So I was on TikTok and I came across some videos saying that if you eat low calories (1000 or 500) a day your metabolism will slow down and you won’t lose weight. Because your body has gotten use to it.
Is that true?? Sounds a bit weird to me? I would imagine your metabolism would slow down but not that much. Would fasting do that?
Pls dont go to TikTok for medical advice. I read something one day, I’ll try remember “See the chicken is bigger than the car 🐔 🚗, not everything you see online is true”. Well something like that lol, you get what I’m trying to say.
As you lose weight your TDEE will get lower; but that’s because you don’t need to maintain as much mass.
Chronic everyday calorie reduction can have an effect as well. Fasting to consume lower calories seems to mostly negate this.
True, a calorie deficit diet if not accompanied by extended periods of fasting, will ultimately slow your metabolism down. Dr Jason Fung stresses a lot on this, and hence you need to fast to regain insulin sensitivity, so the body is able to tap into its fat stores which makes you lose weight. If you keep eating frequently, your insulin stays high, and eventually a calorie deficit diet will cause your metabolism to slow down.
Regularly eating fewer calories than your body needs can cause your metabolism to slow down.
Several studies show that low-calorie diets can decrease the number of calories the body burns by as much as 23%.
What’s more, this lower metabolism can persist long after the calorie-restricted diet is stopped.
In fact, researchers believe that this lower metabolism may partly explain why more than 80% of people regain weight once they go off their calorie-restricted diets.
Article with references here: https://www.healthline.com/nutrition/calorie-restriction-risks#TOC_TITLE_HDR_3
Your body can go into starvation mode and slow down a bit. But there’s a limit to it, your body requires energy to function. 1000 calories a day, you will lose weight no matter what. Just don’t expect to lose at the same rate compared to when you start.
Sweet Jesus, do NOT get medical advice from tiktok.
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On this issue, it’s not a simple answer.
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The roughest way to explain things requires some understanding of how the body works.
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The body is capable of increasing or reducing it’s caloric expenditure. This is crucial to know. It’s ignored by CICO, which is why CICO is a complete waste of time. In truth, it’s not just a complete waste of time but actually misleading and dangerous for fat people trying to lose weight. But like a lot of things, such as your tiktok examples, CICO can appeal to the low-information just heard a generalization that sounds like “common sense” and so it can fool people into believing.
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Since the body can adjust it’s own caloric burning, we need to then know HOW does it do that? Hormones is how. And which hormone is top dog in the body? Insulin. When Insulin is spiking, such as after meals with carbs in them, it’s presence causes many other hormones to either be ignored or to spike as well. Insulin is a storage hormone. It wants to remove glucose from the bloodstream. It gets converted to glycogen and it will shove it into muscle cells until full, then shove it into the liver where it will eventually be converted to fat if it is not required to be sent back out to replace glycogen in the muscles.
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Guess what can’t happen while insulin is high? Fat burning. The insulin is trying to CLEAR excess energy (glucose–>glycogen), so it does not want any more energy piling into the problem. It would be a waste of time for the body to break down fats into usable energy (fatty acids) when there is already an excess of glycogen hanging about.
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If a person is on a restricted calorie diet, but that diet has carbs in it, they can totally have a situation where their metabolism plummets. Because the body is spiking insulin, can’t use it’s own fat, and only sees a severely low amount of available energy so it drops the thermostat. In other words, the body thinks it’s starving even though it’s sitting on literally hundreds of thousands of calories in a fat person.
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But you might wonder: “Why would insulin be such a problem? Normal people don’t have this isssue, why just fatties?” Well, you could keep on heading down the rabbit hole… but suffice to say fat people are fat because they have an insulin resistance problem. Insulin resistance eventually becomes full blown Type 2 Diabetes. But before it is T2D, it’s insulin resistance building up over decades. This is why you can be totally “fit” looking in your 20s, but then as you hit your 40s you start to have that stubborn weight that just won’t go away. You are quietly on your way to Type 2 Diabetes, but your doctor isn’t ever testing you for insulin resistance. So nobody cares until your A1C hits 7.0+. Go watch some Ivor Cummins videos on insulin resistance. Certainly eye opening stuff.
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Am I sounding like I’m saying carbs are the bad guy? Good. They are.
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Suggested reading if you care to explore and get loads more understanding and details: Jason Fung’s book on fasting, Gary Taubes books “Good Calorie, Bad Calorie” and “The Case Against Sugar”, and check out Robert Lustig’s youtube video from 13 years ago “Sugar: the Bitter Truth.”
While I wouldn’t take any med advice from TikTok, it Sort of seems based on the ideology of calorie cycling-taking a break from a caloric deficit at some regular interval, say after losing 10% of your body weight, or after a fast, and eating at maintenance for a few days. The idea is that occasional days of normal caloric intake helps to keep the body from thinking it’s starving. There is anecdotal (and possibly scientific, though I can’t cite it) evidence that the body may reduce how many calories it’s spending each day (below expected BMR) if someone is in a prolonged deficit, however I’ve never heard of it going as low as 500 kcal per day. It’s generally remedied with calorie cycling. When it comes to fasting, I’d ask, how many calories are you feeding your body in between fasts?
Personally I would eat low carb to maximize my fasting results… but assuming you did 1 meal a day 1000 calories is just fine (depending on your size). Here are some example 1000ish calorie meals: https://exercisewithstyle.com/1000-calorie-meals/
A lot of those look pretty good, though some have too many carbs for MY liking.
Don’t listen to TikTok.
If you actually want to UNDERSTAND fasting and the complete answer to your question (and more) watch this Intermittent Fasting - Busting the Myths Lecture by Dr. Jason Fung: https://www.youtube.com/watch?v=S8AsjlM-nwI