Calories are those little units of energy we consume whenever we eat, well, anything.
And they are arguably the most talked-about part of any weight-loss journey.
The general rule is that if you eat more calories than you use, you'll gain weight. And if
you take in fewer calories than you use, you'll lose weight. And if those numbers are more
or less even, your weight will stay about the same. It seems simple, but the number
of calories you need to lose weight, maintain weight, or gain weight from lean muscle depends
on your activity levels, body size, hormones, sleep, and more, explains registered dietitian
Wesley Delbridge, R.D., a spokesman for the Academy of Nutrition & Dietetics. So figuring
out how many calories you need per day can be crazy-complicated.
And, it's also important to remember that, when it comes to cutting calories for weight
loss, lower is not always better. According to the American College of Sports Medicine,
your calories should never dip below 1,200. That's because most women, unless they are
very small, will burn more calories than that doing literally nothing, says registered dietitian
nutritionist Jonathan Valdez, R D N, C D N, owner of Genki Nutrition and a spokesperson
for the New York State Academy of Nutrition and Dietetics. "Less than that and you could
shock your body into starvation mode, which will slow your metabolism, decrease your muscle
mass, and likely keep you from getting the nutrients you need to sustain daily activity,"
Delbridge explains.
So, if you're asking yourself, "How many calories do I need a day?" read on as experts explain
what you need to know to get your calorie intake just right.
How To Determine Your Base Calorie Needs. In order to figure out how many calories you
need to lose, or even gain weight, you first need to determine how many you need to maintain.
As a first step, Delbridge recommends checking out the latest Dietary Guidelines for Americans,
as they can give you a good estimate for what you need to stay the same weight. The guidelines
say young women should aim for 1,800 to 2,400 daily calories, depending on age and activity
level, but that range isn't necessarily tailored to your specific needs—so it's
not as precise as it could be.
For a more exact number, start by finding your basal metabolic rate (BMR), which is
the minimum number of calories your body burns at rest, suggests physical therapist Grayson
Wickham, D.P.T., C.S.C.S., founder of Movement Vault. Your BMR accounts for 60 to 75 percent
of your total daily calorie burn, according to a review in Medicine and Science in Sports
and Exercise.
"To most accurately calculate your BMR, you'd need to go to a lab to have your carbon
dioxide and oxygen analyzed after having fasted for 12 hours and slept for eight. But, that
can be a little pricey and a rough estimation of your BMR can be found using a few different
equations,"says Wickham.
One study published by the Journal of the Academy of Nutrition and Dietetics found the
Mifflin-St. Jeor equation to be highly accurate, so it is now considered the gold standard
when it comes to calculating BMR. For comparison's sake, however, some experts prefer the Harris
Benedict equation for determining BMR.
For women, the Mifflin-St. Jeor equation equation is: BMR = (10 x weight in kg) + (6.25 x height
in cm) – (5 x age in years) – 161.
So, for a 25-year-old woman who is 5'4" and weighs 150 pounds, the BMR equation would
look like this: BMR= (10 x 68) + (6.25 x163) - (5 x 25) -161 = 1,413 calories
For women, the Harris Benedict equation is: BMR = 655.1 + (9.563 x weight in kg ) + (1.850
x height in cm) - ( 4.676 x age in years).
So, for the same woman, the BMR equation would look like this:
BMR= 655.1 + (9.563 x 68) + (1.850 x 163) - ( 4.676 x 25) = 1,490.
As you can see, the results for both are slightly different, but they're pretty darn close,
says Wickham. When you find your BMR on your own, consider it a really good estimate, not
a hard-and-fast rule, he adds.
For both equations, finding your BMR requires your weight, height, age, and gender (yes,
guys have their own equation). Wondering why? "The more you weigh and the more mass you
have, the more fuel you need to sustain your organs," explains Valdez. That's why people
who weigh more have heavier BMRs.
Age is a factor in the equations because, as you get older, muscle mass declines by
5 or so percent each decade after the age of 30, Wickham explains. This might change
as more women start strength training, but as a general rule, that's fair, he says.
And if you're wondering why the formula is different for men and women, it's because
research published in The Journal of Clinical Investigation shows that a woman's BMR is
typically around 5 to 10 percent lower than a man's.
Now what? Once you know your BMR, you know the bare minimum number of calories you would
need to keep your body alive if you were going to lay in bed all day, says Wickham. But you
need to take into account everything else you do that burns calories (walking the dog,
folding laundry, climbing five floors of stairs to your apartment, bi-weekly CrossFit class,
Thursday evening yoga…).
To do that, multiply your BMR by the factor that best represents your activity level.
If you are sedentary = BMR x 1.2. If you do light exercise 1-3 days a week = BMR
x 1.375. If you exercise at a moderate intensity 3-5
days a week= BMR x 1.55. If you are exercise at a high intensity 6-7
days a week = BMR x 1.725. If you are into two-a-days or have a physically
demanding job = BMR x 1.9.
How Many Calories You Need To Lose Weight. Okay, so how many calories do I need a day
to lose weight? Once you know how many calories you need to maintain your weight, you simply
subtract some calories to put yourself into a caloric deficit. How many calories? Well,
to lose roughly one pound of fat per week (a healthy goal) you need a 500-calorie-per-day
deficit, he explains. In other words, just delete 500 calories from the number you found
above.
But a calorie deficit doesn't have to (and, in reality, shouldn't) come solely from eating
less, says Valdez. Exercise can help, too. If you are game for taking your workouts to
the next level, Valdez recommends decreasing your calories from food by 250 per day, and
increasing the intensity or duration of your workouts so that you are burning an additional
250 calories two to three times a week through exercise.
That means if you already take a cycling class three days a week, add in a 30-minute walk
two days per week to keep the calorie burn going. Or, if you currently live a lightly
active life, consider incorporating a yoga class, strength-training class, or hike into
your routine.
However, that does mean that on the days you don't do any physical activity at all, you
should decrease your calorie intake by closer to 500 cals, he says. Your goal is to burn
about 500 fewer calories than you take in per day, through diet, exercise, or both.
You do the math.
How Many Calories You Need To Gain Weight From Muscle.
Not everyone who counts calories wants to lose weight. Some want to gain it from lean,
powerful muscle. Gaining weight from muscle is a great way to improve your health and
even decrease your body-fat percentage. Bonus: Since muscle is metabolically active, it can
also help you shed fat without cutting calories, says Wickham. When you start to gain muscle,
your BMR will increase, which means that your body needs more calories just to go about
its daily function, he explains. (Hit the reset button—and burn fat like crazy with
Women's Health's The Body Clock Diet!)
"If you want to gain weight, the simple trick is to tack on 250 to 500 extra calories
in healthy, whole foods per day. Every one to two weeks, you'll have added a pound
safely," says New York City nutritionist Brittany Kohn, R.D. To gain muscle without
also gaining fat, you need to increase your protein to 1.8 to 2 grams per kilogram of
body weight every day, so the majority of these additional calories should come from
protein, says Valdez. And the rest should come from carbs like whole grains, fresh fruits,
and vegetables, which will help power your workouts.
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