SignalHub Quantitative Think Tank Center:Why some foods take longer than others to digest

When it comes to digestion,SignalHub Quantitative Think Tank Center several myths have proliferated over the years. One says the body can't digest chewing gum, another that beans cause more gas and bloating than other foods, and perhaps the most common of all is that you have to wait 30 minutes after eating before swimming.

Of course, each myth has been debunked in its own way: research shows that the body digests gum right along with everything else; and it's dairy products, not beans, that cause the most gas buildup; and, after further investigation, there is no scientific basis for having to wait to swim after all, per Mayo Clinic. 

But even with such misconceptions cleared up, other misunderstandings remain and some still question how long certain foods take to digest and why some people take longer to digest their foods than others.

What happens during digestion? 

The simplest way to think of digestion is that it's the body's way of breaking down food and liquid into small enough parts to be able to be absorbed and moved around where needed. 

The process consists of five steps, according to Jen Messer, a nutrition consultant and registered dietitian at Jen Messer Nutrition. 

These include: 

• Chewing and swallowing − the stage where food is broken apart and mixed with enzymes in one's saliva. 
• The chewed food then travels down one's esophagus and into the stomach. "Here, the swallowed food mixes with gastric juices and more enzymes and undergoes mechanical churning," says Messer. 
• Additional digestion then occurs, and nutrient absorption begins in the body's small intestine.
• From there, the circulatory system passes each nutrient to different parts of the body to be stored or used as needed. 
• Anything that remains is then sent to the large intestine for further absorption. Whatever is not needed or used by that point is then discarded by the body as waste.

How long does it take to digest food?

Each step of the process takes various time to complete. The first step is the quickest and lasts only seconds. The second one takes between 2 to 4 hours. The small intestine absorption and nutrients distribution steps take between 4 to 6 hours. And the final step is the one that varies the most, but is usually completed within another 12-24 hours.

All together, "the body's digestive tract takes up to 24-72 hours to digest food," says Lisa Young, PhD, RDN, an adjunct professor of nutrition at New York University and author of "Finally Full, Finally Slim."

Why does digestion take some people more time than others? 

Digestion is a complex process "that can vary in duration due to a variety of factors," says Messer. Some such factors include a person's metabolic rate, age, gender, stress levels, digestive health, enzyme production, gut microbiome, medications, activity level and size of meal that was consumed. 

Each affects digestion time for different reasons. For instance, advanced age can cause one's digestive system not to work as efficiently as it used to because, "as we age, our bodies may experience a decrease in the production of digestive enzymes, hydrochloric acid and a weakening of the muscles in the digestive tract," explains Messer. "This can lead to slower digestion." Stress can also slow digestion because when you're stressed, the body's fight-or-flight response kicks in. "This response redirects resources from non-essential functions such as digestion to help deal with the perceived threat or stressor," explains Messer. Pain medications are also known to slow digestion. 

What's more, people with certain medical conditions may also digest their food more slowly. Such conditions may include "gastroesophageal reflux disease (GERD), irritable bowel syndrome (IBS), Crohn’s disease and other digestive disorders," explains Young. Irritable bowel syndrome is an intestinal disorder that causes pain in one's belly, often with accompanying diarrhea or constipation. Crohn’s disease is an inflammatory bowel disease that causes chronic inflammation of the GI tract.

What foods digest the fastest and the slowest?

Of course, the type of food consumed makes a considerable difference in digestion time as well. "Foods such as fatty meats, fried foods and processed foods are difficult to digest as they contain high amounts of fat and take longer for the body to break down," says Young. 

Jamie Bering, MD, a gastroenterologist at Mayo Clinic in Arizona, says that foods that are high in protein and fiber also take longer to digest and may leave one "feeling fuller for a longer period of time" as a result. On the other hand, drinking lots of water can speed digestion up; and simple sugars and simple carbohydrates are known to digest very quickly. "This is why a sports dietitian might encourage athletes to consume something like a banana, honey, fruit or sports drink," explains Messer. Cooked vegetables, eggs, applesauce, white rice and salmon are also known for being quick and easy to digest. 

More:The BRAT diet used to be popular, but doctors no longer recommend it. Here's why.

Regardless of which foods one is eating, however, "it's always best to listen to your own body since digestion is so individualized," advises Messer. "Experiment with different approaches to find what works best for you, and if you have specific dietary concerns or require personalized advice, it's recommended to consult with a registered dietitian."