Almost everyone encounters this at some point: being unable to have a bowel movement for several days, having to strain while on the toilet, feeling bloated, or having the sensation that the bowel has not emptied completely. Constipation is one of the most common gastrointestinal complaints. It is estimated that approximately 16% of adults worldwide suffer from chronic constipation—a figure that can be even higher among people over the age of 60. Women are affected more often than men, and the prevalence of these symptoms increases with age. Despite how common it is, constipation is still frequently dismissed as a trivial inconvenience. Yet, long-term constipation can have a significant impact on daily life and quality of life.
Diet plays an important role in both the development and the treatment of constipation. Among other things, what we eat influences the volume and composition of stool, the moisture content in the gut, intestinal motility, and the activity of gut bacteria. But which foods are truly helpful for constipation? And why can items such as fiber, kiwis, prunes, or flaxseeds improve bowel movements?
When are you constipated?
Many people think that constipation means going to the toilet less than once a day. That is not correct. The normal frequency of bowel movements varies significantly from person to person. Some healthy individuals have bowel movements several times a day, while others go only a few times a week.
Doctors are more likely to speak of constipation when bowel movements are difficult and various complaints are present. Possible symptoms include:
fewer than three spontaneous bowel movements per week;
hard or dry stool;
having to strain significantly;
a feeling that the stool cannot pass easily;
a sensation of incomplete evacuation;
at times, the need to use one's fingers or other methods to assist in passing stool.
In cases of constipation, the movement of intestinal contents through the large intestine is often slower. This gives the large intestine more time to absorb water from the stool, causing it to become harder, drier, and more difficult to pass.
Constipation can have various causes. In addition to diet, factors such as a lack of physical activity, changes in daily routines, certain medications, insufficient fluid intake, and various medical conditions can all play a role.
What are normal bowel movements?
To understand why diet can help with constipation, it is useful to first look at how a normal bowel movement occurs. After digestion in the small intestine, undigested food residue reaches the large intestine. There, water and electrolytes are reabsorbed. At the same time, rhythmic contractions of the intestinal wall—known as peristalsis—propel the contents of the intestine toward the rectum.
Several factors influence this process:
the volume of the intestinal contents;
the water content of the stool;
the activity of the intestinal muscles;
nerve signals from the enteric nervous system;
hormonal signals;
the activity of intestinal bacteria.
Nutrition influences several of these processes. Dietary fiber, in particular, plays an important role in this.
Dietary fiber: an important factor in constipation
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When scientists investigate which dietary interventions can help with constipation, dietary fiber consistently comes to the fore. Dietary fibers are carbohydrates that are not, or only partially, broken down in the small intestine. As a result, they largely reach the large intestine, where they can contribute to better bowel movements in various ways.
Fiber increases the volume of stool. Some types of fiber retain water, thereby increasing the volume of the intestinal contents. The stretching of the intestinal wall can send signals to the nervous system of the gut, which stimulates intestinal movements. A larger volume of intestinal contents can thus contribute to a more efficient propulsion of stool.
Fiber retains water. Certain types of fiber—especially soluble fiber—can absorb large amounts of water. This makes stool softer and easier to pass. That is a key reason why consuming enough fiber can help with hard stools.
Fiber serves as food for gut bacteria. Not all fiber passes through the body unchanged; a portion is fermented by gut bacteria in the large intestine. This process produces substances such as short-chain fatty acids—including acetate, propionate, and butyrate—which play various roles in the gut and can, for instance, influence intestinal function and the activity of the intestinal wall. Consequently, a high-fiber diet does more than just exert a mechanical effect on stool; it also shapes the environment in which gut bacteria reside.
Soluble and insoluble fibersDietary fibers do not form a uniform group.
In practice, there is no need to obsessively distinguish between the two types. A varied diet that includes a range of fiber-rich foods provides both types. |
How much fiber do you need?
The Superior Health Council bases its recommended fiber intake on energy requirements: approximately 14 grams of dietary fiber per 1,000 kilocalories.
For someone who requires about 2,000 kilocalories per day, this amounts to roughly 28 grams of fiber daily.
If you are not used to a high-fiber diet, it is best to increase your intake gradually. A sudden, significant increase can temporarily lead to increased flatulence, a bloated feeling, or abdominal discomfort.
Eating more fiber: whole grains instead of refined grains
Whole-wheat bread, oatmeal, whole-wheat pasta, brown rice, and other whole-grain products contain more dietary fiber than refined grain products. For instance, try replacing white bread with whole-wheat or rye bread, and opt for whole-wheat pasta or brown rice more often.
Rye, in particular, is noteworthy. Research involving individuals with functional constipation has shown that rye bread can help improve bowel movements. Furthermore, it can serve as an alternative to wheat bran, which, for some people, tends to cause a significant amount of flatulence.
Oatmeal also deserves attention. The beta-glucans found in oats are soluble fibers capable of retaining water; they also have a beneficial effect on factors such as cholesterol levels.
The surprising role of gut bacteria
Our large intestine contains a vast number of microorganisms. Together, they make up the gut microbiome. An increasing body of research shows that the composition and activity of the gut microbiome are linked to bowel function. In people with chronic constipation, differences in the composition of the gut microbiota are sometimes observed. However, this does not mean that any single specific bacterium is the cause of constipation, nor does it mean that a probiotic can easily solve the problem.
Short-chain fatty acids
When gut bacteria ferment dietary fibers, short-chain fatty acids are produced. These substances can influence various processes in the gut.
Among other things, they can:
influence the activity of the intestinal wall;
alter the intestinal environment;
influence the fluid balance in the intestine;
influence the communication between gut bacteria and intestinal cells.
Consequently, a high-fiber diet does not merely act as a kind of 'filler' for the gut; it also influences the biochemical environment in which the gut functions.
Can probiotics help?
Interest in the use of probiotics for constipation has grown significantly in recent years. In some individuals, certain bacterial strains may slightly improve the frequency of bowel movements or the consistency of the stool. However, results vary depending on the specific probiotic used; the effect is influenced by the bacterial strain, the dosage, and the individual. Therefore, one cannot simply claim that yogurt, kefir, or other fermented foods treat constipation just because they contain "good bacteria."
A varied diet that includes sufficient fiber remains the most important nutritional foundation.
Why prunes can help with constipation
Plums—and especially dried plums—have long had a reputation as a natural remedy for constipation. There is also scientific evidence to support this. The effect of dried plums is based on several factors.
Sorbitol: Plums contain sorbitol, a sugar alcohol that is only partially absorbed in the small intestine. As a result, some of it reaches the large intestine, where it can draw in water. This can help soften the stool.
Dietary fiber: In addition, plums contain dietary fiber, which contributes to the bulk of the stool.
Other plant compounds: Plums also contain various polyphenols and other bioactive substances. Research suggests that these compounds may influence the gut microbiota, although the extent to which this contributes to the laxative effect is not yet fully understood.
In a randomized study involving people with chronic constipation, both dried plums (prunes) and psyllium were found to be effective in improving bowel movements.
Prunes can therefore be a practical dietary choice for those experiencing constipation. However, consuming large quantities may lead to a temporary increase in gas.
Eating kiwis for constipation?
Kiwis have also been extensively studied in people with constipation. Several studies show that eating green kiwis daily can increase the frequency of bowel movements and, for some individuals, may also reduce abdominal discomfort.
This effect is likely the result of several properties of the kiwi:
kiwi contains both soluble and insoluble fibers;
these fibers are capable of retaining water;
kiwi has a relatively high water content;
kiwi contains the enzyme actinidin. Actinidin is primarily known for its role in the digestion of proteins. Whether, and to what extent, this enzyme directly contributes to the effect of kiwi on intestinal transit has not yet been fully clarified.
Since 2025, a specific health claim has been permitted within the European Union for fresh green kiwifruit (*Actinidia deliciosa* 'Hayward'). The claim relates to an increase in the frequency of bowel movements and applies when at least 200 grams of fresh kiwifruit flesh is consumed daily—an amount roughly equivalent to two large green kiwis. This claim is specific to the green kiwifruit and therefore cannot simply be extended to all types of kiwifruit or to kiwifruit supplements.
Legumes: fiber bombs for the gut
Lentils, chickpeas, white beans, kidney beans, and other legumes are among the richest natural sources of dietary fiber.
A single serving of cooked lentils can easily provide more than 10 grams of fiber. Consequently, legumes contribute to:
a larger volume of stool;
a higher fiber intake;
fermentation by gut bacteria;
the production of short-chain fatty acids.
Those who are not accustomed to eating legumes may experience increased flatulence at first. Gradually increasing the amount consumed allows the body to adapt.
Nuts, seeds, and flaxseed for constipation
Nuts and seeds combine various nutrients that fit into a healthy diet. Among other things, they provide dietary fiber and unsaturated fats. Flaxseed, in particular, receives extra attention when it comes to constipation; in addition to fiber, it contains mucilaginous substances (mucilage) that can retain water. Ground flaxseed, for example, can be added to yogurt, oatmeal, or a smoothie.
Chia seeds are also rich in fiber and capable of absorbing moisture. When consuming large quantities of fiber-rich seeds, it is important to drink plenty of fluids.
Why is it important to drink enough fluids when constipated?
Water plays an important role in the formation of normal stool. The large intestine continuously absorbs water from the contents of the bowel. If you are dehydrated, your stool can become harder. It is therefore important to drink enough fluids—especially when you are also increasing your fiber intake.
However, it is an oversimplification to suggest that everyone with constipation simply needs to drink 'more water.' For those who are already consuming sufficient fluids, there is little evidence that consuming very large additional amounts will resolve constipation.
The key takeaway is this: ensure an adequate fluid intake and avoid dehydration. Water is the most logical choice for this. Individual needs vary from person to person and increase during hot weather, in the event of a fever, or during intense physical activity.
Can coffee stimulate bowel movements?
Coffee deserves a special mention because many people find that they need to use the toilet sooner after having a cup. In some individuals, coffee can stimulate the motor activity of the large intestine. This effect does not appear to be caused solely by caffeine, as even decaffeinated coffee can influence bowel activity. While coffee is not a treatment for constipation, if you notice that a cup helps trigger a natural urge, you can certainly take advantage of that.
A meal can also activate what is known as the gastrocolic reflex—a natural response in which gastrointestinal activity increases after eating, stimulating the large intestine.
Does rhubarb help with constipation?
Rhubarb is traditionally used for its laxative properties. However, it is important to distinguish between the rhubarb stalks that we eat as food and standardized extracts of rhubarb root that are used as a laxative.
Rhubarb root contains anthraquinone compounds that can stimulate bowel movements and the release of water into the intestine. This is a pharmacological effect, which differs from the effect one would expect from a typical serving of rhubarb consumed as a vegetable.
Therefore, for dietary advice regarding common constipation, options such as kiwis, prunes, whole-grain products, vegetables, fruits, legumes, flaxseeds, and psyllium are more relevant.
When is it better to consult a doctor?
Constipation is usually harmless, but persistent symptoms warrant attention. Consult a doctor if symptoms persist for a long time, change significantly, or do not improve despite adjustments to your diet and lifestyle.
Be sure to contact a doctor if you experience warning signs such as:bloed in de stoelgang;
black stools;
unexplained weight loss;
severe or persistent abdominal pain;
persistent vomiting;
fever;
a sudden change in bowel habits.
It is also advisable to seek medical advice if you regularly need laxatives or if constipation significantly affects your daily life.
Conclusion
Constipation does not occur simply because someone "doesn't go to the toilet often enough." It is the result of an interplay between factors such as the speed at which intestinal contents move through the digestive tract, the moisture content and volume of the stool, the function of the intestinal muscles, nerve signals, and the gut microbiota.
Diet influences several of these processes, with dietary fiber playing a central role. Fiber can increase stool volume, retain water, and serve as a food source for gut bacteria. Consequently, whole-grain products, vegetables, fruit, legumes, nuts, and seeds are key components of a diet that supports normal bowel movements.
Furthermore, certain foods have been specifically studied in the context of constipation; green kiwis and dried plums are among the most notable examples. Psyllium can also be helpful for chronic constipation.
However, there is no single food that acts as a "miracle cure" for everyone. A sustainable approach primarily involves a fiber-rich and varied diet, adequate fluid intake, regular physical activity, and good toileting habits.
If symptoms persist or are severe, it is important to consult a doctor, as constipation can also stem from causes other than diet.
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source: Dr. ir. Eric De Maerteleire
author: Sofie Van Rossom, health journalist- Gezondheid.be