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The GI Diet Under the Spotlight
By WLR Dietitian
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It seems every couple of years another diet finds favour
amongst A-list celebs and creates a media storm. This time
it's the turn of the Glycaemic Index or GI diet to jump into
the spotlight.
But before dismissing it as
just another 'celebrity slimming craze' only suitable for the
rich and famous, there's some good news: this is a diet that
most nutritionists and dieticians actually like, too. Here's
the lowdown...
What exactly is the Glycaemic Index?
In 1981, professor of nutrition Dr David Jenkins was
looking at how different carbohydrate-rich foods affected
blood sugar levels in people with diabetes and discovered
that, contrary to popular belief, many starchy foods affected
blood sugar levels quite dramatically, while some sugary foods
had little effect. From his research, he developed a scale
called the Glycaemic Index, which quite simply ranked foods
based on the effect they had on blood sugar levels.
How it works
The Glycaemic Index runs from 0 to 100 and usually uses
glucose - which has a GI value of 100 - as the reference. The
effect other foods have on blood sugar levels are then
compared with this. In simple terms, the GI index tells us
whether a food raises blood sugar levels dramatically,
moderately or a little bit. Foods that have only a slow, small
effect on blood sugar have a low GI value, while those causing
a rapid and massive rise in blood sugar have a high GI value.
So what's the link with weight loss?
The theory behind diets based on the Glycaemic Index is
that foods with a low GI value slowly release sugar into the
blood, providing you with a steady supply of energy, leaving
you feeling satisfied longer so that you're less likely to
snack. In contrast, foods with a high GI value cause a rapid -
but short-lived - rise in blood sugar. This leaves you lacking
in energy and feeling hungry within a short time, with the
result that you end up reaching for a snack. If this pattern
is frequently repeated, you're likely to gain weight as a
result of constantly overeating.
Glycaemic Index of foods
There are many books and websites that list the GI index
for different foods. Food values may vary slightly depending
on the source, but in general, they should all be roughly the
same.
Many lists divide the foods into low, medium/moderate
and high categories. Foods in the low category usually have a
GI value of 55 or less; in the medium category, a GI value of
56 to 69; and in the high category, a GI of 70 or more. This
Glycaemic Index Table gives
examples of the GI values of food. You might be surprised by
some of the foods included in the low and high categories -
for example, 'healthy' rice cakes and branflakes actually have
a high GI whereas salted peanuts and milk chocolate have a low
GI value!
How do GI diets work?
Diets based on GI index simply encourage you to eat plenty
of foods with a low GI value and avoid those with a high GI
value. This helps to prevent swings in blood sugar, helping
you feel fuller for longer. However, most GI diets also
recommend cutting down on fat, especially saturates. This
means many of the foods which have a low GI value but are high
in fat - whole milk, crisps and chocolate, for example - are
still limited.
What affects the GI value of a food?
There are several things. Firstly, the overall nutrient
content of a food will affect its GI. For example, fat and
protein affect the absorption of carbohydrate. This helps to
explain why chocolate, which is high in fat, has a low GI
value. It also explains why high-fat crisps have a lower GI
value than low-fat jacket potatoes. Whole milk also has a low
GI value because it's packed with protein and fat.
How you cook a food, the degree of processing and the
ripeness and variety of a fruit, for example, also affect its
GI. Even the structure of the carbohydrate itself influences
the GI. For example, processed instant oatmeal has a higher GI
than traditional rolled oats used to make porridge. This is
because, as a result of the processing, the starch in instant
oats is more easily exposed to digestive enzymes, causing it
to break down and enter the bloodstream more rapidly.
Meanwhile, some foods have low GI values because they are
packed with fibre, which acts as a physical barrier, slowing
down the absorption of carbohydrate into the blood.
So what happens when I eat a meal?
GI index charts only identify the effect different foods
have on bloods sugar levels when they are eaten on their own
and, consequently, many nutritionists believe this is one of
the main problems with GI diets. Basically, when you eat a
mixture of foods together as in a meal, the GI value of that
whole meal changes. As a guideline though, the more low GI
foods you include in a meal, the lower the overall GI value of
that meal will be.
Are there any cons to the GI diet?
As outlined above, one of the main limitations to GI diets
is the fact it's difficult to identify the GI value of a meal.
Meanwhile, some foods with a low GI value are also packed with
fat and/or salt and contain few nutrients. Chocolate and
crisps, for example, are high in fat and contain few vitamins
and minerals. Meanwhile, a 50g pack of salted peanuts contains
around 5g of salt - that's almost the maximum amount
recommended by nutrition experts for good health!
Consequently, it's possible to follow a GI diet that's packed
with fat and lacking in many of the nutrients you need to stay
healthy. However, most GI diet plans come with advice to cut
down on the amount of fat you eat and recommend avoiding many
of the high-fat, low GI foods. For example, they recommend
choosing skimmed milk over whole milk.
What do the experts think?
In general, most nutritionists and dieticians are
supportive of the basic principles of the GI diet. They do,
however, believe that you shouldn't get too hung up about
avoiding all high GI foods because when foods are eaten
together in a meal, that meal can have a very different GI
value to the individual foods it contains.
How much weight can I expect to lose?
Most GI diets suggest you will lose around 1-2lb a week,
possibly with a slightly greater loss in the first few weeks
when your body loses water as well as fat. This follows the
guidelines recommended by nutrition experts.
How does it differ from the Atkins Diet?
Unlike the Atkins
Diet, which bans most carbohydrates, especially in the
early stages, GI diets actively encourage you to eat many
carbohydrates and antioxidant-rich fruit and veg. The diet is
also high in fibre which means you're less likely to get
constipated and, because carbohydrate isn't restricted to any
great degree, you won't get the other unpleasant side effects
associated with the Atkins Diet, such as bad breath and
headaches. GI diets also tend to follow
healthy eating guidelines and are low in fat, especially saturates. And if
that's not enough, GI diets are much easier to follow if you
are a vegetarian!
Are there any other health benefits to the GI diet?
Following a diet that includes plenty of foods with a low GI
index may have a role in helping to prevent or reduce the risk
of getting Type 2 or maturity-onset diabetes, according to
experts at Diabetes UK, the largest diabetes organisation in
the UK. Research has also shown that lower GI diets can help
improve levels of 'good' cholesterol and so may reduce the
risk of heart disease.
Is a GI diet suitable for people with diabetes?
Anyone with diabetes should always check first with their
doctor before making changes to their diet. However, most
diabetes experts agree that including foods with low GI value
in meals can help to maintain even blood sugar levels.
However, they also agree that eating to
control diabetes,
isn't just about looking at the GI value of foods. You should
also focus on eating a balanced, healthy diet you can stick
with for life.
Juliette's verdict
At last, here's a diet that's popular with the media but
still follows basic healthy
eating guidelines! The diet generally contains plenty of
fruit and veg and recommends eating fewer refined and sugary
carbohydrates. Meanwhile, if you want to give the diet a go,
always remember to apply the general principles of healthy
eating - a healthy diet wouldn't recommend including huge
amounts of chocolate, crisps or whole milk and neither should a
GI diet. Having said this, there's little to argue about with
a diet that recommends swapping baguettes and bagels for
wholegrain breads, cornflakes for porridge, and white rice for
wholemeal pasta.
Further information
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