This week: do cold plunges actually burn fat? Plus red-light masks, probiotics, chlorophyll, and 'fibermaxxing' — real or noise.

The at-home LED mask promises a lot; the measured effect is narrower, and it's real. In a controlled trial of 136 people, 30 sessions of red and near-infrared light produced blind-rated improvements in skin roughness and ultrasound-measured collagen density versus untreated controls (Wunsch & Matuschka, 2013). It's modest and needs weeks of steady use. What it doesn't do: clear acne, regrow hair, or "optimize your mitochondria." Real, specific, and oversold at the edges.

The gut-brain pitch sells a capsule that lifts a healthy person's mood. Pooled across 23 randomized trials in 1,401 people, probiotics did move depression and anxiety scores, but only in people already clinically diagnosed, and framed as an add-on alongside real treatment, not a stand-in for it (Asad et al., 2025). For a healthy, stressed shopper buying a bottle to feel better, that benefit isn't demonstrated. If you're managing a diagnosed condition, this is a conversation with your own clinician, never a supplement-aisle swap.

The kernel is true: fiber is genuinely useful. It slows digestion, helps you feel full, and steadies blood sugar. But "nature's Ozempic" straps a drug's headline onto a bowl of oats. When researchers actually tracked fiber's effect on the appetite hormones that drive how much we eat, the change was minimal, reaching significance only modestly, in people with obesity, over the long term (2019 meta-analysis). Useful groceries, not a GLP-1 shot.

The green shots promise clear skin and a flushed-out system. The only human skin evidence isn't a drink at all: it's a topical gel of chlorophyllin, tested on 10 people with no control group over three weeks (Stephens et al., 2015, via PubMed). That's a hopeful pilot for a cream, not a case for a beverage, and "detox" isn't a measurable endpoint your liver and kidneys need a green drink to handle.

Start with what's true, because the cold isn't fake. Drop into 50-degree water and your body reacts: it fires up "brown fat," the metabolically active tissue that burns energy to make heat. That response is real. The leap the reels make is from "burns a little energy for warmth" to "melts your belly," and that's where the studies stop following along.

Here's the step the plunge clubs skip. When scientists measure it, the amount of active brown fat in an adult is simply too small to move body weight. Reviewing the human evidence, one group concludes brown-fat activation "does not influence body weight" (Fernandez-Verdejo et al., 2019); another finds it contributes "a small amount" to metabolism and is "unlikely to cause weight loss" (Marlatt & Ravussin, 2017); a third, reviewing every way to switch brown fat on, reports that activation alone "is unlikely to achieve significant weight loss in humans" (Harb et al., 2022). Three independent teams, one conclusion.

And the largest look at cold-water immersion to date agrees by omission. A 2025 synthesis pooled 11 randomized trials and 3,177 people, measuring stress, sleep, inflammation, and immunity (Cain et al., 2025). Fat loss and body composition weren't the payoff; they weren't a benefit at all. What the numbers did show is the opposite of "fat-burning furnace": inflammation actually rose right after the plunge and stayed elevated an hour later. Grade the claim exactly as it's sold, "torch fat, fire up your metabolism," and the ice barrel is charging cold-shock prices for a fat-burn the research never hands over.

At the 12-hour mark, that same 2025 review did find something real: a meaningful drop in stress, alongside better-reported sleep and quality of life. So if you plunge because it resets your head or your night, the evidence gives you a nod, just not for your waistline. The effect is on how you feel, not how much you weigh, and the evidence base is still small and short. Real benefit, honest lane.

The cold plunge's warm cousin has the heavier file. In a 20-year study of 2,315 Finnish men, those who used a sauna 4 to 7 times a week had markedly lower rates of sudden cardiac death and cardiovascular death than once-a-week bathers (Laukkanen et al., 2015). It's observational, so frequent sauna-goers may simply be healthier to start with, and it's one group of middle-aged men. An association worth respecting, not a prescription.

The evidence has been in for a decade. Across 29 trials and more than 11,000 people, taking vitamin C every day did not cut the odds of catching a cold in the general population; it trimmed the length of one by about 8% in adults (2013 Cochrane review). Started only once you feel sick, it did basically nothing. It's cheap and safe, and since contents vary bottle to bottle, a third-party mark (USP, NSF) tells you what's actually inside. A minor perk sold as a shield.

This week's gold medal in marketing physics goes to the plunge tub promising to "switch on your brown fat like a newborn's." Newborns run on brown fat because they can't shiver yet; it's a backup furnace for people who can't reach for a sweater. You can. Every winter of your adult life you've been "activating brown fat" for free, waiting for the bus, with worse posture. Charging nine dollars a plunge for it is the real innovation.

One line for the group chat: "raises your metabolism" and "makes you lose weight" are not the same sentence. A cold plunge, a spicy meal, a good fidget, plenty of things nudge the calories you burn for a moment. Almost none of them move the scale. Before you buy the barrel, ask whether anyone measured the pounds, or just the shiver.

One claim. One verdict. Two minutes.

There's a fresh one landing Wednesday: I'm putting a claim you've almost certainly scrolled past this week on the scale, and grading it plainly. Hit reply and tell me what's blowing up your feed right now; it might be the one we grade next.

Be honest: have you taken the cold-plunge plunge yet, or are you still watching everyone else gasp on camera?