Written by Ciara Walsh, Dietetic Student and Intern at EK Nutrition. Reviewed by Elle Kelly, R.D.
Within the fitness space, one of the most common issues that we see among active women is underestimating just how much food and fuel the body actually needs to function and thrive.
It’s completely understandable given that we’ve been raised in a culture that has demonised food and praised smaller portions, lighter options, and restrictive eating as the gold standard of “health.” Somewhere along the way, skipping meals and choosing low-fat everything became normalised, even celebrated.
But unfortunately this messaging has led countless women to under fuel their bodies, often without even realising it’s happening until their period goes missing.
But you don’t have to have lost your period to be underfuelling!
What is Underfueling?
Underfueling refers to when you’re not giving your body enough energy and nutrients to support your training, and can lead to low energy availability (LEA).
Energy availability refers to the amount of energy that the body has remaining for physiological functions when the energy required for training and movement of any kind is accounted for.
Low energy availability, or LEA, describes the state where your body does not have enough fuel to carry out physiological functions to promote optimal health.
When there is not enough energy to support all physiological functions as well as performance, the body essentially prioritises vital functions. This means that other systems such as the immune, reproductive and thermoregulation systems become down-regulated.
Sometimes underfueling can be intentional, like when you’re actively trying to lose weight or following strict food rules. Other times, it’s unintentional, and is caused by a hectic schedule, high training loads, misinformation, or simply not realising how much energy your body actually requires.
What makes underfueling tricky is that it often flies under the radar. You might be eating regularly and think you’re eating “enough,” but that still may fall short of what your body truly needs.
And since underfueling doesn’t always result in dramatic weight loss, the signs can be subtle and often ignored.
Signs You Might Be Underfuelling
Let’s break down some of the more common (and often overlooked) signs of underfueling:
⚡ 1. Persistent Low Energy
Have you ever felt like you just can’t shake off that feeling of tiredness, regardless of how much sleep you got the night before? This persistent fatigue could be your body’s way of saying it’s not getting enough fuel to function.
🩸 2. Irregular or Missing Periods
When you’re not eating enough, your body goes into survival mode, prioritising energy for essential functions like keeping your heart beating and your brain functioning. During this process, it may shut down non-essential functions, like your reproductive system.
That’s why your menstrual cycle is such a powerful indicator of overall health. If your period has gone missing, consider it your body’s way of waving a red flag, letting you know that something is off and it needs more support.
🧠 3. Constant Thoughts About Food
Do you find yourself constantly thinking about food, whether it’s planning your next meal, watching ‘What I Eat in a Day’ videos, or fixating on nutrition labels? That mental food noise isn’t just a quirk, it’s a biological response. When your body isn’t getting enough energy, it shifts into survival mode and ramps up your thoughts about food as a way to encourage eating.
This phenomenon has been well-documented in research, most notably in the Minnesota Starvation Experiment from the 1940s. In this study, 36 healthy men underwent a 6 month period of semi-starvation, and one of the most striking outcomes was their intense, almost obsessive preoccupation with food. These men, who were previously well-nourished, began reading cookbooks, dreaming about meals, and talking about food constantly.
🧊 4. Always Feeling Cold
If you’re always reaching for an extra jumper or complaining about being cold even when others seem fine, you might not be eating enough. All of the systems in your body require energy, and when your body is in a state of LEA, these “non-essential” systems become downregulated- including your thermoregulation system.
💩 5. Digestive issues
Have you ever tried cutting out certain foods to fix bloating or constipation, only to feel more frustrated and confused when nothing changes? If so, you’re not alone, and the issue might not be the food itself. It could be that you’re simply not eating enough.
Just like your reproductive system, your digestive system relies on adequate energy to function properly. When you’re underfueling, your body begins to conserve energy by slowing down less critical processes, including digestion. This slowdown can lead to symptoms like constipation and bloating. So before you put the blame on bread or dairy, consider whether your body is actually getting the fuel it needs to keep things moving.
😴 6. Sleep Disruptions
Do you find yourself waking during the night, struggling to fall asleep, or feeling unusually hungry right before bed? These can all be subtle yet powerful signs that your body isn’t getting enough fuel. Your body enters ‘survival’ mode when your energy intake is too low, and it responds by trying to push you to eat.
💥 7. Mood Changes
Have you noticed yourself feeling more irritable than usual? Snapping at small things, feeling anxious for no clear reason, or just feeling emotionally flat? These mood changes are often overlooked signs of underfueling. Not eating enough not only affects your physical health, but also your mental health too. Many people are surprised by just how much brighter and happier they feel once they begin nourishing themselves properly. You may notice you have regained the energy to fully engage in conversations or have a laugh with friends and family.
🚫 8. Poor Recovery or Frequent Injuries
Underfueling can negatively affect your body’s ability to recover from a workout. Exercise causes tiny tears in your muscles to develop. At the same time, stored glycogen in our muscles is used up to provide us with energy during our workout. Your body needs both protein and carbohydrates to repair and rebuild muscles and replenish your glycogen stores. Without proper fueling, you may notice persistent soreness, injuries, or lingering muscle fatigue.
📉 9. Declining Performance
Have your workouts started to feel harder than usual? Are you struggling to lift the same weights, maintain endurance, or stay focused during training? These could be signs that you’re not fueling your body adequately.
Low energy availability can negatively affect key aspects of performance, such as strength, stamina, coordination, and concentration. And when you’re not recovering properly between sessions (due to underfueling), you’re likely entering your next workout already depleted and sore. Over time, this chronic lack of energy can become a major roadblock to progress and can lead to plateaus, fatigue, and even burnout.
Why Recognising These Signs Matters
Many of these symptoms have been so normalised that they’re often brushed off or ignored. But they’re your body’s way of waving a red flag, and learning to recognise these signs is crucial because our body needs fuel to function properly.
Continued underfueling can lead to serious consequences, like hormonal imbalances, poor bone health, fertility issues, and even cardiovascular problems.
The good news? Once you spot these signs, you can take action to support your body with the nourishment it deserves and requires.
What Can You Do If This Sounds Familiar?
If these signs resonate with you, here are some first steps you can take:
💛 Start prioritising regular meals and snacks.
Follow the ‘rule of 3’ by aiming for:
- 3 balanced meals a day (including carbs, fats, and protein)
- 3 substantial snacks
- No more than 3 hours between eating
Remember that consistency matters just as much as quantity!
🍽️ Add Variety & Satisfaction
Say yes to flavour and variety by including foods that bring you joy and satisfaction. This can look like opting for full fat versions of foods, adding peanut butter to your oats in the morning, squeezing honey or sprinkling nuts and seeds on your yogurt, or actually choosing what you want on the menu.
🧠 Challenge the Food Rules
Some of you may know you need to eat more, but implementing it is another story. To start this journey it can be really helpful to become aware of the food rules you have in place, and why they are there in the first place. Ask yourself: Where did this belief come from, and is it actually serving me?
You Need to Fuel [and REFUEL]
Whether you’ve just realised you may be underfueling or you’ve known for a while but haven’t known where to start, it’s never too late to make a change. For some, increasing food intake may feel relatively straightforward, especially if you simply didn’t realise how much energy your body truly needs.
But for others, particularly those who struggle with their relationship with food, this process can feel overwhelming and even scary.Healing your relationship with food and learning to trust your body again takes time, support, and a lot of self-compassion. It will require you to challenge your beliefs, unlearn harmful behaviours and face uncomfortable emotions. But despite the challenges, this journey is incredibly rewarding. Nourishing your body properly is one of the most powerful and loving acts of self-care you can give to yourself.
Remember, you don’t have to do this alone. Support is essential, whether it’s from a dietitian, friends, family or loved one. If you’re ready to take the next step toward fueling your body and healing your relationship with food, but feel like you need some additional support, I’m here to help guide you.