Signs You’re Not Eating Enough: How Under-fuelling Affects Your Body and Mind
- Lily Hitchings
- Jun 30
- 3 min read
We live in a culture that often praises discipline, clean eating, and grinding through workouts. But beneath the surface of many "healthy" habits lies a problem that’s easy to overlook: under-fuelling.
Whether it's intentional or not, not eating enough can quietly wreak havoc on your body and mind. It's more common than you think—especially among active individuals, those pursuing weight loss, or anyone stuck in diet culture. Let’s break down the signs of under fuelling, why it matters, and how to recognise when it’s time to nourish yourself better.
What Is Under fuelling?

Under fuelling happens when your body doesn’t get the energy (calories) it needs to function properly. This isn’t just about dramatic weight loss or starvation diets—it can happen to people eating three meals a day, working out regularly, or even feeling like they're doing "everything right."
What Is RED-S?
RED-S stands for Relative Energy Deficiency in Sport, a condition that occurs when the body doesn’t get enough fuel to support both exercise demands and basic physiological functions. While initially identified in athletes, RED-S is now recognized across all activity levels and genders. It impacts multiple systems in the body, including metabolism, immunity, bone health, menstrual function, cardiovascular health, and mental well-being. Symptoms may show up as fatigue, frequent illness, stress fractures, hormonal imbalances, and mood changes. RED-S is not just a sports issue—it’s a whole-body, whole-life issue caused by chronic underfueling, even unintentionally.
Not Eating Enough Symptoms: What to Watch For
You may be surprised at how many "normal" symptoms are actually red flags that you’re not eating enough. Here are some of the most common signs of under fuelling:
1. Constant Fatigue
If you're tired all the time, even after sleeping well, your body might be running on empty. Calories are energy—without enough, your body slows down to conserve.
2. Poor Workout Recovery
Sore for days? Plateauing in strength? Underfueling impairs muscle repair and slows recovery. You can’t train your best if you’re not fueling your body adequately.
3. Irritability and Mood Swings
Undereating and mental health go hand in hand. Chronic low energy intake is linked to increased anxiety, depression, and irritability. Your brain needs fuel, too.
4. Losing Your Menstrual Cycle (Amenorrhea)
For women, a lost or irregular period is a major warning sign. Hormonal disruption from under fuelling is a hallmark symptom of RED-S.
5. Cold All the Time
Feel like you’re freezing when others are fine? That’s a sign your metabolism has slowed and is prioritising essential organs over thermoregulation.
6. Hair Thinning or Hair Loss
Your body will prioritise vital organs over non-essentials like hair growth when it's not getting enough nutrients.
7. Obsessive Thoughts About Food
Thinking about food all the time? Undereating can increase cravings and fixate your brain on finding fuel. It's a primal survival response.
8. Digestive Issues

Slowed digestion, constipation, or bloating can result when your gut isn’t getting the fuel it needs to function smoothly.
How to Start Healing
If any of these signs feel familiar, it might be time to reassess your intake and habits. Here’s where to start:
Track your energy, not just your calories. Ask yourself: Do I feel strong? Energized? Focused?
Work with a registered dietitian or sports nutritionist, especially if you’re active or recovering from disordered eating.
Normalize rest and nourishment as part of a balanced lifestyle, not as something to earn.
Let go of rigid food rules. Flexibility in eating supports long-term health far more than perfection ever could.
Recognising the signs of under- fuelling is the first step toward reclaiming your health. Your body isn’t meant to run on fumes—it's meant to thrive. By tuning into these symptoms and honouring your needs, you’re not giving up on your goals—you’re giving your body the foundation it needs to achieve them.
Struggling with RED-S or Under fuelling? We Can Help
If you’re resonating with the signs of under fuelling or suspect you may be dealing with RED-S, you don’t have to navigate it alone. At Nutrition and Co, we specialize in helping active individuals restore balance, rebuild trust with food, and optimize performance through personalized, compassionate support. Whether you're dealing with low energy, missing periods, or feeling stuck in a cycle of restriction, our team is here to guide you with evidence-based strategies and real-life solutions.
Book a free discovery call today to chat with a registered nutritionist and explore how we can support your goals—no pressure, just support. Your health is worth it.
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