Weight loss is simple, right? Eat less, exercise more, and voilà: The pounds melt away. Unfortunately it’s not always that easy. While a low 1200- to 1500-calorie diet works for many people, the number of calories you need depends on your weight, height, age, gender, and activity level. If exercise drains a big chunk of the calories you’re eating and there aren’t enough left to fuel your body’s day-to-day processes—a condition known as low energy availability—your body may think it’s starving and go into conservation mode.

“You don’t want to restrict your diet to the extent you’re left with too few calories to fuel your body to work properly,” says Bronwen Lundy, Ph.D., senior sports dietitian at the Australian Institute of Sport. “You’ll just end up damaging your metabolism, which can mean you’re unable to lose weight, and possibly causing other wide-reaching effects on your body and health.”

What are those effects and how can you tell whether eating too few calories is causing your weight-loss plateau? Read on to find out.

Low energy availability is prevalent among female athletes—you’ve probably heard of the female athlete triad, a medical condition marked by an energy deficiency, irregular periods, and low bone density—but recent research shows the problem may be more widespread.

In 2014, experts writing on behalf of the International Olympic Committee recommended that the term “female athlete triad” be replaced by “relative energy deficiency in sport” to better capture the complexity of the condition and the fact that men are also at risk. And in 2016, researchers from the University of Otago in Dunedin, New Zealand found that many everyday exercisers may be at risk of undereating and can be affected by the condition, too. In fact, low energy availability can begin to negatively impact the body after just five days of calorie restriction, with more serious complications cropping up long term.

Identifying whether or not you have low energy availability can be tricky. Thanks to the belly-filling effect of many healthy, low-calorie and high-fiber foods—like fruits and vegetables— and the hunger-blunting effects of intense workouts, you can be energy deficient without actually feeling hungry. Which means you’ll need to look further than your appetite.  

To figure out if you’re at risk, first consider the signs and symptoms of low energy availability. They include:

• Dizziness

• Anemia

• Chronic fatigue

• Tummy troubles, like cramping, bloating, or constipation

• Cold sensitivity, due to low thyroid hormone

• Mood changes, like irritability or depression

• Recurring infections and illnesses

• Poor athletic performance

• Inability to gain or build muscle

• Raised cholesterol

• Frequent injuries, like stress fractures

• Absent or irregular menstrual cycles

• Low sex drive in men

If you’ve been experiencing any of those symptoms, it’s a good idea to work with a doctor or certified sports dietitian to crunch some numbers and gauge how many calories your body typically runs on each day. Together, you can use your Fitbit app to get a rough estimate. Here’s how:

1. From the Fitbit app dashboard, tap Calories Burned (the flame icon). Tap the double arrow in the top right corner to expand the screen. Tap 1wk and then swipe left to see more results. Note the average number of daily calories burned on last week.

2. Navigate back to the Fitbit app dashboard, and tap the Calories In vs. Out tile (the knife and fork icon). Scroll down to see your average daily calories consumed last week. (If you’re not a food logger, consider doing it diligently for at least 3 days to get a daily average and to ensure your stalled weight loss is due to energy deficiency and not sneaky calories in your diet.)

3. Next, subtract the number you got in step 1 from the number you got in step 2, like this:

 [Average Calories Consumed (food) per day] minus [Average Calories Burned per day] = Energy Deficit

First, the calories you’re consuming (the number identified in step 2) should never go below your basal metabolic rate (the calories your body burns at rest). And second, if the gap between what you’re eating and the total amount of calories you’re burning—to simply be alive and through exercise (your “energy deficit,” calculated in step 3)—is too big, you risk losing vital muscle tissue and slowing your metabolism.

“If you’ve been eating too little and exercising a lot and not losing weight, then it’s a sign your efforts are not working and something needs to change,” says Lundy. “The good news is, the impact on your metabolism is unlikely to be permanent. The solution could be that you simply need to slowly start eating more.”

Increasing your calorie intake to lose weight may seem counterintuitive—scary even—but in order to get leaner and stronger, you’ll want to decrease your body fat while maintaining or building lean muscle. To do this, aim for a calorie target that’s around 500 calories less than the calories you need to maintain your current weight.

“If someone has been following a strict diet for years, it can take longer to restore their metabolism to its full potential,” says Lundy, “but it is possible.” She suggests slowly increasing your food intake by 100 calories a day for two to four weeks—that’s a piece of fruit, a small tub of non-fat plain Greek yogurt, or a small handful of nuts (again, food logging can help). Remember, moderation is key:

• Avoid skipping meals

• Eat enough protein throughout the day

• Eat plenty of whole fruits, vegetables, and grains

• Include low-fat dairy (or soy milk), legumes, and lean meats

• Refuel and rehydrate properly after hard training sessions

• Limit sweetened beverages, like sports drinks

When you step on a scale and can see that your weight isn’t increasing, slowly add more calories (in 100-calorie increments) until your body starts losing fat and maintaining or even gaining muscle. (The Aria 2 smart scale can help you measure this.) This is your sweet spot—the new calorie goal you should aim for each day.

It can seem terrifying to eat more, but rest assured, not only will your metabolism get the kick it needs to jumpstart your weight loss again, your body could also end up shedding more fat and hanging onto precious muscle, which in the long run will help keep you strong and help encourage the weight to stay away.