What's the worst that can happen if I eat 500 calories a day?

Why do they say you should eat at least 1000 calories a day even when you’re trying to lose weight? Can’t the body just suck fat off itself if it needs energy? If I just say screw it and eat only, let’s say, 500 cal a day, what’s the worst that could happen?
Thanks gang!!

You could be wiped out by a nearby supernova along with all humanity.

Is that worst-case enough for ya?

You die of starvation. Before that, you’d get really sick.

You would be so weak and sluggish you wouldn’t be able to do much. Your bod would start eating itself. Yep you’d lose weight, but at what cost? Your muscles and health?

The brain cannot really use the triglycerides releases from fat metabolism. Blood products and the brain require glucose, so just relying on fat stores is not enough.

If the food making up your 500 calories are carefully chosen to include all essential vitamins and minerals, you could last quite a while - humans can and have survived periods of famine and near-starvation - but if not, keep an eye out for scurvy and whatnot.

You need a minimum of about 60g protein a day, and you need vitamins. If you want to try to survive on 500 calories a day, you are going to have to take vitamins, and drink protein supplements. I’m looking a a couple here that I had after I had abdominal surgery 6 weeks ago.

One is a thick shake called Glucerna. It is sugar-free, for diabetics. It has 15g protein, the same mix and percentages of vitamins and minerals you might get from a bowl of fortified cereal, and is 180 calories. It tastes pretty good, and will keep you from being hungry for a couple of hours, but four of them is going to take you over your 500 calories.

So you will need Protein2O (protein infused water). It is also sugar-free, and has no vitamins or minerals. It has 15g protein, and 60 calories. It is less tasty, and doesn’t really fill you up (unless you just had abdominal surgery, and aren’t terribly hungry to begin with).

So you are going to need a multivitamin. Make sure it has iron. Plus, you are going to need a separate calcium supplement. If you read the label of your vitamin, you will see it doesn’t have much calcium. That’s because iron and calcium aren’t absorbed well at the same time. So you need a calcium supplement to take at a different time from your multivitamin. Get calcium citrate, not calcium carbonate, because calcium citrate is much better absorbed. Also, make sure it has Vitamin D in it. You need them together. Make sure the multivitamin has 100% C in it. That will help you absorb the iron.

You are going to be tired on this regimen, and probably REALLY hungry, but try to keep your mind off of it, because you need to keep up your activity level. Your natural inclination is going to be to slow down. You can’t do that. You have to keep burning at least 2,000 calories a day. Otherwise, what’s the point? If you are only burning 1,600 calories, you could be eating 400 more calories a day, feel better, and get more done.

And don’t forget to drink some water. Make sure you get 64oz of fluid a day. Your protein supplements alone won’t give you that. You will need some water.

Good luck!

Can the liver convert fat into glucose?

As far as OP, I’m not sure. According to webMD, they are generally safe as long as you are obese (have a lot of fat mass) and are under medical supervision. Older people, children and pregnant women shouldn’t do them though.

I don’t know about quite a while. Unless you have a very high amount of fat mass, you will burn through it pretty fast on a VLCD.

If you have 100 lbs of fat mass that is 350,000 calories of fat. If you are eating 500 a day but burning 3000, that means you should (ideally) be losing 2500 calories a day in fat (assuming it is a high protein VLCD). After 3 months, about 2/3 of your fat mass is gone.

Granted, I was assuming this was indeed the starting condition. It’s not something I recommend for anyone else. Indeed I wouldn’t even recommend it for an obese person, unless under close medical supervision.

How much you need to eat depends on a lot of different factors. If you are a very small person, with a slow metabolism, and you plan to lie in bed 24 hours a day, 500 calories a day may well be more than sufficient to provide you with all of the energy you need. It’s probably too low, but I actually wouldn’t be surprised if it’s closer than most people here are expecting. I probably eat about 1200 calories a day (last I figured) and, working out three times a week, I can’t go over that without gaining weight. (I’m 170 lbs at 6’, for the record - solidly in the recommended BMI.) I could see half of that sufficing someone smaller and less active than myself, if they had a similar metabolism.

But, I’ll note, before I turned 30, I had to eat twice as much just to maintain weight and was never at risk of gaining.

If you’re an athlete, try thru-trekking, live on an outpost in Antarctica, etc., then you may need to eat 4000+ calories per day.

It really varies a lot more widely by your specific lifestyle and metabolism (which can change with age) than most people give credit.

But if the question is: What if I eat a tiny amount of calories?

As I understand it, your body tries to eat muscle first. So, first, you’ll become very weak. Only once that is done will your body really go for the fat.

In order to make the body preserve muscle instead of fat, you have to work out so that your body prioritizes muscle-retention over fat-retention, and without a sufficient diet, you won’t be able to work out sufficiently to lose weight. You actually have to eat quite a lot in order to be able to work out hard enough to burn fat, paradoxically.

On a tiny amount of calories, it will be easier to be deficient in your nutrients. I’d probably suggest taking a half-dose of a multivitamin. And, obviously, make sure to get your water.

If you use a low-carb diet to try and hit the low calorie count, then your body will produce ketone bodies rather than glucose. Glucose would be used to power your brain and so, without it, you’ll be more sluggish and less able to concentrate. One of the ketone bodies is acetone (nail polish remover), and so if you lose weight fast enough, you may experience issues with your kidney and this can lead to death.

On the whole, it’s better that you maintain a well-balanced diet, even if it’s a low-calorie one.

Eventually, if your body does need more than 500 calories per day in order to function, no matter how still you lie, and it has devoured all of the muscle and fat on your body, then you’ll die.

Wow… guess you saved my life, guys! Your advice often improves my life, but this is a new level! What’s next!?

One thing I really don’t understand… If you burn off calories by intense exercise, do you need a minimum of more than 1,000, or is 1,000 still enough? Running 1 mile burns about 100 calories. So if I run 5 miles in one day, 500 calories, does that mean I need to eat an absolute minimum of 1,500 calories? Like if I ran 5 miles and ONLY ate 1,000 calories, would I then be eating the equivalent of 500 calories a day, and hence wither away into starvation like you’re all saying above?

but the brain can use ketones, though not as effectively as glucose.

The human body is a complicated inter-related system of “bits” all doing complicated things. You can’t just figure in/out calories as a basic arithmetical exercise.

IF your goal is weight loss, you need to see a doctor who can guide you as to how to go about it. Ultimately the aim is good health. There is a lot that goes in to losing weight (and keeping it off) and it isn’t all just physical. Get some good advice. Don’t go starving yourself.

If you’re doing intense exercise, you may lose weight by consuming more than the standard 2500 calories. In fact, I strongly suggest you don’t try to limit yourself to less than that amount. You could injure yourself by eating too little and then doing intense exercise and just 1000 calories would definitely be too little. Professional athletes, especially those in endurance sports, often consume 5000 or more calories a day and they still have to watch their diet to make sure it’s enough that they don’t lose too much weight. Personally, I consume 3500-4000 and I lose a bit of weight if I work out every day.

Are you sure about this?

My understanding - from a college Biochemistry course taken 40 years ago - is that energy storage in the body goes like this:

  1. Adenosine Triphoshate in the cells - this is the immediate energy source for whatever your body needs to do. Once this is depleted, it is refreshed by breaking down
  2. Glucose, otherwise known as blood sugar. When your blood sugar is depleted, the body turns to
  3. Glycogen, a polymer of glucose, stored in the liver. This is used to replenish your blood sugar. When your glycogen is depleted, the body then turns to
  4. Fat stored in fat cells, which is converted to glycogen. Only if there are no fat reserves left, does the body start to break down
  5. Muscle mass.

Now, this is from 40 years ago, so it is entirely possible that knowledge has advanced. But, to my simple mind, it seems crazy for the body to start breaking down muscle mass before fat, which after all is stored specifically for energy.

The body will burn fat, but you will need other nutrients to stay healthy. As you may have read, the human body typically needs a minimum of ~10 cals/lb to maintain your body weight if you’re sedentary. Decide what your target weight is and eat enough calories to maintain the lower body weight. This allows for a healthy amount of calories by any medical standard (someone shooting for a 100 lb weight would still be eating 1000 calories a day, allowing room for the various nutrients you need), but someone weighing 200 lbs simply can’t maintain that weight on 1000 calories a day no matter how sedentary - the 1000 calorie deficit means the weight will come off at ~2 lbs. a week, faster if you exercise.

Apparently, it looks like what both of us learned are both right and wrong.

To quote from the Wikipedia:

“In the absence of dietary sugars and carbohydrates, glucose is obtained from the breakdown of stored glycogen. Glycogen is a readily-accessible storage form of glucose, stored in notable quantities in the liver and in small quantities in the muscles.”

*"After 2 or 3 days of fasting, the liver begins to synthesize ketone bodies from precursors obtained from fatty acid breakdown. The brain uses these ketone bodies as fuel, thus cutting its requirement for glucose. After fasting for 3 days, the brain gets 30% of its energy from ketone bodies. After 4 days, this goes up to 75%.[5]

Thus, the production of ketone bodies cuts the brain’s glucose requirement from 80 g per day to about 30 g per day. Of the remaining 30 g requirement, 20 g per day can be produced by the liver from glycerol (itself a product of fat breakdown). This still leaves a deficit of about 10 g of glucose per day that must come from some other source. This other source is the body’s own proteins.

After several days of fasting, all cells in the body begin to break down protein. This releases amino acids into the bloodstream, which can be converted into glucose by the liver. Since much of our muscle mass is protein, this phenomenon is responsible for the wasting away of muscle mass seen in starvation.

However, the body can selectively decide which cells break down protein and which do not. About 2–3 g of protein must be broken down to synthesize 1 g of glucose; about 20–30 g of protein is broken down each day to make 10 g of glucose to keep the brain alive. However, to conserve protein, this number may decrease the longer the fasting.

Starvation ensues when the fat reserves are completely exhausted and protein is the only fuel source available to the body. Thus, after periods of starvation, the loss of body protein affects the function of important organs, and death results, even if there are still fat reserves left unused. (In a leaner person, the fat reserves are depleted earlier, the protein depletion occurs sooner, and therefore death occurs sooner.)"*

It sounds like the idea of an “order” isn’t quite correct, and the body may be more selective than that and really will just sort of take a bit from everywhere depending on the needs of the moment, genetics, and which muscles are still being used regularly.

This is getting into IMHO territory, but I’ll personally suggest these steps:

  1. Find an activity that you enjoy. If you don’t enjoy it, you won’t do it. Some people enjoy repetitive activities like jogging and weight lifting. If you’re not one of those people, then maybe it’s better if you try a sport, climbing, dancing, circus arts, etc.
  2. Eat better. Eat whole foods. A lot of our foods, here in the US, have added sugars and they’ve carefully stripped out all fiber and other ancillary stuff that doesn’t add flavor and/or that your body has a hard time digesting. I know a bunch of Indians who have complained that cooking their home recipes here, they start putting on weight, simply because they’re using American brands of the same stuff. Once you switch from bread to whole oats, while the caloric content might technically be the same, more of it’s being wasted by your body because it’s harder to get at and your body has to move more chuff through your gut.
  3. If you’re only doing something physically active one hour per day, eat a large meal about 3 hours before it. The rest of the day and on days you aren’t working out, scale back. Eat based on what you’re doing, not based on some need to maintain a regular pattern. This might mean that you’re eating 1000 calories on a lazy day and 2000 on a workout day. That’s fine.
  4. Make sure that you know how to tell when you’re losing weight versus putting on muscle. If your body likes to put fat around your belly, then figure out whether it’s shrinking or inflating (wait a few weeks between looks). That will probably work better than just weighing yourself - until you get into a routine where you’re just maintaining.
  5. If you’re down on energy when you’re trying to work out, suffer tunnel vision, etc. then your workout meal isn’t large enough and you need to eat more.
  6. If you’re putting on fat, scale back the amount you eat for your non-workout time. If you’re still putting on fat then maybe try lowering the size of your workout meal.

What’s y’alls take on whether protein can make you fat or turn into fat? I found very contradictory things on the web. Google “do protein calories turn into fat calories” and the first handful of results have different opinions…