Insulin and Your Heart
Type 2 diabetes is defined as having insulin resistance (IR). At least in the early stages of the disease, you’re producing plenty of insulin, but because of the IR, the insulin doesn’t work very well. (Type 1 diabetes is an autoimmune disease and results in insulin deficiency.)
Thus one would think that any treatment that reduced IR would be beneficial, and in general that is true. However a new paper published in Diabetes suggests that in a specific subset of type 2 patients, IR could be protective. First author, Christopher J Nolan, kindly sent me the full text of the article.
One point made in the article is that type 2 patients are a heterogeneous group. They range from obese to normal weight, and from producing a lot of insulin to producing very little, and this diversity may be one reason the results of various large clinical studies may differ.
The subset of patients the authors are concerned with are those who are overweight or obese, with severe IR, eating more calories than they require, and having high hemoglobin A1c levels, for example in the 9s and 10s.
The authors argue that under these conditions, IR in the heart cells is protective, keeping the heart cells from becoming overloaded with nutrients, which in excess can damage the heart cells.
But because we also know that high blood glucose (BG) levels are damaging, some of these patients are given huge doses of insulin in an attempt overcome the IR and bring their BG levels down. The result, the authors suggest, is that the heart cells take up too much glucose and fatty acids and are damaged by the resulting glucotoxicity and lipotoxicity.
They suggest that this could explain the results of the ACCORD study, which seemed to show that "tight control" resulted in higher mortality, although further analysis showed that the patients who did worse were those who tried to get their A1cs down but didn’t succeed. Many of these patients used insulin to try to do so.
The authors of this paper suggest that the problem was nutrient overload in the heart cells in a subset of overweight and obese patients using insulin to overcome the IR, thus overloading the cells with glucose. And they point out that if a subset of patients in a big trial are harmed by some treatment, the potential benefit of a treatment in other subsets of patients will be masked.
Note again that these comments apply to a subset of type 2 patients, not everyone, and don’t mean that no type 2 should use insulin. If you’re thinking of using insulin and you’re not very obese and with poor control, insulin might be your best bet.
But what if you are obese and in poor control? Then what? The authors say the best approach would be to reduce the nutrient overload, meaning eat less and exercise more, but they do admit that "these measures usually have failed in overweight or obese patients with type 2 diabetes with refractory poor glycemic control."
Hence they suggest other approaches including bariatric surgery, GLP-1 receptor agonists (like Byetta), and the SGLT2 inhibitors that promote increased glucose excretion in the urine would be better than insulin in this subset of patients.
The authors don’t mention it, but another approach would be a low-carbohydrate diet, because the blood ketones that result from such diets tend to reduce hunger. And the less food you eat, the lower your BG levels and hence lower the stress on your heart, as well as other types of cells.
What the body wants to do when BG levels are high is to store that extra energy in fat cells to use when food is scarce. And by causing IR in skeletal and heart muscle, the body diverts extra energy to the fat cells. If this doesn’t happen, the glucose may end up in other places, where it’s harmful. For example, beta cells don’t need insulin to take up glucose, so if your BG levels are high, the beta cells can easily become overloaded with glucose, and glucotoxicity can damage them.
Thus reducing IR in fat cells but not in heart cells would be a good thing, but no one knows how to do that yet.
Until we do, trying a low-carb diet might be the best option for your hunger levels, your weight, and your heart.
More articles on insulin resistance:
Gretchen wrote for HealthCentral as a patient expert for Diabetes.