How Does Undereating Affect the Body?

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Most of us skip a meal from time to time, whether because we’re busy or trying to lose a few pounds. But feeling a little hungry during the day and choosing not to eat is not the same as chronic undereating.

So, how does undereating affect the body, and what are the telltale signs you’re not eating enough calories? Continuous undereating can lead to numerous bodily changes and affect mental health; therefore, it’s vital to take it seriously.

Skipping too many meals over an extended period can occur for different reasons, and we’ll explore most of them. We’ll also point to the common symptoms of undereating and how you can make sure you’re consuming enough calories.

What Is Undereating and How Does It Manifest?

Undereating occurs when people eat fewer calories than their body requires for proper functioning. We can differentiate unintentional and intentional undereating, both of which can adversely affect the body.

Unintentional undereating can happen when a person struggles to find food, whether it’s due to environmental or socioeconomic circumstances.

However, people often don’t eat enough without awareness, even if they have continuous access to food. Essentially, some people are accidentally dieting, which can happen for several reasons.

For example, a person may be too busy to eat, whether it’s because of school or work engagements, or they are a busy parent worrying about the wellbeing of their kids.

Also, people who have taken up intermittent fasting, an eating pattern restricting food intake for specific periods during the day, end up not eating enough.

Another way someone might be undereating without realizing it is by exercising rigorously and not replenishing their body properly after the exertion.

However, in many instances, people undereat because they are trying to lose weight and over-restrict their calorie intake. This is particularly common with people who have been “on a diet” for many months and are trying to expedite the weight loss by taking as few calories as possible.

We also must mention that appetite loss is a common symptom for people who struggle to eat properly due to depression, as appetite loss is a common symptom.

Lastly, undereating can be a side effect of eliminating an entire food group due to health concerns because a person is afraid of gaining weight. For example, excluding fat or carbohydrates from the diet can easily lead to undereating.

Another form of fearfulness of certain types of food is called orthorexia and represents an unhealthy obsession with eating “pure” foods and demonizing specific food items.

How Do You Know If You’re Undereating?

Even when undereating is intentional, it doesn’t mean that a person is fully aware that the significant calorie restriction is damaging their health.

They might understand on a conscious level that their body needs more calories but see their decision to undereat as a path to losing weight faster or being more mobile.

However, even if one has weight to lose, underrating for many months at a time can lead to specific consequences. So, how does undereating affect the body precisely?

Here are a few common symptoms to keep in mind.

Low Energy Levels

Chronic fatigue or frequent low-energy spells can signal many issues, and undereating is one of them. If you’re not eating enough calories to fuel your body properly, it can’t maintain the required energy levels throughout the day.

If you feel like it’s a struggle for your mind or body to do anything during the day, you might need to re-examine how many calories you’re eating.

Remember that regardless of age, gender, or physical activity, eating less than 1,000 calories daily will slow down your metabolism and lead to fatigue.

Hair Loss

Losing hair is an incredibly stressful event, regardless of the cause. When talking about hair loss caused by undereating, we’re not referring to normal hair loss during the day or the seasonal “shedding” that typically takes place in the fall.

Hair loss is not an unusual side effect of undereating because hair requires many nutrients to grow properly.

The human body needs enough protein, iron, vitamin B, and other minerals and vitamins to facilitate hair growth, and excessive hair loss can occur when it’s not nourished well.

Always Feeling Hungry

This symptom may fall under the “obvious symptom” category, but this issue has some nuance. For example, if you’re trying to lose weight, you might think constantly feeling hungry is typical or expected.

Indeed, hedonic hunger, or the drive to eat food strictly for pleasure, not nourishment, is common when trying to lose weight. But feeling physically hungry all the time is not normal, even for obese people.

If a person constantly feels hungry, it’s almost a sure sign they’re either not eating enough calories or excluding a vital food group from their diet.

How Does Undereating Affect the Body

Fertility Issues

Unfortunately, undereating can lead to problems with conceiving because it can cause a hormonal imbalance. The pituitary gland, an endocrine gland located at the base of the hypothalamus, receives signals regarding the woman’s hormone levels which can either stimulate or decrease the production of estrogen, an essential sex hormone.

Research has demonstrated that excessive and prolonged calorie restriction impacts the function of the pituitary gland, which can prevent pregnancy. In addition, a common symptom of undereating affecting fertility is the loss of menstruation for three months or longer.

Disordered Sleeping

Sleep issues can occur for many different reasons, including undereating. For example, we often hear about how sleep quality suffers when a person is overweight, which is accurate, but extreme undereating can cause the same issues.

Not eating enough can cause a person to wake up more frequently at night and have issues reaching deeper stages of sleep.

If you find it difficult to fall asleep because you’re feeling hungry or waking up feeling intensely hungry, you’re almost certainly not getting enough food.

Mood Swings

Some people get immediately irritable if they skip a meal. However, many don’t, and it might take a while to notice that they’re getting moody due to continuous calorie restrictions.

A study has shown that this can be particularly prevalent among high school and college young people. A diet considered even minimally restrictive in terms of calories can lead to frequent mood swings.

Constantly Feeling Cold

If you’re wondering how undereating affects the body, you might be surprised to learn that it can make you feel cold all the time. A person doesn’t even have to consume an extreme calorie-restrictive diet to experience this symptom.

The body will lower the core temperature, and you will start feeling chilly more often, even when it’s not cold outside.

One of the studies that looked at the connection between underrating and feeling cold discovered that T3 thyroid hormone levels dropped. This decrease in T3 production can lead to many issues, including increased sensitivity to cold.

Persistent Constipation

Any dietary changes can lead to digestion and constipation issues, but when they are persistent, you need to take them more seriously.

If you have ever been on a diet, you’ve noticed that infrequent bowel movements can occur, but persistent constipation is often due to underrating.

As there is much less food in the digestive tract, some people may find they go to the bathroom less than three times per week. When undereating, constipation can occur even if your diet is fiber-rich.


We mentioned irritability caused by undereating, but it can lead to general anxiety in some people. In addition, the lack of vitamin B and magnesium can make it difficult for the body to manage stress, leaving you feeling most anxious.

While anxiety can be caused by many factors, an imbalanced or insufficient diet is among the top causes.

Isn’t Undereating Advisable in Some Situations?

The most straightforward answer to this question is no, but some exceptions are worth mentioning. Individuals under strict medical supervision may undergo a very low-calorie diet or VLCD as defined by the National Institute of Diabetes and Digestive and Kidney Diseases.

This typically occurs when they need to lose a large amount of weight and need to jump-start their journey. But, even then, this diet can only last three months.

How to Be Sure You’re Eating Enough Calories

Most people don’t count calories unless they’re trying to shed some weight, but it could be beneficial to have insight into the caloric value of specific foods. That can give you a clue whether you’re undereating or even overeating. Also, age and activity levels will impact how many calories are enough for a person, but here are the general estimates.

Women with a sedentary lifestyle should consume between 1,200 to 1,800 calories per day, and moderately active people can eat between 1,400 and 2,200 calories. Very active women should eat up to 2,400 calories to stay full and healthy.

The situation is slightly different for men, and a sedentary lifestyle means eating between 1,400 and 2,400, depending on height and age. Moderately active men should eat between 1,400 and 2,800 calories, and those even more active should consume around 1,600 and 3,200 calories.

Staying Healthy and Eating Enough

Exploring the question of how undereating affects the body uncovered that there are many adverse outcomes of eating too little for extended periods. Indeed, losing weight requires eating less, but that usually means finding strategies to stop overeating, which doesn’t need to result in undereating.

Still, some people might undereat due to hectic lifestyles or mental disorders and only realize they’re undereating when the symptoms occur.

While skipping a meal from time to time is unlikely to hurt, going for months without proper nourishment is not a great idea. Remember, a balanced diet has many incredible benefits, including anxiety regulation and better sleep.

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