How Does the Body Change Food Into Energy?

Deciding what you want to eat for dinner is one thing. Knowing how your body converts food into energy is another thing entirely.

The process of changing food into a usable form starts with chewing your food. Credit: Westend61/Westend61/GettyImages

The process of changing food into a usable form once you eat it is complex. However, it's helpful to understand the basics so you can achieve your health goals.

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The process of changing food into a usable form starts with chewing your food. Your body then converts food into energy used by your muscles and various bodily systems.

The Food-to-Energy Process

Your body converts food into energy not only for strenuous physical activity, but also for activities of daily living — like getting up out of bed or even just holding a pen. In the process of changing food into a usable form, the action of chewing begins the digestive process. Enzymes in your digestive system further break down the food molecules, explains the National Science Teaching Association (NSTA).

This food-to-energy process results in sugar and fat, and, eventually, a molecule called adenosine triphosphate (ATP) is produced. ATP is then transformed into a similar molecule called adenosine diphosphate (ADP). As this change occurs, energy is released that your cells use to fuel bodily functions — from breathing and holding a cup of coffee to completing your daily workout.

You'll need to strike a careful balance between input and output for this food-to-energy process. If you take in more food than your body uses through daily living and exercise, then your body will store the excess energy — aka calories — as fat, causing weight gain.

When you take in only the calories you need, your body will maintain its weight. Take in fewer calories or use them up through exercise, and you create a caloric deficit. Over time, this deficit can allow for weight loss as your body uses stored fat for energy.

Read more: 13 Everyday Activities That Burn More Than 200 Calories

Focus on a Healthy Diet

Eating a balanced diet within your recommended calorie range will help you properly manage the input and output of calories. The Dietary Guidelines for Americans estimates adult women need about 1,600 to 2,400 calories per day, depending on activity level. Adult men need 2,000 to 3,000.

In addition, aim to eat a balance of macronutrients — about 45 to 65 percent carbohydrates, 25 to 35 percent fat and 10 to 30 percent protein, according to the Dietary Guidelines for Americans. The NSTA notes that carbohydrates and fats are good sources of energy. Proteins, vitamins and minerals are mainly used as building blocks for various processes — like building muscles, for example.

Focus on a healthy eating pattern with a variety of fruits and vegetables, whole grains, low-fat or nonfat dairy, lean proteins, some healthy fats and minimal added sugars and sodium.

This type of eating pattern will help feel full and stave off illness and disease. November 2014 research published in the journal Advances in Nutrition notes that dietary fiber, found in plants, helps to promote satiety and reduce the risk of chronic conditions like diabetes and coronary heart disease.

How Muscles Use Energy

In general, muscle fibers are classified as either slow-twitch or fast-twitch based on how they use energy for fuel. Aerobic exercise like distance running produces more slow-twitch fibers for greater endurance, says the International Sports Sciences Association (ISSA).

Anaerobic exercise like sprinting or powerlifting increases the size and quantity of powerful fast twitch fibers. These fibers fatigue more rapidly and are used for quick bursts of energy. Training these muscle fibers also improves the strength of muscles and enables hypertrophy, or increased muscle size.

Aerobic workouts trigger metabolic changes in the muscle tissue, including an increase in mitochondria — that is, the organelles that use oxygen to help create ATP, explains the American Council on Exercise (ACE).

Along with this increase in mitochondria, there's a boost in the levels of enzymes used to metabolize fat. Your muscles are then better able to access fat and use it for energy, leading to fat loss.

Read more: How Quickly Do You Lose Muscle If You Stop Lifting Weights?

Fast-Twitch for Quick Energy

Meanwhile, fast-twitch fibers use ATP stored in the muscle cells to generate energy. The metabolic changes produced by anaerobic exercise help to increase levels of ATP and supply energy to muscles, according to the ISSA.

Fast-twitch fibers are then able to act quickly and powerfully when recruited. Note that because fast-twitch fibers deplete more quickly, they require longer periods of rest between exercises to replace spent ATP, says ACE.

Your anaerobic workouts fuel fat loss, too. Anaerobic exercise boosts the production of human growth hormone and testosterone, which are both needed to increase muscle size. By growing muscle size and quantity, anaerobic exercise helps your body burn more calories at rest.

There also may be cardiovascular benefits to both aerobic and anaerobic exercise. Research published in the World Journal of Cardiology in February 2017 states that both types of workouts have a favorable effect on lipid metabolism and improved cardiovascular health.

The food-to-energy process allows you to recruit slow- or fast-twitch muscles, depending on the type of exercise. It also gives you the fuel you need to feel alert and go about your daily life.

Read more: Mass vs. Strength

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