Is this formula an underestimate of how many calories I should be consuming daily?

August 6, 2007 10:14 PM

Is this a reasonable way to determine ideal calorie intake?

"Multiply your weight by 11. The figure you get is the approximate number of calories you need to eat to maintain your current weight. If you reduce that amount by just a couple of hundred calories a day, it will create a deficit between the calories you take in and the calories you expend." (from here)

This formula implies that to maintain my weight, I should be taking in 1375/calories a day, and upwards of that I'm looking at gaining weight. Similarly, they suggest that for me to lose weight, I should cut back to, say, 1200 calories.

These seem like unreasonably low numbers for a healthy twenty-something who exercises regularly. Is this formula completely inaccurate, or do I eat a lot more calories than are recommended?

posted by bijou to health & fitness (17 comments total)

What you're looking for is Base Metabolic Rate. You can try googling, but there's no "magic formula" I find the weight multiple ones especially dubious.

I usually try several online calculators and just average them out. Here's a pretty decent one at Exrx.net:

BMR Calculator
posted by unexpected at 10:25 PM on August 6, 2007 [2 favorites]

Everyone has a different metabolic rate, plus exercise requires more calories. You aren't eating a lot more calories than you should unless you are gaining fat (and already have a reasonable body fat percentage). If you aren't, then you are have the right caloric intake for you.
posted by ssg at 10:41 PM on August 6, 2007

Weigh yourself everyday as soon as you wake up and calculate a weighted average every now and then to determine if you're gaining or losing too much weight. Thirty seconds every morning will tell you all you need to know. No need at all to muck around with formulas or guestimations or anything like that.
posted by nixerman at 10:44 PM on August 6, 2007

You know what, out of laziness I've been using sparkpeople to figure this stuff out. Seems to really help me keep track of it.
posted by miss lynnster at 10:45 PM on August 6, 2007 [1 favorite]

Here are another pair of tables to estimate caloric needs, from the Hacker's Diet. But have a look at the rest of the site/book: It is centered around the 'weighted average' approach that nixerman mentioned, and it provides Excel sheets to make the calculating a cinch.
posted by eritain at 10:56 PM on August 6, 2007

Is this formula completely inaccurate

Yes. I've had my BMR calculated by a machine (had to breathe into a tube for 10 minutes, lying perfectly still, in to order to gauge the base caloric needs), which came up with 2,000 calories a day. Based on formula above I need 2,900 calories, and if you subtract 200, that leaves 2,700. There's NO WAY I could eat that eat many calories a day and lose weight.

The BMR calculator was pretty close though.
posted by Brandon Blatcher at 11:08 PM on August 6, 2007

Yep, this is called your Basal Metabolic Rate, or your Resting Metabolic Rate.. Check here for more details and the Harris-Benedict formula (in metric units).

BMR represents how many calories you burn if you sit and do nothing all day but live. Most of the time BMR is adjusted by a percentage that represents your physical activity level, depending on what you do during your usual daily activities.

If you want to know more, the Hackers Diet (above) is a great scientists/engineers guide to weight loss, with all the numbers etc explaining why it all happens...

One more little figure tho... To burn 1kg of fat, you need to create a deficit of around 7700 calories, so a couple of hundred calories a day would only give you about 0.25kg (or 0.5pounds) of fat loss a week, all others things being equal...
posted by ranglin at 11:12 PM on August 6, 2007

FWIW, according to those calculators, my weight * 11 is a pretty good estimate of calories burned at BMR.

Also, to convert what ranglin said to imperial units, 3500 calories = 1 pound. For weight loss purposes, that means a 500 calorie deficit per day = 1 pound a week.
posted by chrisamiller at 12:33 AM on August 7, 2007

Eat 3000 calories a day and see how much weight you gain over a month. For every X pound you gain, multiply by 3500 calories (the number of excess calories) then divide by 30. Subtract that number from 3,000 and thats how many calories you burn each day.

You could also try eating 1,000 calories and seeing how much weight you lose.
posted by delmoi at 12:45 AM on August 7, 2007

My doc suggested keeping a food journal for a few days to get an idea of how many calories I was taking in per day. Obviously this involves recording everything eaten and the amount. Then try to reduce that calorie figure by 500 per day. That adds up to a deficit of 3500 calories per week, equal to a pound of weight loss.
posted by DarkForest at 3:51 AM on August 7, 2007

These seem like unreasonably low numbers for a healthy twenty-something who exercises regularly.

Well, that's why its so hard for people who weigh 125 pounds to lose weight, and so hard for people to maintain 125 pounds in the first place. The numbers are a lot more reasonable when you weigh 200 pounds.
posted by smackfu at 5:50 AM on August 7, 2007

The Daily Plate will do a target calorie level calculation based on height, weight and how much you plan to lose per week. I'm pretty sure it uses a BMR calculator but I'm not 100% sure. It also has a food journal and weight tracker to keep you organized. I've been using it for a couple of months now and it's great.
posted by saraswati at 5:53 AM on August 7, 2007

I think ideal calorie intake has more to do with your eating and working habits than just how much you weigh and how tall you are.

First off, the idea of a straight linear relationship between weight and calorie intake is kind of . . . strange. It seems silly to entirely ignore different activity levels, which do tend to expend energy at different rates.

This paper (pdf) claims that calorie intake in real life is also not proportional to weight.
posted by that girl at 6:48 AM on August 7, 2007

It seems like there would be very different results if your weight was a lot of muscle as opposed to mostly fat, not to mention as that girl points out above, activity levels.
posted by Melsky at 8:11 AM on August 7, 2007

Check out The Hacker's Diet. It's the only explaination of this sort of thing that ever really made sense to me.

From this section: exercise is good for you, but probably isn't going to be the thing that makes you lose any significant weight. If a peanut butter sandwich is 300 calories and bicycling burns 300 calories an hour, you're going to have to ride pretty far and long if you aren't cutting back what you eat.

Here is the calorie chart. It's based on height and frame size, rather than hight and weight.
posted by the jam at 8:15 AM on August 7, 2007

I've used a spreadsheet based on 12KCal per pound of my weight daily maintenance needs, and calories consumed and burned daily tallies, with near perfect accuracy matching the results on the scale. I'm F/26.
posted by Ambrosia Voyeur at 10:40 AM on August 7, 2007

I'm going to go on the record saying I don't think that exrx calculator is very good (for women, at least). First of all, it requires you to put in your daily activity levels at frankly questionable distinctions. Second of all, it apparently gives women a default bodyfat of somewhere around 19%. You are probably not 19% body fat. The BMR measurement seems reasonable, but I would use the Hussman BMR calculator instead, just because it's less likely to mislead you on the "activity" part.
Really, though, the only way to actually know how many calories you need to consume is to very carefully chart what you eat for a few months along with your weight. You will start to get a feel for your caloric needs and you will be much better able to adjust it in the future as your lifestyle changes.
posted by ch1x0r at 5:06 PM on August 7, 2007