Undereating: 5 Alarming Symptoms of Not Eating Enough That You Should Know

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.

Are you undereating or eating enough? 

Undereating is super common (especially nowadays where intermittent fasting (IF) and fasting are all the rage). Read on to learn about the symptoms of not eating enough and what to do about it.

Undereating is So Hot Right Now (Especially Fasting)

Undereating - Young Woman Not Satisfied With Her Food

Fasting or “undereating” is nothing new. 

Humans have fasted for most of their history (ie. we did not evolve with 24/7 access to restaurants and grocery stores), humans were definitely more intuitive “back in the day” then they are today. 

Today intermittent fasting is the practice of not eating for 12-16 hours, followed by a feeding window of typically 8 -12 hours. IF has increased in popularity in recent years. 

Intermittent fasting is the very reason why breakfast is called “break fast”—you’re breaking your fast from your last meal to your first meal after sleeping overnight. The 12 hours between your 8 p.m. last meal is followed by breakfast at 8 or 9 the next morning. Voila! You fasted! 

The idea behind intermittent fasting is to mimic the “optimal human diet”—how our ancestors would have eaten.

The Benefits of Intermittent Fasting

And intermittent fasting does have lots of benefits—such as: 

  • increased cellular autophagy (clearing out dead cells)
  • increased brain alertness
  • improved glycemic markers and insulin levels in people with PCOS, diabetes and pre-diabetes
  • Giving your 
  • And reduced inflammation

The Downsides of Intermittent Fasting

However, despite all these amazing benefits, very little is discussed about some of the side effects of intermittent fasting—primarily undereating (not eating enough).

If you’re not eating enough, this can wreak havoc on your hormones, energy, digestion and blood sugar levels. The effects of “not eating enough” all comes down to the the impact of stress on your body.

Undereating or intermittent fasting is a stressor that can be a great  “hormetic stressor” (a positive stressor)—just like exercise is a hormetic, healthy stressor that pushes your body to work hard, develop muscle, decrease inflammation, and enhance your cardio-respiratory endurance. 

However, if you push your body’s exercise threshold too far (such as upping your miles or trying to squat 500 pounds), this can have a negative impact on your fitness. 

Likewise, while intermittent fasting can be wonderful for giving your gut a break to “rest and digest”…however if your body is already stressed out—such as going to bed at midnight…then waking up at 5 every morning to go on a run…needing coffee to function…or trying to heal from chronic health imbalances…IF may not be your BFF. 

5 Symptoms of Not Eating Enough & Too Much Intermittent Fasting

Undereating - Young Woman Suffering From Bloating, Constipation

Symptom #1: Undereating & Hormone Imbalances

When women in particular are deprived of food, the hypothalamus shuts down fertility, often disrupting their period or causing hormone imbalances.  In animal studies, after just two weeks of intermittent fasting, female rats stopped having menstrual cycles and their ovaries shrunk while experiencing more insomnia than their male counterparts (although the male rats did experience lower testosterone production too).

Thyroid function—your metabolic mothership— is also affected. T3 thyroid hormone is very sensitive to total calorie and carbohydrate intake.  When calories and carbs are too low, your T3 levels drop and thyroid function goes down, leading to decreased energy…resistance for improving your body composition…constipation and bloating.

Symptom #2: Undereating & Gut Problem

Oh yes, constipation and bloating are very common if we are under-eating! When we stop eating, our stomach acid, enzyme production, gut motility and gut bacteria all get suppressed, decreasing food absorption and increasing bloating too. 

Symptom #3: Undereating & Loss of Appetite

Appetite gets altered too. 

Some people find they don’t feel hungry at all after doing IF regularly— a sign their metabolism has slowed…Others fall into the famine-and-feast mentality—not eating for 12-16 hours…followed by a binge since they’ve been “saving up all their calories.” 

Symptom #4: Undereating & Blood Sugar Imbalance

If you have unstable blood sugar, IF can also exacerbate episodes of hypoglycemia—such as feeling shaky, spacey or lightheaded during the day…having low energy…needing coffee or simple sugars—like fruit—to function…and waking up in the middle of the night! Even waking up to pee or waking up from a weird dream can be a sign of low blood sugar…as blood sugar dips it spikes adrenaline, which acts like an emergency brake wake you up. Your gut bugs need fuel—especially protein—to stabilize. 

Symptom #5: Undereating & Food Obsession

Lastly, aside from physical symptoms, Intermittent Fasting can also increase your thoughts about food and the diet mentality. 

Have you ever heard of the Minnesota Starvation Study? 

In it, 36 healthy men were fed a “normal” calorie diet for 12 weeks (approximately 3200 calories per day of a varied, balanced diet), followed by half the amount of calories for 24 weeks (semi-starvation) and finally a recovery phase of their normal diet. 

What do you think happened?

Sure there was some weight loss…however, the biggest finding researchers observed was the men slowly became obsessed with thoughts about food. 

They dreamed about food…talked about food…they became obsessed with meal timing—and agitated and anxious if meals were delayed… some of the men reported experiencing pleasure just by watching others eat or from smelling food…they drank lots of coffee and chewed gum to suppress hunger cues.

Interestingly, at the end of the study, when they were allowed to eat “normal” again, the men still remained obsessed with food—the thoughts didn’t go away. 

Under normal conditions, women think about food twice as much as men—every 62 minutes, as opposed to every 38 minutes…can you imagine what would have happened if women had done that study?

Although many people report that fasting actually helps them “not think about food” as much (duh; the majority of your day you’re not eating)—although this sounds like it could be a dream come true…sometimes this also comes at the cost of not eating enough all around to feel like your healthiest, most vibrant self. 

The Bottom Line

You do not earn a gold star by NOT eating nutrients. 

Although intermittent fasting can be really great for some people…more often than not, I see people who are actually already stressed enough in their life…not eating for extended amounts of time just adds to that stress, especially if you are under-eating or binging as it is.

And, the clincher: You can still give your gut a break to “rest and digest” by doing the classic version of IF—not eating between your dinner meal and next morning’s breakfast. For many people, this is ample time to give digestion a break without sacrificing energy reserves or blood sugar stability. 

So….Are You Eating Enough?

Undereating - Young Man Looking At The Food Uninterested

So now, the question comes to you—are you eating enough?

Even if you are not into intermittent fasting, you can still fall into under-eating or accidental dieting—impairing your digestion, energy and hormone balance without realizing it. 

An accidental dieter is the woman who wakes up, hurried for work, and only has time to grab a coffee for breakfast. She eats a protein bar at her desk for lunch, snacks on trail mix or an apple…then for dinner, re-heats a frozen Lean Cuisine. By the end of the day, she’s only consumed 800 calories—less than half of her body’s daily needs.  

Another accidental dieter may be the guy who is healing his gut— on a strict autoimmune protocol (AIP) and SIBO-cure diet, cutting out many foods he once loved (such as eggs, nuts, fruit, sweet potatoes). As his diet becomes restricted to only 5 to 10 foods, by default he accidentally diets. 

Even though I am not into counting calories or macronutrients, it can be a good baseline to gauge if you are eating enough—because often times low energy is not because you have a coffee deficiency…but because you have a calorie and nutrient deficiency. 

Calorically, the ideal range most women need is: 1800-2200 calories each day, for men at least 2400-2800 calories and a 30% carbohydrate 35% protein and 35% fat is a good place to start for balancing blood sugar.  If you focus on protein-fat-and-fiber with each meal you can easily achieve this. 

How to Eat Enough

Are you eating enough for optimal blood sugar and energy? Count nutrients—not necessarily calories to see where you stack up! 

Take inventory to see if you’re eating the optimal balance of nutrients and practicing the top lifestyle factors that balance your blood sugar. 

Aim to Consume These Nutrients Daily

  • 20 to 30 grams of protein within the first 1 to 2 hours of waking
  • at least 2 healthy fats with meals, a protein and 2-3 colors with all meals
  • 1-2 servings of fruit
  • 1-2 servings of a starchy tuber, root or properly prepared grain
  • 3+ servings of green veggies per day
  • 8 to 16 oz of bone broth
  • snacks as needed: snack on a protein, something green or healthy fat
  • sleep 7-9 hours per night
  • drink half bodyweight in ounces of clean filtered water per day
  • daily movement—but not overtraining
  • avoiding additives and artificial sweeteners
  • 1 gut love treat/day (optional; without going overboard)

Nutrition & Functional Medicine Support 

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