Many women have a warped perspective of what “enough” food really is—especially when trying to lose weight. This warped perspective can hinder fat loss, strength gain, muscle gain, energy levels, and overall health.

Whether this perspective comes from reading fitness magazines that recommend a 1200-calorie-per-day meal plan, or a trainer promoting both a low-carb and low-fat diet for weight loss, countless women are misled into eating far less food than they actually need to support high-intensity training.

And while they might understand that inadequate food intake can negatively impact their performance in the gym, they simply aren't used to eating enough food.

As humans, social cues direct so much of our food intake. Men are typically applauded for eating a lot, but it’s a different experience for women. Have you ever been eating with friends and felt uncomfortable about how much you were eating compared to the other women? Have you tried to make sure you didn’t eat too much in front of your date or significant other? Our social environments can often set women up for chronic undereating, especially those who are highly active but still feel they should eat as much (or rather, as little) as their less active or sedentary friends.

We’ve also been conditioned to believe the body is a static machine, and we can input and output our calories in a calculated way that will lead to fat loss. That’s why many women expect to see rapid weight loss from a significant caloric deficit (I’m talking 800-1000 calories per day or more). Many women simply can’t lose “the last” 10–20 pounds no matter how little they eat. And some even see an increase in body fat the longer they diet!

How Undereating Affects Your Training And Fat Loss Goals

While a slight caloric deficit should cause sustainable weight loss (think 300-500 calories per day), much larger deficits elicit changes in your metabolism to keep your body in an energy balance and maintain homeostasis. The body—this dynamic, adaptable machine—wants to feel "safe.” With survival as the priority, it is constantly regulating what's going on in response to our environment.

In other words, in order to conserve energy and direct calories to necessary functions for survival, your body resorts to burning fewer calories, even as you’re exercising regularly and intensely. This means you will hold onto body fat despite eating a low-calorie diet and training hard.

When you don't eat enough, your body reduces active thyroid hormone, shuts down sex hormone production, and raises adrenal stress hormones like cortisol.1, 2, 3, 4, 5 Chronically elevated cortisol leads to both leptin and insulin resistance, an unhealthy hormonal state that promotes body fat and water retention, and causes long-term health issues that go way beyond weight loss resistance.6, 7

It should be easy to understand why undereating would negatively impact strength training goals.

If you’re hitting a ceiling in your deadlift or you haven’t had a PR on a lift in months despite consistent training, it’s definitely time to evaluate your diet.

When resources (calories) are scarce, the body prioritizes essential functions (like respiration, and regulating body temperature and blood pressure) over things like rebuilding muscle tissue. Inadequate food intake makes it nearly impossible to increase muscle strength or size, and the energy deficit can seriously weaken your power in training sessions in general.

When you’re under-fueled, it may feel like you’re training intensely, but your power output is actually much lower. If you can’t maximize your power when lifting, you won’t be able to achieve the necessary stimulus to promote muscle growth and rebuilding.

Finally, under eating can sabotage your recovery. As top athletes know, proper recovery is just as important as the training itself when it comes to seeing progress in performance. When you train, your muscle tissue breaks down, and without adequate calories and protein in your diet, your muscles won’t have the materials they need to rebuild. And if you’re under-fueled while working out, protein from your muscles will actually become fuel for your body to continue running on.

Undereating also causes disrupted sleep, and evidence shows that high quality sleep is essential for recovery after a tough workout.8 Poor sleep also causes us to hold onto body fat.9 So if undereating is causing your sleep to suffer, you can bet you won’t be performing well in the gym or losing body fat.

Other Symptoms of Under Eating

Undereating doesn’t just affect your training and fat loss goals. I’ve worked with dozens of clients who were not only struggling in the gym, but they were feeling the negative effects of too little food in their daily lives.

The most common symptoms I see in clients who are not eating enough are:

Low energy

Insomnia

Mood swings

Brain fog or poor concentration

Depression or anxiety

Hair loss

Feeling cold

Loss of menstrual cycle

Infertility

Constipation

Low sex drive

Sugar (or other food) cravings

Some of these symptoms can be attributed to other common conditions like PCOS and hypothyroidism, but chronic undereating can potentially worsen (or even cause) these conditions due to the effects of calorie restriction on hormonal production.10, 11, 12

Don’t despair if you’re experiencing more than a few of the issues on this list! The good news is that once you start eating enough to support your activities, you’ll often see rapid improvements in these symptoms.

If you’re experiencing any of these symptoms regularly and you’re not sure why, I’d strongly recommend assessing your diet to determine if you’re eating enough to support your activity levels. You can do this by tracking your food intake and matching your calorie and macronutrient needs to your exercise regimen.

Log your food as precisely as possible (weigh and measure!) using an app like MyFitnessPal, which allows you to set personalized calorie and macro goals. If you have no idea where to start, and you’re looking to build muscle and/or lose fat while training regularly, try setting a macro percentage goal of 25 percent protein, 40 percent carbs, and 35 percent fat. (For more personalized macro percentages that fit your unique health needs and fitness goals, consider working with a nutritionist.)

At the end of each day, review your total intake of calories, carbs, protein, and fat. If you need to make adjustments or eat more food, you can either make those changes the next day or even add a little extra food before bed if you’re significantly below your targets.

Before you can start tracking your diet and modifying your food intake, however, you’ll need to figure out how many calories you need on a daily basis. Keep reading to learn how to estimate your individual calorie needs.

How Much Should You Be Eating?

Figuring out exactly how many calories you need for optimal health and weight control can be challenging. Many factors come into play, including your physical activity, stress levels, sleep adequacy, history of chronic disease, and more. While it’s impossible to determine exactly how many calories your body needs, there are some easy ways to estimate how much you should be eating daily.

My favorite quick and dirty way to determine your “base” calorie target – the lowest amount of calories you should ever be eating – is to multiply your “ideal” body weight by 10. A woman who is 5’ 5” has an “ideal” body weight of around 125 pounds, so she should not eat less than 1250 calories per day.

You can use this calculator to determine your “ideal” body weight. However, please note that this calculator does not take into account frame size or muscle mass – that’s why “ideal” is in quotes. Your weight may easily be higher than this.

It’s also important to keep in mind that this quick estimate is based on a “sedentary” formula. It does not take into account any physical activity beyond sitting and standing. That same 5’5” woman we just discussed might burn around 300 calories or more from a 30-minute run, taking her minimum calorie needs up to 1550 calories per day, assuming she doesn’t do any other exercise that day.

Different workouts will burn varying amounts of calories. A Crossfit WOD can burn 12–20 calories per minute on average, so a WOD that takes 20 minutes could burn 240–400 calories. If you’re aiming for a high step count, 10,000 steps burns around 300–500 calories, give or take depending on body size and gender.

If you do both of those in one day, that’ll bump your daily calorie needs up by 600–900 calories! So if you’re a highly active individual, your calorie needs will go up by several hundred calories per day above the “10 x ideal weight” formula.

Breastfeeding? You’d better add even more food to your plate. Many of my female clients are shocked to hear that breastfeeding raises caloric expenditure by about 500 calories per day or more. Breastfeeding women need at least 300 calories per day above and beyond their needs compared to when they’re not breastfeeding.

What does this look like in a real person?

Using myself as an example, my “ideal” body weight at 5’ 9” is estimated at 145 pounds (but I weigh ~165), and I usually burn around 400–500 calories via exercise most days. My goal is to maximize strength gains while slowly reducing my body fat. So I almost never eat below 1800 calories. On heavier training days, I may eat closer to 2000–2200 total. This allows me to maintain my performance in the gym while slowly losing body fat.

This is just me — I know women who train regularly who eat 2800–3000 calories per day or more. Your mileage will vary, and you should never compare your dietary needs to what anyone else is eating.

Use this easy calculation as a baseline, and tweak up or down as necessary as your health, performance, and weight fluctuates. Once you get the hang of eating enough, you can stop tracking if you want. Don’t get too caught up in the exact number, and always pay attention to how your food intake makes you feel.

Tracking your diet is a great short-term solution to undereating, but don’t panic if your calorie intake fluctuates around your goal, or if you don’t track every day. And be flexible: this number will change as time goes on and your life circumstances change.

If you need to start significantly bumping up your intake, try adding 100–200 calorie increments every week or so in order to minimize weight gain or digestive distress during the refeeding process. Calorie adjustments usually take some experimentation, but correcting undereating almost always results in significant improvements in health, energy, and performance. And once you’re feeling better, you can use a more intuitive eating style to continue making progress. It’s awesome to see the health improvements that come from a simple increase in caloric intake when someone has been chronically undereating!

Remember: eating too little is just as unhealthy as eating too much. Find the right amount of food that works best for you, and don’t be afraid to experiment with eating more if your health and performance aren’t where you want them to be!

Important note: if you’re significantly undereating and struggling with the idea of adding more food into your diet, or if you’re concerned you may have an eating disorder, seek help from a medical professional immediately.