how do we know when our bodies are burning fat? Is it when we’re hungry and our tummies have the rumblies?


how do we know when our bodies are burning fat? Is it when we’re hungry and our tummies have the rumblies?

In: Biology

The rumbling is a self cleaning, it just means you have an empty stomach. Being hungry also just indicates your body things it’s time for another feeding and not that you burn a single bit of fat yet.

Fitness watches can estimate your fat burning through your heartrate, but I doubt thats really exact.

Being in a bad mood (hangry) is usually a good indicator that your bloodsugar is low and your body lives off reserves

We don’t “know” ourselves. Hunger doesn’t necessarily mean we’re burning fat, it just means our stomachs are empty. We will first use up other resources, like ketones, and then we’ll move on to fat burning, but that will be some time after we start to feel hungry, generally speaking.

Hunger is only indirectly related to what macromolecule you’re metabolising.

Hunger is caused by the presence of a hormone, Ghrelin. Ghrelin is produced mainly by your stomach. when your stomach is empty, the surface of it isnt stretched, and this is one of the things that stimulates ghrelin production. this tells your brain ‘im hungry’ because your stomach is empty. when you eat, your stomach physically increases in size, the surface becomes stretched, and Ghrelin stops being produced. There is another hormone involved called Leptin, which does the opposite of Ghrelin, but thats a different ELI5.

Usually, when you eat your body starts to burn macromolecules in a specific order. Carbohydrates usually get burnt first. They’re eaten as carbs, and are burnt relatively quickly. If you eat too many, they get converted to fat (and other things) and stored.

When the carbs run out or run low, your body starts to convert the fats back to carbohydrates and starts burning them. You cant really ‘feel’ this – its like your blood circulation – just something that happens. You can detect this with blood tests and hormone analysis but you cant really feel it.

Depending on the composition of the meal, fat metabolism may begin a couple of hours after eating, or potentially not until the next day. the more often you eat carbs, the more you ‘top up’ the carb tank, so the body never really gets the chance to go into fat metabolism mode.

The thing to keep in mind is that if you go too long between meals your body goes into starvation mode, where it slows down the amount of fat that it burns and burns proportionally less of it compared to other macromolecules.

To ensure your body stays *as much as reasonably possible* in fat metabolism mode, the trick is to eat meals that contain some carbs, but also drink plenty of water (which stretches the stomach and stops ghrelin production) and fiber (which makes you feel full but has little caloric impact). these two things ensure that your ghrelin production remains low, but your carb ingestion also stays low, so your body stays in fat burning mode for longer.

Please, don’t try to lose weight through hunger! When you get hungry, your body goes into emergency mode and tries to preserve every bit of energy it can. When you do it often, you just teach your body how to be more efficient on it, which is the opposite effect.

Do some fasting. You will figure it out after a couple weeks.

When you eat after a fast, even a small snack, you feel your whole body become energized.

You will then recognize that feeling or lack thereof at other times. then you will know most of the time if your body is burning fat or processing food.