The Wellness Brew - Issue 30

Most advice aimed at women who train focuses on programming. Sync your training to your cycle, adjust your rep ranges, change when you eat. The evidence behind a lot of that is thinner than the confidence around it. Meanwhile the things that most reliably derail female athletes sit almost entirely outside the training plan, and they're largely invisible until performance falls apart.

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

Researchers screened 991 blood metabolites in dementia-free middle-aged adults, looking for which ones tracked with cognition and brain MRI markers. Fourteen showed replicated associations with cognition, and ergothioneine had the largest effect of any of them. It also predicted incident Alzheimer's. Ergothioneine is an amino acid your body can't make but goes to real trouble to keep, with a dedicated transporter that absorbs and stores it. Mushrooms are by far the richest source, especially king oyster, oyster, maitake, shiitake, and porcini, with beans and oat bran contributing smaller amounts. The finding worth highlighting: antacid use was associated with worse cognition and lower ergothioneine, and the lower ergothioneine statistically accounted for about a third of that relationship. Given how many people take acid reducers indefinitely, that's worth knowing. This is observational and can't prove causation, and supplementation trials so far have been small with inconsistent results. Start eating more mushrooms. — Ahmad et al., Nature Aging, 2026.

More REM sleep, lower risk across 83 diseases

Researchers pulled wrist-tracker data from 95,559 UK Biobank participants and followed them a median of 8.9 years against more than 1,000 disease outcomes. Each additional 47.6 minutes of REM sleep was associated with lower risk of 83 separate conditions, including heart failure, dementia, and Parkinson's. Deep sleep was associated with lower risk of seven conditions, including type 2 diabetes and major depression. Sleep data is largely observational, and the direction of the relationship is genuinely unclear for some of these (e.g. REM sleep behavior disorder is a well-documented early sign of Parkinson's that appears years before diagnosis, so low REM may be a symptom rather than a cause there). And REM isn't something you can directly command. What you can do is protect it, which mostly means alcohol, consistent timing, and enough total sleep for the later cycles where REM concentrates. — PLOS Medicine, 2026.

8.8 million adults, 51 studies, one consistent answer

A dose-response meta-analysis pooled 51 prospective cohort studies covering 8,819,894 adults, following them for anywhere from 2 to 32 years, to assess ultra-processed food intake against chronic disease. Higher intake was associated with elevated risk of cardiovascular disease, cancer, obesity, type 2 diabetes, digestive disease, depression, anxiety, and death from any cause. Cardiovascular risk rose 24% in the highest consumers, with diabetes and obesity each up roughly 24% and 23%. The more useful number is the dose-response: each additional 100 grams a day was associated with 14% higher risk of cardiovascular events, 11% higher risk of high blood pressure, 4% higher cancer risk, and 3% higher all-cause mortality. A hundred grams is not much food. The consistency across 51 cohorts and nearly nine million people is about as strong as this kind of evidence gets. — Liu X, et al., Family Medicine and Community Health, 2026.

Women are physiologically different from men. If you search for how women should train differently than men you'll find suggestions touching on many different areas. Sync your training to your menstrual cycle. Different rep ranges. Don't train fasted. Different protein timing.

As usual, there is less evidence supporting many of these claims than you'd think. That doesn't mean there are no sex differences worth knowing about. There are, and they're significant. They're just not part of the training plan.

The things that most often derail female athletes are physiological rather than programmatic, and they're largely invisible until it's too late. Here's what the research actually points to.

This is the big one, and it's underdiagnosed almost everywhere.

Up to 60% of female athletes present with iron deficiency. [1] In male athletes the figure is roughly 5 to 11%. [2] One screening study of Division I female athletes found 58% had ferritin below 40 ng/mL. [3] Standard lab reference ranges flag deficiency somewhere around 10 to 15 ng/mL for the general population. But athletes are not the general population. Sports medicine uses 35 to 40 ng/mL as the floor for female athletes, because the research shows performance suffers once you drop below this. [1]

A 2024 systematic review of female athletes found that low iron stores reduced endurance performance by 3 to 4%, even in athletes whose blood counts were normal and who would not be considered anemic. When deficient athletes were treated with roughly 100mg of elemental iron daily, performance improved by anywhere from 2 to 20%. [1]

Three percent doesn't sound like much until you apply it to a race. A few percent off your pace over the course of an hour is a meaningful gap at any level, and at the front of a field it's the difference between a podium and fourth.

Why training makes it worse. Hard training raises hepcidin, a hormone that regulates iron absorption, which reduces how much iron you take up from food. [4] Add repetitive ground impact, gastrointestinal losses, and in menstruating athletes a monthly loss on top of that, and the inputs don't keep pace with the outputs. One study of female runners found 50% were iron deficient at baseline and over 70% were deficient after a training block. [2]

One thing to ask for. Request hs-CRP to be tested alongside ferritin. Ferritin is an acute-phase reactant, meaning inflammation inflates it. A hard training block or a recent illness can push ferritin up by a meaningful margin and hide a real deficiency underneath a normal-looking number. Testing both lets you interpret the result rather than guess at it.

This is the concept that explains more unexplained athletic decline than anything else, and most people have never encountered it. Keep in mind, we're talking about fueling and optimizing for performance below.

Energy availability isn't calorie intake. It's what's left over after training takes its cut. The formula used across the research is:

Energy availability = (calories eaten − calories burned in exercise) ÷ fat-free mass in kg

So it's the energy actually available to run everything else your body does, expressed relative to your metabolically active tissue. [5]

The International Olympic Committee's consensus framework puts the thresholds like this: [5]

The numbers will mean more with an example. Take a 70kg (154lbs) female athlete with roughly 57kg of fat-free mass (18% body fat), training ninety minutes to two hours a day. If she eats 3,000 calories and burns 1,000 of them training, her energy availability lands at 35 (2,000 calories ÷ 57kg). That's subclinical. To reach the optimal threshold she'd need to be eating closer to 3,565 calories. [6]

This is far more than most people would think they'd need. That's the gap.

Two honest caveats. The 2023 IOC consensus notes the 30 threshold isn't universal, and individual thresholds appear to vary considerably. [7] And calculating this accurately can be difficult, because you need a real measurement of fat-free mass and an accurate estimate of exercise expenditure, which is easy to get wrong. Treat it as a screening estimate that tells you more broadly if you're eating enough or not.

What low energy availability disrupts.

When there isn't enough energy left over, the body starts shutting down functions it treats as non-essential. This is where the condition called Relative Energy Deficiency in Sport, or RED-S, comes from. The IOC formalized the framework in 2014, replacing the older Female Athlete Triad model, in part because the same problem affects men. [8]

The affected systems are broad: bone formation and density, thyroid function, resting metabolic rate, immune function, protein synthesis, cardiovascular health, and reproductive function. [8]

That last one is worth a note, because the research treats it as one of the earlier and more visible indicators rather than as a separate issue. Changes in menstrual function, including cycles becoming irregular or stopping, are among the signals that show up in the literature before bone density loss becomes measurable. [8] The practical limitation is that hormonal contraception masks the signal, which means for many athletes that particular indicator isn't available and the other markers carry more weight.

The distinction that matters most

Overtraining syndrome and RED-S look nearly identical from the outside. Performance decline that doesn't respond to rest. Persistent fatigue. Mood changes. Disrupted sleep. Frequent illness. Elevated resting heart rate. You can't tell them apart by how you feel.

The issue is that they have different causes and different treatments.

Overtraining syndrome comes from a sustained mismatch between training load and recovery. The treatment is rest, and a lot of it.

RED-S comes from chronic low energy availability. The treatment is restoring fuel. [9]

Which means that if you have RED-S and you treat it as overtraining, you rest, you eat the same or less because you're training less, and you don't get better. Then you try to return, it falls apart again, and the cycle repeats. People lose years this way.

Stanford's female athlete research program states it plainly: RED-S is commonly misdiagnosed as overtraining syndrome, and low energy availability needs to be ruled out before an overtraining diagnosis is made. [10]

Both are what clinicians call diagnoses of exclusion, meaning they're what you arrive at after ruling out everything else. And there's a lot of everything else that produces the same picture: thyroid dysfunction, iron deficiency, celiac disease, anemia, autoimmune conditions, and sleep disorders are all more common than overtraining syndrome and all more treatable.

If you've been unable to train consistently for months, the odds favor something on that list over overtraining syndrome, and that's a reason for a workup with a clinician rather than another deload week.

Worth saying clearly: there is no validated blood panel for overtraining syndrome. A scoping review of diagnostic markers identified a long list of candidate hormones, metabolites, and immune patterns, and concluded they still require validation in larger samples and specifically in female athletes. [11] Anyone selling you an overtraining panel is ahead of the evidence.

What does exist is a differential panel, which is worth asking for if you're struggling and don't know why:

None of that diagnoses overtraining. All of it rules things in or out, which is the actual job.

The encouraging part

The recovery literature on low energy availability is better than you'd expect.

When energy availability is restored, function comes back. Documented case reports track athletes from amenorrhea through full hormonal and menstrual recovery once fueling was corrected and training volume adjusted. [13] Bone density recovery is slower and less complete, which is the strongest argument for catching this earlier rather than later, but the metabolic and hormonal picture is substantially reversible.

The timeline is months rather than weeks. That's worth knowing going in, because the gap between starting to eat adequately and feeling like yourself again is long enough that people quit partway through and conclude it didn't work.

The things most likely to derail a female athlete aren't in the training plan.

They're iron status that standard lab ranges will tell you is fine. They're an energy availability number that looks adequate until you do the arithmetic. They're a condition that mimics overtraining closely enough that treating it as overtraining can cost you years.

None of this requires training differently than a man. It requires testing for different things, and knowing which numbers actually apply to you.

Four things you can do this week:

1. Get ferritin tested, with hs-CRP alongside it.
Standard lab ranges flag deficiency around 10 to 15 ng/mL, which is a general-population threshold. If you're training seriously, 35 to 40 is the floor that matters. A result that comes back "normal" may not be optimal for you. The hs-CRP matters because inflammation inflates ferritin and can hide a real deficiency underneath a reassuring number.

2. Run your own energy availability number once.
Calories eaten, minus calories burned training, divided by fat-free mass in kilograms. It takes five minutes and most people are surprised by the result. You're not aiming to track this daily. You're finding out whether you're near 45 or near 30, because the answer changes what you do next.

3. If training has fallen apart and rest hasn't fixed it, get the panel.
Ferritin with hs-CRP, CBC, full thyroid, vitamin D, reproductive hormones, and celiac screening if there are gut symptoms. Several of the conditions that mimic overtraining are more common and more treatable than overtraining itself, and none of them resolve with another deload week.

4. If you're eating more to fix this, give it months.
Hormonal and metabolic recovery from low energy availability is real but slow. The gap between starting to fuel adequately and feeling like yourself again is long enough that people conclude it isn't working and stop. Knowing the timeline up front is most of what gets you through it.

If you found this useful, please forward it to your friends and family. If you had this forwarded to you — sign up here.

Wellness, filtered.

The Wellness Brew

Sources:

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.