In our modern society with its seemingly endless supply of fast food and junk food, it seems obvious to most why we’re dealing with an obesity epidemic. Cheap, low-quality food surrounds us, and there’s not enough time in the world to exercise away all the excess calories that exist in our food supply.

However, those of us in the Paleo and ancestral health community seem to have a different problem altogether. It’s one that I’ve seen in dozens of clients.

This problem is chronic under-eating.

Why Under-Eating Is so Common

Yes, I said under-eating, not overeating. While most people would find it hard to believe that many of the health problems people experience when going Paleo are from a lack of calories and appropriate macronutrients, I’ve seen it in my private practice countless times; clients who were experiencing mysterious, nagging symptoms that suddenly disappeared when we evaluated and corrected their daily food intake.

I’ve even seen clients who couldn’t lose weight that were suddenly able to do so after realizing they weren’t eating enough and increasing their food intake. Quite the opposite of the “calories-in-calories-out” mentality!

Why is under-eating so common? It can happen for a number of reasons:

• A restricted diet
• Above average activity levels
• Stress
• Fear of certain foods and food groups
• Busyness
• Chronic dieting
• Pregnancy/breastfeeding

Could something as simple as under-eating be causing your health problems? Could inadequate food intake be the reason why your Paleo diet suddenly isn’t working for you anymore? Is your “rapid weight loss” diet plan the reason your jeans are getting tighter instead of looser?

Signs and Symptoms of Under-eating

Below are the top eight signs and symptoms I see in my clients who are chronically under-eating. Read on to discover if you might simply need some more food to start feeling better today.

1. Your Weight Isn’t Budging

This is one of the most paradoxical symptoms of someone who is under-eating, and it often goes hand in hand with overtraining. You might be surprised to hear that I’ve rarely worked with a weight loss client who was blatantly overeating. In fact, many of my clients come to me on extremely low-calorie diets (around 1,000 to 1,200 calories per day) combined with six to seven days per week of intense exercise like CrossFit or long-distance running.

For good reason, they are extremely frustrated that their weight isn’t changing; for some of these clients, their weight has actually been increasing since they dropped their food intake and started working out more. Many of these clients are also eating a very low-carbohydrate diet with the goal of losing weight quickly.

We’ve been trained to believe that the body is a machine, and we can input and output our calories in a way that will cause weight loss. So it’s understandable why these clients would expect to see weight loss from a significant caloric deficit like that. But the fact is, they simply can’t lose the last 15 to 30 pounds no matter how little they eat. Why is this?

While a short-term, moderate caloric deficit can lead to sustainable weight loss (think 300 to 500 calories per day), much larger deficits induce changes in your body’s metabolism in order to keep your body in a homeostatic balance. Your body does not like major, drastic changes, and it will make modifications to your thyroid, adrenal, and sex hormones in order to reduce your overall caloric output.

These changes include reducing active thyroid hormone, shutting down sex hormone production, and raising stress hormones like cortisol. (1, 2, 3, 4, 5) Chronically elevated cortisol leads to both leptin and insulin resistance, a disastrous hormonal state that can keep body weight high. (6, 7)

These hormonal changes can lead to stalled weight loss and body fat retention, along with many other negative health effects that go beyond weight loss resistance. So, if you’ve been eating much less and exercising much more in a futile attempt to lose weight, consider whether this strategy has been working for you.

2. You Can’t Get Pregnant

Scientists have known for a long time that low-calorie dieting and inadequate body fat can lead to infertility and amenorrhea in women. (8) One of the most commonly seen manifestations of this problem is known as hypothalamic amenorrhea, which is hallmarked by menstrual irregularity or amenorrhea and low energy availability, with or without an eating disorder. (9)

Menstrual irregularity doesn’t necessarily mean a missed period; it can simply mean a woman is having an anovulatory cycle, meaning there is no egg released during the ovulatory period.

Hypothalamic amenorrhea caused by chronic caloric deprivation is also associated with physiological changes like hypothalamic–pituitary–adrenal (HPA) axis overactivity (also known as adrenal fatigue) and disturbances in the hypothalamic–pituitary–thyroid axis (also known as euthyroid sick syndrome).

I’ve worked with many clients who recovered their period after returning to a normal caloric intake. I’ve even had one client who was finally able to get pregnant when she switched to a higher-calorie ancestral diet, after her doctors told her she’d always be infertile.

So, if you’ve been struggling to get pregnant, and you have a history of dieting and exercising for weight loss, it’s possible that your low-calorie diet is preventing you from getting pregnant.

3. Your Blood Sugar Is on a Roller Coaster

While many people blame excessive carbohydrate consumption for wild blood sugar swings, you might be surprised to learn that inadequate calorie consumption can cause just as many issues with blood sugar control. The most common issue that comes from chronic under-eating is hypoglycemia, or low blood sugar.

Hypoglycemia is defined as blood sugar below 70 mg/dL, though some people experience symptoms at higher blood sugar levels. Common symptoms of hypoglycemia include:

• Hunger
• Shakiness
• Anxiety
• Dizziness
• Sweating
• Weakness
• Confusion
• Changes in mood

Severe under-eating can easily cause hypoglycemia, especially when combined with exercise. (10) And because many people feel better eating sugary foods when they’re hypoglycemic, this can lead to the common cycle of high and low blood sugar swings that cause chronic dieters to overeat or binge on junk foods.

This is yet another reason that the most sustainable diet for weight loss provides adequate calories to keep your hormones and blood sugar even-keeled.

4. Your Mood Is Totally Unpredictable

Have you ever heard the term “hangry” before?

It refers to the state of anger and irritability resulting from being hungry. And even though it’s a made-up term, there’s actually scientific evidence for the existence of this volatile emotional state caused by inadequate food intake. (11)

As I mentioned earlier, lack of eating enough food can lead to hypoglycemia, or low blood sugar. Since the brain requires blood sugar to function optimally, when it starts to drop, one of the first cognitive processes that suffers is self-control. (12) Your ability to exert self-control allows you to:

• Focus your attention
• Regulate your emotions
• Cope with stress
• Resist impulsivity
• Refrain from aggressive behavior

So, if you’re always on a short fuse, or your mood is constantly swinging between cheerful and irritable or anxious, make sure that you’re not severely under-eating before making any other significant changes to your diet and supplement or medication routine.

5. You Can’t Fall Asleep (Or Stay Asleep)

Insomnia and other sleep disturbances are one of the top health complaints my clients come to me for help fixing. This is especially common in peri-menopausal women who seem to be especially prone to poor sleep despite generally good sleep hygiene and a health-conscious lifestyle.

Oddly enough, one of the first symptoms that changes when I get my clients eating a more calorically appropriate diet is a significant improvement in sleep duration and quality. Even if they weren’t necessarily waking up hungry, many of my clients find that an increased calorie intake (especially from carbohydrates) can lead them to fall asleep faster and stop waking up at night.

One reason for this likely comes from the improved blood sugar control that arises from an appropriate calorie and carbohydrate intake. As your blood sugar drops overnight, your liver must release its stored glucose (in the form of glycogen) to keep your blood sugar steady.

If you’re constantly under-eating, especially if you’re overexercising on top of that, your liver won’t have the glycogen stores it needs to keep your blood sugar stable. In this case, your body must release stress hormones like cortisol and adrenaline to promote gluconeogenesis, the process of creating new glucose. If these stress hormones elevate high enough, they can actually wake you up in the middle of the night.

Making sure you’re eating enough overall and potentially including a carb- and fat-dense bedtime snack one to two hours before going to sleep can help keep your blood sugar stable overnight, leading to more restful, uninterrupted sleep.

Some of my favorite examples of balanced snacks are:

• An apple and 1 to 2 TB of nut butter
• Half a sweet potato and 1 TB of butter or ghee
• Berries and coconut milk
• A banana and 1 ounce of macadamia nuts
• Full-fat yogurt with a drizzle of honey

6. You’re Chronically Constipated

There are a few reasons why chronic under-eating can cause constipation. The most obvious is that feces is made up of waste matter from the digestion of food, so if you’re not getting enough food, your stool won’t have much bulk to it.

The less obvious but more likely reason that under-eating can lead to constipation is due to the effects of undernutrition on thyroid hormone. As I discussed previously, under-eating causes a downregulation of T3, the active thyroid hormone. This can lead to a condition called euthyroid sick syndrome, where T3 is low, reverse T3 is high, and thyroid-stimulating hormone and T4 are often normal. In this condition, your body develops hypothyroidism symptoms without necessarily showing any change in the typical thyroid function markers that most doctors check.

Constipation is a very common symptom of hypothyroidism. Active thyroid hormone helps stimulate peristalsis in the gut, keeping digestion humming along smoothly. When T3 drops, gut motility slows, and this can lead to chronic constipation. So, if you’re having a bowel movement only every couple of days, check your caloric intake and make sure you’re not under-eating.

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7. You’re Always Cold

Caloric restriction is known to cause a drop in body temperature. (13) While some calorie-restriction proponents suggest that this is a sign of expected longevity, my clients’ (and my own) experience dictates that this is not a comfortable way to live on a daily basis. Whether or not this extends our life span, who wants to constantly feel frigid on a daily basis? Not me, and I’d bet not you either.

A lowered body temperature can be due to a decrease in thermogenesis, since your body needs a certain amount of ingested calories to create heat, as well as due to the hormonal changes that come from caloric restriction, such as thyroid hormone reduction and HPA axis disruption. Low insulin can also lead to low body temperature, so some people on a very-low-carbohydrate diet will experience this symptom, as well. (14)

I may sound like a broken record at this point, but if you’re always cold, even in the summertime, it’s highly likely that you’re not getting enough to eat.

8. You’re Losing Hair by the Handful

Hair loss is one of the first signs of nutritional deficiency, whether that be calories, protein, or both. It is exacerbated by the hormonal changes that develop from chronic under-eating, including a drop in sex hormones like progesterone, testosterone, and estrogen. (15, 16) Hair loss is another common symptom of hypothyroidism, which, as you’ve learned, can develop from long-term calorie restriction.

If your hair is falling out at a scarily fast rate, you need to take a hard look at your diet. Consuming a calorically appropriate, protein-rich, nutrient-dense whole foods diet should be the first step for anyone who wants to stop hair loss in its tracks.

How Do You Stop Under-Eating and Improve Calorie Intake?

Determining exactly how many calories you need to eat on a daily basis for optimal health and weight control is tricky. Many factors come into play, including your physical activity, stress levels, sleep adequacy, history of chronic disease, and more. It’s impossible to know exactly how many calories your body needs on a daily basis, but there are some ways to estimate what you should be eating.

A quick and easy way to roughly estimate your “basement” calorie target—the lowest amount of calories you should ever eat—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 1,250 calories per day. Use this calculator to determine your “ideal” body weight. (Note: this calculator does not take into account frame size or muscle mass—that’s why I put “ideal” in quotes.)

It’s important to note that this quick estimate is a “sedentary” formula, meaning it does not take into account any physical activity beyond sitting and standing. If you’re exercising regularly, you’ll need to add at least 200 to 400 calories on top of that number. That same 5’5” woman might burn around 300 calories or more from a 30-minute run, taking her minimum calorie needs up to 1,550 calories per day, assuming she doesn’t do any other exercise that day.

Different workouts burn different amounts of calories. A CrossFit WOD can burn 12 to 20 calories per minute on average, so a WOD that takes 20 minutes could burn 240 to 400 calories. (17) If you’re aiming for a high step count, 10,000 steps burns around 300 to 500 calories, give or take, depending on body size and gender.

These are just examples of common exercise types in the Paleo community, and the point is to be aware that 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.

Another common factor that will raise your caloric needs is if you are a breastfeeding woman. Many of my female clients are shocked to hear that breastfeeding can raise your caloric expenditure by 500 calories per day or more. (18) So breastfeeding women need at least 300 calories per day above and beyond other women who are not breastfeeding, and that’s only if they have extra weight to lose postpartum.

So what does this calorie target exercise look like in practice? Using myself as an example, my “ideal” body weight is about 140 pounds, and I usually burn around 400 to 500 calories via exercise per day, so I try not to eat below 1,800 calories, especially on heavier training days, where I may eat more like 2,000 to 2,200 total. Your mileage may vary, but it’s a pretty easy place to start from, and you can tweak up and down as necessary as your health and weight fluctuates.

Alternatively, you can use this calculator to estimate your daily calorie needs based on your age, gender, height, weight, and activity level.

As you can see, determining caloric needs can get somewhat complicated, especially with the goal of weight loss thrown into the mix. When I work with clients, my goal is to get them on the least restrictive, most calorically appropriate diet possible. It’s amazing to see the health improvements that come from a simple increase in caloric intake when someone has been chronically under-eating.

If you need help figuring out the right calorie intake for you, let me help you to determine the best diet to keep you feeling and looking your best, without unnecessary restriction or starvation dieting.

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