Glucagon: fat burner and enemy of muscle

Glucagon is a hormone that counteracts insulin. It raises blood sugar and releases stored fat for energy – but unfortunately, muscle pays a price too. Below, I’ll walk you through exactly what happens in the pancreas and why it matters to anyone who trains.

What glucagon is and how it works

Like insulin, glucagon is produced in the pancreas. Its job is simple: to keep your blood sugar stable when you haven’t eaten for several hours. While insulin moves sugar from the blood into cells and stores it as glycogen, glucagon does the opposite – it tells the liver to break down glycogen and releases sugar back into the bloodstream.

In practice, this tug of war is constant. You eat a carbohydrate-rich meal – insulin rises, sugar moves into cells, and glucagon goes quiet. A couple of hours pass and blood sugar falls – glucagon wakes up, activates an enzyme in the liver called phosphorylase, and sends sugar back into circulation. Insulin, in turn, responds to that rise. And so it continues until your next meal.

If you go without carbohydrates for an extended period, your liver’s glycogen stores begin to run low. From there, your metabolism gradually shifts to burning fat. Cravings for sweets subside, and your energy comes from a different source.

Glucagon as a fat burner

Just as insulin is a hormone that stores fat, glucagon is a hormone that releases it. When liver glycogen stores fall and glucagon dominates, your body starts using fat tissue as an energy source. Frankly, this is precisely why fasted training, fasted morning cardio, and low-carbohydrate days work at all.

The simple truth is that when your liver is full of glycogen and insulin stays high, glucagon has no room to work. Fat burning takes a back seat. To truly benefit from glucagon, your liver’s glycogen stores need to be at least partially depleted – a longer break between meals, a modest reduction in carbohydrates, or consistent training will do that.

During winter in Estonia, when you often move less and eat more frequently, this balance tends to tip in favor of insulin. In autumn and winter, it’s worth deliberately leaving longer gaps between meals if your goal is to lower your body fat percentage.

The downside of glucagon: muscle protein under attack

Every hormone is a two-edged sword. Glucagon is no exception. When your liver’s glycogen stores are depleted but blood sugar still needs to be maintained, glucagon takes raw material wherever it can find it – including from muscle protein. This process is called gluconeogenesis: muscle protein is broken down into amino acids, which are then converted into glucose.

This is catabolism in its purest form. If you’re an athlete working hard to build muscle mass, that’s not particularly good news. The more of a “sugar burner” you are – meaning you get most of your energy from carbohydrates – the more aggressively glucagon pulls amino acids from your muscles as soon as carbohydrates run out. For a “fat burner” (someone who gets most of their energy from fat), this effect is noticeably weaker because their body simply doesn’t need as much glucose.

Glucagon’s dark side is most apparent in people with type 1 diabetes, whose pancreas does not produce insulin because of impaired function. Without insulin, there is nothing to counterbalance glucagon – the result is a rapid loss of body fat and muscle mass that stops only after an insulin injection.

Practical points for your training

What does this mean in practice?

• If your goal is to lower your body fat percentage, don’t keep your liver’s glycogen stores constantly full. A longer break between meals or a slightly lower carbohydrate intake gives glucagon room to work.
• If your goal is to build muscle mass, make sure you have a combination of carbohydrates and protein after strength training. This slows glucagon’s catabolic action just when your body is most vulnerable.
• A fasted morning workout is no magic solution, but it does increase the ratio of glucagon to insulin – it works for some people and not for others.
• Extended fasting beyond 14–16 hours also starts to use up muscle protein quite noticeably. That isn’t inherently bad, but it’s worth being aware of.

Glucagon FAQ

Are glucagon and glycogen the same thing?

No. Glucagon is a hormone produced by the pancreas. Glycogen is the storage form of sugar, kept in the liver and muscles. Glucagon is what triggers the breakdown of glycogen when needed.

Can I raise my glucagon levels through food?

Not directly. But indirectly, yes – a lower carbohydrate intake, a diet higher in protein, and longer gaps between meals tip the balance in favor of glucagon.

Does glucagon burn fat even when I’m not training?

Yes, this happens constantly in the background – between meals, especially at night. Training simply amplifies the effect because glycogen stores are depleted faster.

Author: muc

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