How much should I eat? A guide to estimating calories and macros

Lately, I’ve been receiving many questions about how to calculate daily calories and “macros” (macronutrients: protein, carbohydrates, and fats).

There are two aspects to figuring out what your optimal diet may be:

1. Quantity
2. Quality

In this article, we’re going to look at some simple methods for estimating how much food you need to eat. The key word throughout this article is estimate. Any and all methods you could use to attempt to determine how much and what kind of food optimally supports your health and nutrition goals will always and forever be an estimate.

Only through tracking and trial and error can one hone in on their optimal diet.

In this article, I’m going to show you how to calculate your estimated:

1. Protein, carbohydrate, and fat needs
2. Caloric burn rate
3. Resting metabolic rate (RMR)

Not everyone will want to run the numbers, and you don’t have to eat healthily.

But for some, numerical targets help us make informed decisions. If running the numbers isn’t your thing, that’s fine. There are several alternative ways to approach your diet.

If you need help with making lasting changes to improve your diet, registered dieticians can help you navigate the minefield of behavior change around food. If you struggle with food and diet, I strongly encourage you to seek the professional help of a registered dietician.

What I’m offering today is what I’ve learned over the years that has worked for me in making the tweaks and adjustments necessary to dial in my nutrition for life and sport.

Though it works for me, it doesn’t mean it will work for you.

Proteins

Proteins are essential for the human body’s structure, function, and regulation. They are involved in numerous processes, including growth, repair, transportation, and immune response.

Here are some critical uses of proteins in the human body:

Structural Component
Proteins are the major structural component of cells, tissues, muscles, organs, skin, and nails. They provide strength, support, and shape to these structures.

Enzymes
Proteins act as enzymes, biological catalysts that facilitate chemical reactions in the body. Enzymes help break down food, synthesize molecules, and carry out various metabolic processes.

Hormones
Some proteins function as hormones, which are chemical messengers that regulate various physiological processes in the body. Examples include insulin, growth hormone, and thyroid hormones.

Immune Response
Proteins are involved in the immune response and help defend the body against pathogens. Antibodies are proteins that recognize and neutralize foreign substances like bacteria and viruses.

Cellular Repair
Proteins are essential for cellular repair and regeneration. They are involved in the synthesis and replacement of damaged or worn-out cells.

Energy Source
While carbohydrates and fats are the primary energy sources, proteins can also be used when needed. However, the body prefers proteins for their other critical functions and only uses them for energy when necessary.

In the paper “Nutrition and Athletic Performance,” Thomas and colleagues detail the role of nutrition in optimizing athletic performance. Through an extensive review of existing literature and scientific evidence, the authors shed light on the impact of various nutrients, dietary patterns, and supplementation strategies on athletic performance. (1)

According to the paper, daily protein needs are in the range of 0.6–1.0 gram per pound (1.2–2.0 g/kg) per day.

Using the formula, a 150-pound person would require 90–150 g of protein per day.

Carbohydrates

Dietary carbohydrates are essential for providing energy, supporting brain function, fueling muscles, enhancing performance, promoting recovery, and maintaining overall health. Choosing the suitable types and amounts of carbohydrates is essential for optimizing human performance and well-being.

It’s important to note that not all carbohydrates are created equal. Choosing nutrient-dense, complex carbohydrates from whole grains, fruits, vegetables, and legumes is generally recommended for optimal health.

On the other hand, consuming excessive amounts of simple carbohydrates, such as refined sugars and processed foods, can have adverse health effects and contribute to undesirable weight gain and chronic diseases.

Here are some key reasons why dietary carbohydrates are essential:

Energy Source
Carbohydrates are the body’s primary source of energy. When consumed, carbohydrates are broken down into glucose, which is used by cells to produce ATP (adenosine triphosphate), the body’s main energy currency.

Brain Function
The brain relies heavily on glucose as its primary fuel source. It requires a steady supply of glucose to function optimally. The brain uses about 20% of the body’s energy expenditure, and glucose is its preferred fuel.

Muscle Fuel
Carbohydrates are essential for muscle function and performance. During exercise, carbohydrates stored in the muscles and liver, known as glycogen, are broken down to provide energy. Adequate carbohydrate intake helps maintain glycogen stores, enhancing endurance and delaying fatigue.

Recovery and Muscle Repair
Carbohydrates play a vital role in post-exercise recovery. They help replenish glycogen stores and promote muscle repair and growth. Consuming carbohydrates along with protein after exercise can enhance muscle recovery and adaptation.

Nutrient Density
Carbohydrate-rich foods like vegetables, fruits, and whole grains are often nutrient-dense and provide essential vitamins, minerals, and dietary fiber. These nutrients are necessary for overall health, digestion, and disease prevention.

The daily requirement for carbohydrates is affected by the duration and intensity of daily activities.

Use the chart below to determine your estimated daily carbohydrate requirements. Multiply your body weight in pounds by the factor you believe most closely represents your activity level. (1)

For example, a 150-pound person who trains about one hour daily would multiply their body weight by 2.3 and 3.2. This would give them a daily carbohydrate range of 345–480 grams.

Fats

Dietary fat is often misunderstood and gets a bad rap. However, fat is an essential nutrient that provides several significant benefits to our health. Here are some of the nutritional benefits of dietary fat:

Energy Source
Fat is a concentrated energy source, providing 9 calories per gram, compared to 4 calories per gram from carbohydrates and proteins. It is a long-lasting energy source and can help keep you feeling fuller for longer.

Cell Function and Structure
Dietary fats are crucial for the proper functioning and structure of our cells. They are a component of cell membranes and help maintain their integrity.

Nutrient Absorption
Fats absorb fat-soluble vitamins (A, D, E, and K) and other essential nutrients. These vitamins require dietary fat to be adequately absorbed and utilized by the body.

Hormone Production
Certain hormones, such as estrogen and testosterone, are synthesized from cholesterol, a fat type. Adequate dietary fat intake is necessary for the production of these hormones.

Heart Health
Consuming a healthy dietary pattern that includes higher amounts of monounsaturated and polyunsaturated fats can help lower levels of bad cholesterol (LDL) and reduce the risk of heart disease.

Fat should not be less than 20% of total calories, and saturated fat no more than 10%. (1)

Resting Metabolic Rate

Your resting metabolic rate (RMR), sometimes called basal metabolic rate or resting energy expenditure, is the minimum amount of energy your body needs to maintain life support. RMR makes up approximately two-thirds of your daily energy (caloric) needs.

The gold standard for measuring caloric energy needs depends on the context and the specific population being studied, as well as labs with expensive equipment involved.

Two methods commonly used are:

Indirect Calorimetry is often used with critically ill patients who are bedridden. Indirect calorimetry measures the amount of oxygen consumed and carbon dioxide produced to estimate energy expenditure.

The Doubly Labeled Water Method estimates average energy expenditure over a period of time, typically several days to a few weeks, without restricting the subject’s movement or activities, making it a valuable tool for studying energy metabolism in real-life settings.

Unless you have access to a lab and equipment, you’ll use an equation to calculate an estimated RMR using one of the many formulas available. The two offered below are commonly cited.

Owen Equation

The Owen equation is the simplest. It uses body weight and sex only. (2)

You must know your body weight in kilograms (kg) to use the equation. To convert your body weight from pounds to kg, divide your body weight by 2.2.

Female
RMR = (7.18 × body weight in kg) + 795

Male
RMR = (10.2 × body weight in kg) + 879

Revised Harris-Benedict Equation

Regarded as one of the more reliable methods for estimating RMR, the Harris-Benedict equation (RHB) was recently updated in 2023 by Eleni Pavlidou and colleagues at the Department of Food Science and Nutrition at the University of the Aegean in Greece. (3)

The revised Harris-Benedict equation uses body weight, height, age, and sex to estimate RMR.

Female
RMR = 43 + (3.35 × weight in pounds) + (15.42 × height in inches) − (2.31 × age in years)

Male
RMR = 260 + (4.38 × weight in pounds) + (14.55 × height in inches) − (5.08 × age in years)

Inbody 270 Body Composition Analyzer

For those in my training program, we use an InBody 270 body composition analyzer to monitor body weight, muscle, fat, and water changes.

The InBody estimates RMR using your lean body mass and the Katch-McArdle equation (RMR = 370 + (21.6 x lean body mass in kg)).

The InBody is an accurate and convenient method for tracking body composition changes over time.

Which One is Best?

It’s important to note that these are estimates for whichever method you use. Each technique used will give you a different result.

Consider the chart below. Using the results from three InBody weigh-ins, we can compare estimated RMR using the three methods mentioned above.

As you can see, there can be quite a difference between methods. And there is no way to know which one is more accurate.

So, pick one. Any of the equations will help you get started.

Daily Calories

Once you have your estimated RMR, you want to factor in physical activity to calculate the calories you need to support your daily grind.

Again, there are many ways to estimate daily caloric needs. Some are more complicated than others.

This one is simple. Multiply your RMR by the activity factors below to determine your estimated range. (4)

Low  1.2
Moderate  1.4
High  1.6

For example, if your RMR is 1500 calories/day, then:

1500 x 1.2 = 1800
1500 x 1.4 = 2100
1500 x 1.6 = 2400

Your estimated daily burn rate is 1800–2400 calories/day.

Getting Started

If you’re determined to make dietary changes and need help, I encourage you to consult a registered dietician.

If you want to go at it on your own, you can try the following:

1. Use the formulas to estimate your daily calories and macros. Or, you can use the Google Sheets: RMR and Macros Calculator I created to save you time.
2. Download and print the form My Calories and Macros.
3. Enter your estimates for calories, protein, carbohydrates, and fat into the form to record your estimates.
4. Track your food for three days and enter those amounts into the form.
5. Compare what you eat to your estimates.
6. Decide whether making changes might benefit your health and fitness goals.

I just did this recently. Below is a snapshot of my form filled out.

Notice the discrepancy between what I eat over three days and the estimated ranges.

All of my actual amounts are outside the range of my estimate. I eat about two times more fat than the upper range and about 85% of the low end of the estimated carbohydrate.

Is what I’m currently eating working for me?

It seems to be. My recovery and mood are good, my energy for workouts is strong, and my body composition is where I want it to be.

Can it be improved?

Considering the numbers, I may see what effect reducing the fat and increasing the carbs has on my energy, mood, and performance.

If you decide to run your numbers and move to change your diet to support your health and fitness goals better, take your time and go easy on yourself if things don’t go as you planned.

There will be a struggle to alter established patterns of eating. Our eating habits affect not just our body composition and performance but also our mood and sense of self.

What’s more, mealtime is closely tied to your community. Meals with family and friends can sometimes pull us away from what we intended.

When your plans don’t go as intended, pay attention to what happens to your energy and mood. As best you can, simply observe. Then, review your health and fitness goals, make a plan, and reset your intent for the next time. In this way, we move forward toward our better selves.

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1. Thomas, Travis, Loise Burke, and Kelly Anne Erdman. “Nutrition and Athletic Performance.” Medicine & Science in Sports & Exercise 48, no. 3 (March 2016): 543–68.
2. Owen, Oe, E Kavle, Rs Owen, M Polansky, S Caprio, Ma Mozzoli, Zv Kendrick, Mc Bushman, and G Boden. “A Reappraisal of Caloric Requirements in Healthy Women.” The American Journal of Clinical Nutrition 44, no. 1 (July 1986): 1–19.
3. Pavlidou, Eleni, Sousana K. Papadopoulou, Kyriakos Seroglou, and Constantinos Giaginis. “Revised Harris–Benedict Equation: New Human Resting Metabolic Rate Equation.” Metabolites 13, no. 2 (January 28, 2023): 189.
4. National Research Council (US) Committee on Diet and Health. Diet and Health: Implications for Reducing Chronic Disease Risk. Washington (DC): National Academies Press (US); 1989. 6, Calories: Total Macronutrient Intake, Energy Expenditure, and Net Energy Stores.