The Hidden Effect of A1C on Oxygen

You know A1C as a “blood sugar number.” But here’s what’s rarely explained: a high A1C means your red blood cells are literally worse at carrying oxygen.

When sugar sticks to hemoglobin, two things happen:

• Some of the oxygen “seats” are blocked.

• The oxygen that does attach gets held too tightly.

The result? Less oxygen actually makes it to your muscles and tissues. Exercise feels harder. Fatigue sets in faster. And over time, your body adapts to being sedentary, because it’s been trained to.

The SAID Principle:Specific Adaptation to Imposed Demands

Your body becomes good at whatever it’s most consistently exposed to. This is the SAID principle—Specific Adaptation to Imposed Demands. Repeated weight training signals your muscles to grow stronger. Endurance training signals your heart and lungs to deliver oxygen more efficiently. We see this at the highest levels of athleticism, where bodies are fine-tuned by years of repeated training. And long stretches of high sugar exposure with little muscle use signal your blood to adapt as well by binding more glucose to hemoglobin. Over time, that adaptation makes red blood cells less efficient at releasing oxygen, which is part of why exercise can begin to feel harder.

The Flip Side

This isn’t failure, it’s adaptation. The same biology that strengthens your muscles when you lift weights is at work here. And the good news is, it adapts in the other direction too. More movement, more muscle use, and balanced nutrition retrain your cells, lower A1C, and restore oxygen efficiency.

A high A1C doesn’t just measure sugar, it makes your blood worse at carrying oxygen. And if your blood can’t deliver oxygen efficiently, exercise will always feel harder.

That matters for fat loss, because if movement feels harder, you’ll naturally do less of it. In a way, a high A1C is designed to keep you sedentary.

So the first step is lowering the barrier. Get your A1C down, so exercise feels easier and fat loss becomes more possible.

If you’re unsure where to start, this is exactly what I help with. Begin by learning what A1C actually means for your body. And when you’re ready, sign up for a complimentary session I’ll help you design the strategy that fits you best.