does the body really have a ‘starvation mode’ that kicks in if you eat too little and stops you losing weight?

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I hear this from time to time. If you cut your calorie intake too much your body with assume food is scarce and initiate its ‘starvation mode’ which will prevent you losing weight so quickly. Is that actually true or is it a story told to stop people following unhealthy diet regimes?

And, if it is true, how can the body do this? If the body can suddenly run on fewer calories then why doesn’t it do that all the time? I guess it must have to stop burning calories on certain activities?

In: Biology

Yes it does. One method is that it starts converting muscle to energy. When you have less muscle, you use less energy overall. But this is a desperate survival mode. In a hunter-gatherer society this is a bad thing – reduces the ability to hunt and makes you more vulnerable to predators.

Yes, but it doesn’t stop you losing weight, the body will digest body fat and muscle protein, at the same time it basically neglects all repair and maintenance that normally goes on in the body to save energy.

You’d have to miss many meals for this to start, it’s a common misconception that dieting causes it or missing a meal, it’s called starvation mode because you have to be suffering from starvation. Several days of no food…

I just watched a great YouTube playlist by “what I’ve learned” on YouTube about just this.

https://m.youtube.com/playlist?list=PLuOCYTZXw6HYl_57faBEoU4u_Ot2F4-yX

TLDW: not until you’re actually starving. And I mean weeks of not eating. I’ve actually just come off of a 72 hour fast based on the papers quoted in these videos and I feel amazing. Had the energy to work out for the first time in ages this afternoon.

Note: feeling like you are starving is not starvation mode.

There’s no starvation mode until you get to an unhealthy level of body fat. Basically there is a small amount of body fat you need to maintain life such as the fat in the brain or spinal cord. As you get close to this level you subconsciously start to conserve energy, such as simply moving less or slower, one person even mentioned he blinked less.

You can look up the Minnesota semi starvation experiment which is the best of its kind, all the subjects (who didn’t cheat) ended up looking like concentration camp survivors, as one would expect. They lost most if not all their non essential body fat, they also spent most of their day just sitting around and conserving energy.

Yes and no.

No, if you stop eating you will not maintain or gain weight. Your body runs on energy (calories). It has to have energy or you die. Those are the options. You can’t beat the laws of thermodynamics. Use mass for energy, lose weight.

Yes, there is a severe sort of self-destruction that happens during true starvation.

The body gets energy from carbohydrates (glucose & glycogen), fat, & protein (muscle).
It “prefers” to use them in that order, though it’s always using some from each category.

Once you’ve used up the quick-access blood sugar (glucose) the body switches more to glycogen (carbs stored in the liver & muscles), then fat, and if you still haven’t found/eaten food once that’s pretty much gone it will start tearing down muscles.

This. Is. Bad.
Your heart is a muscle. You breathe using muscles. You move (find food, eat) using muscles.
Burning muscle to stay alive in hopes of finding food before you die is starvation.