Diabetes, whether Type 1 or Type 2, is a dysfunctional, wasteful metabolic state. As a result, an uncontrolled diabetic either uses or loses more energy than their non-diabetic selves would otherwise use. As such, the untreated diabetic is essentially "underweight" compared with the body weight that the same energy intake would produce were they not diabetic.
There are differences in endogenous insulin production between the two types of diabetes. In Type 1, there is effectively no insulin production. In Type 2, there is usually elevated basal insulin production, but a relative deficiency in acute insulin secretion, specifically an impaired early insulin response to glucose (GSIS).
The absolute or relative insulin deficiency results in the following to a greater or lesser degree:
- Excessive lipolysis resulting in an increased cycling of the Triglyceride/Fatty Acid cycle.
- Impaired suppression of glucose production in the liver, specifically an increase in glucose production via gluconeogenesis.
- Glycosuria (sometimes called glucosuria) due to impaired re-uptake of glucose in the kidneys and/or hyperglycemia exceeding re-uptake capacity.
All three of these are "Calories Out" in the Calories In - Calories Out (CICO) energy balance model. Thus to greater or lesser degrees, diabetic individuals have greater energy expenditure. When insulin therapy corrects these, energy expenditure is reduced. Thus if the treated diabetic continues to consume their habitual amount of food, they will gain weight accordingly. This is in contrast to the often postulated model whereby insulin treatment either induces hunger and overeating due to hypoglycemia, or the thoroughly debunked TWICHOO (aka the Carb-Insulin Hypothesis/Model) whereby insulin magically traps fat made from carbs in the fat cells thereby starving the rest of the body and causing hunger and overeating.
The diabetic state also increases protein turnover rate, but this post focuses on the energetics. While protein breakdown and synthesis require energy, the difference doesn't seem to be significant compared to total energy expenditure or the contributions of the three processes listed above.