Blog 3 - Weight gain and nutritional guidelines

Problem narrative

The World Health Organisation database on Body Mass Index (BMI) refers to a phenomenon known as “globesity”. This term refers to the increase in obesity that is being seen in many parts of the world (WHO, 2012). This has led to governmental efforts to encourage healthy eating habits, such as the food pyramid guide released by the United States Department of Agriculture (USDA, 2012). However, such efforts have been unsuccessful at curbing this problem and obesity is still on the rise. A recent ideology known as the paleolithic diet operates on the hypothesis that the obesity problem is fuelled by the modern day reliance on grain-rich diets that are carbohydrate based (Lever, 2012). This idea has been supported by scientific investigations, however it has not been incorporated into mainstream nutrition practices (Kopp, 2003). Therefore, governmental suggestions of 6-11 servings of grain a day (USDA, 2012) may be aggravating the problem.  This text shall therefore be discussing the problem of obesity due to high-carbohydrate intake from the perspective of a single average person.

Behaviour over time

This study shall be using BMI as an indicator of weight gain since it takes into account a person’s height, is easily calculated and allows comparison between different individuals. The plot below illustrates the increase in the average BMI of males and females between the ages of 20-74 in the United States between 1960 and 2002:

Figure 1: Plot of average BMI against time (data from Ogden et al., 2004)

The data illustrates the fact that the average BMI increased from 25 to 28 (approximately), with the average woman’s BMI surpassing that of the average male. It should be noted that a BMI between 18.5-24.9 is considered “healthy”, 25-29.9 is classed as “overweight”, while anything above is considered “obese” (CDC, 2012). Therefore in a 40 year period, the average person can be said to have changed from “healthy” to “overweight”.

 

Relevance of a systems perspective

The system being discussed exhibits two main feedback dynamics. First of all, nutrition affects BMI which in turn will result in dieting efforts that should (theoretically) limit what is being eaten. Secondly, the body’s own feedback dynamics that regulate appetite and blood sugar. In addition, the problem with weight gain is witnessed over a whole person’s life and therefore exhibits long time horizons and may occur very gradually. Unfortunately, nutritional efforts to curb weight gain have also failed, as seen in Figure 1 above. These factors indicate that the efforts of a person attempting to control weight gain through nutrition should be looked at from a systems perspective to identify which dynamics are leading to this problem.

Study objectives and questions to be addressed

The objective of this study is to build a systems dynamics model of a person attempting to maintain a healthy weight using official nutritional guidelines. Since the objective is a nutrition analysis, the role of other factors such as physical activity shall not be examined and for the purposes of this study the average person shall be considered to be sedentary.  The study shall use this model to attempt to address whether the grain-based food pyramid guidelines are alleviating or aggravating weight gain in individuals.

Dynamic hypothesis

The discussed system contains only one actor: an average individual trying to lose weight through nutritional efforts. The action this individual takes is to follow government issued nutritional guidelines to reduce weight. The intended consequence is that a high carbohydrate meal controls hunger levels. The unintended consequence is that carbohydrate dense foods cause a spike and crash in blood sugar levels, causing the individual to feel hungry again resulting in overeating.

The table below illustrates the variables used in this model and their significance:

Variable name	Significance
BMI value (dashboard variable)	The individual’s current BMI value, which shall be used to indicate weight gain/loss.
Recommended intake of grains	The amount of grain servings recommended by official guidelines. (Note: This was considered to be exogenous since it is not affected by what the individual does and is based on a series of other systems beyond the scope of this study)
Consumption of food	The amount of food eaten.
Consumption of carbohydrates	Represents the size of the portion of the food eaten which is composed of carbohydrates.
Calorie deficit	The calorie deficit signifies the actual amount of calories needed by the individual for bodily function.
Hunger level	The perceived level of hunger felt by the individual.
Amount of fat in body	The amount of fat present in the individual’s body.
Blood sugar concentration	The current concentration of sugar in the individual’s blood (represents the energy obtained from food that is accessible to the individual’s body)
Insulin in blood	The concentration of insulin currently in the individual’s blood (release of insulin by the pancreas results in sugar being stored as fat, making it less accessible to a body’s cells)
Motivation to limit food intake	The individual’s motivation to limit the amount of food eaten to reduce weight gain.

 

Table 1: Variables used in the study

 

At its most basic level the system being discussed deals with hunger being felt when the body needs energy (calorie deficit) which results in food being eaten, thus addressing the body’s calorie deficit. This can be seen in Loop B1, highlighted in Figure 2 below:

 

Figure 2: Loop B1

If the consumption of food is high, the individual gains weight. This should stimulate the individual to limit food intake, thus controlling weight gain. This can be seen in Loop B2, highlighted in Figure 3 below: 

 

 Figure 3: Loop B2

However, reducing food consumption causes a calorie deficit. This increases hunger levels, resulting in even more food being consumed, thus thwarting dieting efforts. This can be seen in Loop B3, highlighted in Figure 4 below: 

 Figure 4: Loop B3

 

To address this problem, nutritional guidelines suggest a grain based diet. Consuming foods rich in carbohydrates keeps blood sugar levels high, so that less hunger is felt. This leads to food feeling more satisfying, reducing the amount of food consumed. This can be seen in Loop B4, highlighted in Figure 5 below: 

 Figure 5: Loop B4

However, blood sugar levels are controlled in the body by insulin. Once blood sugar levels in the body surpass a certain level, insulin is released in the blood to reduce blood sugar concentration. This can be seen in Loop B5, highlighted in Figure 6 below: 

 

  Figure 6: Loop B5

The insulin cycle means that consumption of food rich in carbohydrate, increases blood concentration causing sugar to be stored as fat. This increases the individual’s BMI value, requiring a reduction in food intake. One of the unintended consequences of a high carbohydrate diet is therefore an oscillation of the individual’s weight, which is often referred to as yo-yo dieting. This dynamic is highlighted as loop B6 in Figure 7 below:

 Figure 7: Loop B6

While the dynamics examined all show balancing feedback it should be noted that they have different and opposing goals. Therefore, the individual dynamics do not give a clear picture of the dominant dynamics as proposed by the paleolithic diet ideology. An increase in the average individual’s BMI can be explained through the fact that consumption of high carbohydrate food items results in a spike and crash in blood sugar. This results in an individual feeling hungry despite there not being a calorie deficit, resulting in even more food being consumed. This dynamic would essentially mean that a person would display weight gain and would find it hard to reach his/her ideal weight, eventually reaching a higher equilibrium weight where all the dynamics become balanced. Therefore the hypothesis of this study supports the suggestion that the government guidelines for a grain based diet are aggravating the obesity problem, highlighting the need for revision of these guidelines to address the dynamics listed in this text.

References

CDC. Body Mass Index. http://www.cdc.gov/healthyweight/assessing/bmi/index.html (accessed January 21, 2012). 

Lever, R. Against the grain, 'caveman' diet gains traction. http://medicalxpress.com/news/2011-09-grain-caveman-diet-gains-traction.html (accessed January 21, 2012).

 Kopp, W.  High-insulinogenic nutrition - an etiologic factor for obesity and the metabolic syndrome? Metabolism 2003, 52(7), 840-844. 

Ogden, C. L.; Fryar, C. D.; Carroll, M. D.; Flegal, K. M. Mean Body Weight, Height, and Body Mass Index, United States 1960-2002. Advance Data from Vital and Health Statistics; No. 347; National Center for Health Statistics: Hyattsville, Maryland, 2004.

USDA. The Food Guide Pyramid. http://www.nal.usda.gov/fnic/Fpyr/pmap.htm (accessed January 21, 2012).

WHO. Global Database on Body Mass Index. http://apps.who.int/bmi/index.jsp (accessed January 21, 2012).