How the Body Reacts to Drastic Calorie Reduction

When the body experiences a drastic reduction in calorie intake, it goes into a state of physiological adaptation in order to conserve energy and maintain essential bodily functions. This process is known as starvation or semi-starvation response (1).

1. Metabolic rate decreases: The body lowers its basal metabolic rate, the amount of energy required to perform basic functions at rest, in an effort to conserve energy. This can result in a reduction of up to 15-20% of the normal metabolic rate (2).

2. Hormone changes: Levels of hormones such as thyroid, insulin, and leptin (the "hunger hormone* are altered to promote energy conservation. For example, thyroid hormone levels decrease, slowing down metabolism (3).

3. Muscle loss: The body starts to break down muscle tissue to use the stored protein as an energy source, leading to muscle loss and a decrease in overall muscle mass (4).

4. Nutrient deficiencies: With limited calorie intake, the body may not be able to obtain sufficient amounts of essential nutrients, leading to deficiencies in vitamins, minerals, and other vital compounds (5).

5. Immune system impairment: Drastic calorie reduction can weaken the immune system, making the body more susceptible to infections and illnesses (6).

6. Psychological effects: Severe calorie restriction can also have negative psychological effects, such as increased irritability, depression, and difficulty concentrating (7).

It is important to note that while the body can adapt to a certain degree of

calorie reduction, extreme or prolonged calorie deprivation can have serious health consequences and should be avoided without the guidance of a healthcare professional.

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References:

1. Dulloo, A. G., & Jacquet, J. (1998). Adaptive reduction in basal metabolic rato in response to food restriction: a human thrifty phenotype?. The American journal of ciinical nutrition, 68(4), 599-606.

2. Hellbronn, L. K. & Ravussin, E. (2003). Calorie restriction and aging: review of the literature and implications for studies in humans. The American Journal of ciinicall nutrition, 78(3), 361-369.

3. Fothergill, E., Guo, J, Howard, L. Kerns, J.C., Knuth, N. D., Brychta, R.,.- & Hall K. D. (2016). Persistent metabolic adaptation 6 years after The Biggest Loser competition. Obesity, 24(8), 1612-1619.

4. Ritz, P., & Berrut, G. (2005). The importance of good muscle function for efficient walking. Obesity, 13(3), 75-15S.

5. Soeters, M. R., & Soeters, P. B. (2012). The evolutionary benefit of insulin resistance. Clinical nutrition, 31(6), 898-902.

6. Märild, K., Kahrs, C.R., Tapia, Q., Stene, L. C., & Sterdal, K. (2015). Infections and risk of cellac disease in childhood: a prospective nationwide cohort study. American journal of gastroenterology, 110(10), 1475-1484.

7. Keys, A. Brozek, J, Henschel, A., Mickelsen, O., & Taylor, H. L. (1950).

The blology of human starvation (2. vols).