Safe dieting

December 19, 2005 2:58 AM

How low in calories can a diet get and still be considered healthy?

Assume that I'm talking about someone going on a 3 day, one week or two week "diet plan" - how low in daily calories can that person go and be considered "safe".

[ assuming that all non-calorific nutritional requirements are met. ]

posted by twine42 to Health & Fitness (28 answers total)

The danger in drastically cutting caloric intake is your body will go into starvation mode and you will lose muscle mass rather than fat.
posted by SteveInMaine at 3:48 AM on December 19, 2005

Ugh... crash diets never work. If this person goes on a 3 day diet, and loses those 3 pounds of 5 pounds or whatever they were hoping to lose, chances are pretty dang good that they will gain that back, and more, when they go back to normal.

Realistically, I think it depends on the person. Some people need more calories per day depending on their activity level, etc. If you are laying in bed all day long for 2 weeks, you need way fewer calories taken in than if you were, say, cycling 5km every day.
posted by antifuse at 4:01 AM on December 19, 2005

For a week, you can fast and it's not unsafe.
posted by Wolfdog at 5:20 AM on December 19, 2005

The National Institute for Diabetes and Digestive and Kidney Diseases has this page on very low calorie diets which is short on information but does include a number: 800-1000 calories (though they can go as low as 500). Keep in mind that these are highly structured diets that are built to be as nutritious as possible within their low calorie guidelines. The sites also advise that going lower than this calorie-wise tends not to produce results that are any better, since people are more likely to actually stick with the 800-1000 range of calories-per-day. Another publication discusses one risk associated with this sort of dieting which is gallstones, stating "Studies have shown that 10 to 25 percent of people on a VLCD developed gallstones." Other than this, I know nothing about the efficacy or safety of more extreme calorie restrictions due to fasting.
posted by jessamyn at 5:46 AM on December 19, 2005

Bearing in mind that the plural of anecdote is not data: I have done several (water-only) fasts, the longest of which was three weeks, with no apparent ill effects at the time. The last one was about ten years ago. I wasn't trying to lose weight at the time - I just wanted to see what happened.

Mind you, I'm enormously fat now :)

voice of bitter experience: never break a fast with KFC.
posted by flabdablet at 5:55 AM on December 19, 2005

There's actually a movement called "Calorie Restriction" that argues long life in the wild only happens when animals spend their lives just above starvation. These aren't people that are into lifelong anorexia, but they describe a lifestyle that gets enough nutrients with the least number of calories.

It's not really about dieting or quick fixes, it's more of a lifetime commitment kind of thing though.
posted by mathowie at 6:02 AM on December 19, 2005

A zero-calorie diet - for a limited time - is perfectly safe.

The human body is quite bright about calories. Assuming you have plenty of fat, your body does not start consuming muscle or any other such nonsense. It consumes fat. That's what fat is - energy storage. Only when you run out of fat does muscle get targeted. For the average American dieter, running out of body fat is not an issue, at all.

Short-term fasts are perfectly healthy and you will lose weight. As everyone will be happy to point out, however, it's long-term commitment that will keep weight off.
posted by jellicle at 6:31 AM on December 19, 2005

I don't really have anything to back this up, but my sports nutritionist and also my fiancee's nutrition class both say that you should not consume fewer than 1200 calories a day if you plan on remaining physically active.
posted by Your postings will be signed with this name at 6:33 AM on December 19, 2005

Um, jellicle is a nut job.

There is a minimum protein requirement, and a minimum fat requirement. Fat and protein aren't the same. If you fall below either of these, your body will take what it needs from what you have on board, i.e. aminos from muscles and fat from, well, fat.

After about 72 hours, if not less, the body will catch on that you are starving yourself and your metabolism will dramatically slow, making your calorie depravation trick more or less useless.

Assuming you aren't an athlete and you don't exercise, you can't really go much below 1200... but this is a made up number because it's about body mass... you can roughly estimate your calorie needs by adding a zero to your weight.

If you were eating 1200 calories... then it should be made up of omega fat and complete proteins... carbs are useful but not essential...

This is probably the worst thing to do to your body other than drink and smoke. Go see a doctor or dietician and get on a real diet...
posted by ewkpates at 6:53 AM on December 19, 2005

I wouldn't go so far as to call jellicle a "nutjob" but he is certainly wrong. The idea that you never lose muscle mass until you're at 0% body fat turns out not to be the case.
posted by Justinian at 7:02 AM on December 19, 2005

Response by poster: I need more good answers - I'll look like a complete brown-nose if two of the (currently) three best answers are Matt and Jess! :)

For the record (not that it matters) this isn't to do with my weight loss since I'm happily on the Slimming World plan, mixed with large doses of staring at my gym membership card. The question comes from a disagreement I had with someone about the healthiness of a specific diet that averaged 900 calories a day when the person in question is probably in the 25-30 BMI (*spit*) range and does above average exercise for your traditional office drone type person.

Any diet that includes eating a slice of toast and half a bananananana for lunch was going to fail my taste test, but it opened up a larger question to me - just how little is enough...
posted by twine42 at 7:07 AM on December 19, 2005

Sounds like a first step toward anorexia. Moderate diet and exercise will probably serve you better.
posted by caddis at 7:33 AM on December 19, 2005

What ewkpates said.

1200 calories is about the lowest any normal person (read: non-athlete) should go. Below that is unsafe and will not help in weight-loss because, as noted above, your metabolism decreases and you aren't going to burn fat off.

Also, do not just drop from a 2000+ calorie diet to 1200. It's smart to cut calories by 300 - 500 every other day, and no more. (Every week would be even easier to make the transition)

Because remember, dieting shouldn't be for the short term, it should be for the long term. Form eating habits you can live with for the rest of your life.
posted by dead_ at 7:42 AM on December 19, 2005

Assuming you have plenty of fat, your body does not start consuming muscle or any other such nonsense.

This is wrong.

It consumes fat.

This is also wrong in that fat is not the only thing it consumes.

Only when you run out of fat does muscle get targeted.

This is - you guessed it - wrong.

Every scrap of evidence shows that calorie-restricted diets (i.e., you burn more than you consume) result in some muscle loss even if you engage in regular weight training. This is why all bodybuilders - who would know about this sort of thing - use bulking and cutting cycles.

Will fasting help you lose weight? Sure. You'll lose water, some fat, and some muscle. Eventually you will have slightly less body fat and weak, atrophied muscles. Congratulations.
posted by Optimus Chyme at 7:48 AM on December 19, 2005

Short-term fasts aren't a problem, I do 24hrs without any food or water quite often. If you're going to go longer on a calorie restrictive diet, make sure you drink enough fluids. No food won't kill you right away, but dehydration will.
posted by blue_beetle at 8:06 AM on December 19, 2005

The reason you burn muscle before fat is precisely because, as jellicle said, fat is energy storage.

You: I am not eating much.
Body: Hmm? This is worrisome. This means I need to focus on storing fat, in case this continues for long. Let me start breaking down muscle.
You: But I want to lose fat, not muscle!
Body: But fat is a very efficient energy storage vehicle. I can store 9 calories in 1 gram of fat, but only 4 in one gram of muscle. If I start breaking down fat now, I won't have any left for the long term. And I will need those carbon chains in order to preserve your basic bodily functions later on (brain, heart, etc).
You: Why can't you do it the other way round?
Body: If you had a trust fund, you would try to live as long as possible off the interest before you dipped into the capital, right? Fat is my capital.
You: Perhaps I should figure out my basal metabolic rate and take it from there.
Body: That is a better idea. Thanks.
posted by chelseagirl at 9:11 AM on December 19, 2005 [1 favorite]

Haha, beautiful, chelseagirl, you should write for a children's science show.
posted by ThePinkSuperhero at 10:18 AM on December 19, 2005 [1 favorite]

You can get by on 800-1000 calories a day. It's safe, even for long periods of time (3-6 mos), and you will not end up with "weak, atrophied" muscles. This is something jocks do quite often to hit a target weight. Be careful: you will lose a lot of weight under such a diet. We're talking 3-5 pounds a week.

Your body responds to severe calorie restriction by going into ketosis. Read up on this process for the details. Ask your doctor. A lot of the answers in this thread are simply wrong.
posted by nixerman at 10:27 AM on December 19, 2005

Just to clarify, such a severe diet is not "safe" and any doctor will strongly advise against such a diet. Still, people do execute such diets all the time because they are terribly effective.
posted by nixerman at 10:32 AM on December 19, 2005

you will not end up with "weak, atrophied" muscles. This is something jocks do quite often to hit a target weight

Jocks also engage in strenuous physical activity including weight training, which is one way you can maintain muscle mass while on a calorie restricted diet.
posted by Optimus Chyme at 10:37 AM on December 19, 2005

Bodybuilders are probably the most extreme example of people who regularly diet down to hit a weight and bodyfat goal. Even with aggressive protein consumption and exercise to maintain muscle mass, they give up a lot of muscle in order to get the ultralean look they are after.

Wrestlers and other may not go to the same extreme, but its still not necessarily healthy. It's a tactic used to gain short term advantage and even when its done very deliberately and carefully, it doesn't necessarily work out. People may hit their weight but don't hit the level of performance they need to win because they got too depleted while dieting down.
posted by Good Brain at 10:49 AM on December 19, 2005

I think most healthy people could go for three days without eating. I don't mean it's totally safe, just that most people could get out of it OK. Wouldn't want to try it if you were a diabetic. Also depends on what you mean by "healthy".

This summer I did a good job of restricting myself to about a 1k/day diet, combined with lots of exercise. I lost weight very quickly, but my caloric intake steadily rose along with the amount of exercise I did, and I'm up to like 1,800 a day now. Oh well.

Your brain (specifically the hypothalamus) tries to keep your bodies mass in balance by balancing chemicals put out by fat cells (insulin and leptin, IIRC). If you have normal brain chemistry and you're too fat you won't have much of an appetite, which is probably why it was so easy for me to stick with the diet at first.
posted by delmoi at 11:43 AM on December 19, 2005

Mod note: fixed delmoi's link
posted by jessamyn (staff) at 11:59 AM on December 19, 2005

There's a lot of misinformation above. People mislead themselves because they are taking information MEANT FOR BODYBUILDERS, and trying to apply to the average fat slob.

If you're a bodybuilder, you get very little definition unless you have almost zero body fat. You can be very strong indeed, but with a layer of fat over your muscle, you don't look it. So bodybuilders are always trying to stay in a state of NO body fat, and maximum muscle. That turns out to be difficult. So they oscillate back and forth, starving themselves of both food and water before competitions to get maximum cut-ness. Then, since this will quickly start breaking down muscle (NO body fat, remember), they have to pump up the protein and carbs to stop that from happening.

This situation, widely explained on the internet, bears little resemblance to an average American carrying an extra 100 pounds of fat. Your body will cheerfully burn fat to supply all of your caloric needs. You do not "burn muscle before fat" - Jesus, what universe do you live in, where it's not possible to lose weight since your skeletal muscle gets used before your fat? Can't you just look around you and prove to yourself that that isn't true? Whatever universe that is, it isn't this one.

Beyond the energy in fat, you need essential amino acids (the "essential" part is there for a reason) and a variety of vitamins and minerals. You said specifically, assume all non-caloric needs are met. So I did. A fast of three days, one week or even two weeks will not harm you, will not eat away your heart muscle or anything else - assuming that you are a 100-extra-pound carrying American and not a zero-body-fat bodybuilder. What it will do: make you feel weak and hungry and irritable.

Humans are evolved to survive long winters with very little food.
posted by jellicle at 12:28 PM on December 19, 2005

I guess the question is how low can you go and still be healthy, with a clarification stated it is for weight loss.

As jellicle said, you can go for quite a while without food, however as noted by a lot of others, just cutting calories drastically will NOT lead to safe, reliable weight loss because--and this is key--your metabolism will lower and put your body into storage mode.

As nixerman said, ketosis is a good thing to read up on, because many diet plans use induced ketosis safely to jumpstart a low-carb/high protein diet.
posted by dead_ at 1:01 PM on December 19, 2005

Jesus, what universe do you live in, where it's not possible to lose weight since your skeletal muscle gets used before your fat?

No one said this. The fact of the matter is that if you do not engage in exercise and just slash your caloric intake, you will lose muscle mass along with fat. You said repeatedly that you will lose all of your fat before any of your muscle. This is wrong in both theory and observation. The keys to minimizing the ratio of muscle loss to fat loss are a) eating above stravation-adaptation levels and b) using your muscles.
posted by Optimus Chyme at 1:15 PM on December 19, 2005

To butt in, the resulting muscle loss found during ketosis is caused by some needs of the body not being fulfilled by ketones. While ketosis is an effective weight loss state, it is not 100% efficient for all bodily function, and glucose is still required (prominently by the brian).

This muscle loss is very small, something like an ounce a day in a normal human being. The fat loss is close to .5 to 1 kg a day.

Ketosis takes a few days to cut in- on a water fast, it's taken me up to 72 hours before ketones appeared in my urine stream.

Ketosis will start when calorie needs are insufficient with glucose alone. (IE low carb diet). I personally believe that this is significantly more dangerous than fasting because you're asking the liver to do twice the work- create ketones and cleanse incoming food / drink / toxins. Fastining elimnates one of these jobs- Atkins-like diets do not.

On a personal note, I've lost over 30lbs simply by fasting. I've done three 1-week fasts, each with at least 10lbs of loss. I've made it a yearly ritual, and I feel great after every fast.
posted by id at 5:05 PM on December 19, 2005 [1 favorite]

Amino acids are essential to biological function, and cannot be derived from fat. If you don't eat protein, sooner or later you will die. I suggest that you consume no less that 20 grams of complete protein a day...

Subjective self assessment after fasting only proves that people continually delude themselves that self assessment is useful.
posted by ewkpates at 11:56 AM on December 20, 2005