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· 13 min read
About half of blood calcium is bound to albumin and inactive, so a total-calcium result on a low-albumin patient reads low even when the active fraction is normal. Here is the correction in both unit systems, a worked case, and the honest verdict on how badly it performs.
· 13 min read
The conversion factor is not 18 — it is 18.016, and it is the molar mass of glucose divided by ten. Here is where it comes from, which countries use which unit, and every diagnostic threshold in both scales with the guideline it belongs to.
· 14 min read
A centile ranks a child against a reference population — it is not a grade, and one reading says almost nothing. Here is the LMS arithmetic behind the number, and why the same boy is on the 90th centile on one chart and the 85th on another.
· 12 min read
A standard drink is a defined mass of ethanol — and the definition changes at the border. The same glass of wine is 1.28 drinks in the United States, 1.79 in France and 2.28 in the United Kingdom.
· 12 min read
Caffeine leaves by first-order kinetics, so what remains is the dose times one half to the power of elapsed time over half-life. The half-life is not a constant — it varies by multiples between people, and that is the whole story.
· 12 min read
Net carbs is total carbohydrate minus fibre minus sugar alcohols. Every term in that line is a modelling choice, the first one is defined differently on each side of the Atlantic, and no regulator anywhere defines the result.
· 3 min read
How much water you really need depends on your body weight, activity and climate — not a fixed "8 glasses". Here is how to estimate your daily target.
· 2 min read
BMI groups weight into ranges relative to height. Here's what counts as healthy, how to calculate it, and the limits of the number.
· 3 min read
Weight loss comes down to a calorie deficit. Here's how to estimate your maintenance calories, set a safe deficit, and turn it into a daily target.
· 3 min read
There's no single ideal weight — it's a healthy range. Here's what the common formulas say, what they miss, and better ways to judge a healthy weight.
· 3 min read
Naegele's rule adds 280 days to your last period — or subtract three months and add seven days. Here's how it works and why it's only an estimate.
· 3 min read
Adults need 7–9 hours, and sleep runs in ~90-minute cycles. Here's how much by age, how to time your bedtime, and why quality counts too.
· 2 min read
Macros are the protein, carbs and fat in your food. Here's what each does, how many calories they hold, and how to set your daily split.
· 2 min read
Ovulation is usually 14 days before your next period, and the fertile window spans about six days. Here's how it works and how to estimate yours.
· 2 min read
BMR is what you burn at rest; TDEE is what you burn in a whole day. Here's how they relate, how the activity multiplier works, and which to use.
· 2 min read
Protein needs depend on your weight and activity, not a single number. Here's the baseline, how much more active people need, and how to spread it.
· 2 min read
Most adults burn 1,600–2,400 a day, mostly just staying alive. Here's the three parts of daily burn, typical totals, and how to estimate yours.
· 3 min read
A quick estimate is 220 minus your age, but it varies widely. Here's what max heart rate means, why it's only a guide, and how to use it for training.
· 2 min read
Body fat percentage is a better health signal than weight alone. Here are the healthy ranges by sex, how it's measured, and how to use it wisely.
· 2 min read
Pregnancy is counted in weeks, but months aren't exactly four weeks. Here's why it's 40 weeks, how weeks map to months and trimesters, and a quick reference.