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The role of proteins during cancer treatment

Dr.Andrea Pereira, Clinical Nutrition Support Physician

Published January 4th, 10h30

A crucial aspect in cancer prognosis is muscle mass, which is higher in women, the elderly, diabetics, and obesity. As we age, we lose muscle mass, but this loss usually starts at age 30, when we lose 3-5% of muscle mass per decade of life, reaching 80 years with 15-25% less muscle compared to age 30.

When there is an even greater loss of muscle mass than expected due to aging-associated with a drop in functionality, we have sarcopenia, whose definition in Greek is little meat. Sarcopenia is a poor prognostic factor in cancer; it causes increased mortality, worse response to chemotherapy and radiotherapy, more chemotherapy-related side effects, longer hospital stay, and more post-surgical complications, such as infections and fistulas addition to worsening quality of life.

The diagnosis of sarcopenia is carried out using diagnostic methods to assess the amount of muscle mass, the main ones being tomography, body densitometry and bioimpedanciometry, in addition to muscle quality, evaluated by force dynamometers (Handgrip). This assessment should be performed periodically at the time of cancer diagnosis since sarcopenia can occur during cancer treatment.

Under healthy conditions, muscle production is in balance with its degradation; hence, lost muscle fibers are renewed. However, in cancer, due to an inflammatory condition, reduced appetite, and physical activity, effects of chemotherapy, radiotherapy, and surgery, we lose this balance, and the loss of muscle fibers is greater than renewal, giving a gap for a reduction in mass. Muscle, worsening the prognosis of this cancer patient, as previously mentioned.

To maintain muscle mass, two factors are essential: an adequate diet, calories and proteins, and physical activity. Muscle depends on physical stimulus and energy substrate, with protein being the main item. In most digital media research on the best diet for cancer, there is a suggestion to reduce the consumption of animal protein, especially red meat. Studies have shown a reduction in protein consumption by cancer patients during treatment leading to greater muscle loss.

As mentioned earlier, there is a strong correlation between high consumption of red meat and cancer prevention. There is no mention of exclusion of this protein but of a reduction in its consumption. However, there are no such data regarding a recommendation after the presence of cancer. On the other hand, several studies demonstrate the importance of muscle mass in the prognosis. Therefore, removing red meat from the diet once I have cancer does not present scientific evidence of improvement of the disease.

The nutritional value of protein is determined by the quantity and quality of the amino acids that make it up. Amino acids are the building blocks of muscle but with different qualities. According to a recent study that brought together several experts published in Clinical Nutrition, those of animal origin have a higher quality for this structural mechanism than vegetables. In addition, vegetable proteins have a lower digestibility than animal proteins, except isolated soy protein.

This lower structural potential for increasing muscle mass on the part of vegetable proteins may be due to their lower amount of leucine; to a greater resistance to its degradation in the digestive tract, reducing its absorption, mainly in people with alterations of the gastrointestinal tract, as in cancer of the digestive system.

An exception of food of plant origin with a higher amount of leucine is corn, but this does not give it greater structural power. Exemplifying the differences between plant and animal proteins, we can compare 100 g of red meat steak with 100 g of beans. They contain, respectively, a protein density/% protein ratio, 33g and 8g.

Final Study Messages:

1. The protein requirement of people with cancer is greater than that of healthy people;

2. Proteins of animal origin provide more stimuli for muscle growth than those of vegetable origin;

3. A combination of animal (65%) and plant (35%) proteins seems ideal for muscle health and preventing malnutrition during cancer treatment;

4. Eliminating animal proteins from the diet is not a recommended nutritional change to follow during active cancer treatment;

5. Vegan or vegetarian diets planned and balanced by a nutritionist, with high and adequate consumption of vegetable proteins, can maintain muscle mass during cancer treatment;

6. Arguments that feeding the patient is feeding the tumor have no scientific evidence, so they should not be followed.

In conclusion, muscle health helps treat cancer and should be prioritized throughout this process and accompanied by specialized professionals.


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