What is BMR and Why Does It Matter?

BMR Explained Simply

Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — just to stay alive. If you laid in bed all day doing absolutely nothing, your BMR is the energy required to:

• Keep your heart beating
• Maintain breathing
• Regulate body temperature
• Support brain function
• Repair cells
• Keep organs functioning

BMR vs. TDEE: What's the Difference?

These terms are often confused. Here's the breakdown:

• BMR — Calories burned at complete rest (just being alive)
• TDEE — Total Daily Energy Expenditure = BMR + activity + digestion

TDEE includes everything: your BMR, plus walking around, exercise, digesting food, and all daily activities. TDEE is what you use to calculate your calorie deficit.

How to Calculate Your BMR

The most common formula is the Mifflin-St Jeor equation, considered the most accurate:

Or skip the math — use our free BMR calculator to get your number instantly.

Factors That Affect Your BMR

1. Muscle Mass (Biggest Factor)

Muscle burns more calories at rest than fat. More muscle = higher BMR. This is why strength training is so powerful for weight management.

2. Age

BMR decreases about 1-2% per decade after age 20. This is largely due to muscle loss (sarcopenia), which can be slowed with resistance training.

3. Sex

Men typically have higher BMRs than women due to greater muscle mass and larger body size on average.

4. Body Size

Larger bodies burn more calories. As you lose weight, your BMR decreases — this is why weight loss can stall.

5. Genetics

Some people are born with faster metabolisms. This variation can be 200-300 calories/day between individuals of similar size.

6. Hormones

Thyroid hormones significantly impact metabolism. Hypothyroidism can lower BMR by 10-15%.

Why BMR Matters for Weight Loss

1. Setting Your Calorie Floor

Most experts recommend never eating below your BMR for extended periods. Your body needs those calories for basic survival functions. Chronic under-eating leads to muscle loss, hormonal disruption, and metabolic adaptation.

2. Understanding Metabolic Adaptation

When you diet, your BMR can decrease slightly as your body adapts to less food. This is partly why weight loss plateaus happen. Knowing your baseline helps you adjust expectations.

3. Building Sustainable Deficits

Understanding BMR helps you create deficits that are aggressive enough to see results, but sustainable enough to maintain. The sweet spot is typically 20-25% below TDEE (not BMR).

Can You Increase Your BMR?

Yes, but the options are limited:

• Build muscle — Most effective long-term strategy. Each pound of muscle burns ~6 cal/day at rest (fat burns ~2 cal)
• Eat enough protein — Has highest thermic effect (burns ~25% of calories digesting)
• Don't crash diet — Severe restriction lowers BMR
• Stay active — While not BMR directly, NEAT significantly impacts total burn
• Get enough sleep — Sleep deprivation can lower BMR
• Manage stress — Chronic stress affects hormones that regulate metabolism

Common BMR Myths

1. "Eating breakfast boosts metabolism" — Meal timing has minimal effect on BMR
2. "Certain foods speed up metabolism" — Effects are tiny (green tea, spicy food = ~50 cal/day max)
3. "Starvation mode destroys metabolism" — Metabolic adaptation is real but modest (10-15%)
4. "Frequent meals boost metabolism" — Total calories matter, not meal frequency