What Happens if You Work Out Regularly But Don’t Eat Enough Calories?

Most athletes strive for peak performance through training and nutrition. Calories from food are an important part of training for success. Calories are what the body uses for energy and energy is required for muscles to move and exercise. Teenagers need to eat enough calories to fuel their bodies for sports. With this in mind, teen athletes should practice caution when making any diet changes that include restriction of food. 

What exactly will happen if you work out regularly, but don’t eat enough calories?

If a teen athlete does not eat enough and still works out, performance will ultimately suffer. The body will not have the energy to meet the demands of the sport and will experience decreased muscle and tissue repair. The athlete will feel dizzy, fatigue early, and may even lose interest in experiences that require more energy, such as training. Long term lack of adequate food and calories will cause muscle wasting, damage to organs, poor hormone function and stunted growth. Not eating enough will really hurt your physical abilities.

Continue to read for more information regarding how not eating enough calories will impact an athlete and how to identify when an athlete does not consume enough calories.

The Dangers of Not Eating Enough for Athletes

When the teenage body is well fed, it can perform incredible feats. However, when there is a lack of food for the body to use as energy, the body will focus on survival over all other activities. This survival tactic means less energy for training and performance. 

What Happens to Your Body When You Don’t Eat Enough:

  • Low energy
  • Early fatigue
  • Poor muscle recovery
  • Poor athletic performance
  • Muscle loss and wasting
  • Heart and brain problems
  • Poor health
  • Frequent injuries
  • Hormone dysfunction
  • Bone loss
  • Stunted growth

In the short term, athletes will rapidly run out of energy due to a low storage of fuel for their bodies. This energy depletion means early fatigue, which never works well for sports. 

Due to under eating, the athlete may also not consume enough protein and carbohydrate for muscle recovery, putting future performance at risk. The body needs protein, carbohydrate, and fat to build and replenish muscle and energy.

When an athlete continues to not eat enough and train hard, the consequences become even more serious. Long lasting insufficient calorie intake puts the entire body at risk.  

The body needs energy from food to keep the heart beating and the body systems working. So, when less energy is available from food, the body begins to convert muscle protein into necessary energy. This protein conversion along with lack of protein for recovery leads to muscle loss and wasting. 

Other essential components of a healthy body will also suffer from the lack of calories. The heart and other organs will begin to suffer causing further negative consequences to health and performance. The body will do all it can to save energy for these essential body systems. With all energy going towards basic survival, teen athletes may lose their passion for the sport. The energy required to move and participate in a sport may become a chore rather than an enjoyment. They may also experience hormone dysfunction, bone loss, and stunted growth as the body fights to survive and diverts resources away from these functions.

See also: Nutrition Meal Plans for Teenage Athletes

Signs You Are Not Eating Enough Before A Workout

Early signs of not eating enough before a workout are hunger pains and the feeling of an empty stomach. Few enjoy working out with a full stomach, but an empty stomach does not help either. There’s a happy medium or being fueled and energized, without digestion problems.

Other signs to watch for include feeling like more effort is necessary for the same results, tiring quickly, obsessive thoughts of food, lightheaded and dizzy. With repeated lack of calories before workouts, athletes will also experience frequent injury and sickness, lack of enjoyment with sport, and amenorrhea (loss of period for girls).

Not eating enough calories before a workout can happen easily. The calorie demands of growth and development during the teenage years along with the additional calorie needs of training can make eating enough of a challenge. Many teenage athletes may not realize they are not eating enough until they notice the signs of undernutrition. However, both female and male teenage athletes are at risk for eating disorders and should seek professional help with signs of an eating disorder. These signs can include secrecy around eating, obsessive thoughts about food and weight, drastic weight changes, and rigid rules around eating and food.

If there are concerns of an eating disorder, the National Eating Disorders Association provides a screening tool at nationaleatingdisorders.org. The helpline is (800) 931-2237.

Female Athlete Triad

Female athletes who work out without eating enough calories can develop a serious condition called the female athlete triad.  This triad is where inadequate calories lead to a disruption of hormones causing a loss of menstruation (period cycles) and low bone mineral density. The lack of calories can happen unintentionally or through disordered eating habits.

This loss of a period (amenorrhea) comes from the body no longer producing an appropriate balance of hormones as it conserves energy for survival. The imbalance of hormones includes a decrease in estrogen. Low estrogen combined with inadequate minerals, such as calcium, from food result in low bone mineral density.

Poor bone mineral density puts a female athlete at high risk for osteoporosis. Osteoporosis is a debilitating disease of weak bones. Those with osteoporosis experience an increase in bone fractures and a decrease in mobility as they age.

Sometimes an athlete will be told that the lack of a period is normal in very active females.The lack of a period is not normal and causes lasting damage. An athlete experiencing this issue should seek the advice of a medical professional.

Tips for Pre-Workout Fueling if You Don’t Like Working Out on a Full Stomach

Finding the right timing for eating before a workout may require some experimentation. Usually, the recommended time is to eat 1 to 3 hours before a workout, no closer than 30 minutes before. An athlete can shift their meal or snack time 30 minutes closer to race time if their stomach feels too empty or 30 minutes earlier if the stomach feels too full during the work out. Eventually the athlete will find the timing that works best for them. Experiment on practice days to know what timing works by competition.

If an athlete chooses to work out on an empty stomach in the morning, emphasis should be placed on a good recovery meal after a workout. This meal should contain a mix of carbohydrate and protein to replenish what was lost. The athlete will also want to make sure they eat enough to meet their calorie needs during the rest of the day. Hydration should never be skipped, even in the morning. Dehydration will negatively impact performance and health.

Another helpful tip for an athlete who prefers an empty stomach before a workout is to eat a balanced meal 3-4 hours prior to the workout. These hours after the meal gives the body time to digest the food. This meal should contain a mix of fat, protein and carbohydrate to help sugar levels maintain stable for long lasting energy. If needed, a lighter snack can be eaten closer to the workout. 

Examples of Meals 3-4 Hours Before a Workout Include:

  • Pasta with chicken and veggies
  • PB&J sandwich
  • Greek yogurt parfait
  • Waffle with nut butter and fruit
  • Rice cakes with hummus (depending on personal tolerance)
  • Bagel sandwich
  • Cottage cheese and fruit slices
  • Cold cereal and milk
  • Tuna pouch with pita crackers
  • Rice with curry and veggies
  • Veggie pita pocket

Examples of Snacks 1-2 Hours Before a Workout Include:

  • Fruit smoothie
  • Energy bar and fruit
  • Trail mix and dried fruit
  • Toast with nut butter and a banana
  • String cheese and crackers
  • Hard boiled egg and juice
  • Pretzels and peanut butter
  • Fruit leather
  • Dates

Teen athletes will have unique needs and preferences. They should find what works best for them before an event. Athletes should not make changes to eating patterns in the days prior to an actual event as these changes could lead to stomach distress. Nutrition should be a part of training and a focus during the season.

See also:

What Does Eating Enough Calories While Regularly Working Out Look Like?

Each athlete will enjoy a different pattern of eating before a workout. One athlete may prefer a meal 2-3 hours before working out and another may choose to eat lighter snacks closer to training time. The most important principle in ensuring that a teen athlete will have the energy needed to perform, is the overall intake. In other words, is the athlete consuming enough calories throughout the day and weeks to meet energy and growth demands?

Teenage athlete needs can vary from 2,000 to 2,800 calories depending on sex, age, weight, height, and activity level. Rather than trying to hit a certain number of calories, an athlete can focus on other indicators such as feelings of fullness, hunger, and overall wellness. Teen athletes typically need about 3 meals per day with 1-3 snacks that are “mini-meals” and provide necessary nutrients and energy.

See also: How Many Calories Should a Teenage Athlete Eat? Ask A Dietitian

The Bottom Line

When an athlete eats enough calories while regularly working out, they will avoid experiencing the consequences of not having enough energy. They will have energy to train and perform well. They will also be in a better position to fight off sickness and avoid injury, build muscle and strength, and enjoy participating in their sport.

Related Questions

Is It Okay to Workout On An Empty Stomach? If you workout on an empty stomach you may not have enough energy for exercise and begin to fatigue early, feel light-headed, nausea, and use body protein reserves for energy. You should eat at least 3-4 hours before a workout.

Do I Have to Eat in the Morning Before I Workout? Eat something small if you can before a morning workout to help your blood sugar. If an athlete chooses to work out on an empty stomach in the morning, emphasis should be placed on a good recovery meal after a workout. This meal should contain a mix of carbohydrate and protein to replenish what was lost. The athlete will also want to make sure they eat enough to meet their calorie needs during the rest of the day.

What Happens When You Exercise While Starving? If you exercise while starving your body won’t have enough stored energy for fuel and movement. Your body might need to revert to using protein reserves for energy, which is not beneficial. By having less energy during exercise you’ll fatigue earlier, feel nauseous and light headed, get irritable, and not be able to recover and heal as easily. Try to eat something small at least a few hours before exercise and be sure to stay hydrated during the day and during your workout.

Is It Better to Workout in the Morning or at Night? The best time for a teenager to exercise is whichever time fits into their schedule and the time that they can commit to regularly. As long as you’re exercising you’ll be getting benefits. Many people like to exercise in the morning to start their day, but later in the day can be beneficial to de-stress, increase endurance, and improve function.

See Also

For more specific help with your eating plan this season, get help from a registered dietitian nutritionist. Check out my latest eBook: Nutrition Game Plan for Teenage Athletes


  • 50+ pages
  • 28-day meal plan
  • Healthy snack list
  • Tips for Gaining or Losing Weight the Healthy Way
  • Calculations for Daily Calorie Needs, Protein Needs, and more
  • Supplement Recommendations
  • Meal Schedule

Check it out here: https://www.fuelingteens.com/downloads/nutrition-game-plan-for-teenage-athletes/

Katherine Harmer, RDN

I'm a Registered Dietitian Nutritionist with a love for coaching others to success in their health goals, especially teenage athletes. Tennis was my sport of choice in high school. Now I'm a little bit older, a little bit smarter, and a little bit worse at tennis.

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