The Connection Between Nutrition and Disease

In the United States, chronic diseases easily outweigh infectious diseases as the primary cause of death.  Indeed, heart disease, cancer, stroke, and diabetes are collectively responsible for 56 percent of deaths in the United States.  It might surprise some people to learn that these diseases are each influenced by diet, some to a large degree.  While it is true that a person's genetics, activity level, lifestyle choices, and environment play a large role in whether he or she will contract a chronic disease, making wise decisions in dietary choices can lessen the likelihood or severity of such chronic diseases (Sizer & Whitney, 2013).

Diabetes

Diabetes, also known as hyperglycemia, is a metabolic disease that is distinguished by elevated levels of blood glucose, caused by a lack of sufficient quantities of insulin, or insulin that is ineffective (American Diabetes Association, 2014).  Diabetes alters the metabolism of cells within the body, which can lead to a host of problems, including blindness, limb loss, kidney failure, circulation loss, and nerve function loss.  As such, it is a leading cause of death in the United States.  Diabetes afflicts nearly 26 million people in the United States, with 7 million not even being aware they have it.  Moreover, nearly 79 million people have prediabetes, a condition dangerously close to becoming fully diabetic.  Identified through a variety of blood tests, those that have prediabetes have a chance to reverse it, if they catch it early enough and alter their diet and behaviors accordingly (Sizer & Whitney, 2013).

Insulin is a hormone used by the body to trigger absorption of glucose in the blood, enabling the body to regulate the quantity of sugar in the blood at any given time.  It is the counterpart to the hormone known as glucagon.  Although Type-1 diabetes is primarily genetic in nature and relates to the body's ability to produce sufficient quantities of insulin, the vast majority of diabetics in the United States have Type-2 diabetes.  In Type-2 diabetes, tissues in the body lose their sensitivity to to insulin and, therefore, do not consume the glucose in the blood as rapidly as desired.  The pancreas will initially attempt to respond by producing more insulin.  However, it is an exercise in futility, and will eventually result in the pancreas significantly reducing insulin levels and leaving blood glucose levels out of control (Sizer & Whitney, 2013).  An illustration of how insulin is used within the body to regulate blood glucose levels is shown below.

Roles of Glucagon and Insulin in Blood Glucose Regulation (Freudenrich, 2014)

The level of body fat contained within tissue is directly related to its ability to respond to insulin and, thus, affects the glucose levels within the blood.  Obesity, a condition of excessive body fat, is directly associated with a large percentage of people that are afflicted with Type-2 diabetes.  Type-2 diabetes can be largely prevented by maintaining a healthy body weight, eating diets low in saturated fat and high in nutritious foods, limiting alcohol intake, and obtaining regular physical activity (Sizer & Whitney, 2013).

Cardiovascular Disease

More than 82 million people suffer from cardiovascular disease in the United States.  Cardiovascular disease (CVD), collectively referring to diseases of the heart and circulatory system, is a leading cause of death for Americans, claiming almost 1 million lives annually.  Nutrition plays a significant role in the development of CVD.  For instance, atherosclerosis, or hardening of the arteries, is a core component of most forms of CVD and is highly correlated to the amount of saturated fat taken in through diet.  Plaque formation is a complicated process, but originates from particles of low-density lipoprotein (LDL) cholesterol in the bloodstream being trapped in blood vessel walls.  Free radicals in the blood cause LDL cholesterol to oxidize and eventually harden into plaque via the formation of foam cells.  The process is exacerbated by muscle cells, in an attempt to heal the damage, but they actually contribute to the hardening process by melding with the foam cells themselves.  As plaque builds up, the risk of rupture increases, which can lead to blood clots.  Blood clots can lead to severe injury or death, caused by stroke or a heart attack (Sizer & Whitney, 2013).  The relationship between LDL cholesterol, foam cells, and the arterial wall is illustrated below.

Cholesterol and Coronary Artery Disease (American Heart Association, 2014)

In addition to atherosclerosis potentially leading to stroke or heart attack, it also heightens the risk of hypertension, also known as high-blood pressure.  In fact, hypertension and atherosclerosis each cause the other to worsen over time.  The stress of hypertension on the arteries causes more injury to them, leading to more blood clots and plaque buildup.  The additional plaque buildup, in turn, leads to addition hypertension in the vicious cycle.  The good news is that Americans can substantially lessen their risk of CVD, and even reverse some of its advancement, by making wise choices in diet, lifestyle, and activities.  Increased physical activity results in the more efficient pumping of blood and the ability of muscle tissues to absorb oxygen, ultimately reducing the amount of heartbeats required to accomplish the same amount of work.  Moreover, exercise increases the amount of HDL cholesterol in the blood, which works to combat the effects of LDL cholesterol and plaque buildup.  The resultant lean muscle tissue has many other benefits, such as improved insulin sensitivity, lessening the risk of diabetes.  Even increasing activity to 30 minutes, 5 times per week, will substantially lessen a person's risk for CVD, along with many other chronic diseases (Sizer & Whitney, 2013).

In addition to physical activity levels, a person's diet plays an important role in the development of CVD.  Following an atherogenic diet, or that which is high in saturated and other fats, has substantial adverse effects on cardiovascular health.  Cutting back on foods high in cholesterol, saturated and trans fats, combats obesity and insulin resistance, as well as promotes neurological function (Sizer & Whitney, 2013).  Regular consumption of fish, with its omega-3 polyunsaturated fatty acids, has recently been shown to lower risk of death from CVD by as much as 25 percent (Weichselbaum, Coe, Buttriss, & Stanner, 2013).

Cancer

In the ranking of leading causes of death, cancer takes second place to cardiovascular disease by a very small margin.  While it generally is not as affected by diet as is CVD, most cancers are influenced by dietary and lifestyle choices, as well as environmental surroundings.  Cancer, which develops from cellular exposure to carcinogens, is more likely to develop as the exposure to carcinogens increases.  From a lifestyle standpoint, smoking has long-been proven to increase the risk of lung and other cancers, but it is less well-known to the public as to the role alcohol consumption plays in cancer development.  Indeed, research has shown that there is a strong correlation between alcohol and tobacco use with head and neck cancers, and alcohol by itself increases the risk of mouth, throat, esophageal, and breast cancers.  Moreover, the adverse impact that alcohol has on the liver promotes liver cancer (Sizer & Whitney, 2013).

The common theme of physical activity, fat intake, and obesity, plays a critical role in cancer, as it does in other chronic diseases.  Obesity is highly associated with colon, breast, endometrial, pancreatic, kidney, and esophageal cancers, and is also suspected to be linked with gall bladder cancer.  The intake of fat and fatty acids speed the development of cancer in laboratory rats, when carcinogens are present.  This has not been proven in humans thus far, however.  Direct evidence of the contribution of fats toward cancer in humans notwithstanding, fat is a direct contributor to obesity, which alone should be enough to discourage its intake in abundance.  Further, red meat has been consistently shown to increase the risk of colon cancer (Sizer & Whitney, 2013).

Curiously, the intake of caloric energy has been shown to have direct correlation to cancer incidence.  Reduction in calorie consumption lowers risk of cancer.  This is further re-enforced by increased physical activity, which also lowers risks for obesity.  Finally, eating sufficient amounts of foods that are rich in fiber, folate, calcium, and vitamins E, C, and D, help to guard against cancer development.  It has been suggested that iron consumption, however, has been linked to colon cancer, but the exact cause is under study (Sizer & Whitney, 2013).

Malnutrition

 

Finally, the body's immune system is crucial in defending itself against chronic diseases.  In order to function properly, the immune system depends on sufficient intakes of vitamins and minerals.  For instance, vitamin C is necessary for white blood cells to kill intruders, while vitamin A supports immune cell and antibody response.  Folic acid is needed for proper cellular replication and zinc plays a role in antibody production.  All of these, and many more, are needed to support a healthy immune system.  Malnutrition, a sustained deficiency in one or more essential nutrients, allows disease to more easily develop.  Disease can then contribute to further malnutrition, leading to an unfortunate spiral of each building upon the other (Sizer & Whitney, 2013).  A recent study in Australia observed that the majority of patients exhibiting end-stage kidney disease were deficient in several vitamins, zinc, and folate.  Malnutrition was determined to be a contributor to decreased renal function and increased symptoms associated with end-stage kidney disease (Chan, Kelly, Batterham, & Tapsell, 2014).

Conclusion

Although there is no silver bullet to ensure someone does not become afflicted with disease, there is no question that the choices people make in diet and behavior directly influences the risks of disease.  It has been suggested by some nutrition experts that many chronic diseases can be reversed through diet, particularly that which is plant-based, including hypertension and diabetes (Gustafson, 2014). Clearly, obesity poses a serious threat in the development of the chronic diseases that are the leading causes of death in the United States.  Eating a varied diet of whole foods, limiting caloric intake, and engaging in regular physical activity are the best ways to lessen your risk of obesity and chronic diseases.

References

American Diabetes Association. (2014). Type 2 Diabetes. Retrieved from American Diabetes Association: http://www.diabetes.org/diabetes-basics/type-2/?loc=db-slabnav

American Heart Association. (2014). Watch, Learn and Live - Interactive Cardiovascular Library. Retrieved from American Heart Association: http://watchlearnlive.heart.org/CVML_Player.php?moduleSelect=chlcad

Chan, M., Kelly, J., Batterham, M., & Tapsell, L. (2014). A High Prevalence of Abnormal Nutrition Parameters Found in Predialysis End-Stage Kidney Disease: Is It a Result of Uremia or Poor Eating Habits?. Developmental Psychology, 50(9), 292-302. doi:10.1053/j.jrn.2014.03.008

Freudenrich, C. (2014). How Diabetes Works. Retrieved from howstuffworks: http://health.howstuffworks.com/diseases-conditions/diabetes/diabetes1.htm

Gustafson, C. (2014). Michael Greger, MD: Reversing Chronic Disease Through Diet; Addressing the 2015 USDA Dietary Guidelines Committee. Integrative Medicine: A Clinician's Journal, 13(2), 22-24.

Sizer, F., & Whitney, E. (2013). Nutrition: Concepts and Controversies (13th ed.). Mason, OH: Cengage Learning.

Weichselbaum, E., Coe, S., Buttriss, J., & Stanner, S. (2013). Fish in the diet: A review. Nutrition Bulletin, 38(2), 128-177. doi:10.1111/nbu.12021