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Underfueling means not eating enough or not eating the right types of foods. If you’ve been underfueling, you could be undermining or even undoing the hard work you put into your exercise routine. 

Eating more of the right foods at the right time can help you achieve the intensities and results you have been missing.


What do the active women in each of these scenarios have in common?

Scenario 1: Katie went out for dinner with friends. She ate a large plate of pasta, as well as a few glasses of wine, appetizers, a salad and dessert. She let loose more than she usually does, so the next morning, she skipped breakfast before her workout so she wouldn’t gain weight from last night’s splurge.

Scenario 2: Jennifer has a high-intensity training session planned for this evening, but she doesn’t want to feel bloated when she changes into her workout gear. She decides to skip lunch and just grab dinner on the way home from the gym. In the meantime, she tides herself over with a cheese stick and water.

Scenario 3: Lisa’s friend told her that active women need to eat mostly protein, so Lisa stopped eating grains, fruits and vegetables so she could build more muscle. She relies on protein shakes, chicken breasts and eggs to get her through the day. She doesn’t like her diet, but she believes she’s doing the right thing to create the body she wants.


Katie, Jennifer and Lisa are suffering from a condition referred to as underfueling, which means either not eating enough or not eating the right types of foods.

What’s more, they’re not getting the results they desire. Yet scenarios like this play out every day as women try to navigate the mixed messaging about training, eating and performing.

You hear the message everywhere: More than two-thirds of Americans are overweight or obese. Consequently, you’re hit over the head with the idea that weight loss is your one-way ticket to better health. 

While it’s true that weight loss can counteract many of the chronic diseases that affect society, the weight-loss mania spills over into areas — like nutrition for the active woman — where it doesn’t belong. It can be easy to fall victim to the false idea that cutting calories is the only way an active woman can reach her fitness goals.

Part of the reason an active woman may think underfueling is a good choice is that it’s been hard to tease apart the world of women’s fitness nutrition and the world of dieting. 

“The dieting industry has swooped in and masqueraded as sports nutrition for women,” says Susan Kleiner, Ph.D., RD, author of Power Eating (Human Kinetics, 4th Edition, 2013) and a member of Oxygen’s advisory board. “Their messaging is not based on the needs of a female athlete, and they promote underfueling, fasting and undercarbing, with little to no research.”

The first place you may notice a symptom of underfueling is at the gym, Kleiner says, where you’ll suffer from fatigue and low training intensity. Though you may think you’re on the path to building muscle by increasing your training and decreasing your food consumption, you might experience a softening of your physique. “Underfueling can cause a loss of muscle mass while increasing body fat,” Kleiner explains.

Other physical signs of underfueling include hair loss, bad skin, brain fog or memory loss, intestinal disturbances, anxiety and poor sleep quality. “Feeling fatigued, lethargic, sore and weak can be common signs of not fueling properly,” explains Jessica Crandall, RDN, CDE, spokeswoman for the Academy of Nutrition and Dietetics.

Longer-Term Health Impact

If the short-term repercussions of not feeding your active body enough food aren’t enough of a wake-up call, consider this: A weakened immune system, bone loss and bone fractures, and loss of thyroid function are among the serious complications that can result from chronic underfueling. 

What’s even worse, it can have the exact opposite effect than you thought it would, Crandall explains. “Not meeting your nutritional needs and creating vitamin deficiencies makes it more difficult for you to lose weight in the future.”

The Female Athlete Triad is the name for a group of serious health implications that result from chronic underfeeding combined with intense training. It includes disordered eating (binge-purge cycling, laxative abuse,) amenorrhea (lack of menstrual periods) and osteoporosis. Disordered eating, whether it’s an intentional or non-intentional underconsumption of calories, can occur because of poor eating habits and because of the failure to increase food intake to match the intensity of exercise.

When your body perceives too great of a gap between calorie expenditure and calorie intake, your estrogen levels drop and menstrual periods become irregular or cease altogether. Normal estrogen levels are needed to maintain the calcium content of your bones; the result of lowered estrogen is that bones become progressively more porous, which leads to osteopenia (reduced bone mass) and eventually to osteoporosis (brittle bones).

Fueling Without Getting Fat

A common worry among female athletes who underfuel is that they will gain weight if they start to eat more. Truth is, the key to keeping up your metabolism and energy levels while maintaining a healthy weight and toned physique takes eating and training strategies, Kleiner explains.

Carb Fuel

High-intensity training requires fuel from carbohydrates, despite the current fashion for carb-restricted diets. Even though you may perceive that you’re training at high intensity when you haven’t eaten carbs, you won’t be. 

“Your work output will be low,” Kleiner says. “You can train at low intensities on fat stores for hours, but it takes carbohydrates to raise your intensity up to 70 percent or greater of your maximum work capacity.”

You can start to see how underfueling doesn’t bring forth the toned body some think it will because it takes energy to achieve the intensity levels required for maximum performance and high-intensity interval training (HIIT.) According to the nutritionist, if you want to do HIIT training at an appropriate level that leads to improving body composition, you simply must have carbohydrates in your system.

Type of Food and Timing

Both the types and timing of the foods you eat matters when it comes to intense training. Diets too low in calories lead to a drop in metabolic rate, meaning you’d have to work out more to burn the same amount of calories as before. 

“Fueling around exercise is very important, too,” Kleiner says. “If you don’t fuel before training and recover with a combination of protein and carbohydrates after, you’ll be wiped out later in the day and, typically, your appetite will be out of control.”

For a low- or moderate-intensity workout, she recommends fueling with whole foods. For higher intensities, she suggests fast-digesting carbohydrates before your workout and then more of the fast-digesting carbs plus whey protein after your workout.

When not training, build a diet based on nutrient-dense choices by eating a variety of fruits, vegetables, whole grains, lean proteins, nuts and dairy. In the hour before training, shift your focus to getting a source of fast-digesting carbohydrates, such as a bowl of cereal or a banana, or a carbohydrate-base sports performance product, as Kleiner suggests.

Within the hour after training, get a mix of carbs and protein, such as a berry and protein shake or two eggs and two slices of toast. Because training goals and workout intensities are so individualized, consider seeking out a registered dietitian nutritionist (RD or RDN) or a certified specialist in sports dietetics (CSSD) who can help tailor a fueling plan to your needs.

5 Tips to Focus on Fueling

Employ these tips to start getting the most out of your meals and your workouts. If you’ve been underfueling, eating more of the right foods at the right time can help you achieve the intensities and results you have been missing.

  1. Trust your appetite: Too often, health-conscious eaters are accustomed to ignoring their hunger. Under the right conditions, your body’s own hunger signals (thirst, grumbling tummy, salivating mouth) are your best tools for learning when to fuel. Find something to eat when you get that first signal of hunger instead of waiting until your appetite reaches an uncontrollable level.

  2. Read your body’s feedback: Your body has ways of telling you what it needs. If the feedback you’re getting after workouts is chronic fatigue, soreness, anxiety, lack of sleep, hair loss, bad skin, GI distress or memory loss, consider changing the types and amounts of food you’re getting — you probably need more, not less.

  3. Don’t skip meals: It becomes hard to fit in enough calories when you skip meals, let alone skipping snacks. If you work out in the morning, eat fast-digesting carbs before your session and a combination of carbohydrates and protein after your workout. If you train in the afternoon or evening, eat a meal three to four hours before your workout and another meal afterward. Additionally, eat a fast-digesting carb source in the hour before your workout.

  4. Eat more carbs: If you’ve been relying on a low-carbohydrate diet or using protein to fuel your workouts, “see how you feel when you add some carbs back to your diet and don’t underfuel,” Susan Kleiner, Ph.D., RD, recommends.

  5. Eat more natural foods: For low- to medium-intensity workouts, fuel up by getting your calories from whole-grain foods, fruits, vegetables, yogurt, milk, nuts and lean protein. You may need to eat these foods in larger volumes than you have before. For high-intensity workouts, it may be necessary to add fast-digesting carbohydrate powders and whey protein to help meet your increased fueling needs.

Written by Jessie R. Shafer for Oxygen Magazine and legally licensed through the Matcha publisher network. Please direct all licensing questions to

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