Are You Undereating? Here Are 6 Common Signs and Symptoms

If this frustrating scenario sounds familiar, you’re not alone. I regularly see these symptoms in my patients—ironically, among those who are most committed to living a healthy lifestyle. The likely culprit surprises them, and it may surprise you too: undereating.

We all know the hazards of overeating. But eating too little on a daily basis has dangers of its own. Studies show it can actually slow your metabolism, put you at risk of muscle loss, and cause a host of other symptoms that make you feel unwell. Fortunately, once you understand the biology of undereating—and recognize the warning signs—it’s fairly simple to find your personal calorie zone so you can lose (or maintain) your weight and feel great too.

You follow your exercise regimen religiously, you focus on healthy foods, and yet you stopped losing weight. What’s the problem? You may be undereating. Here are six signs that you’re not eating enough. #paleo #nutrition #chriskresser

What Happens When You Don’t Eat Enough

Our bodies evolved during an era when food was scarce. As a result, we’re programmed to keep weight on. The brain can’t distinguish the difference between healthy weight loss and starvation, so when we start losing body fat, it senses trouble and triggers a variety of complex hormonal mechanisms designed to prevent us from losing too much.

Eating too little activates this powerful anti-starvation system—and can sabotage your efforts to lose weight or even maintain a healthy weight in a number of ways. For instance, when you start shedding pounds with most traditional diets, your metabolism slows. That’s partly because your body becomes smaller, and smaller bodies burn fewer calories. But it turns out that many people experience an additional metabolic hit that can’t be chalked up to reduced body size. (1) In fact, the number of calories you burn during the day can drop by as much as 40 percent—so even though you’re eating less, you might hit a weight-loss plateau or start gaining. (2)

Eating too little can also lead to muscle loss, which not only decreases your strength and fitness but also contributes to the decline in metabolism because muscle is the tissue that utilizes the most calories. (3) As soon as the quantity and quality of that vibrant sinew drops, your ability to burn off the food you consume declines—and you store the excess calories as fat. Meanwhile, undereating also causes your body to start churning out more of the hormones that drive hunger and diminishes those involved in satiety. (4)

Fortunately, this outcome isn’t inevitable. The Paleo diet, which has plenty of healthy protein, fat, and carbs, fills you up naturally, so you can feel satisfied with fewer calories—without crossing the line into undereating. Because the Paleo diet eliminates processed, refined carbs, most people end up eating fewer carbs overall, which can keep your insulin and blood sugar—and your hunger—in check.

Indeed, research shows that, calorie for calorie, the Paleo diet is more satisfying than either the Mediterranean diet or a low-fat diet. (5) And because it contains a healthy amount of nutritious protein, which has all the building blocks your body needs to maintain muscle tissue, it also helps you maintain muscle mass—along with a healthy metabolic rate—when you lose weight. (6)

The Six Key Signs of Undereating

When you’re trying to lose weight and eat healthfully, it can be easy to wind up restricting your food intake too much. Here are the most common red flags of undereating.

1. You Don’t Have Energy

Calories are fuel—the source of energy that keeps everything from your brain to your muscles functioning optimally. When you don’t eat enough, the level of glucose (the sugar your body uses for energy) in your blood plummets—and your energy takes a dive too.

2. You’re Experiencing Mood Swings

Eating too little can make you cranky—more likely to snap at your spouse or get infuriated at the slow driver in front of you. And there’s a good reason. Serotonin, the brain chemical linked to both mood and appetite, is affected by hunger and may play an important role in the sensation of being “hangry.” (7) When blood glucose drops, every organ in your body is starved for fuel, including your brain—and one of the first noticeable effects is a reduction in self-control.

3. You’re Not Sleeping Well

If you’ve ever gone to bed hungry, you know it can be tough to fall asleep. But eating too little can make it difficult to stay asleep, too. Studies have linked undereating with a reduction in deep sleep—the sleep during which your body is making critical repairs to muscle tissue and other organs—as well as poor sleep quality. (8) The good news: higher-protein diets, including the Paleo diet, may help.

In a study published in the American Journal of Clinical Nutrition, 44 overweight or obese people were put on one of two calorie-restricted diets: one featuring normal amounts of protein, the other high levels of protein. Every month for four months, participants completed a standard sleep-quality questionnaire. At the three- and four-month follow-up, the dieters who ate more protein (1.5 grams per kilogram of body weight) reported improved sleep compared to those in the lower-protein group, who consumed about half the amount of protein. (9)

4. You Feel Cold—All the Time

Calorie restriction decreases your core body temperature. Feeling cold 24/7 isn’t comfortable, and it might be a warning sign that your thyroid hormones have gone awry. Studies show that the drop in body temperature appears to come at least in part from a decrease in T3, a thyroid hormone that helps maintain healthy body temperature. (10) Since low thyroid is linked to low energy, low mood, and diminished health, the impact of feeling constantly cold is far reaching.

5. You’re Losing Your Hair

If you’re seeing more hair in your brush or comb, it could very well be due to inadequate calorie consumption. Hair loss is a sign of both eating too little overall and getting too little protein—so following a Paleo diet, which is chock full of nutritious protein, may help. (11)

6. You’re Daydreaming about Food

Studies show that weight loss triggers cravings for high-calorie foods—and even after 62 weeks, one study found, participants’ levels of hunger and their desire to eat were higher than before they lost weight. (12) Likewise, in one of the earliest, most well-known studies of starvation, conducted in the 1950s, researchers found that when your body is undernourished, it’s natural to become preoccupied with thoughts of food. (13)

The lesson: If you can’t stop thinking about your next meal, you probably need to eat more.

How Many Calories Do You Need?

Most estimates of caloric need are just that: estimates. But if you want to avoid both undereating and overeating, it can help to get a little more specific by taking your individual body type and lifestyle into account. Enter the Mifflin-St Jeor equation, a formula that has been shown to be the most accurate way of estimating your bottom-line caloric needs: the number of calories your body burns at rest.

Yes, you’ll need to do a little math, but we’ll keep it simple. Here’s the step-by-step approach to determining the bare minimum number of calories your body needs to function. (You’ll need your weight and height in metric units for this. Use this conversion calculator.)

For Men

1. Multiply your weight in kilograms by 10.
2. Multiply your height in centimeters by 6.25 and add that to the number above.
3. Multiply your age by 5 and add an additional 5. Subtract that number from the number above.

Here’s how it looks in an equation:

(10 x weight (kg)) + (6.25 x height (cm)) – (5 x age (years) + 5)

For Women

1. Multiply your weight in kilograms by 10.
2. Multiply your height in centimeters by 6.25 and add that to the number above.
3. Multiply your age by 5 and subtract 161. Then subtract that number from the number above.

Here’s how it looks in an equation:

(10 x weight (kg)) + (6.25 x height (cm)) – (5 x age (years) -161)

Now, to find your high number—the number of calories your body needs to maintain your current weight—use this calculator at from the United States Department of Agriculture, which takes into account your age, height, and activity level.

If you want to lose weight at a healthy rate—and feel well while you do it—your calorie consumption should be somewhere between the number of calories you burn at rest (your bare minimum number) and the number you require to maintain your current weight. That’s your ideal calorie range. If you’re having trouble finding a healthy balance that allows you to lose weight and avoid the common symptoms of undereating, reach out to a Functional Medicine practitioner or health coach for guidance. They can review your overall diet and help you identify trouble areas.

After working with patients throughout my career, I’ve found that the Paleo diet is so satisfying that it makes it easier to stay in your safe calorie-consumption zone and still lose weight. It’s one of the few approaches I’ve found that allows you to eat less without really trying—and without suffering the consequences of eating too little.