Is a drastic calorie reduction harmful?
For a long time I was consuming 4000 calories a day. This was between soda and various "junk foods". I was surprised to find my protein, carb and fat levels were pretty close to what they should have been however.
As per of eating healthier and trying to reduce some fat, I have completely changed my diet, eating a lot more veggies, no more soda etc.
According to various online calculators based on my height (6ft) and weight (180lbs) my body burns around 2000 calories just to function.
According to other calculators my weight on my previous diet should have been around 210lbs. However, this is obviously not the case, which makes me think my body consumed far more than 2000 calories just to function.
Given my rather sedentary lifestyle and the fact I didn't really gain weight (the weight I am trying to lose is from a few years ago where I spent a year eating a lot of deep fried foods), I wonder if my body didn't burn a lot more than 2000 calories just to function.
With my new diet I aim to eat 1500 calories a day, with the goal of burning 500 calories a day. I've managed to stay pretty close to this, at least never going above 2000/day.
Can such a drastic drop in daily calorie intake affect the speed of my metabolism (which I don't want to change) or have some other negative consequence?
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Fact is, eating fewer calories causes immediate weight loss! I was feeling poorly yesterday and so consumed only 1148 calories, way below my usual 2200 calories. This morning I've dropped a kilogram on the scales. I've noticed this immediate effect before, when for some reason or other I've eaten less and immediately lost weight. The correlation is as plain as night following day.
That's why I believe fat people (including me!) are fat because they eat more than their body and lifestyle need, in the vast majority of cases. One of the things I immediately notice when watching old movies (from the forties and fifties, say) is how slim everybody is! You've got to scan every scene to see a fat person. They were as rare as hens' teeth back then. And yet most people were healthy without all the plethora of fast-food outlets that we have today.
Short answer: Yes, a drastic calorie reduction can be very harmful, but in your case I don't think you're cutting as many calories as you might think you are.
Long answer: Those calculators are referring to your Resting Metabolic Rate (RMR). Your real metabolic rate can be very different from that. Consuming under your Resting Metabolic Rate is dangerous because you will trigger starvation measures from your body. I doubt you were actually consuming 4000 calories a day if your macronutrients (protein, carb, fat) were where they 'should be'. We ONLY get real calories from these three macronutrients. Anything else are trace nutrients that we might need for various processes but don't provide any real calories. This is reinforced by the information that consuming deep-fried foods DID cause you to gain weight. Deep fried foods are poison, but they do have a lot of real macronutrients in them. Even when a substance (like soda) doesn't have a lot of real calories, though, they can still poison your metabolism.
This poisoning can turn into a failure to absorb major nutrients, which will mean a failure to gain weight even when eating more than we 'should'. This is the crux of being a 'hard gainer'. This will cause a lot of excess junk in your blood stream and possibly bad elimination (urination and defecation) habits, and it will eventually lead to chronic disease (hypertension, cholesterol problems, diabetes).
I mainly say this to let you know that you're not a freak, this stuff is absolutely known, explained, and normal, it's just that you didn't go stereotypically obese so the stereotypical online calculator isn't going to take your situation into account.
Keep doing what you're doing with getting rid of the non-foods, and eat more clean protein and fats from chicken, greek yogurt, and whole milk. These will be very satisfying, especially if you are on a resistance regimen, and you will not be driven to eat as many carbs, which generally don't satisfy as well, gram per gram. Fewer eaten grams means fewer calories taken in, which means more weight that comes off!
Also, as always: If you can afford to find a personal trainer or nutritionist (or both) to meet even just once a month on your progress, that is one of the best investments you can make. They will help you understand what's going on so you can make this change permanent.
In response to the comment below, here are a few links:
Trans fat formation in fried foods
Precedent for using the word "poison"
Yes it might be harmful depending on where you are getting your remaining calories from and how your body reacts to your new diet. Yes cutting calories will make you lose 'weight', but if you are not careful and keep track of your progress your weight loss may end up being mostly lean body mass being consumed. Keep measuring your body composition during your efforts and try not to cut your calories below the point where your lean body mass decrease is an order of magnitude less than your total body mass decrease. Idealy your lean body mass should stay stable or increase slightly while your body fat percentage goes down gradually. Don't buy into the quick weight loss idea. Most of these results are water and muscle mass rather than fat mass you you may end up having lost 20kg of body mass with 10 kg being water (that you will hopefully quickly gain again) and 6 kg being muscle and organ mass. If you were not that fat to begin with. Just do the math. Lets say you go 100 kg with 25% body fat, that is 25 kg of fat. You lose 20 kg (including 4kg of fat). End result: 80kg, 21g fat, that means you "GAINED" 1,25% of body fat even though you dropped 20kg. You end up fatter than you started and dehydrated at that. Most people who stuff like that happens to don't even realize it until they pass out during their workout. Its easy to avoid if you keep tracks of your stats. Track your FFBM, that your ICW and ECW levels and track your body fat percentage. Don't allow yourself a drop in FFBM and accept that it takes time to lose weight.
Can such a drastic drop in daily calorie intake affect the speed of my
metabolism (which I don't want to change) or have some other negative
consequence?
After you calculate your BMR you need to multiply it by an activity multiplier to get your actual calorie burn.
So lets say your BMR is around 2000 and you are somewhat active. You can multiply it by 1.35 (There are some multipliers here).
So 2000 x 1.35 = 2700 calories burned/day
If you want to achieve a 500 calorie deficit you would want to eat around 2200 calories a day. If you eat 1500 calories that's closer to a 1200 calorie deficit. I'd recommend aiming for ~750-800 calories so you'd eat around 2k.
Starvation mode?
It doesn't exist. Your body does take protective measures any time you cut calories, such as slowing down your metabolism, and those measures increase as you increase the deficit. It's not like a switch that happens at a certain amount of calories.
Still, if you ate 500 calories a day you will lose a lot of weight. A lot of it will be muscle and you will feel awful and it's a terrible idea but you won't magically retain fat.
So just aim for a reasonable deficit, eat whole, balanced and satiating meals, increase your activity and you should be able to lose fat without issue.
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