What is the main energy source used by the body when insulin is lacking?

When insulin is lacking, the body primarily turns to fats as its main energy source. Insulin plays a crucial role in regulating glucose levels in the bloodstream and facilitating the uptake of glucose into the cells for energy. In the absence of insulin, the body cannot effectively utilize glucose, leading to a state where fat stores are mobilized for energy instead.

The process involves the breakdown of triglycerides stored in adipose tissue into fatty acids and glycerol, which can then be transported to various tissues and converted into energy. This shift from glucose to fatty acid metabolism helps preserve glucose for critical functions, particularly in the brain, which relies on glucose under normal circumstances.

In situations such as uncontrolled diabetes or periods of starvation when insulin levels are low, the reliance on fat as an energy source becomes even more pronounced. This is why fat is recognized as the primary alternative energy source when insulin is insufficient.