Beyond the Deficit: Why Your Body Needs MORE to Perform & Thrive
As a nutritionist, I often hear a familiar story: "I'm moving more, but I feel constantly drained, I’ve stopped progressing in training and I keep getting injured! What am I doing wrong?"
If this resonates with you, you could be under-fuelling.
Our bodies are incredible, adaptable machines, built for survival. Yet, the modern drive to "push harder" and "eat less" can inadvertently conflict with our fundamental biology.
What is under-fuelling?
Under-fuelling occurs when your calorie intake isn't sufficient to cover your body's essential functions, daily activities, and the demands of your physical training. It's not necessarily about intentional dieting, but rather consistently consuming "too little" for your specific energy output.
Your body requires fuel for every process: breathing, thinking, blood circulation, immune defence, tissue repair, hours spent on your feet at work or in front of the computer and, of course, training sessions. When your fuel tank consistently runs low, your body shifts into a state of survival mode.
The term ’Maintenance calories’ refers to the amount of calories your body requires to function and do the above processes. When you consume more calories, you gain weight, and when you consume fewer calories, you lose weight. While it is possible to be in a calorie deficit while training and performing well, under-fuelling happens when you are either in a deficit that is too extreme or you have been in a deficit too long.
The hidden costs: How to recognise the signs
When your body lacks adequate energy, it begins to downregulate "non-essential" systems to conserve resources. These symptoms may start subtly but can escalate into significant health and performance issues.
Listen to your body for these crucial indicators:
Persistent Fatigue: More than just post-workout tiredness; this is a profound, unshakeable exhaustion. It's often a sign of under-fuelling, which causes a rise in stress hormones that disrupt your sleep and prevent proper recovery, leading to this severe fatigue.
Declining Performance: Are your usual easy runs feeling harder? Do you struggle to get through your workouts? Is your heart rate higher at a lower intensity than normal? These are key signs that your body is stressed and working harder to maintain effort. You might also notice slower recovery, reduced strength, decreased endurance, or hitting performance plateaus.
Frequent Illnesses: Are you constantly on the edge of getting sick, battling colds or infections, or taking longer to recover from them? High training loads can compromise your immune system, and not eating enough only exacerbates this.
Recurrent Injuries: Especially stress fractures, strains, or chronic aches that are slow to heal. Your body lacks the resources for adequate repair and recovery.
Irregular or Absent Menstrual Periods (for female athletes): This is a serious indicator of hormonal disruption, which can have long-term implications for bone health.
Persistent Coldness, Poor Sleep, Brittle Nails, Hair Thinning: These are signs your body is cutting energy to non-vital functions.
Mood Swings, Brain Fog, & Irritability: The brain is a high-energy consumer; insufficient fuel impacts cognitive function, concentration, and emotional regulation.
Obsession with Food: You might find yourself constantly thinking about food, calories, or your next meal as your body desperately seeks fuel.
Why the scale won't budge
While this is frustrating, it's your body's sophisticated survival mechanism at play:
Metabolic Adaptation: Your body learns to operate more efficiently with fewer calories. Your Resting Metabolic Rate (RMR), the calories you burn at rest, slows down significantly. Non-Exercise Activity Thermogenesis (NEAT) – all those unconscious daily movements – may also decrease. Your body becomes a highly efficient, calorie-saving machine. Your maintenance calories become lower. This means the actual gap between what you eat and what you burn shrinks, leading to minimal or no fat loss over time.
Water Retention: Intense training, especially when under-fuelled, stresses your body. This can lead to increased inflammation and elevated cortisol (the stress hormone). Chronic high cortisol often results in significant fluid retention, which can completely mask any fat loss on the scale.
Hormonal Imbalance: When your body isn't getting enough fuel, it shifts into survival mode, and your hormones are often the first to be affected. This can create a domino effect of negative health consequences.
Reproductive Hormones: Under-fuelling can disrupt the hormones essential for a healthy reproductive system in both men and women. For women, this can lead to irregular or absent menstrual periods (amenorrhea), while in men, it can cause a significant drop in testosterone, affecting libido and mood.
Thyroid Hormones: Your body reduces the production of thyroid hormones (specifically T3) to slow down your metabolism. This is a survival mechanism that conserves energy, but it can make you feel constantly cold and tired, and may cause a frustrating plateau in weight loss.
Stress Hormones: Under-fuelling is a form of physical stress, which leads to a constant elevation of the stress hormone, cortisol. Chronic high cortisol can disrupt your sleep, increase inflammation, and even lead to stubborn fluid retention. Additionally, chronic stress can influence fat storage patterns, sometimes leading to preferential fat accumulation in certain areas, even during overall weight loss.
Hunger Hormones: The delicate balance of your appetite hormones is thrown off. Ghrelin, the "hunger hormone," increases, making you feel constantly hungry, while leptin, the "satiety hormone," decreases, making it hard to feel full or satisfied after a meal. This imbalance can fuel cravings and lead to a vicious cycle of restriction and binge eating.
Binge Eating: "Under-fuelling can cause binge eating. It creates both a physical and psychological state of deprivation, which leads to intense hunger and an obsession with food." This biological pressure ultimately overpowers a person's control, triggering a binge to compensate for the perceived starvation and fuelling a vicious cycle of restriction followed by bingeing. This can happen without us realising, especially at the start. Ultimately, it can mean that you are eating more calories than you realise.
In this state, your body prioritises survival over fat loss. It's not "broken," it's simply performing its evolutionary role and keeping you alive.
Reversing the effects of under-fuelling
If you've identified with the signs of under-fuelling, it's time to shift your mindset from restriction to recovery. The most crucial step you can take is to hit the reset button on your metabolism by consistently eating at your maintenance calories. You might be able to jump straight back to maintenance, or you might have to slowly build up to it.
By providing your body with enough fuel to meet all its demands—from daily activities to tissue repair—you are signalling that the threat is over. This gives your metabolism the green light to speed back up and allows your hormones and other bodily systems to re-regulate.
What to expect during the reset phase
One of the most common fears during this process is weight gain, and it's important to understand what's happening. When you first increase your food intake, you will likely see the number on the scale go up. Do not panic. This temporary increase is due to a few key factors:
Water Retention: Under-fuelling is a form of stress that can elevate cortisol, a hormone that promotes fluid retention. As you eat more and inflammation decreases, your body will still hold onto some water initially as it heals.
Glycogen Replenishment: Your muscles store carbohydrates as glycogen, and with every gram of glycogen, your body stores about 3 grams of water. When you've been in a deficit, these stores are often depleted. Increasing your food intake, particularly carbohydrates, will cause your glycogen stores to replenish, which also increases water weight.
Hormonal rebound. After a period of underfuelling, your body is incredibly efficient at storing energy. As your hormones rebalance, your body might temporarily hold onto a bit of fat as a way of preparing for any future "famine" it might perceive.
This initial scale fluctuation is a positive sign that your body is rehydrating and recovering.
How to know when you're recovered
The timeline for metabolic recovery is unique to everyone and can depend on how long you’ve been under-fuelling. It can take anywhere from a couple of weeks to a few months. Instead of obsessing over the scale, pay attention to these clear signs that your body is healing and your metabolism is normalising:
Consistent Energy Levels: The profound, unshakeable fatigue will begin to fade. You’ll have more stable energy throughout your day and won't feel like you're running on fumes during your workouts.
Improved Sleep Quality: As your stress hormones rebalance, you’ll find it easier to fall asleep and stay asleep. You’ll wake up feeling more rested and recovered, which is essential for muscle repair and mental clarity.
A Return of Your Natural Hunger Cues: The obsession with food will start to diminish. You'll be able to recognise true hunger and feel satisfied after a meal, helping you to build a healthier, more intuitive relationship with food.
Increased Performance in the Gym: Your training will feel stronger and more powerful. You’ll be able to lift heavier, complete more reps, or run faster because your body finally has the fuel it needs to perform.
Fewer Injuries and Illnesses: Your body will have the resources to repair muscle and tissue and will no longer be compromising your immune system. You’ll likely get sick less often and recover more quickly.
By focusing on nourishment over deprivation and prioritising these internal markers of health, you can successfully break the cycle of under-fuelling and set yourself up for sustainable performance and long-term well-being.
Fuelling for overall health & performance
True health and peak performance stem from adequate nourishment, not deprivation.
Focus on fuelling for performance.
Eat Enough: Whether you work with a qualified professional to understand your true energy needs or work it out on your own, make sure to consider your activity level, unique metabolism, and individual goals.
Eat Even When You're Not "Hungry": This is often critical for athletes. Sometimes, a heavy training load and demanding daily activity (like working on your feet) can temporarily suppress appetite, even when your body desperately needs fuel. You might need to establish structured eating times or incorporate convenient, calorie-dense options to ensure you meet your energy demands.
Prioritise Nutrient-Dense Foods: Focus on whole grains, lean proteins, healthy fats, and a diverse range of fruits and vegetables.
Listen to Your Body: Honour genuine hunger cues (when they are present!), distinguish true fatigue from a desire to avoid training, and prioritise recovery. This isn’t always obvious and can take practice.
Fuel your workouts: This is especially important if you are in a deficit and trying to lose fat. Fuelling your workouts with a small amount of carbohydrates before and after training can provide the energy needed to maintain performance, preserve muscle mass, and prevent the profound fatigue that can make a calorie deficit unsustainable. It can be the difference between sticking to your plan and giving up.
If you'd like to learn more or need help finding a starting point, schedule a free discovery call below. We'll discuss your goals and create a clear plan for how I can help you get there.
