Guest post by: Dr Mariah Mosley

Diabetes mellitus is unfortunately becoming a very common disease. There are two well known types of DM: type 1 and type 2. But what are the differences between these, and what is this type 1.5 or type 3 being talked about?

Type 1 Diabetes

Type 1 diabetes used to be known as juvenile diabetes, because symptoms started early, usually during childhood.  It occurs due to the pancreas producing little or no insulin (the hormone that prevents glucose–aka sugar–in the blood from rising too high or falling too low). Type 1 diabetics usually have to be on insulin for the rest of their lives in order to manage their blood sugars.  These patients have to constantly be aware of what they are eating, how it may affect their blood sugar, and adjust their insulin dose to keep their glucose level in an optimal range. When blood sugar becomes too low, it may lead to insulin shock, which is life threatening.  When blood sugar stays too high over time and is untreated, it can cause ketoacidosis. This can lead to nausea, vomiting, shortness of breath, weakness, confusion or coma. It can also cause a hyperglycemic state, which can lead to life-threatening dehydration and coma.  Long-term untreated high blood glucose can also lead to cardiovascular disease, nerve damage, kidney failure, damage to blood vessels in eye or blindness, and infections. 

The body’s own immune system is actually what destroys the insulin producing cells in the pancreas for type 1 DM. It is an autoimmune disease, which means the body’s immune system starts to mistakenly attack its own body instead of foreign invaders (bacteria, germs, etc).  Viruses have also been linked to development of diabetes type 1. Coxsackie B virus, Rotavirus, Mumps, Cytomegalovirus, and Rubella have all been associated with type 1 diabetes, specifically the enteroviruses3.  While we do not know exactly how these viruses trigger autoimmunity, it is suspected that when viral infections activate a strong immune response, if they are specifically triggering the Beta cells of the pancreas (the cells that make insulin) and causing significant inflammation inside the cells, this can be the first step in the dysregulation of the immune system and autoimmunity induction. 

However, this viral connection to Type 1 DM has been debated extensively. For example- how can we explain that a REDUCED type 1 diabetes occurrence is observed in countries of lower socioeconomic status, which has a HIGHER rate of infection? Genetics has been known to play a part in Type 1 diabetes; however this is probably not the primary cause either, as DM1 disease occurrence in identical twins is less than 50%.3  Molecular mimicry is another way in which the theory of the virus triggers and genetics might work together.

So taking all the current evidence into consideration, it appears that there is no one straightforward cause of Type 1 Diabetes.

Type 2 Diabetes

Type 2 diabetes is more common than type 1. More than 30 million Americans have diabetes (1 in 10 people) and about 90-95% of them have Type 2 DM6. This disease usually occurs later in life, and is a chronic, slower developing condition in which the body is unable to metabolize sugar like it should. This can be due to the body developing a resistance to insulin, or in more progressive disease, because the body doesn’t produce enough insulin to maintain normal glucose levels. Diabetes type 2 is linked to obesity and our gut microbe (see here for more on this). Diabetes type 2 can be controlled (and REVERSED) with healthy diet choices, weight loss, exercising, and removing any other obstacles to cure.

Type 1.5 Diabetes

Type 1.5 DM is the lesser known of diabetes types. This is because type 1.5 is a non-official term referring to a form of Type 1 DM, also known as Latent Autoimmune Diabetes in Adults (LADA). This  also has a slow onset like type 2. However, it still is an autoimmune disease, often requiring insulin therapy at some point in the future (like type 1 which also attacks the insulin producing cells).

Most physicians are educated that Type 1 and Type 1.5 are irreversible. However, there are studies7 arising that show beta cells being regenerated (therefore reversing diabetes) with a ‘fasting-mimicking diet’ and water fasting.  Granted, these studies are in only mice currently, and we still will have to address the autoimmune portion of the disease. However, it is uplifting to see that there is HOPE.

Type 3 Diabetes

Lastly: type 3 diabetes. This is a form of diabetes associated with Alzheimer’s disease, and occurs when the neurons (the nerve cells which transmit information throughout the body) in the brain become unable to respond to insulin, which is essential for basic daily tasks, memory, learning, etc. So type 3 is a form of diabetes which targets the brain selectively.

The Upshot

So in conclusion, here is a very quick bullet list for you to reference:

      • Type 1: autoimmune, body attacks its own pancreas, childhood onset
      • Type 1.5: autoimmune, body attacking itself (pancreas), adulthood onset
      • Type 2: poor diet/weight/gut microbiome related, usually reversible
      • Type 3: related to Alzheimer’s, affects the brain only


  1. Type 1 Diabetes.
  2. Hyperglycemia in Diabetes.
  3. Viral Triggers for Type 1 Diabetes, Pros and Cons.
  4. Influence of maternal age at delivery and birth order on risk of type 1 diabetes in childhood: prospective population based family study
  5. Type 1.5 Diabetes.
  6. Type 2.
  7. Fasting-Mimicking Diet Promotes Ngn3-Driven β-Cell Regeneration to Reverse Diabetes
  8. Researchers link Alzheimer’s gene to Type 3 diabetes
  9. Alzheimer’s Disease Is Type 3 Diabetes–Evidence Reviewed.