High Fasting Insulin levels are the lock that prevents a person from using body fat.
Of the three macros (fat, carbs and protein) only carbs have a significant impact on blood sugar and as a result can raise insulin levels. Clearly, if you reduce the carb load you also reduce the area under the curve for Insulin while digesting food. But does lower carb consumption at meals impact fasting (basal) insulin levels?
From (Insulin Response to Glucose in Diabetic and Nondiabetic Subjects. John D. Bagdade, Edwin L. Bierman, and Daniel Porte Jr. Journal of Clinical Investigation. October 1, 1967):
Obesity, but not diabetes, was associated with an elevation of this basal insulin level.
Thus obesity predicted with the magnitude of the insulin response to glucose ingestion.
Thus increasing degrees of carbohydrate intolerance were associated with decreasing insulin responses. Elevated levels of insulin, in both the basal state and in response to glucose, were related to obesity.
More specifically from the text of the study:
Fasting insulin levels of obese subjects (36 uU +/- 17.6) were significantly higher (P < 0.001) than those of the thin subjects (14 uU +/- 4.8). … Thus the degree of obesity, and not the carbohydrate intolerance, was associated with the insulin levels maintained after an overnight fast.
So it’s not so much the carb intolerance but the obesity itself which raised fasting insulin levels. The next observation was:
…there was a highly significant linear correlation between fasting insulin and insulin response to glucose in both nondiabetic and diabetic subjects. This demonstrates a tendency for subjects with higher fasting levels to demonstrate greater insulin responses to glucose.
The initial insulin response to glucose in diabetics is attenuated and the total insulin response is also less at the same weight. However, obese diabetics produce a significantly larger amount of Insulin than thin diabetics or non-diabetics.
It is interesting how much of a driving force that obesity is. Fasting Insulin levels were not related to a diabetic response to glucose as much as whether or not a person is obese.
No matter what the cause, the prescription is the same – weight loss.
Explains Some Low Carb Folks
This does explain people who are on low carb and still have high fasting levels of Insulin and are obese. Low carb alone won’t solve the fasting levels of Insulin but loss of weight will.
This goes a long way to explaining why some low carb individuals can’t seem to lose much weight and are still obese even after a long time on Low Carb (Two Keto Dudes, Jimmy Moore come to mind). One of the Two Keto Dudes Richard (I believe it was) commented that he has a high fasting insulin even after years on keto.