Chapter 3: Making Real Choices

Chapter Introduction

You are 13 or 14. You learned in Grade 6 what a calorie is and how to add up a day on paper. You learned in Grade 7 how to read labels, calculate macronutrient breakdowns, and compare meals side by side. Now you are ready for the actual formula scientists use.

This chapter teaches you how to calculate, for your specific body, exactly how many calories you burn just being alive. It also teaches you how to add in your activity to get your total daily energy expenditure. Then it teaches you how those numbers combine with what you eat to determine, over time, what happens to your body.

This is the math that runs metabolic health. It is taught to medical students, to registered dietitians, to elite athletes' coaches. It uses the same equations you'll use if you ever become any of those things. You are old enough to learn it now. Your algebra skills can handle it.

The Bear is direct about why this matters. Most adults in this country do not know their own BMR. They do not know their TDEE. They eat whatever's in front of them and wonder why their body changes. Many of them gain weight slowly across decades because they were never taught the math that would have prevented it. The ultra-processed food industry has spent billions of dollars on foods specifically engineered to override your body's fullness signals — designed to make you eat more before you feel full. Researchers have demonstrated this in controlled trials [1]. The math is your defense.

Once you know your own BMR and TDEE, you have something most adults don't have: a tool to understand exactly what your body is doing and to make food decisions based on actual numbers, not feelings or marketing.

This chapter has four lessons. Lesson 1 teaches BMR — your basal metabolic rate, the calories your body burns just keeping you alive. Lesson 2 teaches the Mifflin-St Jeor equation, the formula doctors and dietitians use to calculate BMR. Lesson 3 teaches TDEE — your total daily energy expenditure, including activity. Lesson 4 ties everything together: energy balance, surplus and deficit, and what the math means for your life.

The end-of-chapter project is one week of tracking your actual food and activity, computing your daily energy balance, and reflecting on what the data shows.

Begin.

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Lesson 3.1: Basal Metabolic Rate — Your Body at Rest

Learning Objectives

By the end of this lesson, you will be able to:

• Define basal metabolic rate (BMR) and resting metabolic rate (RMR)
• Explain what your body does with calories at rest
• List the major organs and processes that consume calories at rest
• Recognize approximate BMR ranges for adolescents
• Understand why BMR varies by sex, body composition, age, and other factors

Key Terms

What BMR Actually Is

Your body burns calories every minute of every day — even when you are completely still. The total calories burned at complete rest, lying down, in a temperature-controlled room, after a full night's sleep and at least 12 hours since your last meal, is called basal metabolic rate, or BMR. This is the most precisely defined version of the number.

A close cousin is resting metabolic rate, or RMR. This is measured under slightly less strict conditions (you don't have to fast as long, the room can be at normal temperature). RMR and BMR are typically within a few percent of each other. In practical use — and in this chapter — the two are nearly interchangeable. The Bear will use the term BMR throughout.

BMR is what your body burns just to be alive. It is the cost of running a human body without doing anything else.

For an active 13- or 14-year-old, BMR is typically somewhere between 1,200 and 1,800 calories per day. That's a wide range because BMR depends on multiple factors you'll learn about in this lesson. But the typical floor is high enough that even a fully sedentary teen burns over 1,000 calories every day they exist — just for organs to keep running.

What Your Body Spends Calories On at Rest

Researchers using a technique called indirect calorimetry (which measures oxygen consumed and carbon dioxide produced at rest) have figured out roughly where the BMR calories go [2]. Approximate breakdown by organ system in an adult at rest:

• Brain: about 20% of BMR. Your brain weighs only about 2-3 pounds in an adult, but it consumes about a fifth of your basal energy use. It runs almost entirely on glucose. Growing brains (yours!) consume an even higher percentage.

• Liver: about 20% of BMR. The liver is one of the busiest organs. It processes nutrients, makes proteins, filters toxins, regulates blood sugar, makes bile, stores glycogen, and dozens of other jobs. The liver is metabolically expensive.

• Heart: about 8-10% of BMR. Your heart beats about 100,000 times a day in an adult. That work has a calorie cost.

• Kidneys: about 8% of BMR. Filtering blood, balancing electrolytes, producing urine — all energy-intensive.

• Skeletal muscle (at rest): about 20-25% of BMR. Even when you're not moving, your muscles are using energy. More muscle = more calories burned at rest.

• Everything else: about 15-20%. Bone marrow, gut, lungs, skin, fat tissue, the immune system, and other tissues collectively use the remainder.

Notice something important: muscle is a big driver of BMR. People with more muscle have higher BMR than people of the same weight with less muscle. This is one of the main reasons two kids of the same weight can have different BMR — one might be more muscular, one might have a different body composition.

Factors That Affect BMR

Several factors influence your BMR:

Body size. Bigger bodies have more cells and bigger organs. They burn more calories at rest. This is the single biggest driver — and it's why BMR equations need your weight and height.

Body composition. Muscle tissue burns more calories at rest than fat tissue. Two people of the same weight can have different BMR if one has more muscle.

Sex. Adult males typically have higher BMR than adult females of the same size, mostly because of differences in average body composition (more muscle, less fat). Before puberty, the difference is small.

Age. BMR per pound of body weight is actually highest in young children and gradually declines through life. This isn't because metabolism "slows down" mysteriously — researchers have shown that the main reason BMR per pound declines with age is loss of muscle mass and changes in organ activity [3]. As people age, they also tend to be less active.

Genetics. Some people have slightly faster or slower metabolisms than others of the same size and composition. The difference is usually small (a few percent), but it exists.

Hormones. Thyroid hormones regulate metabolic rate. People with thyroid disorders can have meaningfully different BMR. (This is a medical issue — if BMR seems very different from predicted, it's worth a conversation with a doctor.)

Growth. Growing bodies have higher metabolic rates per pound than fully-grown bodies. This is why teenagers can often eat large amounts without obvious weight changes — growth is using a lot of the surplus.

Temperature. Cold environments raise BMR (your body burns extra calories generating heat). Very hot environments can also raise BMR slightly.

Recent food. Eating raises metabolism for a few hours (the thermic effect of food). This is why BMR is measured after a fast.

Approximate BMR for Adolescents

To give you a feel for typical numbers, here are approximate BMR ranges based on age, sex, and weight. These are starting estimates — you'll calculate your own precisely in Lesson 3.2.

(Assuming average height for age, average body composition. Real numbers vary.)

Notice that these are just-being-alive numbers. Add activity on top, and total calories burned per day rise significantly. You'll see this in Lesson 3.3.

Lesson Check

1. What does BMR stand for, and what does it measure?
2. Approximately what percentage of BMR goes to the brain?
3. Why does more muscle mean higher BMR?
4. Name three factors that influence a person's BMR.
5. Why is BMR measured after a 12-hour fast?

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Lesson 3.2: The Mifflin-St Jeor Equation

Learning Objectives

By the end of this lesson, you will be able to:

• State the Mifflin-St Jeor equation for both sexes
• Calculate your own BMR using the equation
• Convert between metric and imperial units (pounds ↔ kg, inches ↔ cm)
• Recognize that the Mifflin-St Jeor equation is the current standard used by registered dietitians and doctors
• Understand the limitations of any predictive equation

Key Terms

The Equation

In 1990, Mark Mifflin, Sachiko St Jeor, and their colleagues published a study in the American Journal of Clinical Nutrition comparing several different BMR equations against actual measurements from 498 healthy people [4]. Their study established a new equation that consistently outperformed older formulas in accuracy. It is now the equation used by registered dietitians and many medical professionals as the standard estimate.

Here it is.

For males:

BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5

For females:

BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161

The only difference between the two equations is the constant at the end: +5 for males, −161 for females.

This is the actual formula. Not a rough estimate. Not a simplified version for kids. The formula used in clinical practice.

Converting Units

If you know your weight in pounds and your height in inches (which most American kids do), you need to convert before using the equation.

Weight: pounds to kilograms.

Weight in kg = Weight in pounds ÷ 2.205

Quick approximation: divide by 2.2.

Example: 110 lb ÷ 2.205 = 49.9 kg

Height: inches to centimeters.

Height in cm = Height in inches × 2.54

Example: 5 feet 4 inches = 64 inches × 2.54 = 162.6 cm

Step-by-Step Example

Let's compute BMR for an example student.

Student profile:

• Female
• 14 years old
• 5 feet 3 inches tall (63 inches)
• 115 pounds

Step 1: Convert units.

• Weight: 115 ÷ 2.205 = 52.2 kg
• Height: 63 × 2.54 = 160 cm

Step 2: Plug into the female equation.

BMR = (10 × 52.2) + (6.25 × 160) − (5 × 14) − 161
BMR = 522 + 1000 − 70 − 161
BMR = 1,291 calories per day

That's the BMR. About 1,300 calories per day just to keep this student's body alive at rest.

Let's do one more.

Student profile:

• Male
• 13 years old
• 5 feet 5 inches tall (65 inches)
• 130 pounds

Step 1: Convert.

• Weight: 130 ÷ 2.205 = 59.0 kg
• Height: 65 × 2.54 = 165 cm

Step 2: Plug into the male equation.

BMR = (10 × 59.0) + (6.25 × 165) − (5 × 13) + 5
BMR = 590 + 1031 − 65 + 5
BMR = 1,561 calories per day

About 1,560 calories per day at rest.

Now You Calculate Your Own

It's your turn. Get your most recent height and weight. Plug them in.

Step 1: Convert your weight to kilograms (lb ÷ 2.205). Step 2: Convert your height to centimeters (inches × 2.54). Step 3: Plug into the correct equation (male or female). Step 4: Do the arithmetic.

Write your answer at the top of your notebook. This is your BMR — the calories your body burns at rest. You will use this number in the next lesson.

Limits of Any Predictive Equation

The Mifflin-St Jeor equation is an estimate. It is the best general-population estimate available, but it is still an estimate.

Researchers have measured Mifflin-St Jeor's accuracy against direct measurement (in laboratory settings) and found it predicts BMR within about 10% for most people [5]. That's pretty good. But it's not perfect.

Reasons the equation might be off for an individual:

• Body composition. The equation doesn't know whether your weight is mostly muscle or mostly fat. A very muscular kid will have a higher actual BMR than the equation predicts. A kid with more body fat may have a slightly lower actual BMR.
• Genetics and individual variation. Some people just have slightly higher or lower metabolisms than the average for their size.
• Growth status. The equation was built from adults. Growing adolescents may burn somewhat more than the equation predicts because growth itself uses calories.
• Medical conditions. Thyroid disorders, certain medications, and other conditions can shift actual BMR substantially.

For your purposes, the Mifflin-St Jeor number is a good starting point. If you track for a few weeks and the math doesn't match what's happening to your body, you can adjust. But the equation is the right tool to start with.

Lesson Check

1. Write out the Mifflin-St Jeor equation for males. For females. What's the only difference?
2. Convert 145 pounds to kilograms. Convert 5 feet 7 inches to centimeters.
3. Calculate the BMR for a 14-year-old female who is 5 feet 2 inches and 105 pounds. Show your work.
4. What does it mean that the equation predicts BMR "within about 10%"? Why isn't it exact?
5. Why does the Bear say this is the actual formula used by registered dietitians and not just a simplified version?

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Lesson 3.3: Total Daily Energy Expenditure (TDEE)

Learning Objectives

By the end of this lesson, you will be able to:

• Define Total Daily Energy Expenditure (TDEE)
• List the activity-factor multipliers used to calculate TDEE
• Honestly estimate your own activity level
• Calculate your own TDEE using BMR × activity factor
• Recognize the limits of activity-factor estimates and how to refine them with actual tracking

Key Terms

The TDEE Formula

Your total daily energy expenditure is simple to calculate once you have BMR. You multiply BMR by an activity factor — a multiplier that estimates how much your activity adds on top of resting.

TDEE = BMR × Activity Factor

The activity factors come from research on energy expenditure in different lifestyle categories [6]. They have been validated against measurements using the gold-standard doubly-labeled-water technique, which tracks actual energy use over multiple days.

The Five Activity Factors

For most middle schoolers and high schoolers, the right multiplier is somewhere between 1.375 and 1.55. Be honest about your real activity level. Most people overestimate themselves. Talking to friends at recess is not "moderately active." Walking the dog for 15 minutes is not "very active." Reserve the higher numbers for kids who genuinely train hard most days of the week.

Calculating TDEE — The Examples

Let's bring back the examples from Lesson 3.2 and add their activity levels.

Example 1 — 14-year-old female, 115 lb, 5'3", BMR = 1,291 cal/day.

She walks to school (20 minutes round trip), takes PE three times a week, and plays soccer twice a week. That puts her in Moderately Active.

TDEE = 1,291 × 1.55 = 2,001 calories per day

About 2,000 calories per day total energy use.

Example 2 — 13-year-old male, 130 lb, 5'5", BMR = 1,561 cal/day.

He walks home from school (15 minutes), has PE twice a week, and plays casual basketball at recess but no organized sport. Lightly Active.

TDEE = 1,561 × 1.375 = 2,146 calories per day

About 2,150 calories per day total.

Calculate Your Own TDEE

Your turn. Take the BMR you calculated in Lesson 3.2. Pick the activity multiplier that most honestly describes your real life.

TDEE = Your BMR × Your Activity Factor

Write the result next to your BMR in your notebook. This is your estimated total daily calorie burn — the number of calories your body uses on a typical day in your typical life.

Refining Your TDEE Over Time

The activity-factor method is a starting estimate. To refine it, researchers and dietitians recommend doing what's called metabolic ward observation — tracking food intake and weight changes over weeks to back-calculate true TDEE. You can do a simpler version of this:

1. Track food intake carefully for two weeks (this chapter's end-of-chapter project gets you started).

2. Track your weight at the same time each morning, on the same scale, for two weeks.

3. If your weight is stable, your average daily intake during those two weeks is approximately your true TDEE.

4. If you gained weight, your TDEE is somewhat lower than your average intake (you were in surplus).

5. If you lost weight, your TDEE is somewhat higher than your average intake (you were in deficit).

This method gives you a real-life calibration of the formula. Over a few months of casual tracking, you can refine the equation's prediction to your specific body within a few percent.

For most teens, this level of precision isn't necessary. The starting estimate (BMR × activity factor) gets you within about 10-15% — close enough to make useful decisions. The Bear wants you to know the method exists so you can use it if you want to.

A Note on Tracking and Pressure

The Bear teaches the math directly. The Bear also wants to be straight with you about one thing: tracking is a tool, not a moral activity. People who track their food and activity intermittently to understand their bodies tend to do well. People who track obsessively, every meal every day, sometimes end up in unhealthy relationships with food.

The right use of tracking, for most teens: do it for a focused period (a week, a few weeks) to learn what your numbers actually look like. Then stop tracking and apply what you learned. Come back to tracking when something changes (you're an athlete heading into a heavy training season, you're growing fast and want to make sure you're eating enough, etc.).

You don't need to track every day for the rest of your life. You need to know the math so you can do it when it helps.

Lesson Check

1. What does TDEE stand for, and what does it measure?
2. What is the formula for calculating TDEE?
3. What activity factor would you use for a kid who walks to school daily but doesn't do organized sports?
4. Calculate the TDEE for a kid whose BMR is 1,500 and who is very active.
5. Why is the activity-factor estimate considered a starting estimate that can be refined over time?

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Lesson 3.4: Energy Balance — The Picture That Runs Your Body

Learning Objectives

By the end of this lesson, you will be able to:

• Apply the energy balance equation (calories in − TDEE = energy balance) to real-life eating patterns
• Calculate weekly and monthly energy balance from daily numbers
• Estimate how surplus or deficit over time translates to body changes
• Understand the role of ultra-processed foods in driving chronic calorie surplus
• Take ownership of your metabolic health using the math

Key Terms

Putting It All Together

You now have everything you need to understand metabolic health at the level of medical professionals.

Energy Balance = Calories In − TDEE

That's the whole picture.

• Calories In: from Grades 6 and 7. Add up the food you eat using calorie counts.
• TDEE: from this chapter. BMR (Mifflin-St Jeor) × Activity Factor.
• Subtract one from the other. That's your energy balance for the day.

Surplus (positive number): Body stores the extra. Short-term, your body fills its glycogen stores. Long-term, it stores body fat. During growth, it builds new tissue.

Deficit (negative number): Body draws on stored energy to make up the gap. Glycogen first (short-term), then body fat (long-term).

Maintenance (zero): Energy stores stay stable.

Daily, Weekly, and Monthly Math

A single day's energy balance is just one data point. The interesting numbers are the patterns across weeks and months.

Weekly: Add up the daily energy balances across 7 days. Or use averages.

Example: A kid's TDEE is 2,000 cal/day. The kid averages 2,200 cal of food intake per day. Daily surplus: 200. Weekly surplus: 200 × 7 = 1,400 calories per week.

Monthly: Multiply daily surplus by 30.

In the example above: 200 × 30 = 6,000 calories per month.

The rough rule of thumb: historically, dietitians have used the approximation that 3,500 calories of surplus ≈ 1 pound of body fat gained, and 3,500 calories of deficit ≈ 1 pound lost. Newer research has shown this isn't perfectly accurate — the body adapts to energy changes in complex ways — but the number is still useful as a rough estimate for short-term thinking [7].

Using the rough rule: 6,000 calories/month ÷ 3,500 = 1.7 pounds gained per month.

Over a year? About 20 pounds.

For an adult who isn't growing, 20 pounds per year from a consistent 200-calorie daily surplus is real weight gain. For a growing teen, much of that surplus goes into new tissue — bone, muscle, brain — and the body weight gain reflects actual growth, not fat gain.

The math doesn't care who you are. The math just shows you what happens.

How a 200-Calorie Daily Surplus Sneaks In

Two hundred calories per day is not a lot. Let's see how easily it can happen:

• A 20-oz soda instead of water: 240 calories. There's the surplus.
• An extra handful of chips at lunch: 150 calories.
• A second cookie at dinner: 80 calories.
• Two extra tablespoons of salad dressing: 140 calories.
• A bag of "single-serve" trail mix that's actually 2 servings: 200 extra calories beyond what you thought.

Any one of these, every day, for a year, equals real weight gain in someone who is no longer growing.

The Bear is not saying these foods are bad. The Bear is saying: the math is real. Most people overshoot by 100-300 calories a day across years of their adult life. They don't notice. They wonder why they slowly gain weight. They never connect it to the math because no one taught them the math.

Why Ultra-Processed Foods Make Surplus So Easy

In Grades 6 and 7, you learned about ultra-processed foods — industrially formulated products with long ingredient lists, designed for shelf life, cost, and taste. Here's why they're so important to the energy balance discussion.

Researchers have run controlled experiments on this. In one well-known 2019 study by Kevin Hall and colleagues at the U.S. National Institutes of Health, participants were given access to all-they-could-eat meals. Some were given only ultra-processed foods. Some were given only minimally processed foods. The total calories available, macronutrient ratios, sugar, salt, and fat were carefully matched between the two diets. The only difference was processing level [1].

The result: people eating the ultra-processed diet ate, on average, about 500 calories more per day than people eating the minimally processed diet, without realizing they were eating more. And the ultra-processed eaters gained weight; the minimally processed eaters lost weight. Same calorie availability. Same macros on paper. Different outcomes because of how the food affected fullness signals.

This is the central finding the Bear wants you to understand. Ultra-processed foods are engineered to be calorie-dense and to override the body's natural fullness signals. Food scientists hired by these companies tune the precise ratios of salt, sugar, fat, and texture to maximize how much you'll eat before your body says "stop." That's not the Bear being conspiratorial. That's how the food industry operates. It's documented in industry papers, in former-executive memoirs, in research on food engineering [8, 9].

The result: even people who think they're eating a reasonable amount can end up in chronic calorie surplus if most of their food is ultra-processed. The math seems to "lie" — they don't feel like they're overeating, but they keep gaining weight. The math isn't lying. The fullness signal is being hijacked.

Obesity rates in the United States went from about 13% of adults in 1960 to about 42% by 2020 [10]. The rise tracks closely with the rise in ultra-processed food consumption. People are not weaker-willed than their grandparents were. The food environment is engineered differently.

What the Math Lets You Do

Knowing this lets you take ownership in a way that most adults cannot. You have your BMR. You have your TDEE. You know how to read labels and calculate calories. You know that ultra-processed foods are designed to override fullness.

You can:

1. Build meals around whole foods so your fullness signals work normally.
2. Spot the surplus drivers — soda, oversized portions, calorie-dense snacks — and decide which ones you want and which ones you don't.
3. Track for a week or two when something feels off and find out what your numbers actually are.
4. Adjust intake during growth spurts to make sure you're getting enough.
5. Reduce intake during low-activity periods (sick days, winter holidays, etc.) without panicking about hunger.
6. Recognize when a food is calorie-dense and decide consciously how much to have rather than letting marketing or packaging make the call.

This is metabolic literacy. Most adults never get it. You can have it at 14.

Growing Bodies Need Surplus

One more critical point: growing teenagers generally need to be in positive energy balance, not maintenance and definitely not deficit.

Your body is building new bone, new muscle, new brain, new organs. All of that construction requires energy on top of just keeping you alive. A reasonable surplus during growth years is healthy and expected. The exact size varies — some weeks of fast growth need a lot of surplus; quiet weeks need less.

The math you learned doesn't tell you to eat less. It tells you to know what's happening. For a growing teen, the most common failure mode is under-eating — eating fewer calories than the body needs to build itself. Under-eating during adolescence has documented consequences: stunted growth, weakened bone development, hormonal disruption, impaired brain development, mood and energy problems [11, 12]. The Bear is not in the business of pushing teens toward deficit.

If you do the math and find you're eating 500-1,000 calories below your TDEE every day, and you're still growing, you may not be eating enough. Talk to a parent and a doctor.

Lesson Check

1. Write out the energy balance equation. What does each term mean?
2. If a kid's TDEE is 2,300 cal/day and they eat 2,100 cal/day, what's their daily energy balance? Weekly?
3. Explain the "3,500 calorie rule" and its limitations.
4. According to the Hall et al. 2019 study, how many extra calories did people eating ultra-processed foods consume compared to minimally processed foods?
5. Why does the Bear say growing teens generally need to be in positive energy balance?

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End-of-Chapter Project: One Week of Real Data

This is a major project. You will:

1. Calculate your BMR and TDEE using the Mifflin-St Jeor equation.
2. Track your food and activity for one full week (7 consecutive days).
3. Compute your daily energy balance each day.
4. Average across the week.
5. Reflect on what the data reveals.

Materials

• Notebook or spreadsheet
• A scale (kitchen scale optional, bathroom scale required)
• Calorie reference tables (from Grades 6, 7, and 8) plus USDA FoodData Central or a free food-tracking app for foods you don't know
• A timer or watch
• Adult supervision for the math at minimum

Procedure

Day 0 — Setup.

1. Weigh yourself in the morning. Write down weight in pounds. Convert to kg.
2. Measure your height. Convert to cm.
3. Note your age.
4. Calculate BMR using the Mifflin-St Jeor equation.
5. Pick your activity factor honestly. Calculate TDEE.
6. Write BMR and TDEE at the top of your notebook. These are your reference numbers.

Days 1-7 — Track.

Every day, write down:

• All food and drink, with calorie estimates (use Grade 6 chart, Grade 7 label math, USDA database, or a free app)
• All meaningful activity (walking, sports, climbing, biking, etc.) with minutes and calories burned above resting (Grade 6 table)
• Daily totals: Total Calories In, Total Activity Calories above resting

Each day's energy balance:

Total Energy Out = BMR + Activity Calories Above Resting
Daily Energy Balance = Calories In − Total Energy Out

(Note: you can also use TDEE directly if your day's activity matches your activity-factor estimate, but tracking actual activity gives a more accurate daily number.)

Day 8 — Analysis and Reflection.

1. Add up your 7-day Total Calories In.
2. Add up your 7-day Total Energy Out.
3. Calculate weekly energy balance: (sum of in) − (sum of out).
4. Calculate average daily energy balance: weekly balance ÷ 7.
5. Weigh yourself on the same scale at the same time as Day 0. Compare to Day 0 weight.
6. Write a one-paragraph reflection (8-12 sentences) covering:
   • Your weekly energy balance
   • Whether your weight changed in line with what the math predicted
   • Which single foods or activities had the biggest impact on your daily numbers
   • Anything that surprised you about your data
   • One thing you would do differently if you tracked again next month
   • Whether you think you're eating enough for your current growth and activity, eating too much, or eating about right

Submission

Turn in:

• Your BMR/TDEE calculation
• Your 7 daily logs
• Your weekly totals
• Your reflection paragraph

Total writing: approximately 300-500 words plus the data tables.

Note on Doing This Well

This is the most ambitious math project in the Coach Food middle school sequence. Take it seriously. Be honest with yourself about your food and activity — the data is only useful if it reflects your real life.

Some practical tips:

• Track food right after eating. Memory degrades fast.
• Use the same calorie sources consistently. Variation in different databases can cause confusion.
• Don't change your eating because you're tracking. The point is to learn what your normal looks like.
• Use approximate numbers when you have to. A calorie estimate that's within 20% is still useful data.
• If a day goes off the rails (you eat at a party and don't track), note it and move on.

This is the kind of data work that makes you a serious thinker about your own metabolic health. You are doing it at 14 instead of waiting until 40.

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Vocabulary Review

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Chapter Quiz

Multiple Choice (10 questions, 2 points each)

1. BMR stands for:

A) Body Muscle Ratio B) Basal Metabolic Rate — calories burned at complete rest C) Body Mass Reading D) Basic Metabolic Reset

2. Approximately what percentage of BMR is consumed by the brain?

A) 5% B) 10% C) 20% D) 50%

3. The Mifflin-St Jeor equation for females is:

A) BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161 B) BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5 C) BMR = (weight in lb) × (height in inches) D) BMR = (age × 100) + activity

4. To convert pounds to kilograms, you:

A) Multiply by 2.205 B) Divide by 2.205 C) Add 100 D) Multiply by 10

5. A 13-year-old male weighs 50 kg and is 165 cm tall. Calculate his BMR using Mifflin-St Jeor.

A) About 1,000 B) About 1,500 C) About 2,000 D) About 2,500

6. To calculate TDEE from BMR:

A) Add 500 calories B) Multiply BMR by an activity factor between 1.2 and 1.9 C) Subtract 200 calories D) Multiply by your age

7. A kid is "lightly active" — walks to school daily but doesn't do organized sports. The activity factor is:

A) 1.2 B) 1.375 C) 1.55 D) 1.9

8. A kid's TDEE is 2,200 cal/day. They eat 2,400 cal/day. What's their daily energy balance?

A) −200 (deficit) B) +200 (surplus) C) 0 (maintenance) D) +400

9. The 2019 Hall et al. study at the NIH found that people eating ultra-processed foods consumed approximately how many more calories per day than people eating minimally processed foods?

A) 100 B) 250 C) 500 D) 1,500

10. Why does the Bear say growing teens generally need to be in positive energy balance, not deficit?

A) Because the math doesn't apply to teens B) Because growing bodies are building new bone, muscle, brain, and organs, all of which require energy on top of just staying alive C) Because deficits are forbidden D) Because BMR is unreliable in teens

Short Answer (5 questions, 4 points each)

11. Calculate your own BMR using the Mifflin-St Jeor equation. Show your unit conversions and your math.

12. Take your BMR from question 11. Multiply by an activity factor that honestly describes your activity level. What is your TDEE? Show your math and justify your activity-factor choice.

13. A 14-year-old male is 5'6" (167 cm) and 140 lb (63.5 kg). Calculate his BMR using Mifflin-St Jeor. Then calculate his TDEE assuming he's moderately active.

14. Explain in 3-4 sentences what the Hall et al. 2019 ultra-processed food study showed, and why the finding matters for understanding why so many people gain weight in modern food environments.

15. A kid's TDEE is 2,400 calories. They average 2,500 calories per day for a month. (a) What is their daily surplus? (b) What is their monthly surplus? (c) Using the approximate 3,500-calorie rule, about how much would their body change in a month if they aren't growing significantly? Show your math.

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Teacher's Guide

Pacing Recommendations

Lesson Check Answers

Lesson 3.1:

1. BMR = Basal Metabolic Rate. The number of calories your body burns at complete rest under strict laboratory conditions. 2. About 20% of BMR is consumed by the brain. 3. Muscle tissue burns more calories at rest than fat tissue; people with more muscle have higher BMR than people of the same weight with less muscle. 4. Any three of: body size, body composition, sex, age, genetics, hormones, growth status, temperature, recent food intake. 5. So the measurement isn't affected by the thermic effect of food (calories burned digesting recent meals), which can elevate metabolic rate for several hours after eating.

Lesson 3.2:

1. Male: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5. Female: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161. The only difference is the final constant: +5 for males, −161 for females. 2. 145 ÷ 2.205 = 65.8 kg. 5'7" = 67 inches × 2.54 = 170.2 cm. 3. 105 ÷ 2.205 = 47.6 kg. 5'2" = 62 inches × 2.54 = 157.5 cm. Female equation: BMR = (10 × 47.6) + (6.25 × 157.5) − (5 × 14) − 161 = 476 + 984 − 70 − 161 = 1,229 cal/day. 4. "Within about 10%" means that for most people, the actual BMR (measured in a lab) is within roughly 10% of what the equation predicts. It's an estimate because individual factors like exact body composition, genetics, hormonal status, and individual variation aren't captured in the formula. 5. Because it is the actual formula. The Bear is teaching the medical-grade tool, not a simplified kid version. Once students know this equation, they have the same tool a registered dietitian uses.

Lesson 3.3:

1. TDEE = Total Daily Energy Expenditure. The total calories your body burns per day including BMR plus activity. 2. TDEE = BMR × Activity Factor. 3. Lightly Active (1.375). 4. 1,500 × 1.725 = 2,587 cal/day. 5. Because the activity factor is a rough multiplier based on lifestyle category. Different people in the same category can have somewhat different actual energy expenditures. Tracking food intake and weight changes over a couple of weeks lets you back-calculate your real TDEE and refine the equation's estimate for your specific body.

Lesson 3.4:

1. Energy Balance = Calories In − TDEE. Calories In is total food and drink consumed. TDEE is total energy expenditure (BMR + activity). Energy Balance is the difference: positive = surplus, negative = deficit. 2. Daily: 2,100 − 2,300 = −200 cal (deficit). Weekly: −200 × 7 = −1,400 cal. 3. The rough rule of thumb is that 3,500 calories of surplus or deficit equals about 1 pound of body fat. The rule oversimplifies because the body adapts metabolically to energy changes; in reality the relationship is more dynamic. But it's still useful as a quick estimate for short-term thinking. 4. About 500 extra calories per day. They ate this much more without realizing it because ultra-processed foods are engineered to override natural fullness signals. The matched-macro design of the study showed that processing level itself, not macronutrient ratios, was the driver. 5. Because growing bodies are building new bone, muscle, brain, and organs — all of which need energy beyond just keeping the body alive. Deficits during adolescence can stunt growth, weaken bones, and disrupt hormones. Most teens should be in modest positive balance most of the time.

Quiz Answer Key

Multiple Choice: 1.B 2.C 3.A 4.B 5.B (10×50 + 6.25×165 − 5×13 + 5 = 500 + 1,031.25 − 65 + 5 = 1,471 ≈ "about 1,500") 6.B 7.B 8.B 9.C 10.B

Short Answer (sample target responses):

1. Student-specific. Should show: weight conversion (lb ÷ 2.205 = kg), height conversion (inches × 2.54 = cm), correct equation for male or female, and arithmetic.

2. Student-specific. Should multiply their BMR by an activity factor between 1.2 and 1.9 with a brief justification (e.g., "I walk to school but don't play organized sports, so I picked Lightly Active = 1.375").

3. Male, 14 years old. kg = 63.5. cm = 167. BMR = (10 × 63.5) + (6.25 × 167) − (5 × 14) + 5 = 635 + 1,043.75 − 70 + 5 = 1,614 cal/day. TDEE (moderately active) = 1,614 × 1.55 = 2,502 cal/day.

4. The Hall et al. 2019 study found that when people had unrestricted access to either ultra-processed or minimally processed meals (matched for available calories, macros, sugar, salt, and fat), the ultra-processed group ate about 500 extra calories per day and gained weight, while the minimally processed group lost weight. The finding shows that processing level itself, independent of macro ratios, drives overeating. This matters because most weight gain in modern populations isn't a willpower failure — it's the food environment overriding natural fullness signals through engineered foods.

5. (a) Daily surplus: 2,500 − 2,400 = +100 cal. (b) Monthly surplus: 100 × 30 = +3,000 cal. (c) Using the 3,500-cal rule: 3,000 ÷ 3,500 = 0.86 pounds, so about 0.85-1 pound of body weight gain over the month (assuming no growth offsetting it).

Discussion Prompts

1. The Bear says most adults in this country don't know their own BMR or TDEE. Why do you think this knowledge isn't taught more widely?
2. You now have the same metabolic math tools that a registered dietitian uses. What would you do with this knowledge that you couldn't do a year ago?
3. The Hall ultra-processed food study showed that processing level drives overeating, not willpower failure. How does this change how you think about obesity in your community?
4. What's the biggest difference between knowing TDEE and not knowing it? When might it matter most?
5. Some adults track every calorie every day for years. Some never track at all. What's the right balance for you? Why?
6. The 3,500-calorie rule is a rough approximation. Why might researchers say the body is more dynamic than that? What other factors might be at play?
7. The chapter says growing teens generally need to be in positive energy balance. How does that compare to the way some adults talk about eating?
8. What's the most useful single number from this chapter that you'll remember in 10 years? Why?

Common Student Questions

• "Should I track every day?" No. Track for focused periods (a week, a few weeks) to learn what your numbers are. Then stop and apply what you learned. Track again when something changes (new sport, growth spurt, illness recovery).
• "What if my equation seems off — I eat what it says but my weight is changing?" Equations are estimates. Track for two weeks with stable food, see how weight responds, and adjust your TDEE estimate up or down by the implied amount.
• "Is my BMR going to slow down as I get older?" Per-pound BMR declines slowly through life, mostly due to muscle loss and reduced organ activity. Staying active and maintaining muscle through resistance training can slow this substantially. Grade 9 Coach Move will go deeper.
• "What if I'm trying to gain muscle?" Generally requires a small surplus (a few hundred extra calories per day above TDEE) plus adequate protein and resistance training. Grade 10 Coach Food covers fueling for sport in more depth.
• "What if I'm trying to lose weight?" This is a conversation for your parent and a doctor, especially at your age. Growing kids generally should not aim for deficit. If a doctor has recommended weight management, they will work with a registered dietitian to design a safe plan.
• "Why don't food labels include things like fiber's lower calorie absorption?" They do, partially — current FDA rules account for soluble fiber. But labels are still approximations. Your calculated total from the macro math will typically be within 5-10% of the label's stated calories.

Parent Communication Template

Dear Parents,

This week your student begins Chapter 3 of the Coach Food middle school curriculum — Making Real Choices. This chapter introduces the Mifflin-St Jeor equation and full energy balance literacy.

What the chapter covers:

• BMR (Basal Metabolic Rate) — calories burned at rest
• The Mifflin-St Jeor equation, the standard formula used by registered dietitians and doctors
• TDEE (Total Daily Energy Expenditure) — BMR multiplied by an activity factor
• Energy balance — calories in minus TDEE
• The relationship between ultra-processed foods and chronic calorie surplus

This is algebra-level math — appropriate for Grade 8. Students calculate their own BMR and TDEE.

The end-of-chapter project asks students to track their food and activity for one week and compute daily energy balance. This is the only sustained tracking exercise in the middle school curriculum. The Bear teaches students that tracking is a tool to use intermittently for learning, not a daily lifelong practice.

The chapter is direct with students about the role of ultra-processed foods in driving chronic calorie surplus in American adults. The 2019 NIH study by Hall and colleagues is cited as the central evidence. Students learn that obesity at population scale is not primarily a willpower problem — it's a food environment problem — and that knowing the math is how individuals take ownership of their own metabolic health.

The Bear explicitly teaches that growing teens generally need to be in positive energy balance. The chapter discusses the documented risks of under-eating during adolescence (stunted growth, weakened bones, hormonal disruption, brain development issues). If your student calculates a substantial deficit and is still growing, please consult your healthcare provider.

If you have any questions, please reach out to your student's teacher.

Warmly, The CryoCove Curriculum Team

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Illustration Briefs

Lesson 3.1 — Where BMR Calories Go Placement: After "What Your Body Spends Calories On at Rest." Scene: A simple pie chart showing approximate BMR distribution by organ system: Brain (20%), Liver (20%), Muscle (20%), Heart (10%), Kidneys (8%), Other (22%). Each slice has a small icon (brain, liver, muscle, heart, kidney). Coach Food (Bear) stands next to the chart with one paw resting on the brain slice. Mood: clean, infographic-style, like a textbook diagram. Aspect ratio: 4:3 print, 16:9 web.

Lesson 3.2 — The Equation on the Whiteboard Placement: After "The Equation." Scene: A classroom whiteboard or chalkboard showing the Mifflin-St Jeor equations written out clearly: "MALE: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5" and below "FEMALE: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161." The "+5" and "−161" differences highlighted in coral. Coach Food (Bear) stands next to the board with chalk in one paw, like a math teacher mid-lesson. Mood: instructional, like a real math class. Aspect ratio: 16:9 web.

Lesson 3.3 — Activity-Factor Ladder Placement: After "The Five Activity Factors." Scene: A vertical ladder or staircase with five steps. Each step labeled with an activity-factor category and multiplier: Sedentary 1.2 (kid on couch), Lightly Active 1.375 (kid walking), Moderately Active 1.55 (kid playing sport), Very Active 1.725 (kid sprinting), Extra Active 1.9 (kid in heavy training). A line marked "where most middle schoolers fit" between Lightly Active and Moderately Active. Coach Food (Bear) stands at the base of the ladder pointing at the middle. Aspect ratio: 4:3 print.

Lesson 3.4 — The Ultra-Processed Food Effect Placement: After "Why Ultra-Processed Foods Make Surplus So Easy." Scene: A bar chart showing the Hall 2019 study results — two bars side by side, "Minimally Processed Diet" at about 2,500 calories/day vs "Ultra-Processed Diet" at about 3,000 calories/day. Both bars labeled "same available calories, matched macros." A "+500 cal/day" arrow between them. Below the chart, a small note: "Same access. Same calories on paper. People ate 500 more on the ultra-processed diet." Coach Food (Bear) stands to the side with a measured expression. Aspect ratio: 16:9 web.

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Citations

1. Hall, K. D., Ayuketah, A., Brychta, R., Cai, H., Cassimatis, T., Chen, K. Y., Chung, S. T., Costa, E., Courville, A., Darcey, V., Fletcher, L. A., Forde, C. G., Gharib, A. M., Guo, J., Howard, R., Joseph, P. V., McGehee, S., Ouwerkerk, R., Raisinger, K., … Zhou, M. (2019). Ultra-processed diets cause excess calorie intake and weight gain: an inpatient randomized controlled trial of ad libitum food intake. Cell Metabolism, 30(1), 67-77.

2. Wang, Z., Heshka, S., Heymsfield, S. B., Shen, W., & Gallagher, D. (2005). A cellular-level approach to predicting resting energy expenditure across the adult years. American Journal of Clinical Nutrition, 81(4), 799-806.

3. Pontzer, H., Yamada, Y., Sagayama, H., Ainslie, P. N., Andersen, L. F., Anderson, L. J., Arab, L., Baddou, I., Bedu-Addo, K., Blaak, E. E., Blanc, S., Bonomi, A. G., Bouten, C. V. C., Bovet, P., Buchowski, M. S., Butte, N. F., Camps, S. G., Close, G. L., Cooper, J. A., … IAEA DLW Database Consortium. (2021). Daily energy expenditure through the human life course. Science, 373(6556), 808-812.

4. Mifflin, M. D., St Jeor, S. T., Hill, L. A., Scott, B. J., Daugherty, S. A., & Koh, Y. O. (1990). A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 51(2), 241-247.

5. Frankenfield, D., Roth-Yousey, L., & Compher, C. (2005). Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association, 105(5), 775-789.

6. Institute of Medicine. (2005). Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. National Academies Press.

7. Hall, K. D., Heymsfield, S. B., Kemnitz, J. W., Klein, S., Schoeller, D. A., & Speakman, J. R. (2012). Energy balance and its components: implications for body weight regulation. American Journal of Clinical Nutrition, 95(4), 989-994.

8. Moss, M. (2013). Salt Sugar Fat: How the Food Giants Hooked Us. Random House.

9. Monteiro, C. A., Cannon, G., Levy, R. B., Moubarac, J. C., Louzada, M. L., Rauber, F., Khandpur, N., Cediel, G., Neri, D., Martinez-Steele, E., Baraldi, L. G., & Jaime, P. C. (2019). Ultra-processed foods: what they are and how to identify them. Public Health Nutrition, 22(5), 936-941.

10. Stierman, B., Afful, J., Carroll, M. D., Chen, T. C., Davy, O., Fink, S., Fryar, C. D., Gu, Q., Hales, C. M., Hughes, J. P., Ostchega, Y., Storandt, R. J., & Akinbami, L. J. (2021). National Health and Nutrition Examination Survey 2017-March 2020 Prepandemic Data Files. National Center for Health Statistics.

11. Statuta, S. M., Asif, I. M., & Drezner, J. A. (2017). Relative energy deficiency in sport (RED-S). British Journal of Sports Medicine, 51(21), 1570-1571.

12. Mountjoy, M., Sundgot-Borgen, J., Burke, L., Carter, S., Constantini, N., Lebrun, C., Meyer, N., Sherman, R., Steffen, K., Budgett, R., & Ljungqvist, A. (2014). The IOC consensus statement: beyond the Female Athlete Triad — Relative Energy Deficiency in Sport (RED-S). British Journal of Sports Medicine, 48(7), 491-497.

13. Westerterp, K. R. (2017). Doubly labelled water assessment of energy expenditure: principle, practice, and promise. European Journal of Applied Physiology, 117(7), 1277-1285.

14. Ludwig, D. S., & Friedman, M. I. (2014). Increasing adiposity: consequence or cause of overeating? JAMA, 311(21), 2167-2168.