Evidence is consistent, with known limits.
Studied at up to 30 g a day for five years, in groups from infants to the elderly. The kidney scare has a real source: creatine raises serum creatinine, the marker doctors read as kidney function — while the kidneys' actual filtration rate stays put. The gauge moved, not the engine.
6,421 people across 29 countries, measured by doubly labelled water: energy expenditure is flat from 20 to 60, even during pregnancy. It falls about 0.7% a year after that. The decline is real — it just starts four decades later than everyone thinks.
Measured against no gum, chewing raises energy expenditure by about 0.06 kcal a minute — roughly a third of an almond per hour. A 201-person trial with 95% adherence chewed 90 minutes a day for eight weeks and lost nothing.
Protein genuinely preserves lean mass while you diet — replicated across four meta-analyses. But the effect is small, it mostly fails without resistance training, and the metabolism claim was dismissed by a review the meat and dairy industries paid for.