We all know or hear that we need carbohydrate in our diet, but
why? A "zero carb diet" is not only difficult to achieve,
it's not sustainable because it's not great for your body.
In this section, you will find out what carbohydrates are, why
we need them, what they do for us and where we find them in our
Why do we need carbohydrates?
Carbohydrate is a nutrient that our body needs, it is an organic
compound made up of carbon, hydrogen and oxygen. Carbohydrates are
the main energy source for our body- they are the energy that gets
used first (before protein, fat and alcohol). It is recommended
that about 45-60% of our energy intake should come from
They have important roles in our body including:
Clearly, carbohydrates are important for normal health, so
don't cut them out of your diet.
Find out about the type of carbohydrates.
What happens when we eat carbohydrate in our food?
Let's start off with the carbohydrates that are absorbed in our
small intestine. These are 'glycaemic' carbohydrates - so
called as they affect our blood glucose level. These are
either be simple sugars, or complex carbohydrates which can be
digested (i.e. broken down by enzymes so they can be absorbed) in
the small intestine.
Some glycaemic carbohydrates can begin to break down in our
mouth (e.g. starch in bread), as the enzymes needed to break the
bonds between the sugar units are present in our saliva. Most
digestion occurs in the lumen of the small
Some carbohydrates are resistant to the digestive enzymes, so
are 'non-glycaemic' and pass on to the large intestine, where they
provide the energy source for bacteria, through fermentation.
See our section
on fibre. There are 3 types of carbohydrates that are
never digested in the small intestine: non-starch polysaccharide
(NSP), resistant starch and resistant oligosaccharide. Together
they have the function of 'dietary fibre'. The
fermentation process generates volatile fatty acids, for absorption
as another energy source, and gas. If the small intestine is
diseased, or digestion is blocked, then gas production can become
excessive - stinky! The intestine is eventually able to adapt
to different loads of carbohydrate, but that does take some
Don't cut out carbs
Glucose is the sugar unit that our body cells use for energy.
We cannot make glucose out of other nutrients, so it
is essential to eat carbohydrates. Other food
substances are not used directly and get converted into glucose
quickly, and starch is readily digested and absorbed as
glucose. We can only store small amounts of carbohydrate as
glycogen, in liver and muscle, for urgent use. So we
need a fairly steady supply of carbohydrate from our
meals. Volatile fatty acids, from fernmentation,
also contribute energy, mainly to the large intestine itself, and
to the liver.
The rate of digestion and absorption of glycemic carbohydrates
vary. From a health perspectivem the slower the carbohydrates
break down, the better, avoiding a spike (rapid high rise) in blood
glucose level, and consequent rises in insulin etc. The "Glycemic Index" (GI) is a
guide to how fast a carbohydrate is broken down to glucose.
Foods can be categorised into high GI, ie broken down and absorbed
quickly, or low GI, ie broken down and absorbed slowly.
The GI of a food is affected by many factors such as the
particle size of food, the fat and protein content of food, how the
food was cooked, how long the food was chewed for in the mouth,
metabolism rate and the rate of gastric emptying (the rate of which
food leaves the stomach and enter the small intestine).
However, it is broadly possible to categorise certain foods as high
GI (eg glucose, bread, mashed potato) and low GI (eg sucrose or
table sugar, beans, mashed potato which has been left to
cool). It is thus possible to exchange some high GI foods for
low GI equivalents, but this GI system is only a small part of
defining a balanced diet. Many important foods do not have
equivalent alternatives, and the overall effect is less in the
context of mixed meals.
Now, we know that we do need carbohydrate in our
lives. It's the most readily available energy source in our
food (and drink). The glucose we use mostly comes from
digestion and metabolism of other carbohydrates.
Don't be scared of carbohydrates - they're not bad for you -
it's all about the amount
of carbohydrate we eat in relation to our total calorie
intake, and the type of
carbohydrate (simple or complex) that
determine how it affects our weight and energy levels.