A Brief Explanation of the Area Under the Curve

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A Brief Explanation of the Area Under the Curve


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Old 03-31-2015, 16:48   #1
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Default A Brief Explanation of the Area Under the Curve

During a discussion in another forum I realized that it would be beneficial for diabetics to have a baic understanding of the concept of the “area under the curve”. Here is a simple and brief explanation that I hope can provide some useful information to fellow diabetics.

Scientists say that the effect of blood glucose on our body is dependent on both its level and the duration it remains at that level. This is equivalent to saying that if we plot the BG Vs time curve, the effect is proportional to the area under the BG curve. The impact of BG is measured by this area which is the combined effect of level and duration, and not by the level alone or the duration alone.

The area under the BG curve can be found by integrating the BG function (“f(t)”) over the duration of our interest, as shown in figure 1 a. The figure shows the area between the BG curve and the X-axis (which is the BG=0 line) in the time interval t1 to t2. This area is not very meaningful in biochemistry as normal healthy human beings don't have baseline BG as 0. Let us take a practical BG value of 4.5 mmol/L (=81 mg/dL) and take the "area under the curve" above this line and below the BG curve. This is shown in figure 1 b. As I said earlier, it is neither the absolute BG level nor the absolute time duration but their combined effect, i.e., the area under the curve, that is of real concern. A sharp BG spike reaching high levels but of short duration and a relatively lower BG level but of longer duration can have the same area under the curve and in this case both affect the body similarly. It can even happen that a sharp spike has less area under the curve than a relatively lower BG level lasting a longer duration, and in that case the spike has less damaging effect than the lower BG level. That is one reason I don’t overly worry about being naughty once in a while with delicious, sugary Indian treats . For me the resulting spikes are short and swift, having small “area under the curve.”

Now, compare eating a large amount of sugary sweets that have very less fibre content and eating food with carbs having the same amount of sugar but with also a good amount of fibre and significant amounts of protein and fat. Even though the sugar content is the same, the area under the curve need not be, and often is not the same in both cases. The area is often less in the latter case, i.e., in the case of eating food with fibre, carbs, protein and fat. Why? When the sugary sweets are eaten, glucose is released into blood far quicker than when eating food with carbs, fibre, protein and fat. When a large amount of sugar is quickly released as when eating sugary sweets, the body (especially of a diabetic) is overwhelmed and hence has poorer control over BG with the result that the ensuing spike can have a larger area under its curve than if the same amount of sugar was released slowly over a longer period of time. When sugar is released slowly the body has better control over BG resulting in lower BG and lower area under the curve. This is shown in figure 2 a and b. To put what we just discussed in other words, the BG response of the body is not linear to sugar input. If x amount of sugar input will raise the BG to y, 2x amount can raise the BG to more than 2y (say 2.5y, 3y, or more) because of the non-linearity of the response of the body.

Figure 2 is also based on an actual experiment I once performed eating sugary sweets one day and plotting the BG curve and the next day eating a melange of fruits (apple, blueberry and pineapple) containing roughly the same amount of sugar as in the sugary sweets eaten the day before. Of course this is not a controlled experiment but the theory I just explained holds.

Regards,
Rad
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Old 03-31-2015, 19:21   #2
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So fruit is worse for you than candy? Finally, the study I've been waiting a lifetime to hear.
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Old 03-31-2015, 19:40   #3
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Originally Posted by Tea Rose View Post
So fruit is worse for you than candy? Finally, the study I've been waiting a lifetime to hear.
Sorry to disappoint you, fruit was better than candy .

The figure shows that fruit had a lower "area under the curve" than for candy having same amount of glucose.


Regards,
Rad

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Old 03-31-2015, 19:49   #4
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This, however, is not permission to eat fruit instead of candy. If you eat to your meter, remember that any food which raises blood sugar above 140 (7.8) is off the menu, so you still have to test everything.



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Old 03-31-2015, 20:39   #5
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Quote:
Originally Posted by Rad Warrier View Post
Sorry to disappoint you, fruit was better than candy .

The figure shows that fruit had a lower "area under the curve" than for candy having same amount of glucose.


Regards,
Rad
However your tests fail to take into account fructose, Fructose does the same damage as glucose BUT our meters do not measure the fructose. So the total sugar in your system is actually higher than the meter shows. That and a large portion of fructose gets converted to triglycerides. So I eat little fruit.
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Old 03-31-2015, 22:12   #6
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... Fructose does the same damage as glucose BUT our meters do not measure the fructose.
I don't believe fructose, or glucose, or protein or fat will cause any harm if taken in reasonable amounts. Only when you take unreasonable amounts of these nutrients that damage can happen. By "unreasonable" I mean beyond the capacity of your body to process them safely. The reasonable and unreasonable quantities are of course "YMMV" stuff as they say in many diabetes boards meaning very much dependent on the individual and his or her severity of diabetes. I take a good amount of fruit and my BGs are reasonably good (the peak BG is mostly below 7.5 mmol/L which is 135 mg/dL) lipid levels are in the healthy region espcially with triglycerides around 0.9 (81). A1c latest is 5.4. So, fruits in reasonable quantities are not damaging for diabetics like me.

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Old 03-31-2015, 22:39   #7
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Unfortunately, given the accepted 20% error rate in all glucose meters, a meter reading of 135 can be a factual 162.

This is a powerful reason for keeping well below 120.

An A1c is also a fair indicator of how well we're doing. Unfortunately, it only tells us part of the story, and only after it's happened.

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Old 04-01-2015, 00:09   #8
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Unfortunately, given the accepted 20% error rate in all glucose meters, a meter reading of 135 can be a factual 162.

This is a powerful reason for keeping well below 120.

An A1c is also a fair indicator of how well we're doing. Unfortunately, it only tells us part of the story, and only after it's happened.
When meter manufacturers claim the error as 20% it is the maximum error. It doesn’t mean that every time you take a reading, the error will be 20%. In the past nine years, whenever I had a lab test I have taken my meter along with me and checked my BG just before the lab blood draw. The maximum difference from the lab readings were within ± 0.3 mmol/L (± 6 mg/dL) and only once was the reading off by – 0.5 (-9). When more than 90% of the time I check my BG I see a reading less than 7.5, statistics make me rather very confident that my BGs are indeed below 7.5 . Also an occasional incursion into the region of 160 mg/dL is fine with me . The proof of the pudding is in the eating. I was diagnosed 9˝ years ago and in this period I am glad to say that my diabetes has not “progressed” and on the contrary the severity has reduced as seen in my BGs, lipid levels and A1c’s. So, my moderate carb diet including a moderate quantity of fruit is not apparently causing damage.

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Old 04-01-2015, 03:01   #9
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Rad ... what it means is, I don't know what the error level is each time. I choose not to take the chance. For this reason, I choose to keep below 115.

In addition, non-food factors -- such as stress, infection, sleep changes and the weather -- can also cause spikes. I have no desire to add self-inflicted spikes to those I cannot prevent. Damage is cumulative.

There is also the point that diabetes86 made about fructose, above.

Hence, for me (for most of us), 135 is far too risky. As for 160 -- that's way, way higher than I'd ever recommend.

This is why we advise people to eat to their meters. And, especially if they're new to diabetes or to control, to cut the carbs way, way, way down. This is the only way they can learn what works for them. What works best is to keep below 140, which is the known threshold at which damage occurs.

Some folks may find they have more wiggle-room than others in keeping to that goal, while others require a tight rein.

Calls for "moderation" may work for some. For most, they do not.

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And with that I feel this thread has run its course.

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