Yes, that’s what I said. Chronically elevated cortisol levels can lead to insulin resistance.
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Cortisol and Fat Loss
If you’re familiar with coach Poliquin’s body composition analysis approach (biosignature, bioprint, metabolic analytics) you know the system claims that excess cortisol leads to abdominal fat storage.
But if you remember what the functions of cortisol are, you might see a contradiction here. After all, one of the functions of cortisol is to mobilize stored energy (including fat), not store it.
Cortisol is, in fact, a fat loss hormone, at least when produced in a pulsatile manner. But that doesn’t mean chronic cortisol can’t make it harder to lose fat. While a short-term elevation of cortisol is involved in fat loss, if it becomes chronically elevated it can make the fat loss process harder. How? Two ways…
1 – Cortisol can decrease the conversion of T4 into T3.
Remember, T3 is the thyroid hormone that has the greatest impact on your metabolic rate. When it’s higher, your metabolic rate increases so you burn more calories on a daily basis.
If T3 goes down, so does your metabolic rate. So T4 doesn’t have as much of a direct impact. The body produces mostly T4 and converts it into T3 at the level deemed safe for survival by the body.
If you’re chronically deprived of energy though, the body will reduce the T4 to T3 conversion, decreasing your metabolic rate. During our evolution, when cortisol was elevated chronically, it meant that we weren’t able to find food and that, as a result, cortisol always had to be high to keep blood sugar stable and mobilize stored energy.
It adjusted by reducing T3 levels to lower energy needs. Back then, we needed that adjustment. Sadly, nowadays chronic cortisol elevation can come from many stressors, and even if we aren’t in a deprived state, the chronic cortisol issue will still lead to a decreased T4 to T3 conversion.
2 – It can lead to insulin resistance.
Cortisol increases blood sugar levels. When we were cavemen and women, that wasn’t a big problem because cortisol normally spiked when we had to be physically active (fighting or running away) or were lacking food. So, we’d use the released glucose for energy.
But if blood sugar increases while we’re sedentary, it just stays there, leading to hyperglycemia. The body doesn’t want that, and it will release insulin to bring blood sugar back down to normal levels. All is fine and good, right? Not really.
If cortisol is chronically elevated it means it’ll constantly increase blood sugar levels, which in turn will lead to frequent releases of insulin. That can lead to insulin resistance.
Both a decrease in metabolic rate and insulin resistance can make it harder to lose fat. No, they don’t override the laws of thermodynamics. Establishing a caloric deficit is still the most important thing to lose fat. But if cortisol decreases metabolic rate, it means that it’ll be harder to create a deficit (and easier to create a surplus).
Keep in mind, insulin alone won’t make you fat. It can only store the nutrients you ingest; it doesn’t create new nutrients. If you eat in a caloric deficit and have high insulin you won’t gain fat.
However, insulin can make it harder to mobilize stored fat. As long as insulin is elevated above baseline, it’ll be harder for you to mobilize fat efficiently. When you’re insulin resistant, it means that your cells don’t respond well to insulin. As a result, you need to produce more to do the same job. If you produce more, it takes longer to bring it back down. If it stays elevated for longer, you spend more time in a state where fat mobilization is less efficient.
Cortisol isn’t a fat gain hormone, but its chronic elevation can make it harder to lose fat over time.