Are You Undereating? 8 Red Flags You’re Not Eating Enough

Written By


Expert Reviewed By

Dr. Lauryn Lax, OTD, MS

Dr. Lauryn, OTD, MS is a doctor of occupational therapy, clinical nutritionists and functional medicine expert with 25 years of clinical and personal experience in healing from complex chronic health issues and helping others do the same.

Undereating, Woman Holding An Apple

In a society where we are bombarded with news stories about the diabetes and obesity epidemics, intermittent fasting fads, and low-carb substitutes for practically every processed food on shelves (i.e. peanut butter, yogurt, crackers), the topic of “undereating” is rarely discussed.

After all, overeating is obviously the bigger “problem,” right?

From unwanted weight gain to hormone imbalances, stubborn body fat, constipation, heartburn, bloating, brain fog and feelings of guilt, overeating has zero upsides.

Not so fast. 

Undereating may be equally as detrimental to both your physical and emotional well-being—especially if your undereating becomes chronic—long term.

8 Red Flags You’re Not Eating Enough

Here are 8 Red Flags You’re Not Eating Enough (plus ONE Do-Now Action Step you can take today if you are): 

  1. Your Body Never Changes
  2. You’re Accidentally Dieting 
  3. You’re Chronically Constipated, Bloated or Have “Horrible Digestion”
  4. “Sluggish Metabolism” or Tired (Often)—Even After Sleeping 8 Hours
  5. Your Period is Missing or You Can’t Get Pregnant
  6. You Don’t Have an Appetite 
  7. You Keep Advil in Your Purse at All Times
  8. You Think About Food (All the Time)


Undereating Red Flag #1: Your Body Never Changes

No matter what you do, it always seems like you hold on to those last 5 to 10 pounds, or you can’t put on those last 5 to 10 pounds.

Chicken and broccoli. Egg whites only. Low carb. Vegan. Keto. Paleo. Probiotics. Orange Theory. Yoga. Lifting weights. Running several days per week. You’re doing “all the right things,” but the scale and your body composition WON’T budge. You’re stuck. 

Contrary to popular belief, your body needs more (not less) quality, nutrient-dense foods and calories in order to see any healthy changes you want to make. 

When we are not fueling our body with enough nutrients (or enough balance—enough carbs, proteins or healthy fats), our body gets stressed and, in turn, fights to maintain homeostasis (including a pre-determined set point weight) by slowing down metabolism.

Woman Undereating, Feeling Dizzy, Starving

Consequently it also “slows” down other (less essential) metabolic functions too (like body fat loss, muscle gain, improved fitness, etc.), in order to ultimately survive and keep your other basic operations functioning (heart rate, breath rate, etc.). 

The “Biggest Loser” study (Fothergill et al, 2016) is a great example. Researchers followed several contestants from the weight loss reality show “The Biggest Loser” six years after the show, discovering that, just after spending  a mere 12-weeks in diet mode (i.e. undereating), the contestants’ metabolisms slowed down by an average of 500 calories per day, and their bodies fought to regain weight. On the flip side, “hardgainers” (people who struggle to gain weight) have been shown to have increased mitochondrial activity in their own fat cells, resulting in a higher fat burning rate and higher fat synthesis. These mechanisms lead to increased energy expenditure by the body (faster metabolism) and thus, resistance to weight gain. Hence, if you are not eating enough to fuel your revving metabolism and mitochondria, then your body equally won’t change (Ling et al, 2019). 

An analysis of dozens of other studies (Tomiyama et al, 2010) shows strong connections between stress and weight resistance (weight loss or weight gain difficulties) through the prolonged activation of the HPA axis (your body’s stress system), and increased insulin resistance (blood sugar imbalances). Restricting calories forces your body to reduce energy expenditure and increase total cortisol output—eventually followed by plummeting cortisol levels as well. 

The bottom line: Chronic cortisol output (stress) works against your body’s ability to “change” (even if you are just accidentally under-eating—not purposely dieting).

Undereating Red Flag #2: You’re Accidentally Dieting

You don’t have to “purposely” diet or restrict your calories to under-eat .

In fact, accidental dieting is often the bigger culprit for under-eaters than straight up calorie restriction. Accidental eating is what happens when you don’t feel like you need to eat often, and can happen due to several reasons:

Accidental Dieting Causes

  • You’re super busy at work or school
  • You’re on an elimination diet
  • You cut out an entire food group (protein, fat, carbs)
  • You’re exercising alot and not refueling appropriately
  • You’re intermittent fasting or fasting

Accidental dieting is one of the trickiest “red flags” for under-eating—primarily because accidental dieters typically are unaware that they are not eating enough in the first place. 

An accidental dieter may be the chick who wakes up, hurried for work, and only has time to grab a cup of coffee for breakfast; then eats a protein bar at her desk for lunch; maybe snags an apple or trail mix in the break room for a snack; and by dinner, she re-heats a frozen Lean Cuisine. Maybe 800 calories in a given day—less than half of her body’s daily needs.  

Another accidental dieter may be the gal who is “healing her gut”— on a strict autoimmune protocol (AIP) or “SIBO-cure diet, cutting out many foods she once loved (such as eggs, nuts, fruit, sweet potatoes). As her diet becomes restricted to only 5 to 10 foods (limited to meat, fish, greens and coconut oil), by default she “accidentally diets” or even ends up with ARFID—desperately just wanting her body to feel better.

One more accidental dieter may fall “victim” to food rules—without recognizing that food rules govern her eating decisions. After all, everyone is doing keto, or intermittent fasting, or vegan. It can be easy to get caught up in joining the masses. Even if her goal is not weight loss, she finds herself caught up in the noise of Instagrammers, fad diet bloggers and body hacking experts—seeing her body as a “project” to hack, instead of intuitively nourishing it. 

Common side effects of accidental dieting include:

Common Accidental Dieting Side Effects

  • Low energy or fatigue
  • Needing coffee to function
  • Thinking about food, talking about food or reading about food
  • A missing period
  • Irritability 
  • Bloating and constipation
  • Vitamin and mineral deficiencies 
  • Autoimmune disease 
  • Poor fitness progress
  • Skin problems
  • Brittle nails and hair 
  • Thyroid problems
  • Anxiety over food

A study in 100 patients with Inflammatory Bowel Disease (IBD), compared half of them on an elimination diet to the other half—NOT on an elimination diet (“accidental dieting”), and found those on the strict elimination diet experienced greater malnutrition than those in the non food exclusion group, especially for iron, calcium, vitamin B12, and vitamin D (Lim et al, 2018). These results were also observed in patients with eczema—many who cut out eggs, milk, eggs, wheat, soybeans, beef, pork, and/or chicken to improve their skin health. Across the boards, the 225 eczema patients were low in B1, B2, niacin, cholesterol, calcium, potassium, iron, Vitamin K, zinc and Vitamin A—further perpetuating their skin conditions and suggesting the necessity for food substitutions, as opposed to restriction, in order to avoid accidental dieting (Kim et al, 2013).

Ketogenic Diet With Nutrition Diagram Written, Undereating

The same thing can be said for any diet that prohibits any entire food group. Ketogenic  diets, for example, extremely high in animal and refined plant fats (60-70% of calories) are virtually devoid of minerals like potassium, calcium, magnesium, folate, and vitamin C, and it becomes difficult or impossible to design extremely high fat, very low carb diets that are not deficient in one or more of these essential nutrients. Interestingly, many folks on a high fat diet often lose their appetite—not only a side effect of eating more fat, but also potassium, magnesium and calcium deficiencies. Similarly, vegan or vegetarian are void in Vitamin B12 and iron—explaining low energy, brain fog and poor digestion in accidental dieters (Medwar et al, 2019). 

Accidental dieting is a sticky situation that will keep you stuck in under-eating (and consequently, not feeling 100-percent amazing). 

Undereating Red Flag #3: You’re Constantly Constipated, Bloated or Have “Bad Digestion”

Constipation, bloating and other gut issues may be related to inadequate food intake. This isn’t surprising, since consuming very little food will result in less motility and less waste in your digestive tract. 

Although it seems like symptoms constipation and bloating should happen when you overeat, when we under-eat, we also suppress our body’s own natural production of digestive enzymes and stomach acid to assist in the breakdown of foods in the first place. Hello bloating, chronic constipation or lingering gut “issues”—even when we try to eat “enough”.

Ironically, people with “gut issues” also tend to naturally eat less or avoid certain foods in order to minimize symptoms. Consequently, you keep your body stuck in the process—nutrient deficiencies, increased stress (cortisol), suppressed appetite cues, altered brain health and hormone balance. 

In fact, undernutrition down regulates the production and activity of other key hormones and neurotransmitters responsible for “healthy digestion”—namely serotonin, 5-HT and T3 Hormone.Serotonin and our 5-HT receptors (that uptake serotonin) aid in our “intestinal motility” and the body’s ability to “go” #2 (Camilleri, 2010). If you don’t have enough serotonin, then you’re not going to go #2.  Additionally, calorie restriction suppresses thyroid function—namely T3, the “active thyroid hormone” responsible for regulating metabolism. Suppressed T3 is significantly correlated with constipation and GI “issues” like bloating (He et al, 2017). Additionally, calorie restriction shows decreased intestinal absorption capabilities—like a muscle, your gut doesn’t get worked as much (Renaud et al, 2016). 

Undereating Red Flag #4: “Sluggish Metabolism” or Tired (Often)

Simply put: Food equals energy. If you’re undereating, you are lacking energy. Not only are you lacking nutrients that drive energy levels, but undereating also wreaks havoc on your hormones that boost energy and metabolism—especially your thyroid (as previously mentioned). 

Hypothyroidism and Hashimoto’s are two common thyroid disorders hallmarked by a “sluggish metabolism” and fatigue (even after sleeping 8 hours), along with constipation and bloating, hormone imbalances, food sensitivities and inability to lose or gain weight.

The unfortunate reality is that many hypothyroid problems are often a byproduct of nutrient deficiencies (not eating enough or enough balance), and many thyroid issues go undiagnosed for years since traditional medical blood work primarily looks at one or two blood markers on a blood panel (when there are more than a full-handful to look at).

 “Subclinical” hypothyroidism (defined at a TSH above 2.0, or Free T3 (lower than 2.5) affects upwards of 1 in 5 people.One of my favorite ways to further understand this conundrum are podcasts! Chris Kresser has an excellent podcast episode on Subclinical Hypothyriodism.

Undereating Red Flag #5: Your Period is Missing or You Can’t Get Pregnant

Low overall calorie intake affects your period. One of the most commonly experienced manifestations of under nutrition in women is known as “hypothalamic amenorrhea”—lack of your period for 3-plus months due to low energy supply (i.e. food), with or without an eating disorder (Williams et al, 2014).

Undernutrition also disrupts hormone balance and production—downregulating estrogen, and up-regulating cortisol production—the stress hormone that tells your body, “I don’t want to have a baby right now, I’m too stressed.” If Red Tide has not been flowing for some time, or you can’t make a baby—no matter how “clean” you’re eating or vitamins you take, look into what your overall daily nutrition entails.

Undereating Red Flag #6: You Don’t Have an Appetite

You can go hours between meals without feeling hungry; or you wonder, if or when you’ll “get your appetite back.” 

Are you superhuman or are you undereating?

Since undereating is related to nutritional deficiencies, when we miss out on essentials—especially zinc and B vitamins—our appetite gets suppressed. Zinc deficiency is highly connected to both “gut issues,” [(Hibberd et al, 2017) (Elmasta et al, 2007)] and appetite suppression (Suzuki et al, 2011) (Khademian et al, 2014)—including “accidental” anorexia (lack of appetite). B Vitamins are also responsible for helping balance healthy gut bacteria, and play a critical role in formation of stomach acid (HCL) for digestion and appetite.

Additionally, under-eating hijacks your “appetite cue” hormones—ghrelin and leptin; promoting ghrelin and leptin resistance. Ghrelin is your “hunger hormone”—the hormone that goes up when your body is hungry and needs to eat. Leptin is your “fullness” or “satiety hormone”—the hormone that goes up when your body is nourished and satisfied with your meal. In an ideal world, ghrelin and leptin work in tandem with your body’s energy, digestive and cellular needs. After several hours of not eating, ghrelin levels go up, signaling “feed me.” As you finish your meal, ghrelin levels go down and leptin levels rise, signaling, “All done.”

However, in the case of losing your appetite, “ghrelin resistance” is often at play—the inability to feel hunger (even if circulating ghrelin levels are still high). This happens because cortisol (stress) from not eating enough ends up blunting hunger. The last thing your body wants to do when it is “running from a bear” (stressed) is eat and digest food. Goodbye hunger.

Long term central stimulation of your HPA axis (chronic stress) blocks the synthesis of cortisol (metabolized cortisol), consequently decreasing ghrelin levels in your body (Azzam et al, 2017). On cortisol hormone urine testing (like the DUTCH test), I often see this presentation in my patients with histories of chronic dieting, eating disorders and lack of intuitive eating. The patient may have high circulating levels of free cortisol and feel like they have plenty of energy to get through the day without a lot of food, but their primary cortisol production is pooped out (“adrenal fatigue”). Consequently, these folks don’t feel hunger because their disrupted HPA Axis blocks their cues. 

Undereating Red Flag #7: You Keep Advil in Your Purse at All Times

Headaches are a “norm” in your daily life.

Woman Sitting On The Ground Feeling Weak After Running Because She Is Undereating

Whether it’s waking up with a pounder every morning, popping an advil every morning around 10 a.m. or hitting that 3 p.m. “crash” (and needing to just close your eyes), you’ve gotten used to headaches, like some people get used to pimples, bloating or seasonal allergies.Headaches are totally preventable though—especially when you’re eating enough (and digesting your food appropriately). One of the most common reasons people get headaches in the first place is due to a blood sugar imbalance.

Headaches and other symptoms (like shakiness before meals, low energy, sugar cravings, coffee dependence), most often strike in conjunction with Hypo- and Hyper-glycemic episodes.

Hypoglycemia is defined as blood sugar below 70 mg/dL (although some experience symptoms at higher blood sugar levels)—the times when energy is taking and a headache strikes.On the opposite end of the spectrum, Hyperglycemia (high blood sugar levels from imbalances in our nutrition, coffee or sugar) also invites headaches and brain fog. For both, you are more prone to these extremes when you are undernourished because your body is more sensitive to changes in food intake throughout the day. 

Undereating Red Flag #8: You Think About Food (All the Time)

When we are undernourished or underfed, our body (and brian) naturally thinks about food. This is a hardwire, survival mechanism.  Whatever foods or meals you can’t get out of your head (both “healthy” or “unhealthy” foods), there is a reason why: YOUR BODY (and gut bacteria) IS NOT GETTING WHAT IT NEEDS.

Although many people call these thoughts “food cravings”, obsessive thoughts are also a sign that our bodies are deprived. One of the most insightful studies on this phenomenon is the Minnesota Starvation Experiment (Kalm et al, 2007)—when 36 healthy male volunteers went on a restrictive low calorie diet for 12 weeks, the male participants became obsessed with thinking, dreaming, planning and aspiring to work with food (chefs, nutritionists, etc.). Interestingly, when the study ended and the men were allowed to resume a normal diet, they continued to obsessively think about food as their body fought to catch up and restore their nutrients. 

The bottom line: When we are properly and adequately nourished, our body (and brain) are able to focus on other things—outside food

But what if I am eating food—but still get food cravings?

We can be eating, but starving, at a cellular and bacterial level. If you have gut imbalances (dysbiosis, low stomach acid, low digestive enzymes, bacterial overgrowth) or you’re simply not digesting your food appropriately, then your body will still be deprived of nutrients. The average American consumes more than 3,600 calories daily—plenty of food on paper (FAO, 2017). However, considering the fact that over 1 in 2 people also have a gut-related health condition, this goes to show that many folks are not feeding their gut biomes appropriately and/or not absorbing their nutrients appropriately. 

Undereating, Woman On The Diet Craving To Eat Cake. Young Attractive Woman Really Wants To Eat Delicious Cake

Moreover, did you know that the specific gut bacteria living inside of you dictate your food preferences and cravings? An unbalanced gut may make us avoid healthy foods and instead seek out the junk food adored by some of our more selfish bacteria. Gut microbes can manipulate your eating behavior and food obsession by hijacking your host’s nervous system through the gut-brain axis and the vagus nerve highway (gut bacteria send signals to your brain, depending on what gut bacteria are inside you). 

Gastric-bypass patients are a great example of the role of microbiota in cravings. After a bypass surgery, the gut microbiome undergoes a major shift. Along with that comes a big change in cravings. People who once plowed through Ben & Jerry’s every night suddenly stop craving sweets. They also lose their taste for fatty foods (Behary et al, 2015). Another example: Individuals who are “chocolate desiring” have different microbial metabolites in their urine than “chocolate indifferent” individuals, despite eating identical diets (Rezzi et al, 2007). And the reason why probiotic bacteria, such as strains found in fermented foods like cultured yogurt, are beneficial for all around health is because they can alter the plasma levels of neurochemicals—like serotonin and dopamine, making you feel good (and obsess less over food) (Desbonnet et al, 2010). 

Are You Eating Enough? 

Are you eating enough

Healthy eating goes far beyond counting macros, low carb, plant-based or “eating less”. It entails eating enough for your body to fully function. 

If you need help problem solving or figuring out what that looks like for you, apply to become a client today so we can design a completely customized nutrition template for your individual goals and needs.

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