The Wellness Brew - Issue 26

Twenty-six weeks ago this newsletter went out for the first time. Since then it's covered microplastics, sleep, glyphosate, sunscreen, peptides, cancer screening, and a fair amount in between. This week is a look back at what actually changed my mind along the way. Some things turned out to have far more evidence behind them than I expected. Others turned out to be resting on almost nothing.

But first, we filtered the noise — here's what's worth knowing this week.

Researchers at Washington University enrolled 55 adults with obesity, prediabetes, and fatty liver disease, and randomly assigned them to a ketogenic, Mediterranean, or very-low-fat plant-forward diet for about five months. Every meal was provided, adherence topped 95%, and the diets were designed to produce identical weight loss of roughly 10%, which isolates diet composition from weight change. All three improved health, and muscle insulin sensitivity rose about 50% regardless of diet. But keto reduced liver fat by 67% versus 45% for the others, and about half the keto group no longer met criteria for prediabetes, compared with 29% on Mediterranean and 7% on plant-forward. The lead author's stated surprise: the high-saturated-fat group saw no worsening of cholesterol, and cardiovascular risk factors tended to improve. Worth flagging that 42 people completed it, which is small, and everyone had fatty liver at baseline, so this doesn't necessarily generalize to metabolically healthy people. — Petersen et al., Cell Metabolism, 2026.

Your TSH probably didn't change

If you track bloodwork, this one saves you some worry. Researchers drew blood from 21 healthy volunteers once a week for five weeks and measured how much thyroid markers drifted on their own. TSH varied by about 22% within the same person, week to week, with no illness or change in circumstances. Free T3 and free T4 were far steadier at roughly 4% and 5%. From that they calculated what's called a reference change value, the threshold a result has to cross before the change is real rather than noise. For TSH it's a 68% increase or a 40% decrease. Anything smaller is most likely your body doing what it always does. The authors also concluded that TSH is individual enough that comparing your result against a population reference range is less useful than comparing it against your own history. Small study, 21 people, but it lines up with larger European data. If your TSH went from 2.1 to 2.6, nothing happened. — Yıldız et al., Biochemia Medica, 2025.

300,000 tons of beef, and no label telling you where it came from

On August 21 the administration suspended out-of-quota tariffs on up to 300,000 metric tons of imported beef for 90 days, with foreign suppliers reportedly committing to sell at roughly 25% below current market prices. The stated goal is bringing down grocery bills while the US cattle herd sits near its smallest level in decades. Set aside the politics and there's a practical problem for anyone who cares where their food comes from. Country-of-origin labeling for beef has been voluntary since 2015, and "Product of USA" can legally appear on beef raised and slaughtered abroad as long as it's processed here. So a large volume of cheaper imported beef is about to enter the supply, most of it destined for ground beef, and the package won't tell you whether you're buying it. The takeaway here isn't about reading labels more carefully. Instead, it’s to buy from a trusted local rancher, a butcher who knows their supply chain, or a brand that names the farms it works with.

After six months of writing this newsletter, I found myself doing some reflecting. I’ve learned a lot over the last 25 issues and I hope you have too. I’ve also had my fair share of surprises after diving into new topics each week. 

Some things I assumed were minor turned out to have more behind them than I thought. Other things I assumed were well established turned out to be resting on very little evidence. 

1. Sauna.

Of everything covered in six months, this is the one with the widest gap between how strong the evidence is and how seriously people take it.

The core finding comes from a Finnish cohort of 2,315 men tracked for a median of nearly 21 years. Men who used a sauna four to seven times a week had 50% lower cardiovascular mortality and 40% lower all-cause mortality compared to men who went once a week. [1] The relationship was dose-dependent, meaning more sessions tracked with better outcomes, and later work from the same cohort linked frequent sauna use to lower dementia risk and lower respiratory disease risk.

The caveat is that this is observational, in a country where sauna is woven into daily life. People who sauna four times a week may differ in other ways. But the size of the effect, the dose-response pattern, and the consistency across outcomes make it hard to dismiss. Most people think of sauna as "nice if you have one." But the data puts it closer to a cardiovascular intervention. (Issue 12)

2. Cardiorespiratory fitness as a mortality predictor.

A study of 122,007 adults who underwent treadmill testing found that the least fit group had a mortality rate nearly four times higher than the fittest group. For comparison, smokers in the same study had a mortality rate 1.4 times higher than non-smokers. [2]

Once again – the gap between the least fit and the most fit was larger than the gap between smokers and non-smokers.

Worth being precise here, because superlatives get thrown around. "Strongest predictor" always means in this study, in this population, measured this way. What makes this finding unusually strong is that fitness was measured on a treadmill rather than self-reported, and the sample was enormous. It sits among the most reliable relationships in the literature. (Issue 06)

3. Sleep.

An analysis of survey data across all 3,143 U.S. counties found insufficient sleep ranked ahead of diet, physical activity, and social isolation as a predictor of shorter life expectancy, surpassed only by smoking. [8]

That's a county-level analysis of self-reported data, which is weaker evidence than a treadmill test, and it can't tell you what will happen to you personally. But it points at something worth sitting with: sleep is the input people cut first when life gets busy, and it may be the one they can least afford to. (Issue 03)

4. Muscle.

The fact that muscle matters for aging isn't news. What surprised me was how specific and how strong the evidence has become.

Grip strength, which takes about ten seconds to measure, is one of the most consistent predictors of long-term outcomes in the literature. Every 5kg reduction is associated with an 8% increase in all-cause mortality risk. A study across 28 countries found a clean dose-response relationship between muscle strength and mortality in adults over 90, with no threshold below which more strength stopped helping. [3]

The reason goes beyond being able to carry groceries. Muscle is the body's primary site of glucose disposal, which ties it directly to insulin sensitivity and metabolic health. It also produces signaling proteins during contraction that have measurable anti-inflammatory effects on the brain, liver, and cardiovascular system. Muscle behaves less like a feature of fitness and more like an organ. (Issue 06)

5. It is almost never too late.

Researchers put ten frail nursing home residents with an average age 90 through eight weeks of resistance training. Strength gains averaged 174%, close to tripling. Muscle area grew 9% and walking speed improved 48%. The oldest participant was 96. [4]

Ten people and no control group, so hold it loosely. But the same lead author ran a randomized controlled trial four years later with 100 frail residents and found the same thing, while nutritional supplements without exercise did nothing.

It’s never too late to start and exercise should never have a finish-line as we age.

6. Cold plunge.

This one has the largest gap between popularity and evidence of anything covered.

What holds up: cold water immersion after hard exercise reduces soreness and improves how recovered you feel. That's real and replicated.

What doesn't: nearly everything else it's marketed for. A 2024 meta-analysis, memorably titled "Throwing cold water on muscle growth," found that cold immersion right after resistance training modestly blunts muscle growth compared to lifting alone. [5] Follow-up work found reduced blood flow to muscle and blunted amino acid uptake after post-exercise cooling. If you're lifting to build muscle and plunging immediately afterward, you may be paying money for a worse result. 

One important note: every study looked at immersion within about fifteen minutes of training. Plunging on a rest day or hours later is a different question that hasn't been properly tested. 

7. Electrolytes.

The average American eats around 3,400mg of sodium a day. The guidance is 2,300mg, meaning roughly 90% of Americans are over the limit already.

In terms of sweat loss during a workout, endurance athletes lose about 1,190mg of sodium per hour of training, but a typical gym session from the average person will cost considerably less than that. Yet a single electrolyte packet can contain 1,000mg, which is 43% of the daily guidance in one drink.

There are real cases where supplementation matters: long sessions in heat, heavy sweaters, illness, low-carb diets. I'm in that group myself. But the category has been marketed to everyone, and most people simply don’t need more sodium. (Issue 22)

8. Peptides.

BPC-157 and its relatives are backed by substantial and consistently positive animal literature, a great deal of confident testimony, and mechanistically make sense. However, human trial data is close to nonexistent.

That doesn't mean they don't work. Absence of trials isn't proof of absence. But there's a wide gap between what's being claimed and what's been tested, and the risks that would matter most are the ones that take years to surface in people nobody is tracking. (Issue 21)

9. Supplement quality.

This one could slot under “Bigger than expected” or smaller, depending on the viewpoint you take. Here, the takeaway is that the quality of most supplements is worse than even I realized. The importance of buying directly from high-quality brands is larger. 

An independent lab bought 44 of Amazon's best-selling supplements and put them through accredited testing. Twenty-two failed to meet their label claims. Of those, twenty contained between 0% and 3% of the main ingredient on the label. [6]

Not a rounding error. Effectively counterfeit. Buy direct from brands that are third-party tested. (Issue 05)

10. The 10,000 step target.

It came from a 1960s Japanese pedometer marketing campaign, not from research.

The largest analysis of its kind, covering 57 studies, found that 7,000 steps a day was associated with nearly half the mortality risk of 2,000 steps, with measurable benefits for cardiovascular disease, diabetes, dementia, and depression at that threshold. [7] More useful still: moving from 2,000 to 4,000 steps produced meaningful gains. The biggest returns go to the least active, not to people grinding out the last thousand steps at 10pm. (Issue 06)

If there's a pattern across all ten, it's that the confidence around a claim rarely matches the evidence behind it, and the mismatch runs in both directions.

Some of the strongest evidence in the entire field sits behind things nobody markets, because nobody owns them. There's no sauna lobby. Nobody is running ads for grip strength or about the importance of consistent sleep timing. Meanwhile the things with the loudest marketing budgets tend to have the thinnest files.

To everyone who has read along each week, thank you. And to those who have reached out with a note of support or passed an issue along to someone else, that means more than you know.

As usual, if you found this useful, please forward it to someone you care about. If you had this forwarded to you — sign up here.

Wellness, filtered.

Anthony - The Wellness Brew

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Disclaimer: The Wellness Brew is for informational purposes only and does not constitute medical advice. The content published here is not intended to diagnose, treat, cure, or prevent any disease or health condition. Always consult a qualified healthcare professional before making any changes to your diet, supplement routine, or lifestyle.