Could your PMOS Diagnosis actually be RED-S?
The short answer: RED-S is caused by under-fuelling relative to activity. PMOS is a hormonal condition. They look almost identical on the surface — but they require completely different treatment.
In my clinic, I see women who have spent years managing what they’ve been told is PMOS – Polyendocrine Metabolic Ovarian Syndrome, previously known as polycystic ovarian syndrome (PCOS). Many have tried multiple treatment approaches. Most have been put on hormonal contraception to regulate their cycles. Some have changed their diet, adjusted their training, and learned to live with a diagnosis that never quite fitted. The condition they’re more likely to have is RED-S — and the misdiagnosis of RED-S as PMOS is a pattern I see repeatedly. A significant number of them don’t have PMOS at all.
What they have is RED-S: Relative Energy Deficiency in Sport. The two conditions can share an almost identical surface presentation- missing or irregular periods. But their causes are different, their long-term risks are different, and treating one as the other can delay the right care by years. This is the diagnostic question I believe is being asked too rarely, and not loudly enough.
What is RED-S?
RED-S stands for Relative Energy Deficiency in Sport. It occurs when the body is not receiving enough fuel to cover both the demands of physical activity and the basic requirements of everyday physiological function. When that energy gap opens, the body begins to make decisions about which systems to prioritise. Reproduction is not considered essential for immediate survival — so the reproductive system is typically one of the first things switched off.
The result is a cascade of effects that extend well beyond a missed period. Bone density decreases. Immune function is compromised. Cardiovascular health is affected. Mood, concentration and motivation deteriorate. Fertility can be impacted in ways that may not become apparent until much later. And critically — menstrual function is disrupted, often for months or years, in ways that look almost indistinguishable from hormonal conditions like PMOS.
RED-S is not a niche condition affecting only elite athletes. It affects any woman whose energy output consistently exceeds her intake — and that includes recreational runners, gym regulars, cyclists, and women who simply train hard and don’t eat quite enough to support it.
What is PMOS — and why has the name changed?
Polyendocrine Metabolic Ovarian Syndrome (PMOS) was until recently known as polycystic ovarian syndrome (PCOS). The name change reflects a growing consensus in the medical community that the original term was both inaccurate and misleading — not all women with the condition have cysts, the condition is mostly an endocrine disorder not a gynaecological one and “polycystic ovary” as a descriptor was creating significant confusion for patients.
PMOS is a hormonal condition involving many metabolic disruptions, resulting in elevated androgens, irregular or absent ovulation, and in some cases visible follicles on the ovaries on ultrasound to name just a few symptoms. It is associated with insulin resistance, and its management typically focuses on regulating hormones, managing metabolic factors, and supporting fertility where that is a goal.
The condition is real, it is common, and it requires proper clinical management. My concern is not with the diagnosis itself — it is with how often it is applied when it does not fit, particularly in women who are physically active.
Why the RED-S and PMOS misdiagnosis happens
Both conditions can present with irregular or absent periods. Both involve hormonal disruption. Both can cause fatigue, changes in mood, and in some cases changes to hair and skin. Both can affect fertility.
The difference lies in the cause. PMOS is a hormonal condition with a distinct physiological basis. RED-S is a consequence of an energy deficit — remove the deficit, and the symptoms resolve. But in practice, when a woman presents with a disrupted cycle, the standard pathway often leads to a blood panel, a hormone assessment, and in some cases a PMOS diagnosis, without anyone asking about her training load, her relationship with food, or whether she might simply not be eating enough to support the life she is living.
For lean, active women in particular — those who don’t have the more visible metabolic features sometimes associated with PMOS — RED-S can go entirely unrecognised. The label gets applied because the presenting symptoms fit. The underlying cause is never examined.
Warning signs I see in my clinic
If you are an active woman and you recognise several of the following, RED-S deserves to be on your radar — regardless of what you have previously been told:
- Irregular or absent periods, particularly in the context of increased training
- Persistent fatigue that does not improve with rest
- Recurring stress fractures or unexplained bone pain
- Frequent illness or slow recovery from infection
- Performance plateaus despite consistent training
- Mood changes, anxiety or difficulty concentrating
In my clinic up to 90% of patients who present have either a previous history of REDS or current issues with REDS, and those attending having been diagnosed as ‘lean PCOS’ actually have a mix of REDS and some elements of PMOS.
Why the right diagnosis matters
The consequences of unmanaged RED-S are serious and, in some cases, long-term. Bone mineral density lost during periods of RED-S may not fully recover. Research has indicated a significantly elevated risk of preterm birth in subsequent pregnancies in women with a history of the condition. Fertility implications may not become apparent until a woman is trying to conceive, sometimes years after the original symptoms first appeared.
These are not small risks. They are the reason getting this right, early, matters.
Hormonal contraception — a common first-line response to irregular cycles — can mask the symptoms of RED-S without addressing the underlying energy deficit. A woman can spend years on the pill, apparently managed, while the real condition continues untreated beneath the surface.
What to do if this resonates
If you have been told you have PMOS and you are physically active, it is worth asking whether RED-S has been considered as part of your assessment. The two conditions can co-exist, but they require different approaches, and a diagnosis of one does not rule out the other.
A proper RED-S assessment considers energy availability, training load, menstrual history, bone health and hormonal profile together. It requires a clinician who understands both the physiology of sport and the complexity of female hormonal health — and who will ask the right questions, not just run the standard panel.
If you would like to explore this further, I offer consultations in London, Windsor, as well as nationally and internationally virtually. You can book via the link below.