Most patients with adult-onset diabetes or type 2 diabetes will require insulin therapy at some point. Typically, it happens toward the second decade of the disease. In many cases, patients gain weight during the first six to 12 months after they start insulin therapy. On average, people gain about 10 pounds.
Interestingly, insulin therapy does not actually cause weight gain – insulin deficiency does. One of the major risk factors for gaining weight once starting insulin therapy is the A1C preceding it. The higher the A1C or glucose before someone starts insulin therapy (or the more severe their insulin deficiency is), the higher the chance they will gain weight.
Here’s why. When a person lives with elevated glucose or elevated A1C, their kidneys excrete glucose and they urinate hundreds of kilocalories per day. For example, if they live with A1C higher than 10%, they likely excrete more than 500 kilocalories per day, equal to a full meal. Once they receive enough insulin and stop urinating calories, they tend to retain those calories.
Accordingly, the person does not gain weight because of the insulin therapy, they gain weight because of the insulin deficiency they had before they started insulin therapy. To avoid this weight gain, insulin should be started as soon as A1C begins to trend upward, and before it becomes exceptionally high.
There is no clear danger in gaining weight while using insulin. Conversely, it is very dangerous to not use insulin therapy when it’s needed. When a person becomes insulin deficient and their A1C becomes elevated, they tend to lose weight because their body breaks down tissue. This condition is highly damaging and shortens one’s lifespan.
This condition is so dangerous, that the relationship between weight and survival becomes paradoxical. At that stage of the disease, weight loss is associated with higher mortality and weight gain is associated with lower mortality. It doesn’t mean that gaining weight is preferable, it means that weight at that stage becomes a marker of one’s insulin-deficiency. This is like age and wrinkles. It does not mean that wrinkles are dangerous, but they are a marker of how old someone is.
In summary, I would be much more concerned about insulin deficiency than weight gain. People should not delay starting insulin therapy. It is a much higher clinical priority to replenish one’s insulin deficiency than to avoid some weight gain.
It is very simple. If someone lives with high glucose or A1C, they are more likely to suffer from complications and die prematurely. If they live with optimal glucose or A1C, they are more likely to avoid that outcome.For more scientific information, please refer to this review article: https://pubmed.ncbi.nlm.nih.gov/29785843/