10) GLYCEMIC INDEX
c) Glycemic Index and A1c
Generally speaking A1c is directly proportional to the average amount of carbohydrates consumed over a two to three month period, irregardless of whether or not those carbohydrates are high glycemic index or low glycemic index. But with most insulin resistant type 2 diabetes, a constant diet of high glycemic foods can raise the A1c by about 0.7%, even if the amount of carbohydrate consumed remains the same. The mechanism is really very simple and obvious. In a person with type 2 diabetes who can still produce insulin (those people with diabetes that don't inject insulin) it takes time for the beta cells in the pancreas to begin to produce insulin, on the order of roughly half an hour. The glucose from very high glycemic index foods can be in the blood stream very rapidly, in just a few minutes.
As a result the high glucose levels are unrestrained for at least half an hour and "protein poisoning" (glycating) freely for at least half an hour. A1c is simply a measure of "protein poisoning" (glycation) so the A1c rises. After the half hour is up the insulin kicks in for most type 2 diabetics and the glucose levels drop as glucose is shunted into fat storage by the action of the insulin. The "half hour" delay is a minor effect and, by itself, probably isn't a good enough reason to be religious about the glycemic index. And, if a person is injecting insulin, it has no affect what so ever. However, for some people the cycling brought about by high glycemic index foods and the weight problems this brings on are very important reasons to watch the glycemic index of foods they eat. High glycemic index foods create food cravings and hunger.
Quoting from Wikipedia:
"Several lines of recent scientific evidence have shown that individuals who followed a low GI diet over many years were at a significantly lower risk for developing both type 2 diabetes and coronary heart disease than others. High blood glucose levels or repeated glycemic "spikes" following a meal may promote these diseases by increasing oxidative damage to the vasculature and also by the direct increase in insulin levels. In the past, postprandial hyperglycemia has been considered a risk factor mainly associated with diabetes. However, more recent evidence shows that it also presents an increased risk for atherosclerosis in the non-diabetic population.
Conversely, there are regions such as Peru and Asia where people eat high-glycemic index foods such as potatoes and high GI rices, but without a high level of obesity or diabetes. The high consumption of legumes in South America and fresh fruit and vegetables in Asia likely lowers the glycemic effect in these individuals. The mixing of high and low GI carbohydrates produces moderate GI values.
A study from the University of Sydney in Australia suggests that having a breakfast of white bread and sugar-rich cereals, over time, may make a person susceptible to diabetes, heart disease, and even cancer.
The glycemic index is supported by leading international health organisations including the American Diabetes Association.
Weight control
Recent animal research provides compelling evidence that high GI carbohydrate is associated with increased risk of obesity. In human trials, it is typically difficult to separate the effects from GI and other potentially confounding factors such as fibre content, palatability, and compliance. In one study, male rats were split into high and low GI groups over 18 weeks while mean bodyweight was maintained. Rats fed the high GI diet were 71% fatter and had 8% less lean body mass than the low GI group. Postmeal glycemia and insulin levels were significantly higher and plasma triglycerides were threefold greater in the high GI fed rats. Furthermore, pancreatic islet cells suffered "severely disorganised architecture and extensive fibrosis". The evidence in this study showed that continued consumption of high glycemic index carbohydrates would likely have led to the development of severe metabolic abnormalities."
What makes the glycemic index even more important to type 2 diabetics is the effect that high glycemic index foods have on triglycerides. Highly refined, high glycemic index foods raise the triglyceride levels considerably. When high levels of blood sugar circulate in the blood, such as after a meal of high glycemic index refined carbohydrates, then the liver begins to rapidly convert those high levels of blood sugar to triglycerides. High triglyceride levels are one of the major contributers to heart disease in all its forms (heart attack, PAD, pulmonary embolism, stroke, heart failure, etc.).
Current Chapter: 10) GLYCEMIC INDEX
a) Introduction
b) Types of Common Carbohydrates
c) Glycemic Index and A1c
d) Glycemic Index and Losing Weight
e) Glycemic Index Controversy
f) Using Bad Statistics to Judge the Glycemic Index
g) The Occasional High Glycemic "Splurge"
h) Glycemic Load
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