Bowel Movement Soft and Hard – Causes and Diet

The consistency of bowel movement is a good indicator of bowel health as is the frequency of bowel movements and even the color of stool. Normally stool should be soft but firm. However, there are cases where some people may experience either extreme – very soft stool that cannot maintain its form and may even be watery or very hard stool that can be large and even painful to pass out.

Why is stool soft or hard?

There are various factors that affect the consistency of stool but the three main factors are:

  • Water
  • Fiber
  • Motility

The type of foods consumed and even levels of physical activity also play a role in that they contribute to fiber and motility, respectively.


Water is an important part of digestion and plays a major role in the consistency of stool. It accounts for as much as 60% of stool weight for normal soft but firm stool. Water in the gut is sourced in two ways. Firstly it is derived from the fluids that are consumed. Secondly the body pumps water into the small intestine during digestion. In the colon however, the body starts reabsorbing the water to form soft but firm stool.


Fiber is acquired from plant-based foods and cannot be digested by the human body. It remains in the gut where it absorbs water and provides bulk. This allows partially digested food and waste to move easily through the bowels. Fiber also helps to increase the water content of stool to ensure that it is soft while ‘binding’ stool to maintain a solid consistency. A lack of dietary fiber is one of the main reasons for hard stool.


Gut motility refers to the movement through the gut. This is facilitated by the contraction and relaxation of the muscles in the gut wall which is known as peristalsis. It takes up to 72 hours for undigested food that enters the mouth to eventually be passed out as stool. Peristalsis should neither be too fast or too slow. If rapid then water may not be fully reabsorbed and stool can be very soft or watery. If slow the excess water may be reabsorbed causing the stool to become hard.

Read more about bowel motility.

Causes of Soft Bowel Movement

Very soft bowel movement, also referred to as loose stool or watery stool, usually falls under the category of diarrhea. However, diarrhea is also defined by the frequency of bowel movements. With diarrhea, there is more than three bowel movements n a 24 hour period and the stool is watery to loose in consistency.

  • Infections: This is one of the most common cause of bowel movement that is suddenly soft and frequent. It is mainly due to viral or bacterial infections and sometimes may occur with protozoal infections. Most of these infections are acute and often accompanied by nausea and vomiting.
  • Foods: Certain foods can irritate the gastrointestinal tract even without an infection. However, diarrhea is more likely to arise with a food intolerance where the body cannot digest and absorb specific nutrients like in lactose intolerance.
  • Medication: Many drugs apart from laxatives can cause diarrhea, usually as a side effect. One of the more widely known is antibiotics which can cause antibiotic-associated diarrhea (AAD). Other drugs like certain antacids and cancer drugs are also know to lead to diarrhea.
  • Bowel disorders: Several non-infectious bowel disorders present with diarrhea as a symptom. Inflammatory bowel disease (IBD) is one of the more serious conditions. Irritable bowel syndrome (IBS) is another common cause where the bowel motility is faster than normal.
  • Colorectal cancer: Change in bowel resulting in diarrhea can occur with colorectal cancer. This is one of the most common types of cancers globally and also among the deadliest. There are usually other symptoms like rectal bleeding and unintentional weight loss.

Causes of Hard Bowel Movement

Hard bowel movement is usually a sign of constipation. However, constipation is also defined by the frequency of bowel movements, in the same way as diarrhea. With constipation, there is less than three bowel movements in a 7 day period, the stool is hard and difficult to pass.

  • Insufficient water intake: This is a leading cause of hard stool. Adults require at least 2 liters (approximately 68 ounces) of water daily. However, the modern diet is not as abundant in water. Apart from not consuming water, many people also consume diuretics like coffee and cola drinks which causes water loss.
  • Inadequate dietary fiber: This is another common cause of hard stool. The modern diet is deficient in foods that are high in fiber such as fruits and vegetables.  Without fiber bulking up stool and retaining water within stool, the bowel movement becomes hard.
  • Sedentary lifestyle: Being physically inactive or not sufficiently active is another major contributor to constipation and hard bowel movement. This is a common problem in developed nations and correlates with the rise in obesity rates in these countries.
  • Obstruction: Any blockage within the bowel will also lead to constipation. This can occur for various reasons like narrowing of the bowels, twisting of the bowels, foreign objects in the gut, tumors (both benign and malignant) as well as impacted feces.
  • Nerve and muscle problems: Movement through the bowels is facilitated and coordinated by nerves and muscles. Many conditions that affect these nerves and muscles can lead to constipation. This includes diabetic neuropathy, stroke, spinal cord injury, multiple sclerosis, Parkinson’s disease, anismus and related conditions.
  • Hormonal conditions: A range of endocrine diseases can present with constipation. This includes diabetes, hypothyroidism (underactive thyroid gland), hyperparathyroidism (overactive parathyroid gland) and even physiological conditions that lead to hormonal changes such as pregnancy.

It is important to note that many cases of constipation are due to unknown factors. Therefore these cases are referred to as idiopathic constipation or functional constipation when bowel motility is slower than normal but not due to any disease.

Diet for Soft Stool

There are several simple dietary measures to maintain soft but firm stool. It is also important to note that lifestyle changes should also be implemented with the dietary modification.

Read more on easy bowel movements.

  • Drink at least 2 liters (about 68 ounces) daily. The water intake should be spread out throughout the day. Do not count other drinks like tea, coffee, sodas or even fruit juices within this daily requirement. A higher water intake may be necessary for people living in hot climates or people who are more physically active.
  • Avoid substances that promote water loss such as alcoholic beverages and caffeinated drinks such as coffee, tea or cola. If these beverages are to be consumed then it is important to moderate the intake and drink extra water.
  • Increase fresh fruit and vegetable intake. This is one of the best natural sources of fiber. Vegetables should comprise at least half the daily diet by volume and at least 2 whole fruit should be consumed every day. Although crunchy fruits and vegetables may have more fiber, all fruits and vegetables can be beneficial.
  • Incorporate larger amounts of high fiber foods like bran and fiber supplements in the daily diet if constipation is a problem. It must be accompanied by sufficient water intake. However, this does not preclude the need for a a diet abundant in fruits and vegetables.
  • Become physically active on a daily basis. Ideally a person should workout for at least 120 minutes per week in 30 minute sessions. In addition, it is important to be more active in everyday tasks beyond just workouts. Try to ensure that walking equates to at least 6,000 steps daily.

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