How to fix underfueling to boost performance and health

January 8, 2026 •

4 min read

According to sports dietitians, consistently underfueling can lead to a state of Low Energy Availability (LEA), which negatively impacts performance and recovery. If you're experiencing chronic fatigue, decreased performance, or mood shifts, learning how to fix underfueling is critical for your overall health and athletic progress.

Quick Summary

This guide provides actionable steps for increasing calorie intake, balancing macronutrients, and timing meals strategically to reverse the effects of underfueling and restore energy levels for better performance and health.

Key Points

Identify Symptoms: Learn to recognize the signs of underfueling, such as chronic fatigue, low performance, and frequent illness, to address the root cause effectively.
Increase Caloric Density: Safely add more calories to your diet by incorporating nutrient-dense foods like nuts, seeds, avocados, and healthy oils into your meals and snacks.
Master Meal Timing: Strategically consume carbohydrates before workouts and a carb-protein mix within 60 minutes after exercise to maximize performance and recovery.
Balance Macronutrients: Ensure your diet includes an optimal balance of carbohydrates, protein, and healthy fats to fuel training, support muscle repair, and maintain overall health.
Listen to Your Body: Pay close attention to your body's hunger and recovery signals, and don't ignore persistent issues that suggest an energy deficit.
Seek Professional Help: For persistent issues or suspected disordered eating, consulting a sports dietitian or other health professional is the safest path to recovery.

Recognize the Signs of Underfueling

Before you can effectively address the problem, it’s vital to recognize the symptoms that point toward a nutritional deficit. Underfueling can manifest in various physical and psychological ways, often subtly at first. Early signs include lethargy, constant fatigue even after rest, and a noticeable lack of progression in your training. Long-term underfueling can lead to more serious health issues, known as Relative Energy Deficiency in Sport (RED-S), which affects metabolic rate, bone health, immunity, and reproductive function.

Common symptoms to watch for:

Chronic Fatigue: Feeling tired all the time, not just after a hard workout.
Decreased Performance: Noticeable drop in strength, endurance, or overall athletic ability.
Frequent Illness or Injury: A weakened immune system can lead to more frequent colds, while poor bone density can cause stress fractures.
Sleep Disturbances: Difficulty falling asleep or staying asleep, or waking up frequently during the night.
Mood Changes: Increased irritability, anxiety, and general low mood.
Digestive Issues: Problems like constipation or other gastrointestinal distress.
Hormonal Imbalances: For women, this can include irregular or lost menstrual cycles.

Implement a Structured Refueling Strategy

Fixing underfueling requires a deliberate and consistent approach to increase your energy intake. This isn't about simply eating more junk food; it's about adding nutrient-dense calories that support your body's recovery and performance needs. A sports dietitian can help tailor a plan, but several key strategies can be implemented immediately.

Increase Calorie Density

One of the simplest ways to increase your caloric intake is to make small adjustments to your meals and snacks. Focus on adding calorically dense but healthy ingredients throughout the day.

Add a handful of nuts or seeds to your oatmeal or yogurt.
Drizzle olive oil or a creamy dressing on your salads and vegetables.
Top toast or pancakes with nut butters, honey, or syrup.
Incorporate avocados into meals, such as with eggs or in a smoothie.

Prioritize Meal Timing

Strategic meal timing is crucial, especially around your workouts. Fueling before and recovering after exercise is essential for replenishing glycogen stores and repairing muscle tissue.

Pre-workout: Consume a carbohydrate-rich snack or meal 60-90 minutes before your session. A banana with a spoonful of nut butter or a bowl of oatmeal can provide the necessary energy.
Post-workout: Aim for a combination of carbohydrates and protein within 30-60 minutes after training to maximize recovery. Chocolate milk, a smoothie with Greek yogurt and fruit, or two eggs on toast are excellent choices.
Daily Schedule: Rather than three large meals, try eating smaller, more frequent meals and snacks throughout the day to keep energy levels stable.

Balance Your Macronutrients

While it's important to increase overall calories, ensuring you get the right balance of macronutrients is also key. Carbohydrates are your body's primary fuel source, and protein is critical for muscle repair and growth.

Carbohydrates: Don't shy away from carbs. They are essential for fueling intense training. Ensure you are getting enough whole grains, fruits, and vegetables.
Protein: Aim for adequate protein intake to support muscle recovery. Excellent sources include lean meats, fish, eggs, dairy, and legumes.
Healthy Fats: Include healthy fats from sources like nuts, seeds, and avocados to increase calorie density and support hormone function.

Comparison of Fueling Strategies

This table outlines the key differences between underfueling and an optimized fueling approach, helping you understand what changes to prioritize.


Aspect	Underfueling	Optimal Fueling
Energy Intake	Consistently below energy expenditure, leading to a deficit.	Balanced intake matching or slightly exceeding training demands.
Meal Frequency	Irregular meals, often skipping breakfast or lunch.	Regular meals and strategic snacks throughout the day.
Macronutrient Focus	Often restricted in one or more macros (e.g., low-carb).	Balanced diet focusing on complex carbs, lean protein, and healthy fats.
Workout Timing	Not fueling before or after exercise, running on empty.	Consuming carbs before and a carb/protein mix after workouts.
Performance	Decrease in strength, endurance, and coordination.	Improved endurance, strength, and training adaptation.
Recovery	Impaired muscle repair, chronic soreness, longer recovery times.	Efficient glycogen replenishment and faster muscle recovery.
Health Markers	Hormonal imbalances, weak bones, poor immunity.	Stable hormones, strong bone density, robust immune system.

Listen to Your Body and Seek Professional Help

Beyond structured dietary changes, fixing underfueling involves becoming more attuned to your body's signals. Trusting your appetite, eating when you feel hungry, and recognizing your body's feedback are powerful tools. If you've tried adjusting your diet without success, or if you suspect you may have an eating disorder, seeking help is crucial.

For personalized, expert guidance, consider working with a sports dietitian nutritionist who can create a tailored fueling plan based on your unique needs, training load, and individual goals. This professional support can be invaluable for long-term health and performance.

Conclusion: Your Path to Re-energized Performance

Addressing underfueling is a critical step for anyone struggling with consistent fatigue, performance plateaus, or recurring health issues. By implementing a strategic approach that includes increased calorie density from nutrient-rich foods, prioritized meal timing around workouts, and balanced macronutrient intake, you can effectively reverse the negative effects of underfueling. Listening to your body and considering professional guidance are also essential steps on this journey. Committing to a healthier, more intentional fueling strategy will not only enhance your athletic performance but also lay the foundation for sustainable overall health and energy. For a deeper understanding of Relative Energy Deficiency in Sport (RED-S), consult the comprehensive resources provided by the International Olympic Committee.

Frequently Asked Questions

The fastest way to initiate recovery is to immediately increase your daily calorie intake with nutrient-dense foods, focusing on getting adequate carbohydrates before and after exercise to replenish glycogen stores quickly.

Early signs often include persistent fatigue, poor workout performance, increased irritability, and difficulty sleeping. These symptoms can be subtle and mistaken for overtraining or stress.

Yes, chronic underfueling can paradoxically lead to fat gain. In a state of low energy availability, your body may increase fat storage to conserve energy, while simultaneously breaking down muscle mass.

Start by gradually increasing your intake by 300-500 healthy calories per day and monitor how your body responds. This can be achieved by adding nutrient-dense snacks and slightly larger portions.

Within 30-60 minutes post-workout, consume a meal or snack containing both carbohydrates and protein. Examples include a smoothie with Greek yogurt, a turkey sandwich, or eggs on toast.

Nutrient-dense whole foods should be the primary focus. However, high-calorie protein shakes or sports nutrition supplements can be a convenient way to boost calorie and protein intake, especially post-workout or when appetite is low.

Some individuals may start feeling and performing better within days or weeks of consistent and proper refueling. Full recovery can take longer, depending on the severity and duration of the underfueling.