Why Knowing Your Body Fat is Uber Important To Your Meal Prep

Do you know how many calories you should eat in a day? If you haven’t heard the names Katch and McArdle, then you’re probably wrong about your energy needs.

The number of calories your body needs to function at a basic level every day is called your Basal Metabolic Rate, or BMR. This is the key piece of information you’ll need when creating a meal plan to support your fitness goals and is easy to determine, but the standard methods often produce inaccurate results.

We’re going to take a look at how to accurately determine the number of calories you should eat in a day, and why knowing your body fat percentage is a critical aspect in creating a meal plan to fit your goals.


Your Phone Doesn’t Know Your BMR

Relying on a diet app to determine how many calories you burn is newbie mistake #1. If this is how you’ve been calculating your daily calories, you’re not alone — we’ve all installed one of those calorie counting apps on our phone, plugged in our height, casually selected our level of activity, and accepted the number it spits back as what we should eat in a day. The problem is, that number is inaccurate (more on that later), and likely won’t help you achieve your fitness goals.

To find an accurate value, we’re going to take a look at a few methods for determining your BMR. Once you’ve got an idea of how many calories you need to eat in a day, you’ll be prepared to start creating a meal plan that is tailored to your needs.

How to Find Your Actual BMR

There are several well-known methods for determining how many calories you need to consume in a day. All involve a little math, but that can be done with online calculators. We’ll be comparing the basics of the three most commonly used methods, to determine which is most accurate in helping you achieve your fitness goals.


Most BMR calculations done by medical professionals use the Harris-Benedict equation. This calculation was developed in 1919, utilizing height, weight and age as the variables, then multiplying this by an activity factor. The activity factor is meant to guess how many calories above the baseline can be added to your intake. This is most likely the equation those apps on your phone are using.

The studies that led up to the development of this equation looked at how various disease states, like cancer and diabetes, can impact metabolic rate, and focused on a more active lifestyle than the one we live now. The Harris-Benedict equation was revised in the 80s for accuracy, though studies have since shown that this equation can overestimate daily energy expenditure by up to 300 calories in some groups

Mifflin-St. Jeor

Similar to the Harris-Benedict method, the Mifflin-St. Jeor calculation also uses age, height, weight and an activity factor to arrive at the number of calories an individual should eat. Mifflin-St. Jeor is a 1990s conception of the calculation, accounting for a sedentary lifestyle.

A study done at the University of Massachusetts compared this energy expenditure calculator with the Harris-Benedict method described above, and noted that while Harris-Benedict more accurately predicted resting energy expenditure (REE) in active individuals, the Mifflin-St. Jeor method proved most successful with overweight or obese populations.

To put this in perspective, the calculator which has been shown to overestimate energy expenditure by up to 300 calories in some populations, is considered to be the more accurate of these two. Thankfully, there is a better way.


If you want the most accurate measure of how much energy your body burns at rest, smart money’s on Katch-McArdle. A simpler calculator than Harris-Benedict and Mifflin-St. Jeor, Katch-McArdle requires only weight and body fat percentage to reach your REE.

This formula finds the weight of your lean body mass (muscle, organs, bones and all other tissue that isn’t stored fat), and then determines how many calories you should eat in a day to maintain the function of this tissue. You can then either multiply this number by an activity factor, or track exercise separately, to reach the total energy expenditure.

Because neither age, sex nor height impacts how much energy is required to maintain a pound of lean mass, these variables aren’t used to calculate BMR with the Katch-McArdle equation.

Body Fat Percentage Matters

Knowing how much lean mass you have is a far more important piece of data than weight alone. Lean mass is metabolically active tissue that keeps your body running and burns calories, while most fat is not. Because body composition can vary so wildly from person to person, factoring in body fat percentage is really the best way to determine energy requirements.

Body fat percentage is also important in determining your fitness goals. You may know on a basic level that you want to cut fat while preserving or building muscle, but knowing your body fat percentage will give you concrete data on which to base your goals.

You can then plug this information into your meal planner, along with your activity level, to create a plan around these goals. High-quality meal planning programs, like Meal Plan Magic, have a built-in calculator to help you determine your ideal weight, as well as caloric needs and the recommended macronutrient breakdown for your fitness goals based on your weight and body fat percentage.


How Fat Are You?

The next step in determining your daily energy requirements using the Katch-McArdle formula is to find out your body fat percentage. If you have no idea what your body fat percentage is, this process can be confusing at first. But after taking a few measurements and doing a little research, things will clear up.

DEXA Scans & Hydrostatic Weighing

The most accurate ways to measure body fat percentage are DEXA scans and hydrostatic weighing. In hydrostatic weighing, an individual is submerged into a dunk tank and weighed. Body fat percentage is determined based on the difference in weight in and out of water. DEXA scans are even more advanced, and can account for body fat distribution, as well as determine percentage. Both of these methods involve a trip to a sports medicine facility, and a few hundred dollars, but there are a few ways to measure body fat at home.

The US Navy Method

The simplest method for measuring body fat percentage at home is grabbing a tape measure and using the Navy Method for determining body fat. All you need to do is measure the circumference of your neck and abdomen, and plug those into a calculator. While this will provide a good reference point, the accuracy of this method is uncertain, as actual body fat isn’t being measured.

Skin Fold Calipers

Taking measurements with skin fold calipers can be an accurate way to measure your body fat percentage, as long as you measure correctly. If you haven’t used calipers before, don’t be scared off by how technical it sounds — it’s actually an easy process. Skin fold caliper measurement involves grabbing a fold of tissue in specific locations, and pinching it with a tool to determine how much fat is under your skin. The trickiest part of calipers is learning which sites to use, and those over 35% body fat may run into difficulties, but this method is otherwise accurate.

Body Fat Analyzing Scales

Many home scales and pieces of gym equipment now include body fat measuring capabilities, known as bioelectric impedance analysis. The device sends an electric impulse through your body, and then measures the resistance in various tissues. The analysis is based on the difference in density and water content of muscle and fat. Dehydration will skew readings, and this method gives inaccurate readings for those with lower body fat percentage.

If you’re itching for an idea of where your body fat is now, and don’t feel like grabbing a measuring tape or set of calipers, you can check out these images of body fat comparisons to get a basic idea of where you stand.


Create that meal plan!

Once you know your body fat percentage, you can plug it into MealPlanMagic and start building customized meal plans that are ultra accurate.  Find out how many calories you need to fuel your body per day and apply this information to your meal plan and start prepping meals that are catered to your body type and goals.  As your body and goals change, so should your meal prep!

Whether you want to burn fat or build lean muscle, knowing your body fat percentage provides a valuable benchmark for creating fitness goals and can help you to measure your progress along the way.



Harris-Benedict equation: http://www-users.med.cornell.edu/~spon/picu/calc/beecalc.htm

Harris-Benedict studies: http://www.ncbi.nlm.nih.gov/pubmed/9550168

Harris-Benedict over-estimate studies: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2598419/

Comparison of calculations: https://www.researchgate.net/publication/50987389_Accuracy_of_four_resting_metabolic_rate_prediction_equations_Effects_of_sex_body_mass_index_age_and_raceethnicity


Body Fat Calculator: http://www.linear-software.com/online.html