What is diabetes, its types, pathophysiology, symptoms, causes, and dietary management?

Diabetes Mellitus: Types, Pathophysiology, Symptoms, Causes, and Dietary Management

Diabetes mellitus is a group of metabolic diseases characterized by chronic hyperglycemia resulting from defects in insulin secretion, insulin action, or both, leading to long-term damage and dysfunction of various organs, especially the eyes, kidneys, nerves, heart, and blood vessels. 1

Types of Diabetes

Type 1 Diabetes

• Characterized by autoimmune destruction of pancreatic β-cells leading to absolute insulin deficiency 1
• Presents with rapid onset, especially in children and adolescents 1
• Markers include islet cell autoantibodies, autoantibodies to insulin, GAD65, and tyrosine phosphatases IA-2 and IA-2 1
• Strong HLA associations with linkage to DQA and DQB genes 1
• Always requires insulin treatment for survival 1
• Can be staged into three phases:
  • Stage 1: Multiple autoantibodies with normoglycemia (presymptomatic)
  • Stage 2: Multiple autoantibodies with dysglycemia (presymptomatic)
  • Stage 3: New-onset hyperglycemia with clinical symptoms 1

Type 2 Diabetes

• Most common form, characterized by insulin resistance and progressive insulin secretory defect 1
• Often asymptomatic at early stages and discovered during screening 1
• Frequently associated with obesity and physical inactivity 1
• May initially be managed with lifestyle modifications and oral medications, but may eventually require insulin 1
• Early stages characterized by excessive post-prandial hyperglycemia due to insulin resistance 1

Other Specific Types

• Genetic defects of β-cell function (MODY) 1
• Genetic defects in insulin action 1
• Diseases of the exocrine pancreas ("Pancreatic diabetes") 1
• Endocrinopathies 1
• Drug or chemical-induced diabetes 1
• Infections 1

Gestational Diabetes

• Hyperglycemia that develops during pregnancy 1
• Diagnosed if one or more criteria are met in a 75g OGTT:
  • Fasting plasma glucose ≥92 mg/dL (5.1 mmol/L)
  • 1-hour value ≥180 mg/dL (10.0 mmol/L)
  • 2-hour value ≥153 mg/dL (8.5 mmol/L) 2
• Approximately 70% of women with gestational diabetes will develop diabetes over time 1

Pathophysiology

Type 1 Diabetes

• Results from autoimmune destruction of pancreatic β-cells 1
• Rate of destruction varies - rapid in children, slower in adults 1
• Both basal and prandial insulin secretion are affected 1
• Leads to absolute insulin deficiency and dependence on exogenous insulin 1
• Ketoacidosis may occur when insulin is severely deficient 1

Type 2 Diabetes

• Characterized by a combination of:
  • Insulin resistance in muscle, liver, and fat tissues
  • Progressive decline in β-cell insulin secretion 1
• Impaired insulin secretion and defects in insulin action frequently coexist 1
• Hyperglycemia develops gradually as β-cell function deteriorates 1
• Metabolic abnormalities in carbohydrate, fat, and protein metabolism 1

Metabolic Consequences

• Deficient insulin action results in abnormalities of carbohydrate, fat, and protein metabolism 1
• Leads to catabolic state with increased protein breakdown and muscle wasting 3
• Chronic hyperglycemia causes oxidative stress and inflammation 4
• Results in microvascular and macrovascular complications over time 4, 5

Symptoms and Clinical Manifestations

Classic Symptoms

• Polyuria (excessive urination) 1, 3
• Polydipsia (excessive thirst) 1, 3
• Polyphagia (excessive hunger) in some cases 1
• Unexplained weight loss 1, 3
• Blurred vision 1

Other Manifestations

• Impaired growth (particularly in children with type 1) 1, 3
• Increased susceptibility to infections 1, 3
• Fatigue and weakness due to muscle protein catabolism 3
• Delayed wound healing 1
• Recurrent skin or genital infections 6

Acute Complications

• Diabetic ketoacidosis (primarily in type 1) 1
• Hyperosmolar hyperglycemic state (primarily in type 2) 1
• Hypoglycemia (treatment-related) 1

Chronic Complications

• Microvascular:
  • Retinopathy with potential vision loss 1
  • Nephropathy leading to renal failure 1
  • Peripheral neuropathy with risk of foot ulcers and amputations 1
  • Autonomic neuropathy affecting cardiovascular, gastrointestinal, and genitourinary systems 1
• Macrovascular:
  • Increased risk of atherosclerotic cardiovascular disease 1
  • Peripheral arterial disease 1
  • Cerebrovascular disease 1

Causes and Risk Factors

Type 1 Diabetes

• Autoimmune destruction of β-cells 1
• Genetic predisposition (HLA associations) 1
• Environmental triggers (poorly defined) 1
• Association with other autoimmune disorders (thyroid disease, celiac disease, etc.) 1

Type 2 Diabetes

• Genetic factors 1, 6
• Obesity and central adiposity 1
• Physical inactivity 1, 6
• Advancing age 5
• History of gestational diabetes 1
• Ethnicity (higher risk in certain populations) 1, 5
• Family history of diabetes 6

Diagnostic Criteria

• Fasting plasma glucose ≥126 mg/dL (7.0 mmol/L) on two occasions 1
• 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during OGTT 1
• HbA1c ≥6.5% 1, 2
• Random plasma glucose ≥200 mg/dL (11.1 mmol/L) with classic symptoms 1, 2

Dietary Management

General Principles

• Individualized approach based on metabolic goals and personal preferences 3
• Focus on overall healthy eating patterns rather than single nutrients 7
• Regular monitoring of blood glucose to assess dietary impact 7

Caloric Requirements

• 25-35 kcal/kg body weight for most adults 3
• Adjust based on activity level, age, and weight goals 3
• Avoid overfeeding as it can exacerbate hyperglycemia 3

Macronutrient Distribution

• Carbohydrates:
  • Focus on complex carbohydrates with low glycemic index 7
  • Monitor carbohydrate intake (carbohydrate counting) 7
  • Distribute carbohydrates throughout the day 7
  • Limit refined carbohydrates and added sugars 6
• Proteins:
  • 1.0 g/kg for mildly stressed patients 3
  • 1.5 g/kg for moderately to severely stressed patients 3
  • Choose lean protein sources 7
• Fats:
  • Limit saturated and trans fats 7
  • Include sources of monounsaturated and omega-3 fatty acids 7

Specific Dietary Approaches

• Mediterranean diet pattern shows benefits for glycemic control 7
• DASH (Dietary Approaches to Stop Hypertension) diet may benefit those with concurrent hypertension 7
• Plant-based diets can improve insulin sensitivity 6
• Low-carbohydrate diets may help with short-term glycemic control and weight loss 6

Practical Considerations

• Regular meal timing to maintain stable blood glucose 7
• Portion control for weight management 7
• Adequate fiber intake (25-30g daily) 6
• Limited alcohol consumption 6
• Adequate hydration, especially when blood glucose is elevated 3

Common Pitfalls in Diabetes Management

• Misdiagnosis of diabetes type (e.g., adults with type 1 misdiagnosed as type 2) 1
• Missing early stages of type 2 diabetes due to gradual onset 3
• Focusing only on fasting glucose while ignoring postprandial hyperglycemia 1
• Overemphasis on single nutrients rather than overall dietary pattern 7
• Inadequate protein intake during catabolic states 3
• Failure to adjust dietary recommendations based on medication regimen 1
• Not accounting for individual metabolic responses to different foods 7