Weight loss relies on a fairly straightforward equation: To drop the number on the scale, you must consume fewer calories than your body burns. With this in mind, it seems logical that cutting as many calories as possible can help you shed pounds faster. Makes sense, right?
Hate to break it to you, but this calorie-slashing strategy may actually be sabotaging your efforts. In fact, eating too far below your specific calorie needs not only halts weight loss but may also negatively affect your health.
The rub is that everyone's calorie needs are different, so there's no one-size-fits-all when it comes to calorie counts for weight loss.
Here, Lisa Moskovitz, RDN, dietitian and founder of The NY Nutrition Group, helps you identify red flags that indicate you're not eating enough, plus offers guidance on how to determine the right number of calories you personally need for healthy, safe weight loss.
In general, women shouldn't cut their calories below 1,200 a day and men should stay above 1,500 unless they're under the supervision of a health care professional.
1. You're Hungry All the Time
When you begin a weight-loss plan, your body might need time to adjust to eating fewer calories, so a hunger pang here or there is common. But if you're constantly craving your next meal or snack after a few days, something might be up.
"Thinking about food all the time is a sign your body needs more," Moskovitz says. That could mean more calories and/or a better balance of food groups to supply all necessary nutrients.
In other words, your diet might be lacking in major macros like carbohydrates, fats and proteins or other filling nutrients like fiber, which can keep your blood sugar stable and appetite in check.
That's why it's essential to heed your hunger cues. "Even if you think you ate enough based on specific portions, that doesn't mean your body agrees," Moskovitz says.
2. You Feel Woozy
Lightheadedness is another indication that you're not eating enough. "Your blood sugars may be too low and thus causing you to feel weak or woozy," Moskovitz explains.
That's because when your blood sugar dips below what your body needs to function properly, your systems go into conservation mode to use less energy, according to Harvard Health Publishing.
This faint feeling may also be a result of dehydration, Moskovitz says. Without sufficient water, your blood volume decreases, leading to a decline in blood pressure, per Harvard Health Publishing. When this happens, your brain doesn't get enough blood, causing dizziness.
With that said, it's always a good idea to talk to your doctor if you experience these symptoms to be sure that you're not dealing with a more serious underlying health condition, Moskovitz says.
3. Your Workouts Are Suffering
Wiped out during workouts? Poor performance in the gym is a hallmark of consuming too little food, Moskovitz says.
Here's why: Calories equal energy, so if you're not ingesting an adequate amount, your body must use all its strength to support basic functions and it won't have much oomph left over for anything extra, including your workouts.
Not only does undereating sap your energy, it also curbs your ability to build lean muscle, Moskovitz adds. Since muscle burns more calories than fat, even at rest, having more of it aids weight loss.
Remember, to gain muscle, you need to pack plenty of protein onto your plate, per the American College of Sports Medicine. If you're over-restricting calories, though, odds are you're not getting enough of the macronutrient.
If you're in a calorie deficit, you should be aiming for 1.3 grams of protein per kilogram of body weight (a kilogram is about 2.2 pounds, for the record).
4. You're Constipated
A diet that's too low in calories can leave you backed up.
"Not eating enough means there is nothing to push through your digestive tract, which can lead to bowel movement irregularities such as constipation," Moskovitz says.
Plus, a lot of trendy diets ditch (or significantly cut) carbs — including healthy whole grains, veggies and fruits — which are full of fiber. The thing is, fiber bulks up your poop and helps food pass from your stomach to your intestines, per the U.S. National Library of Medicine. So, without enough of it, your stool gets, well, sort of stuck.
To avoid this and speed up your stool, Moskovitz recommends eating at regular intervals throughout the day — with plenty of gut-healthy fiber — as well as hydrating with water to keep things moving smoothly.
Psst: A study published February 2015 in the Annals of Internal Medicine found that simply aiming to eat 30 grams of fiber each day could help you lose weight as effectively as a more complicated diet.
5. You're Not Losing Weight
If your weight loss grinds to a halt, you might think that slashing more calories is the solution. It's probably not.
Though it sounds counterintuitive, your low-calorie diet could be the reason you've stopped shedding pounds in the first place.
"Whenever you limit calories to lose weight, your metabolism can go through a process called adaptive thermogenesis," Moskovitz says. When this happens, your metabolism may slow down.
Essentially, when you cut too many calories, your body goes into survival mode, so it burns fewer calories to preserve energy. In short, your body is protecting you from what it perceives as starvation.
To make matters worse, restrictive dieting may even raise your levels of cortisol, a stress hormone linked to increased appetite and belly fat, according to a May 2010 study published in Psychosomatic Medicine.
6. You're Getting Sick
Catching colds regularly? Your low-calorie diet may be to blame.
"Eating too little can negatively affect the immune system and stress out the body," Moskovitz says.
When this happens, your body produces fewer lymphocytes, aka infection-fighting white blood cells, according to the Cleveland Clinic. Consequently, with lower lymphocyte levels, you run a greater risk of getting sick.
What's more, restrictive dieting "usually means you're not getting key immune-building nutrients like vitamin C, zinc, vitamin D and probiotics," Moskovitz adds.
Put simply, your body's defenses suffer when you cut too many calories in the form of wholesome, nutritious foods.
How to Eat the Right Number of Calories
First, determine the number of calories you should be eating each day to maintain your weight by using the chart in the Dietary Guidelines for Americans, which breaks it down by age, sex and physical activity level.
For healthy weight loss (about 1 pound per week), you should aim to cut about 500 calories a day from that amount, according to the Mayo Clinic. (As long as you're not falling below 1,200 calories for women or 1,500 calories for men.)
To make it even easier on yourself, you can download LIVESTRONG.com's MyPlate tracker, which will do the calculating for you. The app also makes it easy to update your needs as your weight and exercise regimen change.
Moskovitz suggests consulting with a registered dietitian, who can take a look at your complete medical, lifestyle and diet history. A nutrition expert can also help you devise a proper meal plan to ensure you get the nutrients you need when cutting calories.
- Harvard Health Publishing: “Lightheaded? Top 5 reasons you might feel woozy.” https://www.health.harvard.edu/diseases-and-conditions/lightheaded-top-5-reasons-you-might-feel-woozy U.S. National Library of Medicine Medline Plus: “Soluble vs. insoluble fiber.” https://medlineplus.gov/ency/article/002136.htm Psychosomatic Medicine: “Low calorie dieting increases cortisol.” https://www.ncbi.nlm.nih.gov/pubmed/20368473 Cleveland Clinic: “What Happens When Your Immune System Gets Stressed Out?” https://health.clevelandclinic.org/what-happens-when-your-immune-system-gets-stressed-out/ Mayo Clinic: “Counting calories: Get back to weight-loss basics.” https://www.mayoclinic.org/healthy-lifestyle/weight-loss/in-depth/calories/art-20048065 American College of Sports Medicine: “Protein Intake For Optimal Muscle Maintenance.” https://www.acsm.org/docs/default-source/files-for-resource-library/protein-intake-for-optimal-muscle-maintenance.pdf?sfvrsn=688d8896_2 Journal of the International Society of Sports Nutrition: “Metabolic adaptation to weight loss: implications for the athlete.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3943438/
- U.S. National Library of Medicine Medline Plus: “Soluble vs. insoluble fiber.”
- Psychosomatic Medicine: “Low calorie dieting increases cortisol.”
- Cleveland Clinic: “What Happens When Your Immune System Gets Stressed Out?”
- Mayo Clinic: “Counting calories: Get back to weight-loss basics.”
- American College of Sports Medicine: “Protein Intake For Optimal Muscle Maintenance.”
- Journal of the International Society of Sports Nutrition: “Metabolic adaptation to weight loss: implications for the athlete.”
- Annals of Internal Medicine: "Single-Component Versus Multicomponent Dietary Goals for the Metabolic Syndrome"
- U.S. Department of Health and Human Services: "2015-2020 Dietary Guidelines for Americans"