The glycemic index describes how carbohydrate-containing
food affects blood glucose levels.
When we eat carbohydrates, our body breaks them down to
produce glucose. For glucose to move from the blood into the body’s cells,
it needs insulin, which, along with glucagon (stimulated through protein
intake), plays a key role in determining whether our body burns fat or
carbohydrates for energy.
The pancreas produces both insulin and glucagon.
Whenever glucose is present in the blood, insulin is stimulated; whenever
protein is present, glucagon is stimulated. If the insulin is insufficient,
however, glucose levels rise. A high level of insulin forces the body to burn
carbohydrate rather than fat, which allows fat to accumulate in the body.
Therefore, if we control the rate of glucose our body absorbs, we will also
control the amount of insulin secreted. This is where the glycemic index (GI)
comes into play.
The GI is a ranking of carbohydrates on a scale from 0
to 100 according to the extent to which they raise blood sugar levels after
eating. (Visit www.glycemicindex.com
for the index and database.)
Foods and drinks with a high GI, such as fruit juices
and sugary sweets, are those that the body rapidly digests and absorbs and
result in an excess of insulin in the blood stream. Controlling the glucose
levels of these foods and drinks allows for control over food-driven insulin
stimulation and reactive hypoglycemia.
Low-GI foods, by virtue of their slow digestion and
absorption, produce a more gradual rise in blood sugar and insulin levels,
allowing the body to utilize the glucose formed from the breakdown of complex
carbohydrates, instead of storing it in a fat cell as glycogen. When excessive
amounts of fat are stored, they enlarge the fat cells in adipose tissue and
increase the risk of chronic disease, such as cancer and diabetes. As a result,
low-GI foods have proven benefits for health.
While the GI is an important concept, there is also the
glycemic load, which is a ranking system for carbohydrate content in food
portions based on their GI and the portion size.
The usefulness of glycemic load is based on the idea
that a high glycemic index food consumed in small quantities would give the
same effect as larger quantities of a low glycemic index food on blood sugar.
For example, white rice has a somewhat high GI, so
eating 50 g of white rice at one sitting would give a particular glucose curve
in the blood, while 25 g would give the same curve but half the height. Because
the peak height is probably the most important parameter, multiplying the
amount of carbohydrates in a food serving by the GI gives an idea of how much
effect an actual portion of food has on blood sugar level.
So, why is this important to the eye care practitioner?
Nearly 60 studies link obesity to chronic eye disease, and diet and weight
definitely influence the development of age-related macular degeneration. As a
primary care practitioner, you may be the first professional to discuss these
issues with your patient – so it’s best to be prepared.
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