What Happens to Your Body When you get Chemotherapy?

PLN coach reviews what happens to your body composition when you go through chemotherapy

Published May 17, 2023

7 minute read

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What Happens to Your Body When you get Chemotherapy?

As individuals continue to live longer, cancer will become increasingly prevalent. Chemotherapy is one of the essential remedies for cancer. Chemotherapy refers to the use of chemical agents and substances in the treatment of cancer.

Chemotherapy treats cancer by preventing the division of malignant cells using chemical substances. Unfortunately, these anti-cancer compounds can also affect the patient's metabolism and caloric absorption. These therapies may also have an effect on the patient's body weight, which may affect his or her survival prospects.

This article will examine the alterations in body composition that occur during chemotherapy. We will also discuss practical methods to combat these changes in order to minimize the negative effects of treatment on body composition.

Gain in Weight and Chemotherapy


There are numerous varieties of chemotherapies, but they all slow the uncontrolled division of cancerous cells that characterizes this condition. Typical examples of chemotherapy agents include:

Alkylating agents: These attack cancer cells during their dormant phase, before they begin to divide.

Antimetabolites are substances that are ingested by cancer cells and inhibit their ability to divide.

Enzymes necessary for DNA replication and cell division are known as topoisomerases. These chemotherapy agents inhibit the activity of these enzymes, preventing cancer cells from dividing.

Sadly, these chemotherapy agents also target healthy, normal cells. These are the causes of adverse effects. Examples of common adverse effects of chemotherapy include:

  • Sickness and vomiting
  • Hair reduction
  • Having a puffy appearance on the face.
  • Insensitivity and sensation
  • Weight increase
  • Retention or incontinence of urine
  • Acoustic impairment leading to hearing loss
  • In some cases, pulmonary fibrosis and cardiotoxicity occur

The average breast cancer patient gained approximately 4 kilograms (about 10 pounds), according to an analysis of more than 200 women undergoing treatment.

In a cohort of over 100 women, similar findings published in Clinical Oncology revealed an average weight gain of 3.7 kilograms (approximately 9 pounds). Numerous studies, including these ones, indicate that numerous cancer patients gain weight during chemotherapy treatment.

Numerous hypotheses have been proposed to explain why patients gain weight during treatment. Examples include:


  • Alterations in the capacity to digest and assimilate nutrients
  • Individuals feel ill and exhausted, preventing them from exercising.
  • Fluid retention caused by cancer treatment or chemotherapy
  • Utilizing steroids to mitigate some of the side effects of cancer and its treatment.


Having excess fat (obesity) is unquestionably associated with increased cancer risk. However, acquiring weight due to treatment does not necessarily increase your risk of cancer recurrence, as weight gain is not synonymous with fat gain. The first study found no correlation between weight gain and the recurrence of cancer. However, these variations in body composition are strongly linked to weight gain, which is frequently associated with increased disease risk.

Although these variables may contribute to weight gain, weight is not the greatest indicator of changes in body composition. Because significant changes in body composition occur during treatment, it is essential to monitor these alterations in order to comprehend how health hazards can evolve over time.

Why is Body Composition so Crucial?

For those who are unaware, body composition refers to your body's substance or, more commonly, your body weight. While weight and BMI have been used as health indicators for decades, body composition provides a more accurate representation of your health and health concerns. Typically, body composition is classified as:

  • Total body water is present in all human body tissues.
  • Protein is present in muscles and organs.
  • Minerals include vitamins, calcium, iron, and other trace metals necessary for a variety of bodily functions.
  • Fat is the body's primary source of energy storage.

Each component of body composition is significant for a unique cause. Your health is affected not only by weight gain or loss but also by the fluctuation of the various components of your body composition. Cancer and chemotherapy can have a significant effect on body composition, making it crucial to comprehend and monitor body composition in these patients.

How does chemotherapy affect the composition of the body?

  • Cancer Treatment and Fat Mass
  • Chemotherapy can cause undesirable changes in body composition as well as unpleasant adverse effects.

A study analyzing the body composition of breast cancer patients undergoing chemotherapy was published in Clinical Breast Cancer. Before beginning chemotherapy and one year later, body composition measurements were performed. This assisted in determining not only whether the participants gained weight, but also where and how their body composition changed.

Those with a normal weight gained approximately 4 pounds and gained fat in their torso and extremities, according to the findings. Those who were overweight or obese prior to beginning chemotherapy, however, lost between 3 and 4 pounds.

Another study published in the Journal of Clinical Endocrinology and Metabolism examined changes in body composition and weight in breast cancer patients undergoing treatment. This study, which was conducted in a similar manner, found that the patients' weight did not change significantly; however, their fat mass increased and their fat-free mass decreased.

Why do these alterations take place?

These researchers also surveyed women about the alterations in their lifestyles caused by chemotherapy. The survey reveals that a significant number of women reduce their physical activity, their work activity, and their appetite. All may have contributed to the aforementioned alterations in their body composition.

Despite the fact that these studies demonstrated that women gained weight in the form of fat and lost lean mass, they are essential because they help patients anticipate what may occur as chemotherapy is administered. If patients are aware that these changes in body composition may occur, they can take measures to prevent or reduce their severity.

Cancer Treatment and Muscle Mass

A study was conducted to examine the specific metabolic alterations that occur in cancer patients with cachexia. Researchers discovered that patients lost an average of 4 kg of muscle mass as they neared mortality. In addition, these patients lost fat mass and expended more calories, representing a significant metabolic shift.

Patients who lost more than 9 percent of their total muscle mass had substantially lower survival rates, according to a similar study. Those who lost more than 9 percent of their muscle mass were almost three times less likely to survive than those who lost less than 6 percent.

Since body composition and muscle mass play a significant role in the survival of cancer patients, treatments should focus on maintaining muscle mass and preventing or minimizing the effects of cachexia through appropriate nutrition.

Novel Treatments and Body Composition Maintenance

In addition to dietary modifications, there are additional interventions that can help halt the progression of cachexia and increase survival.

Novel cancer cachexia treatments include:

  • Exercise mimetics: Since many chemotherapy patients are confined to a sedentary lifestyle, medications that help the body mimic exercise may help stimulate muscle fibers and preserve muscle mass.
  • Metabolic targets: An early study on the effects of AR-42 inhibitors (a form of cancer therapy) on cancer-stricken animals revealed that those who took the medication experienced less decrease in muscle fiber size and strength than the control group.
  • Digestive targets: During chemotherapy, probiotics are essential for maintaining a healthy digestive tract. Certain bacteria, including Lactobacillus Reuteri and other probiotics, can stimulate genetic targets and modulate inflammation, thereby assisting in the reduction of cachexia.

What does this implication have for the cancer patient? People should consider integrating various dietary and exercise modifications to preserve muscle strength and prevent muscle loss. Fish oils, amino acids, nutritional support, and muscle-building exercises should be recommended because not only will they improve mood, but they may also improve prognosis.

Chemotherapy can have a substantial effect on a patient's weight and body composition.

According to studies, cancer patients gain weight, but it is predominantly fat and body water due to inflammation. Due to this, body composition must be monitored in order to comprehend how physiological changes can affect health risks. This monitoring can assist medical professionals in detecting fluctuations in fat, water, and even skeletal muscle mass, thereby aiding in the prevention of detrimental changes in body composition and improving survival and quality of life.

Due to the aforementioned alterations, it is crucial that all cancer patients maintain a healthy diet and remain physically active throughout their treatment. This can be difficult due to adverse effects like nausea and vomiting, but it will help people maintain their body composition and may increase their chances of survival.

When cancer cells proliferate, alterations to the body are unavoidable. Priority number one is to treat cancer, but the next stage is to manage the health of the body. Changes in body composition are associated with health hazards; therefore, a combination of diet and exercise can help counteract these changes. Due to increased knowledge of exercise's benefits, cancer exercise is a rapidly expanding field.

Since the objective is not to become a bodybuilder, weights are not always required. The objective is to stimulate the muscle fibers by using them, sending the body a signal that these muscles are still required. This will prevent muscle atrophy and assist the body in incorporating consumed protein into new muscle fibers.

There are treatment options available, such as vitamins, minerals, and amino acids, for those who develop cachexia. Through education and collaboration with healthcare professionals, patient outcomes can be improved and the effects of cancer and subsequent chemotherapy on body composition can be delayed.


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