Your body functions — and your good health and energy — rely on nutrients and calories absorbed after eating. Understanding how digestion works can help ensure you're properly fueled for your next exercise session or three-hour meeting.
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And although you can't see it, you need those digested nutrients for cell repair and muscle growth, per the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
Breaking Down Digestion
How long food takes to digest is a question many people have when making decisions about things like scheduling a workout and going to bed. Although the exact time it takes you to digest food and absorb nutrients varies, there are average estimates.
According to Jonathan Waitman, MD, an internist specializing in endocrinology and nutrition at Weill Cornell Medicine in New York City, it can take anywhere from 24 to 72 hours to break down foods into components that can be more easily absorbed. And while that may seem like a long time, food has to go through a complicated process in order to be fully digested.
"Once food is taken in orally, it then passes through the digestive system in a specific sequence: mouth, esophagus, stomach, small intestine, large intestine, and finally, expelled through the anus," Dr. Waitman says.
In general, Dr. Waitman says that most food — about 90 percent — is emptied from the stomach within four hours. As part of overall digestion, Dr. Whitman explains, the pancreas, liver and gallbladder help by secreting enzymes and bile into the gastrointestinal tract.
How Nutrients Are Absorbed
According to Dr. Waitman, your body will start accessing most nutrients about six to eight hours after eating. Some may take longer, some less. For example, simple carbohydrates such as sugars are digested quickly and pushed into your bloodstream faster than other food, according to the Harvard T.H. Chan School of Public Health.
Most of the nutrients in your food are absorbed by the small intestine, according to NIDDK. Nutrients are then passed onto other parts of your body to use or store. Once in your bloodstream, nutrients like amino acids, simple sugars and some vitamins are carried by your blood to the liver where they're processed and delivered to the rest of your body for things like cell repair and muscle growth.
Calories and Your Body
You probably know that you can boost your health and reduce your risk of disease by eating a healthy set of nutrients and calories. This way, your body and all its moving parts and processes can continue to function properly, even when at rest.
Your body and brain need vitamins, minerals and other key nutrients to carry out a range of normal functions, and you can't make them on your own, according to Harvard T.H. Chan School of Public Health, so this is where healthy foods come to the rescue.
To determine individual needs, the USDA's 2015-2020 Dietary Guidelines for Americans gives calorie estimates based on age, sex and physical activity level. In general:
- Adult women should take in between 1,600 to 2,400 calories every day.
- Adult males should take in 2,000 to 3,000 calories every day.
The lower end of these estimates applies to people who are more sedentary, whereas the higher end is for people who are moderately to very physically active.
Some people may enjoy the challenge of making nutrient-rich food choices, while others may find it daunting. These recommended healthy food groups can help you stay on the track to vitality:
- Fruits and vegetables (eat a rainbow of colors in each group).
- Whole grains as much as possible.
- Fat-free or low-fat dairy.
- Protein, including lean meats, poultry, eggs, seafood, legumes and seeds.
- Plant-based fats like olive oil.
Balancing Your Needs
If you're ever having a difficult time putting together a meal plan that meets these goals, or you're experiencing disordered eating or worried that you or someone you know might be at risk of developing disordered eating, help is available.
The first place to start is with your doctor, who can help you with community resources, including mental health experts and dietitians specializing in eating disorders. Beyond your doctor's office, there are several online resources, such as:
- Harvard T.H. Chan School of Public Health: “Carbohydrates and Blood Sugar”
- Harvard T.H. Chan School of Public Health: “Vitamins and Minerals”
- Jonathan Waitman, MD, internist, comprehensive weight control program, Weill Cornell Medicine; medical director, specialized nutrition support, New York Presbyterian Hospital, New York City
- National Institute of Diabetes and Digestive and Kidney Diseases: “Your Digestive System & How It Works”
- U.S. Department of Agriculture: “2015-2020 Dietary Guidelines for Americans”