When you are trying to lose weight, eating less may seem like the most obvious thing to do. After all, you’ve probably heard the adage “calories in versus calories out” and the abundant testimonials of how cutting calories helped people lose weight. But did you know there is a point where cutting calories begins to work against your weight loss goals?
Constant fatigue, irritability, stalled weight loss and even hair loss can all be signs that your body is not getting enough fuel. And if exercise is part of your weight loss plan, eating too little can make it harder to perform, recover and maintain the muscle you are working to build.
Sarah Sagullo, a health coach and registered dietitian with Memorial Hermann Employee Wellness, says the goal should not simply be to eat as little as possible. Instead, think of your body as a responsive mechanism—it needs enough nutrition to support everyday activities, exercise and sustainable progress.
“The main takeaway is that you need food to fuel your basic functions, then your performance. On top of that, you need enough nutrition to recover from activity and promote future progress,” Sagullo says. “That can be a lot of fuel, depending on your activity level. And that's why you must focus on making sure you’re eating enough when you’re on a weight loss journey.”
How Do You Know if You’re Not Eating Enough?
Eating in a calorie deficit means consuming fewer calories than your body uses, but there’s a difference between eating in a way that achieves the deficit and eating that makes you feel depleted or malnourished. If your diet leaves you feeling exhausted or makes everyday activities difficult, it may be time to reconsider how much you are eating.
“One of the biggest warning signs is persistent fatigue,” advises Sagullo. “This isn’t the kind of fatigue you feel after a good workout or a long week at work. It’s when you just feel like you don't have the energy to get up and complete any activities of daily life; that's a sign you may not be getting enough fuel.”
Other signs can include:
- Irritability or mood changes. Eating too little can leave you feeling more irritable, particularly as blood glucose levels drop.
- Constant hunger or fixation on food. Feeling persistently hungry or spending significant amounts of time thinking about your next meal can indicate that your calorie deficit is too restrictive.
- Poor workout recovery. Without adequate nutrition, your body may have difficulty recovering from exercise and preparing for your next workout.
- Hair loss. While some shedding is normal, significant changes in hair density can be a sign that your body is not getting the nutrition it needs.
- Constipation or bloating. Restricting food may also mean consuming less fiber and other nutrients that support normal digestion.
- Dizziness or feeling faint. Feeling like you may pass out or becoming frequently dizzy is another indication that your body may not be adequately fueled.
Why Eating Less Does Not Always Mean Losing More
Weight loss naturally requires some degree of calorie restriction, but your body still needs enough energy to carry out basic functions. If you’ve been consistently losing weight but suddenly hit a plateau, it could be that your metabolism has begun to adjust to the lower caloric intake and changing body weight. “Your body needs a minimum number of calories to function, so when you're not getting enough calories, it goes into what I sometimes call ‘conservation mode,’ which may prevent you from losing weight,” Sagullo says.
Plateaus are a normal part of a weight loss journey. And they do not necessarily mean you should respond by cutting calories even further.
For someone who has consistently maintained a calorie deficit for 12 to 14 weeks, Sagullo says it may be appropriate to temporarily increase calories to a maintenance level. That gives the body time to recover and can help restore energy, mood, workout performance and normal hunger cues before another period of weight loss.
Taking that break can feel counterintuitive, especially for someone who has worked hard to lose weight and is worried about regaining it. However, continuously cutting calories is not sustainable: There is only so low you can safely go.
From both a physical and mental health perspective, giving your body periods of adequate fuel may help prevent fatigue and burnout while setting you up for more sustainable progress over time.
GLP-1 Medications Can Make Adequate Nutrition More Challenging
Eating the correct amount of calories can require even more attention for people taking GLP-1 medications for weight management or blood sugar control. These medications can reduce appetite, cravings and what is sometimes described as “food noise.” While that can support weight loss, reduced hunger can also make it easier to unintentionally eat too little, making the nutritional quality of the food you do eat especially important.
Protein is one of the biggest priorities. During weight loss, the goal is not simply to make the number on the scale smaller. You also want to preserve as much lean muscle mass as possible, which can hinder the scale’s movement. Sagullo recommends approximately 1.2 to 1.6 grams of protein per kilogram of body weight for people trying to lose weight, depending on their individual needs.
Adequate protein can help support lean muscle mass during weight loss, particularly when combined with resistance exercise. Preserving muscle is also important for healthy aging and maintaining the strength needed to remain active and independent later in life.
Fiber deserves attention, too. GLP-1 medications and changes in food intake can affect bowel habits, making constipation a concern for some people. Fiber from plant-based foods can support regularity, so it’s important to ensure your diet continues to include fruits, vegetables, whole grains, beans and other nutrient-rich foods.
Don't Be Afraid of Carbohydrates and Healthy Fats
Protein may receive much of the attention during a weight loss journey, but a balanced diet also includes carbohydrates and fats. Low-carbohydrate and ketogenic diets have become popular approaches to weight loss, which can sometimes create the impression that carbohydrates should be avoided altogether. However, Sagullo disagrees. “Carbs are not the enemy,” she says.
Carbohydrates are one of the body's primary sources of energy, making them especially important when exercise is part of your routine. “You need carbs, especially if you're working out as part of your weight loss routine,” Sagullo says.
Instead of cutting carbs completely, focus on minimally processed carbohydrate sources like fruits, sweet potatoes, squash, other starchy vegetables, beans and whole grains.
Healthy fats are important as well. The body needs dietary fat for many functions, including hormone production and healthy hair, skin and nails. Foods containing unsaturated fats, including avocados, olive oil, fatty fish, nuts and seeds, can also help make meals more satisfying.
The goal is not to eliminate an entire macronutrient category. Instead, build meals that provide the protein, carbohydrates, fats, fiber and other nutrients your body needs to support both weight loss and exercise.
Fuel Your Workouts
The timing of your meals matters, too, particularly if you are exercising after a long workday or several hours after your last meal. If you know you will exercise later in the day, plan your nutrition so you do not start your workout depleted. A meal containing protein and carbohydrates several hours beforehand can provide energy for your workout.
If you are exercising within about 30 minutes after you eat, keep your snack lighter to reduce the chance of digestive discomfort. Fruit or an apple with peanut butter, for example, can provide a quick source of energy without feeling overly heavy.
After a strenuous workout, nutrition helps support recovery. If you plan to eat a meal within 30 minutes to an hour, that meal can serve as your postworkout fuel. If dinner will be later, consider a smaller option in the meantime, such as a protein shake, protein bar or another combination of protein and carbohydrates.
The idea is not that every workout requires a complicated nutrition routine. You simply want to avoid going long stretches without eating when you’re asking your body to exercise and recover.
Listen to What Your Body Is Telling You
A moderate calorie deficit often begins around 300 to 500 calories below a person's typical needs, according to Sagullo. But calorie requirements vary considerably based on factors like age, activity level, starting weight and gender. This is why paying attention to how you feel matters just as much as watching the numbers.
Hunger cues can sometimes be difficult to interpret. Stress, boredom and poor sleep can all make people want to eat even when they are not physically hungry. On the other hand, someone who is committed to losing weight may become accustomed to ignoring genuine hunger pangs.
If you are consistently hungry at the end of the day, fixated on food or exhausted while maintaining a calorie deficit, those are reasons to reassess your plan. A sustainable plan should provide enough energy to exercise, recover, get through your day and continue making progress over time.
“The goal is never for you to feel miserable when you're on a weight loss journey,” Sagullo says. “There will definitely be some work and lifestyle changes, and that does require some discipline and maybe discomfort, but you should also feel confident in sustaining those changes.”
