The Dangers of Chronic Under-Eating.

Updated: Mar 2, 2021

Think of your body as a machine. Most machines need some type of fuel source to function and run all it’s systems. Your body also needs fuel. Otherwise, all of its functions and systems will begin shutting down or not performing as they should.

There isn’t much that under-eating does not affect inside the body. This includes cognitive function and mental health, the muscular system, the endocrine system, the immune system and the digestive system. All of these systems rely on the consumption of a balance of vitamins, micronutrients and macronutrients, which is obtained from food.

The brain relies on glucose as its main source of fuel. The body gets glucose from carbohydrates. (Barefield, 2020) Therefore, if enough carbohydrates are not consumed cognitive function will suffer. Have you ever heard the term ”brain fog?” Maybe you have actually experienced what it feels like for yourself. This can be a symptom of under-eating. According to Medical News Today, mental health can also be negatively impacted when not enough food is eaten. Vitamin D comes from sun exposure, but it can also be obtained from certain foods. When vitamin D is lacking, mood can be impacted. (Mandolin, 2019)

When the body is not properly fueled it will start looking for another fuel source. If protein is not attained through diet muscles can be broken down for the body to get the protein it needs. This leads to a drop in muscle mass, which in turn leads to a decrease in basal metabolic rate. This means less calories have to be eaten to avoid negative health impacts. (Kronemer, 2019)

Crash dieting, even for a short period of time, can lead to a disruption of the endocrine system. The endocrine system controls the hormones inside the body which are what tell all of the other systems inside the body what to do. The hunger hormones are disrupted by very-low calorie diets. The hormones we want more of decrease and the hormones we want less of increase. This can happen even a year after energy consumption has returned to a more normal level. The result is an increase in appetite because the body wants to stay the same in order to survive. This can make it difficult to keep the weight off. The longer someone eats at an extreme deficit the more the hormones are disrupted. (Trexler, Smith-Ryan, & Norton, 2014)

Reproductive hormones can also be affected by under-eating. (Barefield, 2020) Low-calorie diets, particularly those very low in fat, can lead to a decrease in testosterone. A decrease in testosterone is due to the rise of cortisol, which crash dieting can cause. This can lead to a loss of muscle mass. Which, as stated above, leads to a decrease in basal metabolic rate. If the caloric deficit is very severe estrogen can also decrease, which can lead to the loss of a menstrual cycle. (Your

Under-eating can cause a lack in the nutrients the body needs to power the immune system. The immune system relies on a balanced diet consisting of a variety of vitamins and minerals. Poor nutrition lacking in one or more nutrients can impede the production of immune cells and antibodies. All the nutrients are necessary for the body’s functions, but vitamin C, vitamin D, zinc, selenium, iron and protein are necessary for the immune system to function properly. (Nutrition, 2021)

A decreased intake of protein and energy can lead to a loss of myocardial muscle. Myocardial muscle is the type of muscle, which makes up the heart. The loss of myocardial muscle can reduce cardiac output. (Webb, Kiess, & Chan-Yan, 1986) A lack of fiber, potassium, magnesium, antioxidants, and phenolic, due to inadequate fruit and vegetable intake, can also have an impact on cardiovascular health. These nutrients and minerals have been shown to reduce blood pressure and cholesterol. The optimal intake of fruits and vegetables are 300 grams and 400 grams respectively. (Phillips, Rapaport, & Welch, 2019)

Chronic constipation can be a symptom of under-eating. When the body does not get enough energy, everything slows down. T3, the active thyroid hormone, decreases, which slows down gut motility. (Schoenfield, 2015) When the body doesn’t get enough water or fiber the stool lacks the bulk it needs to move through the intestinal tract. (Team, 2020)

If the body, which is just like a machine, doesn’t get the fuel it needs all of the systems inside it are affected. The digestive system slows down. The cardiovascular system can be negatively impacted. The immune system does not function properly. Reproductive and appetite hormones can be disrupted. The muscular system can be broken down. Fuel your body, transform your life.



Barefield, Kat., et al. “Nutrition.” NASM, 2020,

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Phillips, Q., Rapaport, L., & Welch, A. (2019, June 12). Not eating enough fruits and vegetables contributes to cardiovascular death: Everyday health. Retrieved February 24, 2021, from

Mandolin, A. (2019, May 29). 9 signs and symptoms you're not eating enough. Retrieved February 24, 2021, from

Schoenfeld, L. (2015, June 2). Are You An Under-Eater? 8 Signs You’re Not Eating Enough. Retrieved from

Team, D. (2020, August 31). Constipation: 6 tips to help you return to Regular bowel movements. Retrieved February 24, 2021, from

Trexler, E. T., Smith-Ryan, A. E., & Norton, L. E. (2014). Metabolic adaptation to weight loss: Implications for the athlete [Abstract]. Journal of the International Society of Sports Nutrition, 11(1), 7. doi:10.1186/1550-2783-11-7

Webb, J. G., Kiess, M. C., & Chan-Yan, C. C. (1986). Malnutrition and the heart. CMAJ, 135(7), 753-758. doi:10.5999/aps.2020.01697.s003

You and your hormones. (2016, December). Retrieved February 24, 2021, from

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