Are you eating enough to support your workouts? 7 signs you're under-fueling your training

In this article, we explain:

• ‍The most common signs of low energy availability
• Why carbohydrates matter for performance
• Whether fasted training is a good idea
• How to fuel your workouts for better energy and results
• What is Relative Energy Deficiency in Sport (REDS) and why should gym-goers care?

What is relative energy deficiency in sport (RED-S)?

RED-S occurs when your energy intake is too low to support both training and normal bodily functions, which can reduce performance and negatively impact health.
Relative Energy Deficiency in Sport (RED-S) develops when your body doesn't have enough available energy to support both exercise and normal physiological function.

Nutrition scientist Penny Matkin-Hussey explains: "RED-S, or Relative Energy Deficiency in Sport, is a complex syndrome of adaptations your body makes to conserve energy for essential survival. It's the result of something called low energy availability. Low energy availability occurs when we're not eating enough to support the exercise we're doing."

In simple terms, you're consistently burning more energy than you're replacing through food.

To compensate, your body redirects resources away from functions it considers less essential, prioritizing immediate survival and movement requirements instead.

This can impact:

• Exercise performance
• Recovery
• Muscle growth
• Hormone production
• Bone health
• Mood and wellbeing
• Cardiovascular health

The surprising part is that you don't need to be an elite athlete to be affected.

How common is low-energy availability?

Matkin-Hussey says it’s hard to determine accurately, but in a recent review of thirteen studies investigating the prevalence of low energy availability in various sports, up to 58% of athletes were reported to be in low energy availability. In 2016, a survey was conducted on women aged 18-40 who participated in group fitness in New Zealand, and 45% of those surveyed were at risk of low energy availability – which is huge.

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7 signs you might not be eating enough for your training

Dizziness and fainting are often associated with lack of food, but under-fueling doesn't always announce itself dramatically. Sometimes it shows up as subtle changes that are easy to dismiss.

1. Your performance has stalled

Despite training consistently, your strength, endurance, or fitness stops improving.

2. You're always tired

Persistent fatigue can indicate that your energy intake isn't matching your training load.

3. Recovery takes longer than expected

Muscle soreness lingers and you struggle to bounce back between workouts.

4. You keep getting injured

Low energy availability can affect tissue repair and long-term musculoskeletal health.

5. Your mood has changed

Irritability, low motivation, and difficulty concentrating can all be signs that your body isn't getting enough fuel.

6. You're experiencing digestive issues

Digestive discomfort can sometimes accompany chronic under-fueling.

7. You're noticing hormonal changes

For women, menstrual changes can be one of the clearest warning signs. Insufficient fuel can cause periods to become irregular or stop altogether. For men, the signs can be less obvious.
Matkin-Hussey explains: "Obviously, the menstrual cycle isn't a factor, but we do get a downregulation in testosterone, which will have an impact on libido."

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"We can't give our best or get the most from our workouts if we are chronically under-fueled, not recovered, or injured."
Penny Matkin-Hussey

What nutrient are most gym-goers undereating?

For many active people, carbohydrates, not protein, are the nutrient most commonly lacking.

Mention sports nutrition and most conversations quickly turn to protein. According to Matkin-Hussey: "Nine times out of ten, I'm getting athletes to eat less protein, more carbohydrates."

For many exercisers, carbohydrates are the missing piece needed to support training performance and recovery.

Why are carbohydrates important for workout performance?

Carbohydrates are the body's preferred fuel source during moderate and high-intensity exercise. They provide readily available energy that supports:

• Training quality
• Workout intensity
• Recovery
• Adaptation and progress

Without enough carbohydrates, workouts can feel harder, recovery may slow, and results can stall.

Is fasted training a good idea?

Fasted training may work for some people, but it is unlikely to support optimal performance, recovery, or training adaptation. Regularly exercising without fuel may increase the risk of low energy availability.

Matkin-Hussey explains: "If you go into a workout in a fasted state, you are training in low energy availability. Training in a fasted state is not going to bring about your best performance, or maximize the gains from your workout."

How to fuel your workout for better performance

Group Fitness Manager Geena Pannett recommends matching your fuel to the time available before exercise.

Less than 30 minutes before training

Focus on fast-digesting carbohydrates:

• Dates
• Dried fruit
• Toast with honey or jam
• Fruit juice
• Sports drink

30 to 60 minutes before training

Choose carbohydrates with a little more staying power:

• Banana
• Fruit toast
• Cereal
• Crumpets

Two to three hours before training

Aim for a balanced meal containing:

• Carbohydrates
• Protein
• Healthy fats
• Fiber

Examples include:

• Chicken poke bowl
• Salmon bagel
• Protein smoothie with oats, berries, and peanut butter

Training early in the morning?

Pannett's advice is simple: "A little something is far better than a whole lot of nothing." A small glass of fruit juice, a teaspoon of honey, or a couple of dates can provide quick-access energy without feeling heavy.

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Five smart fueling habits for gym-goers

1. Prioritize carbohydrates before training

Matkin-Hussey recommends simple, easily digested options for early workouts:

• Banana or oiece of fruit
• Rice cakes with jam or honey
• Dried fruit
• Sports drink or orange juice

For morning training sessions: "What you want is to be getting at least 45 grams of carbohydrate into you to fuel the morning workout."

2. Hydrate consistently

Don't wait until you're thirsty. Carry water throughout the day and consider electrolytes when sweating heavily.

3. Ensure you're eating enough carbohydrates overall

Smaller, frequent meals and snacks can help maintain energy levels and support recovery. Sports drinks and chocolate milk can also be practical options when convenience matters.

4. Spread your protein intake across the day

Matkin-Hussey recommends distributing protein intake across meals rather than consuming large amounts at once. For most active people: Aim for approximately 1.6 to 2.0g of protein per kilogram of body weight per day.
Make room for sufficient carbohydrate intake alongside protein. The goal is balance. Protein supports repair. Carbohydrates fuel the training stimulus that drives adaptation.

5. Use caffeine strategically

Personal Trainer and Group Fitness Instructor Sarah Shortt recommends using caffeine as a supplement to good nutrition, not a replacement for it. "If you need a pick-me-up, have a cup of coffee or green tea about 30-45 minutes before your workout. Pairing caffeine with a balanced snack can help smooth out the energy boost and reduce the likelihood of a crash."

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Key takeaway

If you're training consistently but feeling fatigued, underperforming, struggling to recover, or hitting a plateau, the issue may not be your workout plan.

For many active people, the missing ingredient is adequate fuel.

Getting enough energy, especially enough carbohydrate to support your training demands, is fundamental to performance, recovery, adaptation, and long-term health.

Sometimes the most effective nutrition strategy isn't eating less. It's eating enough to support the work you're asking your body to do.

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About the expert

Penny Matkin-Hussey holds an undergraduate degree in Sport and Exercise Science and is undertaking PhD research at the University of Otago focused on Relative Energy Deficiency in Sport (RED-S) and athlete health.

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This article features insights originally shared in this article: www.lesmills.com/articles/should-you-be-eating-more