Type 1 diabetes, formerly known as insulin-dependent diabetes mellitus, is characterized by the absence of insulin. It accounts for 5% to 10% of diabetes cases. Although type 1 can occur at any age, it is most often diagnosed before the age of 18 years. Type 1 diabetes occurs from an autoimmune response that damages or destroys pancreatic beta cells, leaving them unable to produce insulin. Interaction between genetic susceptibility and environmental factors, such as viral infection, is thought to be responsible. The classic symptoms of polyuria, polydipsia, and polyphagia appear abruptly. Sometimes, the first sign of the disease is ketoacidosis. There is no known way to prevent type 1 diabetes. All people with type 1 diabetes require exogenous insulin.

Type 1 Diabetes diabetes characterized by the absence of insulin secretion.

Polyuria excessive urine excretion.

Polydipsia excessive thirst.

Polyphagia excessive appetite.

Ketoacidosis the accumulation of ketone bodies leading to acidosis related to incomplete breakdown of fatty acids from carbohydrate deficiency or inadequate carbohydrate utilization.

Insulin Resistance decreased cellular response to insulin.

Impaired Fasting Glucose fasting plasma glucose levels of 100 to 125 mg/dL.

Impaired Glucose Tolerance 2-hour values in the oral glucose tolerance test of 140 to 199 mg/dL.

Hyperinsulinemia elevated blood levels of insulin.

Type 2 diabetes, previously referred to as non-insulin-dependent diabetes, is most often diagnosed after the age of 45 years and accounts for 90% to 95% of diagnosed cases of diabetes. Unlike type 1 diabetes, in which there is a relatively abrupt and absolute end to insulin production, type 2 diabetes is a slowly progressive disease characterized by a combination of insulin resistance and relative insulin deficiency. When cells do not respond to insulin as they should, the pancreas compensates by secreting higher than normal levels of insulin. Impaired fasting glucose and impaired glucose tolerance occur despite high levels of circulating insulin. Over time, chronic hyperinsulinemia leads to a decrease in the number of insulin receptors on the cells and a further reduction in tissue sensitivity to insulin. Insulin production progressively falls to a deficient level, and frank type 2 diabetes develops. Because hyperglycemia develops gradually in type 2 diabetes and is often not severe enough for patients to recognize any of the classic diabetes symptoms, type 2 diabetes may go undiagnosed for years. Many patients will have already developed complications by the time of diagnosis (Ahmad & Crandall, 2010).

Excess weight is strongly linked to type 2 diabetes. Other risk factors are listed in Box 19.1. Metabolic syndrome (MetS) is a cluster of risk factors, such as central obesity, insulin resistance, dyslipidemia, and hypertension that, when combined, increases the risk of type 2 diabetes fivefold and cardiovascular disease threefold (O’Neill & O’Driscoll, 2015).

Metabolic Syndrome (MetS) a clustering of interrelated risk factors that includes hypertension, low high-density lipoprotein (HDL) cholesterol, high triglycerides levels, elevated serum glucose, and central or abdominal obesity, as indicated by waist circumference.

Prediabetes is the period of impaired glucose metabolism that precedes the diagnosis of type 2 diabetes (see Fig. 19.1). In 2011 to 2012, the prevalence of prediabetes was 38% of the overall population (Menke et al., 2015).

Prediabetes fasting plasma glucose of 100 to 126 mg/dL or an oral glucose tolerance test of 140 to 199 mg/dL.

Identifying and treating prediabetes is a fundamental strategy for preventing or delaying diabetes (Selph et al., 2015). Lifestyle interventions can significantly reduce the rate of diabetes onset in people at high risk for developing type 2 diabetes, namely, those with impaired fasting glucose, impaired glucose tolerance, or both (ADA, 2016h). Because of the strong link between excess weight and insulin resistance/type 2 diabetes, modest weight loss achieved through a healthy, hypocaloric eating pattern, increased physical activity, and behavior change is the primary focus of diabetes prevention (Box 19.2). A major, multicenter clinical trial called the Diabetes Prevention Program (DPP) found that in a diverse group of overweight people with impaired glucose tolerance, nutrition therapy, physical activity, and behavior change decreased the incidence of diabetes by 58% (DPP Research Group, 2002). Average weight loss among study participants was a modest 5% to 7% of initial weight. Participants also benefited from improvements in their lipid profiles, blood pressure, and markers of inflammation (Haffner et al., 2005; Ratner et al., 2005). A 10-year follow-up on the original participants showed that the lifestyle intervention group maintained a decreased risk of diabetes over time (DPP Research Group, 2009). Strategies have been observed to promote weight loss are listed in Box 19.3.

Current recommendations for prediabetes screening are primarily focused on adults who are overweight or obese based on BMI until patients meet age-related screening at 45 years old (ADA, 2016c). However, a study by Mainous, Tanner, Jo, and Anton, (2016) found that in healthy weight adults aged 20 years and older, the prevalence of prediabetes was 18.5% in 2012 compared to 10.2% in 1988 to 1994. Although the reason for the increase in prevalence is unclear, researchers speculate that sedentary lifestyle could in part be responsible (Mainous et al., 2016).

It is recommended that all people with diabetes participate in diabetes self-management education (DSME) and diabetes self-management support (DSME/S) at diagnosis and thereafter as needed to learn and sustain the knowledge, skills, and ability needed to manage their diabetes (Fig. 19.2) (ADA, 2016d). Examples of self-care behaviors include healthy eating, being active, monitoring glucose and eating, taking medication, problem solving, and healthy coping. Although DSME/S has been shown to reduce hospital admission and lower estimated lifetime health-care costs due to a lower risk for complications, only a very small percentage of people with newly diagnosed type 2 diabetes actually participate in such a program (Powers et al., 2015).

Nutrition therapy is recommended for all people with type 1 or type 2 diabetes (Evert et al., 2013). Because atherosclerotic cardiovascular disease (ASCVD) is the most common cause of death among adults with diabetes (Go et al., 2013), nutrition therapy for diabetes includes strategies to reduce the risk of ASCVD. The goals of nutrition therapy for adults with diabetes are to (Evert et al., 2013)

Atherosclerotic Cardiovascular Disease (ASCVD) diseases of the cardiovascular system caused by atherosclerosis, which is the accumulation of plague within arteries. Includes acute coronary syndromes, myocardial infarction, stable or unstable angina, coronary or other arterial revascularization, stroke, transient ischemic attack, or peripheral arterial disease.

People with diabetes generally have the same nutritional requirements as the general population and dietary recommendations to promote health and well-being in the general public—lose weight if overweight, limit saturated fat, trans fat, and added sugars, eat more fiber and less sodium—are also appropriate for people with diabetes.

An ideal macronutrient composition for all people with diabetes has not been determined nor is there a universal “diabetic diet” that is recommended for all people with diabetes (Evert et al., 2013). An individualized approach is used to accomplish the goals listed earlier. The ADA’s nutrition therapy recommendations for diabetes management are presented in the following sections. Box 19.5 translates nutrition recommendations into healthy eating guidelines.