diseases, such as thyroid disorders.

12. Joint and Muscle Pain

Man with Elbow Joint Pain
There are numerous reasons why people experience joint and muscle pain.
There is a theory that those with celiac disease have a genetically determined over-sensitive or over-excitable nervous system.
Therefore, they may have a lower threshold to activate sensory neurons that cause pain in muscles and joints (6768).
Moreover, gluten exposure may cause inflammation in gluten-sensitive individuals. The inflammation may result in widespread pain, including in joints and muscles (8).
Bottom Line: Gluten-intolerant individuals commonly report joint and muscle pain. This is possibly due to an over-sensitive nervous system.

13. Leg or Arm Numbness

Another surprising symptom of gluten intolerance is neuropathy, which involves numbness or tingling in the arms and legs.
This condition is common in individuals with diabetes and vitamin B12 deficiency. It can also be caused by toxicity and alcohol consumption (69).
However, individuals with celiac disease and gluten sensitivity seem to be at a higher risk of experiencing arm and leg numbness, compared to healthy control groups (707172).
While the exact cause is not known, some have linked this symptom to the presence of certain antibodies related to gluten intolerance (73).
Bottom Line: Gluten intolerance may cause numbness or tingling in the arms and legs.

14. Brain Fog

No Wheat Allowed Icon
“Brain fog” refers to the feeling of being unable to think clearly.
People have described it as being forgetful, having difficulty thinking, feeling cloudy and having mental fatigue (74).
Having a “foggy mind” is a common symptom of gluten intolerance, affecting up to 40% of gluten-intolerant individuals (87576).
This symptom may be caused by a reaction to certain antibodies in gluten, but the exact reason is unknown (7778).
Bottom Line: Gluten-intolerant individuals may experience brain fog. It involves having difficulty thinking, mental fatigue and forgetfulness.

Take Home Message

Gluten intolerance can have numerous symptoms.
However, keep in mind that most of the symptoms on the list above may have other explanations as well.
Nevertheless, if you regularly experience some of them without an apparent cause, then you may be reacting negatively to the gluten in your diet.
In this case, you should consult with a doctor or try temporarily removing gluten from your diet to see if it helps.