Type 2 diabetes mellitus (T2DM) is a non-communicable disease caused by the body’s gradual resistance to insulin resulting in the over accumulation of glucose in the bloodstream (Diabetes Australia, 2015). This disease can have a genetic disposition and is linked to lifestyle risk factors such as poor diet (Diabetes Australia, 2015) and has become a global epidemic affecting over 425 million individuals worldwide in 2017 (Forouhi, Misra, Mohan, Taylor, & Yancy, 2018, p. 1). Given that a poor diet contributes to this condition, this assignment will identify the role that diet modifications can play in the prevention, management and possible reversal of T2DM.
In 2017-2018 4.1% or 1 million members of the Australia population were reported as having T2DM, this figure having increased from 3.5% in 2007-2008 (Australian Bureau of Statistics, 2019) showing that the prevalence of T2DM is rising in Australia and remains a major health concern. T2DM can lead to further macrovascular and microvascular complications such as cardiovascular disease, nephropathy, retinopathy, and neuropathy greatly reducing the lifespan if not correctly diagnosed and managed (Kim, Keogh, & Clifton, 2015, p. 769). In 2011 this condition was ranked Australia’s 6th leading cause of death (Australian Bureau of Statistics, 2013) with 65% of cardiovascular disease mortality rates resulting from those individuals with either T2DM or pre-diabetes (Kim et al., 2015, p. 769).
The pancreas is an organ that contains beta cells whose function it is to secrete the hormone insulin into the bloodstream which is then used by the body to transfer the glucose from the breakdown of ingested food into the muscle, fat and liver cells to be used for energy (The National Institute of Diabetes and Digestive and Kidney Diseases, 2018). T2DM develops as a result of insulin resistance, a pathological condition where the muscle, fat and liver cells do not acknowledge the insulin released from the pancreas resulting in the restriction of glucose being transported from the blood into the cells (The National Institute of Diabetes and Digestive and Kidney Diseases, 2018). When this occurs the pancreas then releases more insulin to combat the developing insulin resistance (The National Institute of Diabetes and Digestive and Kidney Diseases, 2018). Eventually this results in an overworked pancreas causing an impaired secretion of insulin by the beta cells in response to the body’s requirements (The National Institute of Diabetes and Digestive and Kidney Diseases, 2018). When the pancreas does not produce enough insulin for the glucose to be taken up by the cells, it results in a rise in glucose levels in the bloodstream. To date the role of dysfunctional pancreatic beta cells and insulin resistance has been the focus of studies to identify the causation of T2DM (Hurrle & Hsu, 2017, p. 257), however there are several key mechanisms that have now been identified as contributing to the cause of insulin resistance namely intramyocellular lipids (IMCL) activity (Li, Xu, Zhang, Yi, & Cichello, 2015), oxidative stress (Hurrle & Hsu, 2017), advanced glycation end-products (AGEs) (Uribarri et al., 2010), and these mechanisms show a connection to dietary intake as a main cause associated with this process.
Intramyocellular lipid (IMCL) are lipids that are stored in skeletal muscle cells within the body. IMCL are stored as triacylglycerol, diacylglycerol, sphingolipid, and phospholipid which are needed for energy metabolism (Li, et al., 2015, p. 90). However, an over-abundance of free fatty acids circulating in the blood lead to IMCL promoting a toxic state that gives rise to the development of insulin resistance (Li, et al., 2015, p. 90) and subsequently T2DM. Sakurai et al performed a study to determine whether a high-fat dietary intake that contained 45% saturated, 30% monounsaturated, and 25% polyunsaturated fatty acids would increase the levels of IMCL. This study involved the participation of 37 non-obese men over a 3-day period and resulted in a significant increase in IMCL levels rendering a high-fat diet to be detrimental in the causation of insulin resistance (Sakurai et al., 2010).
Oxidative stress is a disruption in the body’s balance of reactions between pro-oxidant and antioxidant levels (Ottum & Mistry, 2015, p. 2). It can be described as the overabundant endogenous oxidative species which influences the signal pathway and causes harm to the cells (Hurrle & Hsu, 2017, p. 257). The mitochondria and peroxisomes mostly produce the medium of oxidative stress through production of reactive oxygen species (ROS) such as low levels of superoxide, hydroxyl radical ions, and hydrogen peroxide (Hurrle & Hsu, 2017, p. 257) which causes harm on the cellular level resulting in insulin resistance (Hurrle & Hsu, 2017, p. 258) and subsequently T2DM. A diet with excessive intake of refined carbohydrates, dietary fats (namely saturated fat), and animal-based protein generates ROS leading to oxidative stress (Tan, Norhaizan, & Liew, 2018, p. 1). To reduce the production of ROS/oxidative stress and inflammation that is fuelling insulin resistance diet modifications need to be implemented. This can be achieved by replacing refined carbohydrates with unrefined, removing dietary fats, and introducing a wholefood plant-based diet which will also provide the needed antioxidants (Tan, et al., 2018, p.13).
AGEs are compounds that are produced by a chemical reaction, also referred to as the Maillard reaction, that occurs by joining sugars and proteins through heat (Merriam-Webster, 2019). AGEs are also produced in the cooking of some foods with the highest level of these compounds found in animal products (Uribarri et al., 2010, p. 911). These pro-oxidant compounds also known as glycotoxins are a normal part of the metabolic process, however when levels increase they have been found to contribute to oxidative stress and inflammation (Uribarri et al., 2010, p. 911) correlating to the development of insulin resistance (Ottum & Mistry, 2015, p. 2, 3) resulting in T2DM. Dietary AGEs make a large impact toward the total AGE load within the body by absorbing as much as 6% of these AGEs ingested (Ottum & Mistry, 2015, p. 5). The “Western diet” increases the formation of AGEs through its highly processed, high fat, and high protein content of the foods that this diet promotes, along with the method, high temperature, and long cooking durations that are used during the cooking process (Ottum & Mistry, 2015, p. 5). Animal products contain and produce higher amounts of AGEs when cooked than do those of plant-based origin (Uribarri et al., 2010, p. 911). The cooking method of frying, grilling, broiling, roasting, and searing all produce the browning effect of the Maillard reaction that increases the AGEs formation with methods such as boiling and poaching producing lesser amounts (Uribarri et al., 2010, p. 912) showing that food preparation is important in decreasing AGEs formation.
Dietary choices have been recognised as a key element in the identified mechanisms of oxidative stress, AGEs, and IMCL that are associated with the pathological condition of insulin resistance that leads to T2DM. A review of meta-analyses (Kim, et al., 2015) showed a positive interaction between the consumption of both processed and red meat with the increased risk of insulin resistance. These animal products contain components that trigger the mechanism of oxidative stress and AGEs resulting in insulin resistance that may then progress to T2DM (Kim, et al., 2015, p. 8). The adoption of the western diet that is high in animal protein, high in fat, high in processed meats and refined carbohydrates while promoting sugar laden beverages has shown to be the diet that is associated with insulin resistance (Ley, Hamdy, Mohan, & Hu, 2014, pp.1-2). This dietary trend responsible for the global rise in T2DM has developed from transitions in society that has resulted in refined food production, accessible fast food and unhealthy food choices, with the implementation of supermarkets and the decrease of the neighbourhood fresh produce markets, and the rise of sedentary occupations and lifestyles (Ley, et al., 2014, pp. 2).
Healthy dietary interventions that are low in animal protein, low in unhealthy fats, void of processed and refined foods, and low in salt and sugar intake is the suggested diet necessary in preventing, managing, and reversing T2DM. This gives rise to a wholefood plant-based diet that adopts whole grains, legumes, nuts, seeds, fresh fruit and vegetables all in their natural state, and is high in dietary fibre as the foods of choice that are supported by research to be protective against chronic disease (McMacken & Shah, 2017, p. 343). Anderson & Ward performed a study involving 20 men with T2DM who were administering insulin. They were fed a normal diet for 7 days during their hospital stay where this study was conducted, and then switched at a high carbohydrate, high fibre diet (HCF) for 16 days (Anderson & Ward, 1979, p. 2318). The results showed a reversal of insulin resistance with a reduction in blood glucose levels, and insulin dosages (Anderson & Ward, 1979, p. 2318).
Further research studies have shown the link between lifestyle and disease with a wholefood plant-based diet showing preferences for lowering the risk factors for chronic diseases such as T2DM. These studies consist of the Adventist Health Study 2 conducted between 2001 and 2007 with 96,000 Adventist participants ranging from ages 30 to 112 years (Loma Linda University School of Public Health, 2019). This group consisted of differing dietary preferences of 8% vegan, 28% lacto-ovo vegetarian, 10% pesco-vegetarian, 6% semi-vegetarian, and 48% non-vegetarian (Loma Linda University School of Public Health, 2019). The study concluded that those who consumed the vegan diet were healthier than those who consumed a non-vegetarian diet seeing reductions in diseases such as T2DM, hypertension, obesity, high cholesterol, and metabolic syndrome (Loma Linda University School of Public Health, 2019). The study also showed those diet preferences that were closer to vegan saw more disease reductions than those who were not (Loma Linda University School of Public Health, 2019). The Rotterdam study that included a large number of participants also found that a diet consisting of high amounts of plant-based options was found to lower insulin resistance and decrease the incidents of pre-diabetes and T2DM in comparison to individuals who consumed an animal-based diet (Chen et al., 2018).
In conclusion, T2DM is a chronic disease caused by insulin resistance associated with oxidative stress, AGEs, and IMCL. These mechanisms have been shown to be related to the western diet that is high in fat, animal products and refined/processed foods. Replacing the western diet with a wholefood plant-based diet will play an important role in the prevention, management and reversal of insulin resistance. This is supported by several studies that show a diet of vegan origin that is wholefood plant-based and high in fibre and unrefined/unprocessed foods can lower the risk factors for insulin resistance and therefore T2DM.
References
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