Carbohydrates are one of the three macronutrients classes that provide energy to our bodies.
Carbohydrates contain carbon, hydrogen and oxygen. Plants make one type of carbohydrate,
glucose, through the process of photosynthesis.
Simple carbohydrates include monosaccharides and disaccharides. Glucose, fructose, and
galactose are monosaccharides; lactose, maltose and sucrose are disaccharides.
All complex carbohydrates are polysaccharides. They include starch, glycogen, and fibre. Starch
is the storage form of glucose in plants, while glycogen is the storage form of glucose in animals.
Fibre forms the support structures of plants; our bodies cannot digest fibre. Different types of
fibres have different physical properties. Soluble fibres absorb water and swell to form gels,
which slow down movement of material through the intestinal tract. Insoluble fibres attract water
and speed up the movement of material through the large intestine.
Carbohydrate digestion starts in the mouth and continues in the small intestine. Glucose and
other monosaccharides are absorbed into the bloodstream and travel to the liver, where non-
glucose sugars are converted to glucose. Glucose is either used by the cells for energy or is
converted to glycogen and stored in the liver and muscle for later use.
Two hormones, insulin and glucagon, are involved in regulating blood glucose. Insulin lowers
blood glucose levels by facilitating the entry of glucose into cells. Glucagon raises blood glucose
levels by stimulating gluconeogenesis and the breakdown of glycogen stored in the liver.
The glycemic index is a value that indicates the potential of foods to raise blood glucose and
insulin levels. Foods with a high glycemic index cause sudden large increases in blood glucose
and insulin, while foods with low glycemic index cause low to moderate fluctuations in blood
glucose. The glycemic load may be of greater value that the glycemic index alone because it
takes into account the amount of the food eaten.
Carbohydrates are an excellent energy source for us at rest and during exercise, and provide 4
kcal (17 kJ) of energy per gram. Carbohydrates are necessary in the diet to spare body proteins
and prevent ketosis.
Complex carbohydrates contain fibre and other nutrients that can reduce the risk for obesity,
heart disease, and diabetes. Fibre may reduce the risk of colon cancer; helps prevent
hemorrhoids, constipation, and diverticulosis; may reduce risk of heart disease; and may assist
with weight loss.
The RDA for carbohydrates is 130 grams per day; this amount is sufficient only to supply
adequate glucose to the brain. The AMDR for carbohydrate is 45% to 65% of total energy intake.
Added sugars should provide 25% or less of total energy intake.
Added sugars are sugars and syrups added to foods during processing or preparation. Our intake
of added sugars should be 25% or less of our total energy intake each day. Sugar causes tooth
decay but does not appear to cause hyperactivity in children. Higher intakes of simple sugars are associated with increase in triglycerides and low-density lipoproteins. Diets high in sugar can
cause unhealthy changes in blood lipids but do not cause diabetes. The relationship between
added sugars and obesity is controversial.
The adequate intake for fibre is 25 grams per day for women and 38 grams per day for men. May
Canadians eat only half the fibre they need each day. Foods high in fibre and complex
carbohydrates include whole grains and cereals, legumes, fruits and vegetables. The more
processed food, the fewer complex carbohydrates it contains.
Alternative sweeteners can be used in place of sugar to sweeten foods. Most of these products do
not promote tooth decay and contribute little or no energy. The alternative sweeteners approved
for use in Canada are considered safe when eaten in amounts less than the acceptable daily
intake. Some are not recommended for pregnant and breastfeeding women, however.
Diabetes is a disease that results in dangerously high levels of blood glucose. Type 1diabetes
typically appears at a young age; the pancreas cannot secrete sufficient insulin injections are
required. Type 2 diabetes developing over time and may be triggered by obesity: the body’s cells
are no longer sensitive to the effects of insulin or the pancreas no longer secretes sufficient
insulin to meet body needs. Supplemental insulin may or may not be needed to treat type 2
diabetes. Diabetes increases the risk of dangerous complications, such as heart disease,
blindness, kidney diseases, and amputations. People with type 2 diabetes also must monitor their
blood glucose levels closely.
Lifestyle plays an important role in controlling diabetes. Many cases of prediabetes and type 2
diabetes could be prevented or delayed with a balanced diet, regular exercise, and the
achievement and maintenance of a healthy body weight.
Hypoglycemia refers to lower than normal blood glucose levels. Reactive hypoglycemia occurs
when the pancreas secretes too much insulin after a high-carbohydrate meal. Fasting
hypoglycemia occurs when the body continues to produce too much insulin even when someone
has not eaten.
Lactose intolerance results from the inability to digest lactose because of insufficient amounts of
lactase. Symptoms include intestinal gas, bloating, cramping, dia