Effects of large calorie deficit

Hi everyone,

Just curious what people think the effect of having a too large calorie deficit ?

if you were to be under consuming by too much say 1000 calories what would the effect be on your bod? would it be dangerous ?

Depends on what your TDEE is. Say it’s 2500, then eating 1500 calories a day will be fine until you reach your desired weight as you’ll start off losing 2lbs/week.

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what’s TDEE ?


You’ll lose weight for as long as your calorie intake is less than your calorie expenditure. Carry on losing weight and you’ll eventually hit malnutrition, which isn’t a fun place to be. I know.

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Hi - TDEE, Total Daily Energy Expenditure. You can get a device to track it, such as a Polar watch. Without a device, you can only estimate your TDEE. Remember we all burn calories all day, even without exercise. I wake up in the morning having burned 600 calories since midnight until around 9am. It is all about losing BODY FAT, NOT WEIGHT. Over a day, if I do no exercise, I burn 2200 cals. I always aim for a 15% calorie reduction on my TDEE. So I would eat 1870 approx. Eat according to your energy needs, I.e. TDEE. Hope this helps

thanks for the clarification

I did exactly the 1500 for 2500 Huel only route for 10 months. The only side effects I had were a few mineral issues, in particular iron. I added an Iron heavy vitamin pill and all was well.

I sometimes have lighted headedness and i am keeping to a low calorie deficit, i’m trying to up my intake but i dont feel hungry enough too eat more

Hi, eating less can be very healthy. Check out the 8 week 800 calorie blood sugar diet and the Michael Mosley video on YouTube: Eat, fast and live longer

I’m following Lyle McDonal’s Rapid Fat Loss at the moment, and have lost 5lbs in a week. I followed it a few months ago leading up to my beach holiday so know it works.

It’s purely a short-term diet though (2-6 weeks), based on a Protein Sparing Modified Fast. You eat a high amount of protein and less than 20g of fat and carbs each day. I’m only having around 1100 calories a day and I feel okay. You have a break once a week where you can have good carbs again over a short window. The diet differs though depending on your starting bodyfat (I’m in the middle group, out of the 3 groups).

I also don’t eat breakfast and start my first meal of the day around noon (although this is IF and not part of the PSMF). I’ve found a black coffee around 9 or 10am helps keep hunger at bay until then, plus 1-2 cups a day is shown to reduce the risk of developing Parkinson’s etc.

I’d recommend it if anyone needs to lose weight quickly for an upcoming event!

Hi ElectroDan. I have a question for you that relates to TDEE. I use a POLAR A300 sports watch, which shows me my calorie expenditure at any given time of the day. When i wake in the morning, it says that my calorie burn is something like 600 cals, I exercise and get the calorie expenditure upto 1000 cals. Then I consume a breakfast that is 30% lower than my expenditure, i.e. 700 cals, 300 cal deficit. Throughout the day i tend to hold a deficit of between 20-30% depending on how i feel. Am i correct in my understanding of how a calorie deficit works?

No expert, but if you consume less calories than you burn then the short fall is taken up by burning fat reserves. Once those run out then you’re in trouble as your body starts going after muscle and other materials in your body. So long term it’s a matter of finding a diet that matches your needs approximately. Very hard to know exactly how much you’re burning, very hard to know exactly what you’re eating (unless you’re 100% Huel)

I don’t know the exact mechanics, but I’m pretty sure our body doesn’t wait til it burns up your fat reserves before targeting muscle…that’s why people always recommend doing strength training, eating more protein and not having too huge a caloric deficit when trying to lose fat.
Which I suppose would make sense since fat also protects internal organs and are deemed by the body as kinda useful regardless of our societal beauty standards.