There's a runner you might recognise. The one who pulls a fleece on when everyone else is peeling layers off. Hands wrapped around whatever hot drink is going, even when it's 28°C outside. Swears she just runs cold and that's how she's always been. Maybe you know her. Maybe, on a quiet read of yourself, she's you.

What I've learnt, watching the pattern for years, is that "I just run cold" usually isn't a quirk of circulation. It's a signal, and it's worth catching before it gets louder.

So if you're a runner who's always reaching for a jumper, who finds 20°C still feels chilly, whose hands and feet are cold most of the year, it's worth ruling out one quiet, common cause before anything else: under-fuelling.

Why being under-fuelled makes you cold

When you train hard and don't eat enough to cover it (training, daily life, basic function), your body starts to triage. It keeps the lights on for the essentials: heart, brain, the muscles you're working. Things that aren't strictly load-bearing get turned down. Body temperature is one of the first dials it touches.

This is called low energy availability, and it's worth being precise about. It isn't the same as being thin or underweight. You can look completely fine on paper, train consistently, hit your sessions, and still be running on a quiet deficit your body is compensating for in ways you don't immediately link to food. Cold hands, cold feet, feeling chilly when nobody else is, goosebumps at room temperature. These are signals, not personality traits.

Some of what's happening sits at a cellular level. When energy is genuinely scarce, the thyroid responds by reducing the conversion of T4 to T3 (the active form of the hormone that sets your metabolic rate). A slightly lower T3 means a slightly slower metabolism, less heat production, and a body that feels cold for no obvious reason. It's an efficient response to a real signal, but it's a signal worth catching early, because the same downshift affects more than just temperature.

Most of the runners I've watched move through this assumed, for a long time, that they just ran cold. What I learnt watching them is that the body keeps you warm when it has spare energy, and quietly cools you down when it doesn't.

The other signals to look for

Cold hands rarely travel alone. The clues that often appear alongside them are:

  • You're always tired, but sleep is fine.
  • Niggling injuries that take forever to heal.
  • Periods that have gone light, late, or absent.
  • Brain fog in the afternoon.
  • Hair that's thinner, or falling out more than it used to.
  • Mood lower than it should be for someone who runs this much.

One or two of these on their own, probably nothing. A cluster of them, in someone training consistently, is worth paying attention to. The body has a thousand ways of telling you it's running short, and most of them look at first glance like ordinary life.

What low energy availability actually is

The formal term is Relative Energy Deficiency in Sport, or RED-S, and the research on it has grown fast over the last decade. It describes what happens when an athlete, of any size and any training level, isn't taking in enough energy to cover both their training and the basic functions of being alive. The body responds by quietly down-regulating things it considers optional: thermoregulation, the menstrual cycle, bone-building, immune function, mood.

It isn't a weight-loss problem. Some women with RED-S lose weight, many don't, and some gain it. The most useful frame isn't a number on the scale, it's the question of whether what you're eating actually matches what you're doing.

That matters because the culture around women's running has historically pushed in the opposite direction: smaller portions, fewer carbs, "earning" your food. A lot of women who run end up under-fuelled not because they're trying to be, but because that's the message they grew up on.

The numbers are bracing if you go looking. Studies of female endurance athletes routinely find that somewhere between a quarter and half are running at low energy availability at any given time, and many of those women have no idea. The research lags behind the prevalence, partly because the symptoms map so neatly onto things we've been taught to normalise: small portions, periods on the pill that nobody questions, tiredness as a personality trait, and yes, being cold.

How to fix it

The fix is unglamorous and it works.

Eat more, and earlier

Most under-fuelled runners skip fuel before easy runs, and aren't eating enough in the morning generally. Breakfast with carbs and protein, not just coffee, is the single biggest lever. Porridge with fruit and yoghurt, eggs on toast, peanut butter and banana on something, whatever you'll actually eat consistently. Carbs are not the problem. They're the energy your runs are made of.

Fuel the session, not just recover from it

Running over an hour, or doing intervals or a long run? Eat something in the hour before, and bring carbs for the harder efforts. Yes, even at easy pace. No, you will not undo your training by eating a banana before your run.

Add a snack in the evening, instead of cutting one

Late hunger after a hard day is your body asking for the deficit back. Listen to it. A bowl of cereal, a slice of toast, leftovers from dinner: not a problem to solve, a request to honour.

Notice the warmth come back

If you start eating more and a week later you feel less cold, that's your answer. The body turns the dial back up surprisingly fast when it gets what it needs. Cycle changes can take longer to settle, but the temperature signal is one of the most responsive ones the body has.

When to get help

If you've started eating more, given it a few weeks, and the symptoms aren't shifting, talk to a GP or a sports doctor. Especially if your period is irregular or has stopped, because that's the body's loudest signal that something needs attention. Mention RED-S by name. Not every doctor will reach for it on their own, and naming it gives them a framework to work in.

It can be worth asking for a few baseline checks while you're there. A full blood count, ferritin and a full iron panel, thyroid function (TSH, T3, T4), vitamin D, and where relevant, sex hormones. Not because any one number will tell the story, but because together they sketch a picture, and they give you a starting point to track changes against as your fuelling settles.

Cold hands aren't a quirk. They're a message. Heatwave or no heatwave, if you're shivering through summer, the question worth asking isn't "what's wrong with my circulation". It's "am I eating enough for what I'm doing".

Eat the breakfast. Bring the snack. Stay warm.

This article is general information, not medical advice. If your periods have changed or stopped, or you're worried about your fuelling and recovery, please speak to a GP or a sports doctor.