# Why BMI misclassifies athletes

**BMI 29.2 (Overweight). Daily energy need is somewhere between 3859 and 4397 kcal — the formulas disagree by 283 kcal before the activity factor is even applied.**

> These are population-level estimates from formulas fitted to population averages. They are not medical advice and know nothing about your health, medication, pregnancy, or history. BMI in particular is not a measure of health. Talk to a clinician or a registered dietitian before acting on any of it.

## Input

- Height: 185.0 cm (6' 1")
- Weight: 100.0 kg (220.5 lb (15st 10lb))
- male, age 26, extremely active
- Body fat: 10%

## BMI

**29.2** — Overweight

By the WHO cutoffs for South and East Asian populations: High risk

Healthy range for this height: 63.3–85.2 kg

## Energy

**3859–4397 kcal/day.** The range is the answer.

| Formula | Resting kcal | Note |
| --- | --- | --- |
| Mifflin-St Jeor | 2031 | The most widely recommended of the three for general use. |
| Harris-Benedict (revised) | 2168 | Older, and tends to read higher than Mifflin-St Jeor. |
| Katch-McArdle | 2314 | Uses lean mass rather than total weight, so it is the better estimate when body composition is known — especially at either extreme of muscularity. |

The formulas disagree by 283 kcal (13%) before the activity factor of 1.9 is applied.

## Protein

**72–108 g/day** — General health

Computed on lean body mass (90 kg). The RDA floor is 0.8 g/kg; many bodies recommend more for older adults.

## Warnings

### The formulas disagree by 283 kcal (13%) (caution)

Resting expenditure comes out between 2031 and 2314 kcal depending on which standard equation you use, and both are fitted to population averages rather than to you. After the activity factor the plausible range is 3859-4397 kcal. Any calculator that reports a single number to the calorie is implying precision that does not exist.

**What to do:** Treat the range as the answer. Pick a point inside it, hold it for a few weeks, and adjust based on what actually happens to your weight — measured response beats any formula.

### The activity multiplier is the largest source of error (info)

The multipliers run from 1.2 to 1.9, so the choice between two adjacent bands moves the estimate by roughly 355 kcal — more than the disagreement between the formulas. Most people overestimate their own activity level.

**What to do:** If you are between two bands, take the lower one and adjust upward from evidence.

### Not medical advice (info)

These are population-level estimates from formulas fitted to population averages. They are not medical advice and know nothing about your health, medication, pregnancy, or history. BMI in particular is not a measure of health. Talk to a clinician or a registered dietitian before acting on any of it.

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