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Nutrition and daily life

Energy needs: how much fuel the body needs during treatment

The body uses energy every minute: the heart beats, we breathe, cells renew themselves. Leukemia and its treatment can change how much energy you need, while appetite often drops at the same time. This topic explains in plain words what energy is, why it deserves special attention during treatment and how to keep an eye on the balance.

Last updated: ~4 min read
On a dark navy background, a plate with hot lentil soup, bread, rice with chicken and steamed vegetables; golden light rises from the food towards a translucent human silhouette behind it.
Figure 1.Food is the fuel the body uses every hour.

01Short answer

Energy comes from food and is measured in calories. During treatment the body repairs tissues and fights infections, and fever burns extra energy — while appetite, taste and digestion may all suffer. As a result, energy intake is often lower than the body needs, and people lose weight and muscle. The aim is to keep weight stable and protect muscle. Small frequent meals, foods rich in energy and protein, and regular weighing all help. Your specific calorie target is set by your doctor or dietitian.

02Simple explanation

Energy is the body’s fuel. We get it from carbohydrates, fats and proteins, and it is measured in kilocalories (kcal).

Even at complete rest, most of our energy goes to running the heart, brain, liver and other organs. This is called the basal metabolism.

During leukemia treatment, the bone marrow and the linings of the mouth and gut rebuild themselves, and the immune system fights infections. All of this needs extra energy and protein.

The difficulty is that this is exactly when appetite drops: nausea, mouth sores, taste changes and tiredness make eating hard. So many patients eat too little without realising it.

When energy runs short, the body draws on its reserves — first fat, then muscle. Losing muscle can reduce strength, stamina and how well you tolerate treatment.

03Scientific explanation

Overall needs: according to the 2017 and 2021 guidelines of ESPEN (the European Society for Clinical Nutrition and Metabolism), total energy expenditure in people with cancer is usually similar to that of healthy people and in practice is estimated at about 25–30 kcal/kg per day. This is a starting point; individual needs are refined by following weight over time.

Fever and inflammation: inflammation and infection speed up metabolism, while the illness and its treatment reduce appetite. The 2021 ESMO guidelines on cachexia stress early detection of weight and muscle loss and timely nutrition support.

Screening: ESPEN recommends assessing food intake, weight change and body mass index in all people with cancer at diagnosis and regularly afterwards. Losing even a few per cent of body weight is a signal that needs attention.

Steps of support: according to NCI and ESPEN, the first step is changing what and how often you eat; nutritional drinks (oral nutritional supplements) may be added; if eating is still not enough, doctors may consider tube or intravenous feeding. Your team makes these decisions.

04What happens in the body?

Where does the energy go?

Most daily energy is used by the organs: heart, brain, liver and kidneys. The rest goes on movement and digesting food. During treatment, tissue repair and the immune response are added on top.

Fever and infection

When body temperature rises, metabolism speeds up and the body burns more energy. That is why weight loss often becomes noticeable after a period of infection.

On a dark navy background, a translucent human body lying calmly, with warm golden light and repair sparks in the heart, leg muscles and the marrow of the pelvis.
Figure 2.Even at rest the body spends energy, and healing needs extra.

Why does appetite drop?

Nausea, vomiting, mouth sores, taste changes, constipation or diarrhea, tiredness and worry all make eating difficult. Some medicines, on the other hand, can increase appetite.

Reserves and muscle

If food intake is low, the body first uses glycogen stored in the liver, then fat, then muscle protein. Muscle loss may not show on the scales — especially if there is swelling.

How to keep track

Weigh yourself once or twice a week, at the same time, on the same scales. Looser clothes, less strength and getting tired on the stairs are important signs too. Tell your team what you notice.

On a dark navy background, bathroom scales seen from above, surrounded like a clock face by six small dishes: porridge, yogurt, a banana, a small sandwich, soup and crackers.
Figure 3.Small frequent meals and regular weighing keep energy balance on track.

What helps when you eat little?

Small portions 5–6 times a day; protein- and energy-rich food first on the plate; adding olive oil, butter or pasteurized cheese to dishes; not drinking a lot just before meals. Nutritional drinks are recommended by your team.

05Energy balance: four steps

Fuel is needed, needs rise, small meals help, weight is tracked.

Fuel for every cell — Food is turned into energy.1Fuel for every cellFood is turned into energy.
Needs go up — Fever and repair burn energy.2Needs go upFever and repair burn energy.
Little and often — A small portion every 2–3 hours.3Little and oftenA small portion every 2–3 hours.
Track your weight — Weekly check, report changes.4Track your weightWeekly check, report changes.
Stable weightReserves are protected.
More strengthDaily tasks feel easier.
Better toleranceThe body is ready to recover.

06What affects energy needs (simplified)

FactorEffectWhat you can do
Fever, infectionRaises needsIncrease portions during recovery, tell your team
Tissue repairRaises needsAdd protein and energy to every meal
Bed restLowers needs, but muscle is lostGentle movement when allowed
Nausea, mouth soresReduce intakeSoft, cool or lukewarm small portions
SteroidsMay increase appetiteNourishing choices, fewer sweets
Worry, tirednessReduce intakeKeep simple ready-to-eat food at home

* The table is general information. Your individual energy and protein targets are set by your doctor or dietitian.

07Key terms

Kilocalorie (kcal)
The unit used to measure energy in food.
Basal metabolism
Energy the organs use at complete rest.
Energy balance
The ratio of energy taken in to energy used.
Cachexia
Illness-related loss of weight and muscle.
Sarcopenia
Loss of muscle mass and strength.
Nutritional drink
A ready-made drink enriched with energy and protein.
Dietitian
A specialist in clinical nutrition.
Screening
A regular simple check for risk of undernutrition.

08Key points

  • During treatment the body needs extra fuel.
  • Fever and infection increase energy use.
  • If appetite drops, eat little and often.
  • Add protein and energy to every meal.
  • Weigh yourself once or twice a week.
  • Do not hide weight loss — tell your team.
  • Your dietitian sets the calorie target.
  • Use nutritional drinks only as your team advises.

09Frequently asked questions

Isn’t losing weight during treatment a good thing? I was overweight.

Treatment is not considered a good time to lose weight, because part of what is lost is muscle. Discuss weight goals with your doctor after treatment.

How many calories do I need a day?

It depends on your weight, height, treatment and condition. Your doctor or dietitian calculates the figure and adjusts it as your weight changes.

I have no appetite at all. How can I eat?

Eat by the clock in small portions, even if you are not hungry. Favourite foods with little smell, served cool or lukewarm, are easier to manage. Ask your team about medicines for nausea and mouth sores.

Can I make up calories with sweets?

Sometimes, but sweets alone provide no protein, vitamins or minerals. It is better to combine energy with protein: yogurt with honey, cottage cheese, egg dishes, milk porridge.

My weight is the same but I feel weaker. Is that possible?

Yes. Swelling or fluid retention can hide muscle loss. If your strength is falling, tell your team about that too.

I eat a lot while on steroids. What should I do?

Steroids can increase appetite. Choose fruit, vegetables, and foods rich in protein and fibre, cut down on sugary drinks and follow your doctor’s advice about blood sugar.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. Isn’t losing weight during treatment a good thing? I was overweight.

  2. How many calories do I need a day?

  3. I have no appetite at all. How can I eat?

  4. Can I make up calories with sweets?

  5. My weight is the same but I feel weaker. Is that possible?

  6. I eat a lot while on steroids. What should I do?

My questions

12Sources

  1. Clinical Nutrition (ESPEN), 2017. Arends J et al. ESPEN guidelines on nutrition in cancer patients
  2. Clinical Nutrition (ESPEN), 2021. Muscaritoli M et al. ESPEN practical guideline: Clinical Nutrition in cancer
  3. ESMO Open, 2021. Arends J et al. Cancer cachexia in adult patients: ESMO Clinical Practice Guidelines
  4. National Cancer Institute (NCI). Nutrition in Cancer Care (PDQ) — Patient Version
  5. National Cancer Institute (NCI). Eating Hints: Before, During, and After Cancer Treatment
  6. American Cancer Society. Benefits of Good Nutrition During Cancer Treatment
  7. American Cancer Society. Nutrition Once Treatment Starts
  8. NHS. Understanding calories
  9. British Dietetic Association. Malnutrition: Food Fact Sheet
  10. World Health Organization (WHO). Malnutrition — fact sheet
  11. Cancer Research UK. Diet problems and cancer
  12. MedlinePlus (U.S. National Library of Medicine). Nutrition
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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