Carbohydrates (also called saccharides) are a chemical group of substances found in bread, flour, cereals, sweets, fruit and vegetables. They represent the most common source of nutrients
for the human body, followed by proteins and fats.
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Our body uses carbohydrates mainly as energy sources. They represent the fuel of choice for the organism, since they can be burned more easily than fats or proteins.
One gram of carbohydrates provides 4.5 kcal of energy to our body.
If the body's energy needs exceed the carbohydrate supplies available, the organism starts breaking
down fat reserves to produce the necessary energy. (Long-term, this would result in weight loss.)
Understanding this point is essential for the success of any weight loss program. (The much acclaimed Southbeach Diet is predicated to a large extent on this difference.)
In fact, sugars are a particular type of carbohydrates: More precisely, sugars are simple carbohydrates (containing 1 or 2 molecules in their structure), as opposed to complex carbohydrates (which contain a higher number of molecules).
Why is it important to know this? Because the sugars most commonly used in the food industry, especially in processed foods, have a high glycemic index and are detrimental for weight control. Whereas, complex carbohydrates such as fiber and starches (especially starches from whole grain products) constitute staples of a healthy diet, and if used in proper portions are beneficial for weight control.
Therefore, learning to recognize and avoid foods rich in sugars is essential for a weight loss program.
The most common examples of sugars are:
- sucrose (the sugar used in most sweet food products)
- lactose (the sugar in milk and dairy products)
- fructose (the sugar in fruit and certain vegetables)
|Remember: Simple Carbs are referred to as "Sugars"
For most prepackaged food products, the amount of "sugars" can be found on the nutrition label. A number greater than 6-7 grams of sugars per serving usually indicates the respective food is a poor choice for a weight control diet.
Milk and dairy products constitute exceptions to the rule above, since lactose (the sugar present in dairy) has a reasonable glycemic index (about half that of glucose). As such, even though one serving (8 fl. oz) of milk brings in about 12 grams of sugars, this is an acceptable number for a weight control diet.
Fruit represent another exception, since fructose (the sugar present in fruit) has a low glycemic index (about 1/5 that of glucose). Therefore, even though fruit may contain 20 gram of sugars per serving, this is acceptable from the point of view of weight control.
Carbohydrates (Carbs) can be classified as simple or complex (dependent on how many molecules are present in their structure):
- If a limited number of molecules are present, we talk about simple carbohydrates (sugars).
- If a large number of molecules are present, we talk about complex carbohydrates (starches, glycogen, fiber).
- Monosaccharides (containing a single carbohydrate molecule in their structure). Among these, the following are commonly encountered in foods:
- Disaccharides (containing 2 carbohydrate molecules bound to each other). Among these, the following are commonly encountered in foods:
- Sucrose - the refined sugar generally used for sweetening and cooking ( contains one molecule of glucose + one molecule of fructose)
- Lactose - the sugar present in milk and other dairy products (contains one molecule of glucose + one molecule of galactose)
- Maltose - the sugar found in germinating cereals such as barley (contains 2 molecules of glucose bound together)
As a rule of thumb:
- Starches (which are chains of multiple glucose molecules bound to one another) - mainly
found in bread, cereals, certain fruit (such as bananas) and certain vegetables (such as
- Glycogen (chains of multiple glucose molecules bound together, but in a different
arrangement than in starches) - found mainly in the body tissues of animals and humans.
- Cellulose (chains of glucose molecules bound together in such a way that they are not
digestible in the gut). Cellulose is found primarily in plants, including vegetables and the skin of fruit. It provides the so-called "dietary fiber" (or
insoluble fiber), which forms the intestinal bulk and ensures regularity. It also regulates and stabilizes blood glucose levels, by prolonging the emptying time of the stomach, and delaying the absorption of various nutrients which it binds to in the gut.
- Soluble fiber - complex carbohydrates which are not digestible in the small intestine, but do undergo fermentation in the colon. The end-products of this fermentation process are absorbed into the bloodstream and transported to the liver, where they play an important role in decreasing LDL cholesterol ("bad cholesterol"). Similar to dietary fiber, soluble fiber also regulates and stabilizes blood glucose levels, by prolonging the absorptions time of sugars and other nutrients from the intestine. Soluble fiber can be found in fruit (other parts than the skin), oat bran, vegetables such as carrots, dried beans and peas, nuts, barley, flaxseed, and psyllium husk.
| Simple Carbs are more likely to cause weight gain than Complex Carbs.
| Simple Carbohydrates are often referred to as "Bad Carbs".
Exceptions to the rule above:
- Fructose - a monosaccharide found in fruit and certain vegetables - is considered a good carb. It's glycemic index is about 1/5 that of glucose.
- Lactose - a disaccharide found in dairy products - is also an acceptable carb.
Complex carbohydrates from whole grain products are more beneficial for weight control
than those from refined (enriched) products, since they cause a smaller and more gradual
increase in blood glucose (see detailed explanation below).
In any weight control program, knowing what carbs to eat can mean the difference
between success and failure. In order to understand why carbohydrates behave so differently in
our body, we have to understand the way carbohydrates are absorbed, broken down and used for
- Simple carbohydrates (sugars) are quickly absorbed from the bowel into the blood, causing a sharp rise in blood glucose levels (hyperglycemia). Hence,
these carbs are called "bad carbs", or carbs with high glycemic index. The sharp
rise in blood glucose causes the secretion of the hormone insulin (which is meant
to remove the excess sugar from the blood). Unfortunately, insulin also mediates
the synthesis of fat and its accumulation in fat tissues.
Under the influence of insulin, the simple carbohydrates (sugars) are rapidly
removed from the blood - either broken down for immediate energy usage, or
converted to glycerol and used to synthesize fats, or stored in the liver as
The resultant swing in blood sugar levels (from high to low - as the glucose is removed from the bloodstream) is likely to cause fatigue
and hunger shortly after eating, which in turn may prompt repeat food intake.
- Complex carbohydrates behave quite differently from simple carbohydrates:
- Starches are complex carbohydrates present in bread, flour, cereals, certain fruit
(like bananas) and certain vegetables (like potatoes). Due to their long chains
and high number of molecules, starches take longer to be broken down in the
bowel and absorbed into the bloodstream. Therefore, blood sugar levels rise
more gradually, causing a lesser degree of insulin secretion. As such, the
negative effects mentioned above are largely attenuated. This is especially true
for starches coming from whole grain products (such as whole grain breads,
cereal, rice, pasta), which take longer to be digested than starches from refined or
enriched products. Refined bread products such as white breads, pastries, dough,
etc, where the starches can be broken down to glucose more rapidly, have a
higher glycemic index and a more marked effect on blood glucose levels than
whole grain bread products. Cooked or baked items such as potatoes are also
easily digestible and therefore cause a higher increase in blood glucose.
- Cellulose (another complex carbohydrate present in vegetables and in the skin of
fruit) is entirely non-digestible, i.e. it cannot be broken down in the bowel and hence
is not absorbed into the blood. As such, it doesn't contribute any calories into the
body, and does not cause any change in blood sugar levels. Cellulose remains in the
intestine as insoluble fiber (dietary fiber), promoting regularity and good bowel
- Soluble fiber is represented by complex carbohydrates present in oat bran, the pulp of fruit, certain vegetables, barley, flaxseed, nuts, etc. Soluble fiber is non-digestible (i.e., it cannot be broken down in the small intestine), but does
undergo a process of fermentation in the colon (large intestine). The products of this fermentation
process are absorbed into the bloodstream, and appear to play a role in lowering
cholesterol and regulating blood sugar. As such, soluble fiber is a member of the "good carb" family.
- Processed foods rich in refined sugars have a high glycemic index and are highly detrimental for weight control.
- Most fruit are beneficial for weight control
(in adequate portions) - since the sugar in fruit is represented by fructose, which has a low glycemic index.
- Most vegetables
are highly beneficial for weight control (especially green leafy vegetables) - since they contain very few sugars and are rich in fiber (which is non-digestible).
- Whole grain products containing starches and fiber (such as whole grain breads, cereals, pasta, etc) have a relatively low glycemic index and are largely beneficial for weight control if consumed in adequate portions.
So in conclusion, it's not only about the amount of carbs in your food, but also about the type of these carbs. Frequently, the generic term low-carb diet is used to encompass both these aspects. In fact, the term is so frequently used it has become a main staple of our dieting vocabulary.
To see how and when it started, visit History of Low-Carb.
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