It's not just your blood sugar: why insulin matters too

Most talk about blood sugar is about the spike: the line on a glucose monitor shooting up after a bowl of pasta. But glucose is only half the story. Every time it rises, insulin rises to bring it back down, and insulin has jobs of its own.

What insulin actually does

Insulin is a hormone made by your pancreas. Its best-known job is moving glucose out of your blood and into your cells. But it's also a storage hormone: while insulin is high, it tells your body to store energy, including as fat, and to hold off burning what's already stored.

A rise in insulin after a meal is normal and necessary. The problem is insulin that stays high.

When insulin stays high

If your cells stop responding well to insulin, your pancreas makes more of it to get the same job done. This is insulin resistance, and the extra insulin it leads to is called hyperinsulinaemia.

Here's the catch: while your pancreas keeps up, your blood sugar can look completely normal, sometimes for years. High insulin can be quietly doing its thing well before a blood sugar test picks anything up [1].

The traditional view is that insulin resistance comes first and high insulin follows. Some researchers now argue it can work the other way too: that high insulin can come first and help drive insulin resistance and weight gain. In mice, lowering insulin production protected them from diet-induced weight gain and fatty liver. The human evidence is less clear-cut, and the order probably differs from person to person [1].

The PCOS link

This is where insulin matters most for me. Insulin directly tells the ovaries to make more testosterone, and it lowers SHBG, the protein that binds testosterone and keeps it in check [2]. More testosterone and less SHBG means more free testosterone, which is behind many PCOS symptoms: irregular periods, acne and unwanted hair growth.

So for a lot of women with PCOS, keeping insulin in check isn't just about energy. It goes to the root of the condition.

Doesn't protein raise insulin too?

Yes, and this is the part most people miss. In the study my real-life GL method is based on, adding chicken to mashed potato lowered the blood sugar rise but pushed the insulin response higher than the potato on its own. Adding oil did the opposite and brought it down.

The interesting result was the full plate. With chicken, oil and a salad all on the plate together, the insulin response came in lower than plain potato [3]. Protein alone wasn't the answer. Protein, fat and fibre together were.

That's one of the reasons I never cut the fat.

Give insulin a break

If insulin rises every time you eat, then eating constantly keeps it up for most of the day. In one trial, 54 people with type 2 diabetes ate the same reduced calories either as six small meals or as two larger ones, for 12 weeks each. On two meals, they lost more weight (3.7kg vs 2.3kg), and their fasting blood sugar, insulin production and insulin sensitivity all improved more [4].

It's one study, the two meals were breakfast and lunch only, and I'm not suggesting you skip dinner. But it backs up something I believe strongly: proper, filling meals beat grazing all day.

What this means for how I eat

None of this means fearing insulin. You need it, and it's meant to rise when you eat. What matters is the pattern: meals that don't send it soaring, and enough time between them for it to come back down. That's exactly what a full plate does. Carbs with protein, fat and fibre keep both blood sugar and insulin steadier, and keep you full enough that you're not reaching for a snack an hour later.

This is general information, not medical advice. If you have diabetes, PCOS or another condition, speak to your GP or care team about what's right for you.