Evidence is consistent, with known limits.
Soluble fibre supplements produced about 2.8 lb more weight loss on average across 22 trials — an average, not a prediction for any one person, and most of those trials paired fibre with a calorie-restricted diet. The Lancet's 25–29 g/day target comes from a review that excluded supplement trials entirely.
Ten adults did the same 14-day diet twice: once on 8.5 hours' sleep, once on 5.5. The scale showed the same loss both times. On short sleep, 55% less of it was fat and 60% more of it was muscle. A separate 80-person trial found sleeping longer cut intake by 270 calories a day, with no change in what people burned.
22 randomised trials say brisk walking takes off about 4.7 lb — and 5.7 lb of fat, because fat-free mass went up at the same time. The famous step target is not a finding: it is the name of a Japanese pedometer sold in 1965.
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.
A randomised trial in 120 older adults found aerobic exercise grew the hippocampus by 2% and improved memory — that part is real. The famous 'four times faster' figure comes from mouse cells in a dish, and the phrase does not appear anywhere in the paper it is credited to. It entered at the press release.
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.