Carbohydrates as a source of energy

While we often hear that we should be "cutting back" on calories, it is important to understand that our bodies need calories for energy - to grow, function, and be active. A calorie is a unit of measurement. Calories measure the energy in foods as well as the energy used by our bodies. To reach and maintain a healthy body weight, it is important to find the right balance of "calories in" from the foods you eat with "calories out" that your body uses for basic body functions and physical activity. 

Foods and beverages containing carbohydrate, fat, and protein all provide energy in the form of calories. The number of calories in a food or beverage depends on the calories coming from the combination of these nutrients. You can use the Nutrition Facts table on food and beverage packaging to find out how many grams of carbohydrate, fat, and protein the product contains, as well as the total number of calories in each serving. 

  • Carbohydrates (sugars and starches): 4 Calories per gram. Carbohydrate foods include bread, cereal, pasta, rice, legumes (peas, beans, lentils), fruits and fruit juices, starchy vegetables like potatoes, table sugar, and other sugars like honey or corn syrup. Fibre is also a carbohydrate, contributing 2 Calories per gram because it is not fully digested into energy. Fibre can be found in vegetables, fruit, legumes, and whole grains and cereals. 
  • Protein: 4 Calories per gram. Foods that contain protein include meat, fish, poultry, eggs, milk products and soy products. 
  • Fat: 9 Calories per gram. Examples of foods that contain fat are butter, margarine, oils, salad dressings, fried foods, meats, cheeses, and nuts. 

Don't forget about alcohol! It has 7 Calories per gram. 

To learn more, see our resource Clips on Sugars - Calories and Body Weight

Carbohydrates in a balanced diet

The eating pattern in  Canada's Food Guide  recommends that about half of our energy come from carbohydrates (45-65%). Protein and fat make up the balance of our energy needs and the recommended amounts vary by different age groups (see table). 

Recommended Percentage of Daily Calories
Age Group Carbohydrate Protein Fat
0-4 years 45 - 65% 5 - 20% 30 - 40%
4-18 years 45 - 65% 10 - 30% 25 - 35%
19 years and over 45 - 65% 10 -35% 20 - 35%

Carbohydrates in the Food Guide come from starches, sugars and fibre in Vegetables and Fruit, Grain Products, Meat Alternatives (legume) and Milk and Alternatives. We also get carbohydrates from the starches and sugars added to foods and beverages. 

A healthy eating pattern has the right balance of carbohydrate, fat, and protein, as well as enough of the essential vitamins, minerals, and other nutrients our bodies need.

How the body uses sugars for energy

Sugar (sucrose) is a carbohydrate. During digestion, carbohydrates (sugars and starches) are broken down by enzymes into single units (glucose, fructose, and galactose), which can easily be absorbed into the blood stream for use as an important energy source throughout the body. In fact, glucose is the primary energy source in the body, especially for the brain and red blood cells. Fibre is digested by bacteria in the large intestine. 

Here is a look at how we track the digestion and absorption of carbohydrates through the human body:

Mouth: Carbohydrates are eaten as sugars and starches. The saliva in our mouths contains a digestive enzyme called amylase, which begins to break down some of the starch contained in the foods we eat. 

Stomach: Chewed carbohydrate mixes with stomach juices to produce a thick liquid called chyme, which empties into the small intestine. 

Pancreas: The pancreas releases digestive juice into the small intestine; enzymes in the juice break down starches and sugars into single molecules such as glucose that can then be absorbed by the small intestine. The pancreas also releases insulin into the blood that lets other parts of the body (like muscles) know when it's time to use glucose from the blood for energy. 

Small Intestine: With the help of enzymes, all carbohydrates break down into three single molecules - glucose, fructose, and galactose, which are absorbed into the blood and carried to the liver. 

Liver: The liver releases glucose into the blood and directly to the cells for use. Extra glucose can also be stored by the liver for future use, usually in the form of glycogen in the liver or muscle. 

Large Intestine: The large intestine receives non-digested food from the small intestine, absorbs water and some vitamins and minerals, digests dietary fibre, and stores waste before it is excreted.