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Updated on 11/18/20 – Added a link to Peter Attia’s podcast #136 which contains a thorough discussion of the various methods used to measure body composition.
Introduction
If you want to read about nutrition, biochemistry, macronutrients, and you want to find out how I decided that it’s worthwhile to calculate daily macronutrient requirements, read this introduction. If you just want to see how to calculate your macronutrient requirements, skip ahead.
How can we know what to eat?
We could rely on intuition. But, many people have realized, myself included, that the modern food environment has disrupted this approach. It has been repeatedly argued, most recently and thoroughly (in my opinion) by Stephan Guyenet, Ph.D, that in the modern food environment, our intuition, our hunger and cravings, often betray us. This is not true for everyone. Some people have well regulated and healthy metabolisms and do very well by listening to their internal cues. But, some people have limited success when they follow their internal cues, and many others are high performers who want to gain every advantage they can find from nutrition.
For these people, another approach is possible. This approach is to try to understand which substances the human body and mind requires to function and thrive, and then to figure out how to get these substances from food.
The useful substances that we absorb when eating food, at base, are elements and molecules. Potassium is an element, EPA (a fat) is a molecule, lysine (an amino-acid) is a molecule. The subset of elements and molecules obtained from diet that are required for our bodies and minds to grow and function properly are collectively called "nutrients."
There are a multitude of nutrients; too many to know and understand, even for the professional biochemist. So, in order to make use of expert knowledge of nutrition and biochemistry, we need simple but accurate categories of nutrients that we can apply to our individual diets.
One of the most useful methods of categorizing our food is by its energy content and type. There are three major classes of biomolecules that contribute to the energy content of our food. These three classes are fat, protein, and carbohydrate. In nutrition, these 3 classes of biomolecules are commonly referred to as the macronutrients because they are the three most abundant classes of biomolecules in our diet. There are other macronutrients, and there are also "micronutrients," the discussion of which is out of the scope of this article.
All nutrients, macro, micro, and otherwise, are important because they each support one or more of the 3 needs of a living human: the structural elements, the functional moving parts, and the fuel.
Structure
The structure of our body can be thought of as the framework, like the chassis of a car, the case of a watch, or the frame of a house.
We need building blocks to make the structure of the physical body – the hair, skin, muscles, bones, brain, nerves, vessels, and other organs.
In this category I place protein, fat, and minerals. Proteins are present in every cell as enzymes, channels, and signaling molecules, but structurally comprise much of the skin, hair, and muscles. Fats make up the cell membrane of every cell and insulate our nerves. Minerals such as calcium make up our bones.
Function – Moving Parts (or "the mechanism")
I created this category, which, to my knowledge doesn’t exist elsewhere in the nutrition or biochemistry lexicon. If you find it somewhere else, let me know so I can give proper credit. If it doesn’t make sense, you have only me to blame. I won’t claim too much originality, because this concept is really implicit in biochemistry.
I think of this category as akin to the movement of a watch; the springs, levers, jewels, lubricant, and crown; or like the motor and transmission of a car; the pistons, cranks, fly-wheel, steering wheel, axles, gears, fans, coolant, and oil; in short, the moving parts.
Though these are attached to the framework, they’re more functional fixtures than structural elements. These are the parts that make a machine or human live and breathe. These parts make the watch tick and the car drive (which in this era of "self-driving" cars, is a turn of phrase that actually makes sense).
In humans, the analogous parts are the enzymes, channels, pumps, shuttles, binders, transporters, signaling molecules, vesicles, cilia, and more.
Fuel (or energy)
We need fuel, or energy for the engine to run. Fuel is any form of stored energy that can be released. In the case of humans, we’re quite similar to gas powered engines or fires – we break down hydrocarbons – fats and carbohydrates to release the energy stored in their bonds. The details of the process whereby this happens inside of human cells is different than what happens in a fire or inside of a gas powered car engine, but in essence it’s the same.
The fuels are originally made by fusing atoms together – either under heated and pressurized conditions in the earth’s crust in the case of fossil fuels, or by photosynthesis in the case of plant life, or by the work of animal metabolism. When the atoms and molecules in these fuels are broken down, when they’re separated, they move around. This movement is undetectable to us on the atomic scale, but if you combine the movement of millions of such atoms into a tiny space and make them all move in the same way, the movement adds up to bigger and bigger movements – the up and down movement of a piston in the cylinder of a car engine, or the contraction and relaxation of the biceps muscle of a weight-lifter doing curls.
Unlike in a car where there is usually one motor and one fuel tank, or a watch where there is one movement and one spring, the human body can burn multiple types of fuel (in a nutritional context), has no central fuel tank, and has multiple tiny motors in each cell as opposed to one big motor. The human body has a distributed fuel tank – most cells can store fuel; some cells store fuel as carbohydrate, some as fat, and some as both. Just like a car’s fuel tank, the human fuel tank does have a limited, if expandable, capacity.
To fuel properly, we need to understand the types of fuel we can process, and in what amounts they’re each needed.
In this category are all three macronutrient fuel sources – fats, protein, and carbohydrates.
All three needs (structure, function, and fuel) are important, but on a daily basis, it’s primarily the fuel that needs to be replenished (unless fuel stores are over-flowing, in which case the primary nutrients that are needed are structural and functional elements). Of course, we need a constant intake of nutrients like calcium and electrolytes to keep our cells functioning properly as well, but if we eat a diverse whole-food diet with the proper quantities of macronutrients for our individual needs, we’re likely to fulfill most of our structural and functional needs automatically.
You might be asking, why don’t we just calculate total energy needs then? What reason is there to look at individual macronutrients?
Why Calculate Macronutrient Requirements?
Reason #1
We have separate (though overlapping) pathways for absorbing, processing, storing, and utilizing each macronutrient, and thus, different requirements for each.
By Chakazul – Own work, CC BY-SA 4.0, Link
Carbohydrates
For example, after being eaten, carbohydrates are broken down into sugars in the small bowel (Holmes 1971). These sugars are then directly absorbed across the bowel wall into the bloodstream, and can be immediately delivered and used by almost any cell of any organ. Excess carbohydrates are taken up by different cell types such as liver and muscle and stored as a conglomerate of sugar molecules, called glycogen. Excess sugar can also be stored in fat cells through a process called de novo lipogenesis which actually creates fatty acids by stringing together carbon molecules from sugar.
Fats
Fats, on the other hand, are absorbed into cells that line the bowel, packaged into little fat bubbles called chylomicrons, which are then absorbed into the lymphatic system before being dumped into the circulation, and then have to be delivered to cells using transfer enzymes and lipases. Before these fats can be used for energy, they often have to undergo further processes to break them down and shuttle them to the location where they can be used. If they’re not used, they can be stored as lipid droplets in fat or muscle cells, or they can be sent back to the liver and stored or reprocessed there. Most of what I’ve learned about cholesterol and fat metabolism, I’ve learned directly from, or as a result of Peter Attia’s work.
Proteins
Proteins (large molecules built from many amino acids) are broken down in the bowel into amino acids and absorbed as amino acids or strings of two or three amino acids called di- and tri-peptides. Once absorbed, amino acids can be shuttled to muscle cells to synthesize new muscle, incorporated into new enzymes, or broken down into their subparts – nitrogen and carbon skeletons. The nitrogenous component can be used in nitrogen containing compounds, or it can be excreted in urine, feces, and sweat as urea, uric acid, and creatinine. The carbon skeleton goes into the same metabolic pathways that use hydrocarbon molecules from carbohydrates and fat to generate energy. Excess carbon skeletons can be glucogenic. It can be converted into blood glucose (sugar) by the liver and released into the blood stream. Ultimately, the carbon is either stored as glycogen, fat, or it’s burned for energy (Pellett 1990).
You can learn more about nutrient absorption here.
Reason #2
Each macronutrient tends to have different neuro-hormonal effects on satiety and metabolism, which means that a proper macronutrient balance should reduce excess hunger and therefore excess energy intake.
Reason #3
Foods that predominate in each macronutrient class tend to be more or less dense in other nutrients that are important for structural or functional reasons. As a result, a proper intake of diverse foods from each macronutrient category makes it more likely that we’ll have a nutritionally complete diet.
For example, foods that are mostly made out of fat, such as butter and oil are often relatively poor in most vitamins and minerals, but can be rich in fat soluble vitamins like D and E. Dairy, which, depending on processing, can be either high or low fat, is rich in calcium. Most foods that are mostly carbohydrate are poor in fat soluble vitamins and calcium, but may be rich in other nutrients. Starchy vegetables like potatoes, for example, are rich in magnesium and potassium, which are hard to find in most foods that are primarily fat. There are exceptions, like liver, for example, which is high in fat and rich in vitamins and minerals. Foods that are predominantly protein, like chicken breast, are rich in vitamin B3, B6, and choline, but relatively poor in many other micronutrients.
Specific Nutritional Requirements are for Individuals
Specific nutritional requirements are not necessarily generalizable across people or within the same person across time. It’s true that there are are general requirements that apply to almost all people, but specific requirements can be significantly different.
People differ from one another in lean body mass, activity level, ability to absorb certain nutrients, ability to tolerate certain foods, not to mention personal preferences. The macronutrient amounts and ratios that work for one person may not work for another. Just because my protein intake is 100 grams daily, doesn’t mean that will work for someone else or that it will work for me in 3 months from now. Avoiding dietary dogma is important. The best writing I’ve seen on the topic is by Chris Masterjohn, PhD in his article "Against Dietary Dogmatism.".
Calculating Macronutrient Requirements
Now that we’ve discussed macronutrients and the reasons for calculating them, here are two ways to do it.
The first method is to use a nutrition tracking app called Cronometer. The second method is to perform the calculations manually.
I prefer the first method, which is to use the calculators built into Cronometer.com. I like this method because it’s fast, simple, and once you calculate your macronutrient requirements, you can easily track your nutrition, your weight, and your lean body mass in the same app. It’s useful to check that your diet is concordant with your calculations, and that your calculated requirements actually work for you (in the sense that your outcomes are moving in the desired direction: e.g. weight loss or weight gain, increase in lean body mass, etc.).
Information You Need
Before you perform either method, you’ll need to know 3 things:
- Your body weight
- Your height
- Your % body fat.
Body Weight
Obtain your body weight in pounds or kg from any accurate scale. If you don’t have one, consider buying an "impedance scale" which will also allow you to measure % body fat.
Height
Measure your height in feet and inches, or cm.
Your % Body Fat
This is the hardest number to obtain accurately. You can obtain your estimated % body fat using any of the following methods in the table below (in order by price and accuracy – most expensive and accurate last). The sweet spot of convenience, price, and accuracy is probably to use an "impedance scale".
Methods of Measuring % Body Fat
| Method | Price | Notes |
|---|---|---|
| guess | $0 | Completely inaccurate. |
| use images | $0 | Variable accuracy depending on visceral fat and fat distribution. The link sends you to a pretty cool website which helps with this. |
| use calipers | ~$13 | May be inaccurate for amateurs and requires familiarizing yourself with the technique. |
| measure neck, waist, and hip circumference with a tape measure and then use this calculator | ~$14 | Variable accuracy. |
| impedance scale | ~$45 | This scale was recommended by Tim Ferris in his book The 4-Hour Body |
| BodPod | ~$50 | Will tell you your weight, body volume, fat and fat-free mass, and your lung volumes |
| DEXA scan | ~$50 and up | Most accurate. Might require a physician’s order. Will tell you bone mineral density and body composition of individual body parts |
Peter Attia’s Podcast on Body Composition Measurement
Method Number 1: Cronometer.com
I use this method because it’s the easiest and most accurate individualized method that I’m aware of. The overview of this method is – enter your information (height, weight, % body fat) into Cronometer, and use their built in calculators to determine your macronutrient requirements.
Step 1 – Create an Account and Login
Navigate to the website Cronometer.com and create an account if you don’t already have one.
OR – use the mobile app.
Tip: If you use the mobile app, just know that my screenshots of Cronometer are from the website. The web app and mobile app are very similar, so it shouldn’t be too hard to find the corresponding screens on the mobile app if you choose to do it there.
Step #2 – Enter Your Body Measurements
After you create an account and login, find the settings menu and then go to "Profile. "Enter your sex, weight, height, and body fat %. Make sure the BMR is calculated. Select an activity level.
Tip: For most people, I recommend selecting the activity level one step down from what you initially consider selecting. If you’re trying to gain weight, then just select the activity level that you deem most accurate. My reasoning here is that it’s easier for most people to compensate on the backend by consuming more food rather than assume they are using more energy than they are in reality.
Here’s the screen you should see (with your own data):
Step 3 – Choose your Protein and Carbohydrate Requirements
Go to the "Targets" tab, which is at the top of the screen next to "Profile." For "Tracking carbohydrates as:" select "Net Carbs without Sugar Alcohols" For "Set macro targets using" select "Ketogenic Calculator." Do this even if you have no interest in a ketogenic diet.
Below that you’ll see a box that says "Your Keto Calculator."
Here’s the screen you should see at this point.
(Yours may or may not have the exact same selections.) 
Make the following selections:
- Ketogenic calculator: Custom
- Protein: 1-1.5 g/kg/lean body mass/day
A good starting point for an active individual who exercises on a daily basis is 1.5 g/kg/lean body mass.
- Carbohydrate: 50-100 grams
This number, "grams of non-fiber carbohydrates per day," is the big decision. Based on this number, the calculator will determine your carbohydrate and fat requirements.
With these parameters now set, Cronometer should automatically calculate your macronutrient targets. You can navigate to the diary to view your numbers.
Here’s what you should see in your "Diary"
And if we zoom in on the gauges:
If you hover over any of those items in the web app, or click them in the mobile app, you’ll get more information.
Here are my personal macronutrient requirements from the image above:
- Protein 90 g
- Net Carbs 50 g
- Fat 177.8 g
Note: On this particular day, I consumed more protein than needed, hit my carbohydrate target nearly spot on, and I had significant room to go in my fat intake. You can see in the purple box I had 491 kcal (calories) left – this is the difference between my energy (in kcals or calories) consumed and burned. So, I didn’t follow my own requirements to the letter on this day. It’s important to realize that you might need different nutrition on different days, but that over time, your average intake should approximate these requirements that we’re calculating.
That’s it, you now have targets for your daily macronutrient intake. If you chose this method, there’s no great reason to read on. Most of the remainder of the post is about a manual method of doing this calculation without Cronometer.
An Aside on Carbohydrate Requirements
"Optimal" carbohydrate intake is currently a very controversial topic. I should write about this separately, but here is a brief discussion of my thoughts at the time of this article’s original publication (July, 2020).
For the vast majority of people, I think 50-100 grams of non-fiber carbohydrate per day is likely adequate. It’s enough to allow for liberal vegetable and fruit consumption, and even some bread, pasta, and starches, but restrictive enough to prevent you from eating candy, processed foods, baked goods, soda, juice, and other foods with added sugar. For individuals with a lot of lean body mass (very muscular), athletes, highly active people, or people who prefer a primarily plant based diet heavy in root vegetables and fruits, it may be necessary to push this to 200 or 300 grams per day, or perhaps even higher in some circumstances.
For people with very high activity levels – like endurance athletes, CrossFit athletes, or just someone with a very high level of activity throughout the day, a higher carbohydrate intake might be desirable. This is an individualized decision and might require some careful thought and experimentation.
Conceptually, I currently think that "high quality" whole food sources of carbohydrate should be included in the diet as much as necessary to meet energy demands and micronutrient requirements without causing metabolic disruption.
To execute this on an individual level, it’s necessary to assess an individual’s current metabolic health, genetic predispositions, activity level, type of activity, glycemic response to various food sources of carbohydrate, daily schedule, and then based on all of those variables, make a decision as to how much of their fuel is best taken from carbohydrates versus fat, and then which sources to use and when. This is a process that requires a lot of work, but is possible to execute for a disciplined and committed individual.
To give you some rough idea of why I think 100 grams is a good starting point, look at this list below.
Here are some examples of what you can eat with a daily allowance of 100 grams of carbohydrate:
You could have all of these foods in the following amounts:
- 1/2 cup of white rice
- 1 cup of blueberries
- 1/4 cup of ice cream
- 3 6-inch long carrots
- A large tomato (3 inch diameter)
- 1/2 cup of pecans
- 1 large red bell pepper
- 1.5 cups of broccoli
- 2 tbsp of half and half
- 1/2 cup of whole milk yogurt
- 1/2 of a sweet potato (5x2 inches)
Or:
- 13 heads of romaine lettuce (626 g in weight each)
Or:
- 3 snickers bars
Or:
- 2.5 bags of potato chips ("grab bag" size)
Or:
- 4 bananas
Or:
- 2 cups of Ben & Jerry's (Chocolate Chip Cookie Dough)
Or:
- 2 cups of granola
Or:
- 5 slices of store bought white bread
Or:
- 6 slices of whole wheat bread (homemade/bakery)
Method Number 2: Manual Calculation
This method should get you very similar results to the first, but it doesn’t require any reliance on Cronometer. The basic method is this:
- Calculate your total energy needs.
- Calculate your protein requirement.
- Calculate your carbohydrate requirement.
- The remaining energy requirement is supplied by fat.
For this method, we need to know the energy content of each macronutrient type.
Protein contains 4 kcal (calories) per gram, carbohydrates 4 kcal/g, and Fat 9 kcal/g. Those numbers come from a technique called calorimetry. You can read all about the science behind the energy content of food here.
Step 1: Calculate your TDEE (total daily energy expenditure)
Use this calculator. On the calculator webpage, expand the "+Settings" and select: "Katch-McArdle and enter your body fat %"
Example:
Step 2: Calculate your Lean Body Mass
You can do this manually, or you can use a lean body mass calculator. I recommend doing this manually.
Lean body mass =
weight in kg * (1 - body fat %)
Note: Here’s why I don’t use calculators for this: If you navigate to this link, it’ll start out populated with my personal data. You can see the system is calculating my body fat % at 24-30 depending on the equation used. I know that this is inaccurate by at least 10%. This is why I recommend measuring body fat % using one of the above methods, and then calculating lean body mass based on that number.
Step 3: Calculate Energy Obtained from Protein
Daily protein requirement =
1.5 g/kg of lean body mass * lean body mass.
Example for a lean body mass of 70 kg at a dose of 1.5 g/kg/day
Note: The dose of protein was discussed within method 1 earlier in this article here and was based in part on this article.
1.5 g of protein/kg * 70 kg
= 105 grams of protein
105 grams * 4 calories / gram
= 420 calories from protein
Step 4: Determine Remaining Energy Requirements
Remaining Energy Needs =
TDEE - Calories from protein
Example:
TDEE = 2300 kcal
- 420 kcal from protein
= 1880 remaining kcal
Step 5: Calculate Energy Obtained from Carbohydrate
A good starting dose is 50-100 grams per day. But, this is a nuanced topic that was discussed in a bit more detail above in this section.
Example: Based on 100 grams of carbohydrate daily.
Note: Remember, carbohydrate has 4 kcal of energy per gram on average. Also, notice that I’ve used kcal and calorie interchangeably in this post. In nutrition, people often use the term calorie to refer to a kilocalorie. A calorie is a unit of measure of energy.
4 kcal/g * 100 grams of carbohydrate
= 400 kcal
Step 6: Calculate Remaining Energy Requirements
Subtract energy from carbohydrate from remaining daily energy requirement. Our remaining requirement from the previous step was 1880 kcal.
Example:
TDEE = 1880 kcal
- 400 kcal from carbohydrate
= 1480 kcal
Step 7: Calculate Fat Requirement
Remember from above we learned that fat containes 9 kcal of energy per gram.
Example:
Remaining energy requirements
= 1480 kcal
1480 kcal / 9 kcal/g
= 164.4 grams of fat
Step 8: Review the results – we have made the following determinations:
- Total daily energy expenditure: 2300 kcal
- Protein requirement: 105 grams, which is 405 calories
- Carbohydrate requirement: 100 grams, which is 400 calories
- Fat requirement: 164.4 grams, which is 1480 calories
What to Do Once You’ve Calculated Your Macronutrient Requirements
Now that we have these macronutrient requirements calculated, what are we going to do with them?
Test them out.
I recommend using Cronometer.com to track your diet for short periods of time to check that you’re on the path you want to be on.
Now that you have some rough idea of your macronutrient requirements, it’s easier to make the necessary adjustments. You need some starting point or framework to start from, and this is it. These quantifications eliminate the tendency to over or underestimate your intake of one thing or another (e.g. total calories/energy intake, carbohydrate intake, protein intake, etc.).
While this is just one way to obtain some control over your nutrition. It’s a time tested strategy that forms the basis of the nutrition plan for most athletes. It’s also implicit (or sometimes explicit) in almost any marketed diet plan that you might be interested in trying (not that I’m recommending any of these) – zone, paleo, Atkins, "low-carb high-fat," "keto," and so on and so forth.
Overall, this is another tool that you can use to gain control over your nutrition.
And lastly, if you don’t feel like going through all of this work, it is possible to hire someone to do it for you. But, doing these calculations is the easy part. The hard part is following your nutrition plan consistently, which requires a clear purpose followed by discipline.
Other people have written informatively on this topic. Here are some of the resources I used in researching this article.
References
- “Protein requirements in humans, The American Journal of Clinical Nutrition, Oxford Academic.” link (accessed Jul. 25, 2020).
- A. L. Merrill and B. K. Watt, Energy Value of Foods: Basis and Derivation,**. Human Nutrition Research Branch, Agricultural Research Service, U. S. Department of Agriculture, 1955.
- M. A. Tarnopolsky, S. A. Atkinson, J. D. MacDougall, A. Chesley, S. Phillips, and H. P. Schwarcz, “Evaluation of protein requirements for trained strength athletes,” Journal of Applied Physiology, vol. 73, no. 5, pp. 1986–1995, Nov. 1992, doi: 10.1152/jappl.1992.73.5.1986.
- “How do you determine if you’re getting enough protein? – Masterjohn Q&A Files #18" Chris Masterjohn, PhD, Dec. 03, 2019.
- “How to Calculate Macronutrient Ratios that Work for You,” Chris Kresser, Aug. 23, 2019.
- “How Much Protein Should You Be Eating?”, Mark Sisson
- C. K. Martin et al., “Change in Food Cravings, Food Preferences, and Appetite During a Low-Carbohydrate and Low-Fat Diet,” Obesity, vol. 19, no. 10, pp. 1963–1970, 2011, doi: 10.1038/oby.2011.62.