There are many types of different sugar, but we are going to look at the "big four". We will look at others, such as maltose and galactose in a different entry.
You've probably heard the terms fructose, glucose, lactose and sucrose before, and you may know
that they're all types of sugar. But do you know how they differ from one
another, or whether some are better for you than others?
Sugar is very much linked to carbohydrates:
Carbohydrates are classified into two
basic groups, complex and simple.
Complex carbohydrates are composed of
multiple simple sugars, joined together by chemical bonds. The more
chains and branches of simple sugars, the more complex a carbohydrate
is and in turn, the longer it takes to be broken down by the body and the
less impact it has on blood sugar levels. Examples of complex carbohydrates
include wholegrains such as jumbo oats, brown rice, spelt, rye and
barley.
Simple carbohydrates are either
monosaccharides (one sugar molecule) or disaccharides (two sugar molecules).
They are digested quickly and release sugars rapidly into the
bloodstream. The two main monosaccharides are glucose and fructose.
The two major disaccharides are sucrose (composed of glucose
and fructose) and lactose (which is made up of galactose and
glucose)
GLUCOSE
What is
glucose?
Glucose is
the primary source of energy your body uses and every cell relies on it to
function. When we talk about blood sugar we are referring to glucose in
the blood. When we eat carbohydrates, our body breaks them down into units of
glucose. When blood glucose levels rise, cells in the pancreas release insulin,
signalling cells to take up glucose from the blood. As the cells absorb sugar
from the blood, levels start to drop.
The nutritional
profile of glucose
The glycaemic
index is a ranking of how quickly foods make your blood sugar levels rise after
eating them. High GI foods are very easily broken down into glucose. Glucose is
the defining standard and has a GI value of 100. Glucose alone does not
taste particularly sweet compared to fructose and sucrose.
How does
glucose affect your body?
Research
suggests that, as glucose stimulates insulin release from the pancreas, it also
results in the release of two other hormones, leptin and ghrelin. Leptin is known as the appetite suppressor and ghrelin the
appetite increaser. It is thought that lower GI foods (such as wholegrains,
proteins and those lower in glucose) suppress ghrelin, therefore
regulating satiety
FRUCTOSE
What
is fructose?
Fructose or
fruit sugar, is a simple sugar naturally occurring in fruit, honey, sucrose and
high fructose corn syrup. Fructose is very sweet, roughly
one-and-a-half times sweeter than sucrose (white sugar). Because of
the worldwide increase in the consumption of sweeteners - in soft drinks
and foods containing high fructose corn syrup (HFCS) - fructose intake has
quadrupled since the early 1900s.
The
nutritional profile of fructose
Fructose
is absorbed directly into the bloodstream during digestion and has no impact on
insulin production or blood glucose levels. Consequently, its GI value is much
lower, on average around 19. It was once thought this made it a good substitute
for table sugar, but there is now a growing body of research to question
this.
Sweeteners
such as HFCS have a higher GI value due to the presence of glucose. It has
been suggested that it is the glucose content of these sweeteners that may
have contributed to the increase in cardiovascular disease and type 2
diabetes. (sweeteners are artificial sugars).
How
does fructose affect your body?
Fructose
is handled by the body in a different way to glucose as it is metabolised in
the liver. As a result, blood sugar (glucose) levels do not rise as rapidly
after fructose consumption compared to other simple sugars. When you eat too
much fructose the liver cannot process it fast enough and instead, starts
to make fats that are carried in the blood and stored as
triglycerides- the body's main form of fat. Studies have shown that the consumption
of large amounts of fructose may lead to increased appetite by
impairing the body's ability to use insulin and to suppress
circulating ghrelin (the appetite-stimulating hormone).
While
most diabetics cannot tolerate sucrose, most can tolerate moderate amounts of
fruit and fructose without loss of blood sugar control. Research is yet to
show any detrimental health effects of moderate consumption of fructose as
part of a balanced diet.
SUCROSE
What is sucrose?
Sucrose is
crystallised white sugar produced by the sugar cane plant and can be found
in households and foods worldwide. Sucrose is a disaccharide made up of 50%
glucose and 50% fructose and is broken down rapidly into its constituent parts.
The nutritional
profile of sucrose
Due to its glucose
content, sucrose has a GI value of 65. As it is made up of glucose and
fructose, the latter is metabolised in the liver and holds the same issues as
those mentioned for fructose above. Due to its glucose content, sucrose does
lead to an elevation in blood glucose. Diabetics should therefore be mindful of
foods containing sucrose
LACTOSE
What
is lactose?
Lactose
is a sugar found in milk. It is a disaccharide made up of glucose and galactose
units. It is broken down into the two parts by an enzyme called lactase. Once
broken down, the simple sugars can be absorbed into the bloodstream.
The
nutritional profile of lactose
Whole
milk has a GI value of 41 and is considered to be a low GI food. It is broken
down slowly and helps to increase the absorption of minerals such as
calcium, magnesium and zinc. Some people experience lactose intolerance– an
inability to produce the lactase enzyme that breaks down milk. Lactose
intolerance can lead to diarrhoea, bloating and other gastrointestinal symptoms
HMHB Conclusion
The
current recommendations from the World Health Organisation (WHO) are that
only 5% of your daily calorie intake should consist of added, or 'free'
sugars. This equates to approximately seven teaspoons (30g) for an adult.
To put this into perspective, one can of fizzy drink may contain
seven teaspoons or more, so it's easy to reach the recommended daily
amount, especially when you consider the sugar added to food that you don't see.
Eating
excess sugar can lead to weight gain, which increases the risk of heart disease
and type 2 diabetes. Your body needs
sugar, but you have to control its intake
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