Health Tools

DEXA, hydrostatic weighing, BIA scales, and skinfold calipers can give different body fat percentages for the same person on the same day. Here's what each method actually measures, why BIA scales are so sensitive to hydration, and how to choose between accuracy and practicality for tracking your own body composition.

The three trimesters represent distinct developmental phases — all major organs form in the first, growth accelerates in the second, and lung maturation dominates the third. Here's a week-by-week guide to key milestones, screening tests by trimester, and specific nutritional priorities at each stage.

EPOC ("afterburn") adds approximately 6-15% to a workout's calorie burn — real, but smaller than fitness marketing implies. Here's what EPOC actually measures, why HIIT's real advantage is time efficiency rather than metabolic magic, how HIIT and steady-state compare for fat loss, and how resistance training's EPOC differs from cardio's.

Adding up exercise calorie estimates to calculate weekly expenditure overstates the benefit by 30-50% — because NEAT drops on exercise days, appetite partially compensates, and training efficiency improves. Here's the dose-response relationship between volume and actual burn, why MET values have a ±20-30% accuracy ceiling, the long-term resting metabolism boost from added muscle (13-22 kcal/kg/day), and why fasted exercise doesn't reliably burn more fat over 24 hours.

A controlled NIH experiment showed people spontaneously ate 508 more calories per day on ultra-processed food vs. whole food — with identical macros. Here's why ultra-processed food drives overconsumption, what the satiety index reveals, and how food quality affects whether a calorie target feels effortless or exhausting.

BMR calculators don't all use the same formula — Harris-Benedict (1919, revised 1984), Mifflin-St Jeor (1990), and Katch-McArdle (lean-mass-based) can disagree by 100-200 calories for the same person, which represents 20-30% of a typical weight-loss deficit. Here's how each formula was developed, why they diverge more for people at the extremes of body composition, and why any formula's output should be treated as a starting point rather than a precise target.

A landmark study tracking 6,400 people found metabolism is remarkably stable from age 20 to 60 — what actually changes is muscle mass. Here's the Pontzer 2021 findings, how sarcopenia drives the "skinny fat" phenomenon, why protein needs increase with age, and why resistance training is the primary evidence-based intervention.

Skinfold caliper sites aren't arbitrary — they're the locations where subcutaneous fat thickness best predicted total body fat in the 1970s regression equation development studies using hydrostatic weighing as the reference. Here's why the Jackson-Pollock and Durnin-Womersley equations underestimate body fat in East Asian populations, caliper inter-rater reliability (±3-5% between trained technicians), and why calipers are better for tracking changes than determining absolute percentage.

A pregnant person's BMI increases throughout pregnancy simply because of the pregnancy itself — applying standard BMI categories to this changing number would be meaningless. Here's why clinical weight-gain guidance uses pre-pregnancy BMI as a fixed reference point instead, why "total weight gain from that reference point" is the relevant question rather than "current BMI category," and how postpartum BMI takes time to become meaningful again.

Only 4–5% of babies are born on their due date. Here's how the 40-week calculation works, why it's imprecise, what "term" actually means, and the real distribution of when babies arrive.