Glycemic Index - Control Of Pancreatic Endocrine Secretions - Assessment Answer

January 09, 2017
Author : Ashley Simons

Solution Code: 1AEHB

Question:Glycemic Index

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Glycemic Index Assignment

Assignment Task

Using the class data calculate the mean plasma glucose concentrations for each time point.

Plot the mean values (+/-SD) for changes in plasma glucose concentration against time for both carbohydrate loads.

Determine the total rise in blood glucose after eating a test food (3 slices of bread) and for the standard reference food (50g glucose), by calculating the area under the curve of your graph. The spreadsheet calculates this for each individual subject. The formula for the calculation is based on the following method (Chlup et. al., 2004):

A horizontal line (baseline) is extrapolated across the graph from the fasting blood

glucose level at t=0.

Vertical lines are run from the baseline (fasting glucose levels) to where the glucose concentration is after consuming the glucose/complex diet.

The incremental area under the curve (IAUC) is calculated by the summing of the triangles and trapezoids given by the length of the base times the average heights of the two vertical sides over the 120 min. The IAUC reflects the total rise in glucose after eating a test food.

Calculate the mean incremental area under the curve (IAUC) (+/-SD) for the test food and the standard reference food.

Calculate the GI:

GI (%) = IAUC(test food) / IAUC(Std) *100

From your height and weight calculate your body mass index and determine your BMI

category:

BMI = Weight (kg)/[Height (m)]2

BMI Categories (https://www.nhlbisupport.com/bmi/):

Underweight = <18.5 Normal weight = 18.5-24.9 Overweight = 25-29.9 Obesity = ?30

Separate the data according to BMI into the four categories (see above) and determine whether their corresponding IAUC curve differs between the groups. Is there any significant difference between the mean values of IAUC for the different BMI categories and what might this indicate?

What is white-coat hyperglycemia?

Describe the role of insulin and glucagon in the regulation of plasma glucose.

What is the prevailing nutritional view regarding the consumption of foods with a low GI index in terms of risk protection from obesity, metabolic syndrome and cardiovascular disease?

Did you note the presence of ketones in the urine at t=0 and t=120min? Explain the mechanism responsible for the presence of urinary ketone and for any change.

Uncontrolled diabetes is characterized by hyperphagia, polydipsia, glycosuria and polyuria.

What are the mechanisms occurring to produces these effects?

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Solution:

Introduction

The glycemic index is a value assigned to different foods (carbohydrates) based on how much time they take to increase the level of glucose in the blood. This value generally ranges on a scale of 0 to 100. The normal fasting blood glucose level, also known as “blood sugar” generally lies in the range of 3.9-5.5 mM (70 - 100 mg/dL).  This blood glucose level varies with the time of the day, being lowest during the morning and rising after meals for about an hour.  However, persistent blood sugar above the normal range is toxic to the body and can lead to blindness, kidney failure or increased risk of cardiovascular disorders. An increase in blood glucose levels after a meal stimulates the release of insulin from the pancreas, which stimulates target cells to increase glucose uptake and storage. The impact of food on the blood glucose concentration is referred to as the glycemic response. Foods with low glycemic index (GI) release the glucose slowly and steadily into the blood, whereas foods high on the glycemic index do it rapidly. Food with high GI is often consumed for instant recover from energy loss or hypoglycemic condition. On the other hand food with low GI has the capacity to foster weight loss (1, 2).

Insulin, a peptide hormone produced by beta cells of the pancreatic islets helps in controlling the blood sugar level by preventing it from getting too high. In diabetic condition, patients are not able to produce sufficient amount of insulin and hence tend to have higher blood glucose than healthy people. Thus to keep a strict check on their blood sugar they must consume low-glycemic food (3). The concept of GI was originally introduced for the patients with diabetes to guide them with proper food selection, preferably with lower GI. Here we have assessed the ability of insulin to regulate blood glucose levels following the consumption of an oral dose of glucose either in simple or complex forms. The standard procedure involves an oral glucose tolerance test (OGTT).

MATERIALS AND METHODS: Subjects were made to fast for at least 12-14 hours. They were asked to avoid Caffeine and juices and intake plenty of water. Urine samples were collected from the subjects and glucose and ketone levels were measured using Keto-Diastix test strips. Ketone and glucose levels were recorded at 15 and 30 seconds respectively. The change in the color of the strips was then compared to color chart to obtain the urine ketone and glucose levels. Blood sample was then collected from each of the subject by pricking their fingertip using Accu-chek safe-t-pro plus.  Blood glucose and ketone levels were measured in the samples using the Accu-chek blood glucose meter and ketone meter respectively. The same glucose and ketone meters were used each time. At t=0, half of the subjects consumed glucose solution (simple carbohydrate: prepared by adding 50g of glucose in 200ml of water) and rest half consumed 3.5 slices of bread (complex carbohydrate: medium GI white bread, brand- Tip Top bakery The One White Sandwich, CHO- 29.5g with sugar- 2.2g per 1 serve, 1 serve=2 slices) along with water to help in swallowing. Then after 15 mins finger-prick blood samples were collected and the blood glucose concentration was measured. This step was repeated again after 30, 60, 90 and 120 mins. The second reading for blood ketone concentration was measured only after 120 mins.  Urine samples were again collected at 120 min for measurement of urinary glucose and ketone concentration.  Body mass and height for all the subjects was also measured using AND UC-321 electronic weight scale and S+M 200cm wall-mounted stadiometer respectively. Body mass index (BMI) was calculated as BMI= (Mass, kg)/ (Height2, m2).

RESULTS: To study the effect of glucose solution on the blood sugar, we firstly calculated the blood glucose concentration of all the subjects (t=0) before making them to drink the standard glucose solution. The mean glucose concentration was found to be 5.1 mmol/L. Similarly the mean blood glucose for subjects in the treatment group was also found to be 5.1 mmol/L. The normal fasting glucose for all the subjects (measured at t= 0 mins) was found to be within the standard range of 3.9 - 5.5 mM. The glucose concentration in the blood of all the subjects was then again monitored at t=15, 30, 60, 90 and 120 mins and the mean blood sugar for subjects administered with standard glucose solution was found to be 7.0, 7.8, 7.7, 6.4 and 5.2 mmol/L respectively and the ones given 3.5 slices of bread was 5.8, 7.1, 7.0, 6.1 and 5.7 mmol/L respectively. This has been shown in figure 1 and 2 below.

To study the effect of glucose solution

The blood glucose level was observed to rise after the consumption of carbohydrates in the both the cases- standard glucose solution and 3.5 slices of bread. The level of blood glucose remained high for about an hour after which it again started to decline to fall within the standard range.

The area under the curve gives us the total rise in blood glucose after eating a test food (3.5 slices of bread) and for the standard reference food (50g glucose solution). The incremental area under the curve (IAUC) for both the cases was calculated using the method suggested by Chlup et. al. in 2004 (4) and was found to be 157.4 and 215.5   respectively.

Further we aimed at calculating the GI of the test food, i.e. white bread, using the following formula- Glycemic Index (%) = IAUC (bread slices) / IAUC (glucose solution) *100, which was found to be 67.92 %. GI being high, white bread showed a similar effect on the blood glucose level as compared to the standard glucose solution.

The body mass index (BMI) is a measure of an individual’s body fat using his/her weight and height. It can help in categorizing the person into underweight, normal weight, overweight, or obese group so that necessary action can be taken to lead a healthy life. Obesity puts strain on the heart and can lead to serious health problems like heart diseases, high blood pressure, sleep apnea, type 2 diabetes and varicose veins. BMI of all the subjects was thus calculated using the relationship, BMI = Weight (kg)/ (Height (m))2 and the results are shown in the table below.

The body mass index (BMI)

Most of the subjects under study were found to possess normal weight as per their height. Two of the subjects were under weight and must take care of their diet, while six of the subjects were found over weight and require proper monitoring and routine exercise to control their weight to avoid future diseases and stay healthy.

DISCUSSION: Fasting blood glucose representing the lowest levels of glucose in the blood during the day has being the most common method for measuring hyperglycemia. It can be measured easily and accurately both in clinical practice and in large-scale epidemiologic studies. However, it does not directly account for the manner in which our body handles the mealtime glucose load as it is calculated using the hepatic glucose production and residual circulating glucose. Thus determining the appropriate functioning of the pancreas and counter response of the peripheral tissues becomes difficult. Another approach is to use postprandial glucose to determine the time take to metabolize and clear the glucose contained in the meal. It is a bit harder to estimate. The oral glucose tolerance test takes about two hours and is not really consistently reliable (5). This is referred to as the glycemic index of the food. Here in this experiment we have used the same approach to calculate the GI of standard glucose solution and white bread.

Glycemic index (GI) is considered to be an important factor in weight regulation. Obesity has become a major concern nationally and worldwide (6). In general western style diet and lack of physical activity has been attributed to the cause of obesity however the exact dietary factors contributing to the cause of obesity still need to be explored further. Therefore there is a need for finding certain dietary patterns that can be used for checking the problem of excess weight gain in people of various age groups (7). It is generally recommended to focus on more carbohydrate rich diet and lowering the fat content in the food to control the weight gain. Even though the percentage of dietary energy being derived from the fat content in the food has steadily fallen down in the last few years, the problem of obesity on the other hand side is accelerating (7). These findings emphasized the need to look into the dietary factors apart from fats to understand the trend being observed.

Brand-Miller et. al. in 2002 conducted an experiment where they showed that most of the food products that are a part of the western diet are high in glycemic response. The food with high GI alters the food partitioning system of the body thereby promoting the oxidation of carbohydrates contained in them at the expense of fat decomposition. This change in the metabolic activity of the body is generally accompanied by gain in weight. Contrary to this they showed that low GI food helps in controlling the weight as it releases the glucose in the blood slowly giving the feel of being sated, minimizing postprandial insulin secretion and maintain insulin sensitivity (8).

Another large scale study provides evidence to support the rationale that GI of the diet has a direct effect on the weight control. In a study conducted with the help of around 3000 adults suffering from type 1 diabetes, it was observed that an overall low GI diet lead to lower waist-to-hip ratio and waist circumference. The amount of carbohydrate or fat or fiber in the diet was not a matter of concern (3). A very recent study conducted by Pereira et al. in 2015 further supports the fact that low GI food stimulates the body to oxidize postprandial fat more and hence results in reduction in waist circumference (9).

Glucose and white bread are generally used as reference for calculating the GI of various foods as they show similar effect on the blood glucose level. White bread has quite high GI as observed in our experiment as well. That is why, white bread is not recommended as a healthy food. Attempt are being made to alter the ingredients and make it low on GI so that it can be consumed safely without bothering much about its consequences related to weight gain. An experiment reported that addition of Phase 2, a dietary supplement derived from the common white kidney bean has the capacity to lower the GI of a commercially available high glycemic food like white bread (10).

Thus low GI diets have been majorly documented to decrease the risk of developing obesity (7), diabetes (3), and coronary heart disease (11).

CONCLUSION: The rate with which carbohydrates are released from the food and absorbed in the body can be quantified by the glycemic index of the food. It actually controls the hormonal and metabolic response of the body after the intake of a meal. Meals with high glycemic index rapidly increases the glucose and insulin levels along with free fatty acids in the serum. It further promotes the surge for more food, damage to insulin producing beta cells and endothelial, and dyslipidemia. So, constant uptake of high GI food increases the risk for obesity, diabetes, and many other heart diseases. Therefore, despite of many controversies, the clinical use of GI for selecting food appropriate for the prevailing health condition can prove beneficial.

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