Can You Have Diarrhea from Not Eating Enough?

Not eating enough or undernutrition can cause changes to your gastrointestinal (GI) system. Short-term and long-term undernutrition leads to intestinal atrophy of various degrees. Intestinal atrophy is when intestine cells shrink and do not absorb nutrients or function properly. These changes can result in diarrhea from a malfunctioning GI system. 

Diarrhea from not eating enough is more common in long-term undernutrition. However, any changes in bowel regularity or movements (constipation or diarrhea) are a sign to evaluate your diet and health. 

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Can You Have Diarrhea from Not Eating Enough?

Limited research exists related to undernutrition and malnutrition for a good reason.

It is known that depriving the body of nutrients is harmful. Most research on undernutrition and its effect on the GI system is observational in the settings of famines, war, extreme poverty, or ill patients. Insight into gut changes from not eating enough can be gained from observational and animal research. 

Historical Diarrhea from Malnutrition

Research from events in history indicates diarrhea was present after lengthy periods of eating less than half of recommended needs daily. Individuals also lost significant amounts of weight in a short amount of time. Reports of distended stomachs and intestines, and slow movement through the intestines were noted, along with diarrhea. 

The largest study on GI changes and undernutrition was conducted from 1944 to 1966 in Minnesota on 32 healthy young men.

The participants ate about 1,600 calories daily for 26 weeks, followed but 58 weeks of replenishment and follow-up. While the men did lose over 20% of their body weight from being semi-starved, none exhibited diarrhea, only distended stomachs. 

Animal Research

Extensive research on animals has shown that undernutrition causes increased intestinal permeability, gut inflammation, intestinal cell shrinkage, gut bacteria changes, and diarrhea.

The animal results reflect common symptoms and problems present in people with undernutrition. 

These changes in the GI system prevent the body from absorbing carbohydrates, fat, protein, vitamins, and minerals correctly.

The lack of nutrition leads to further issues in humans and animals with prolonged illness and delayed healing, stunted growth and development in younger populations, and increased risk of becoming sick from contagious diseases throughout life.  

Adverse gut bacteria changes have been observed in animals and people following a significant reduction in nutrient intake. It is unclear what causes the difference, but hormones and digestive processes are altered, leading to shifts in how the body absorbs and uses nutrients from food.

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Other Signs You’re Not Eating Enough

Diarrhea is one sign of not eating enough but is typically a later symptom. Other symptoms can show up first. 

• Other digestive symptoms: pay attention to any prolonged or new constipation. Constipation can be a sign of not eating enough. If you are not eating enough, there is a reduction in stool and slowed elimination. Constipation is fewer than three bowel movements per week. 

Feeling sluggish or weak

Your body cannot perform its best when not fueled well. If you are eating less than your body needs, the body will reduce the energy allotted to do non-essential tasks. It will prioritize critical functions, like pumping blood and breathing. 

Prioritization of essential body functions means you may feel slower and tire quickly.

‍Research among 16,911 older adults screened for varying degrees of nourishment and then tested their physical performance.

The meta-analysis showed that well-nourished older adults had better hand grip strength, faster walking speed, and the ability to stand up and walk compared to malnourished ones. Daily physical abilities improved among nourished individuals.

You’re more irritable

Maybe you notice you get “hangry” or irritable when hungry. Pay attention to your mood as it relates to hunger.

A small study on 64 adults over three weeks found that increased self-reported hunger was associated with increased irritability and anger. Reflect on your emotions throughout the day and see if they coincide with increased hunger. 

You’re underweight‍

Body weight is not a perfect indicator of nutrition status, but it is one tool that can help assess changes. The CDC categorizes being underweight if the body mass index is under 18.5. 

Other Causes of Diarrhea

Infections are the most common cause of diarrhea, followed by medication side effects. Viral, bacterial, and parasitic infections can all cause diarrhea. These types of diarrhea resolve in about one to four weeks. 

Chronic or long-term diarrhea can be caused by food allergies or intolerances, digestive diseases or problems, surgery, and long-term medications.

Whereas diarrhea quickly occurs after the following conditions. Lactose intolerance causes diarrhea shortly after eating or drinking foods with milk products. IBS, or celiac disease, commonly causes rapid diarrhea. 

A health professional should evaluate diarrhea to prevent any long-term complications. 

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Making Sure You’re Eating Enough

It can be hard to determine if you are eating enough. An excellent first step is to eat regularly spaced meals and snacks.

The 2020-2025 Dietary Guidelines for Americans recommends meeting your daily needs through three meals and one or two snacks.

They provide further guidance on how much of each food group (fruits, vegetables, grains, dairy, and protein) and specific calories, carbohydrates, fat, and protein to aim for based on age and life stage.  

Takeaway

Diarrhea can be a symptom of not eating enough in the short or long term. The GI tract changes in response to inadequate nutrition, sometimes causing diarrhea.  

It is important to note that infections, digestive disorders, food allergies or intolerances, surgery, or medications can cause diarrhea. Diarrhea is a sign that your body is not processing food optimally. 

Additional symptoms of not eating enough include constipation, feeling sluggish or weak, irritability or “hangry,” and a body mass index categorized as underweight. 

Seeking Help from a Dietitian

Gut health dietitians are trained to help you determine the right amount for your body and life stage. They are also trained to help you resolve your diarrhea and replenish the nutrients needed to thrive. 

Nourish has a team of expert dietitians available for online appointments. Find a dietitian near you to better understand the link between nutrition and healthy bowel movements.