Radiation therapy, weight loss, and how to cope

Radiation therapy can lead to weight loss, most often by reducing appetite, causing fatigue, or making eating painful or difficult depending on the area treated. ^[1] Weight change is especially common during head and neck radiation because mouth and throat side effects can make swallowing hard, which may result in weight loss, dehydration, and less energy. ^[2] If significant weight changes occur during head and neck treatment, the immobilization mask may not fit correctly, which can affect treatment positioning. ^[2]

Why radiation therapy can cause weight loss

• Reduced appetite and taste changes can make it harder to take in enough calories during external‑beam radiation. ^[1]
• When the mouth or throat is sore, or swallowing is difficult in head and neck treatment, people may avoid eating, leading to weight loss and dehydration. ^[2]
• For chest radiation, appetite may decrease and fatigue can lower overall intake, so maintaining weight requires extra attention. ^[3]

Why maintaining weight matters during treatment

Keeping weight stable helps preserve strength, supports healing, and allows you to tolerate treatment better. ^[3] In head and neck radiation, avoiding large weight changes also helps ensure the treatment mask continues to fit so you can stay in the correct position. ^[2]

Practical strategies to prevent and manage weight loss

• Choose soft, moist, easy‑to‑swallow foods if you have mouth or throat pain (e.g., scrambled eggs, yogurt, soups, smoothies). ^[2]
• Aim for a high‑calorie, high‑protein diet to maintain weight and feel better during treatment. ^[4]
• Use liquid nutritional supplements; there are many options and flavors you can try based on your needs and preferences. ^[4]
• If your care team agrees, a daily multivitamin can be considered as part of your routine. ^[4]
• For chest radiation, focus on enough calories and protein to support recovery; your care team can provide resources with food ideas. ^[3]
• Let your doctor or nurse know about appetite loss, fatigue, or any eating problems so they can evaluate and support you. ^[1]

When to involve a dietitian

A clinical dietitian can tailor a plan to your symptoms, food preferences, and treatment area to help keep your weight steady. ^[4] Regular check‑ins and adjustments can prevent excessive weight loss and ensure you’re getting adequate protein and calories. ^[3]

Simple daily tips

• Eat small, frequent meals and snacks to make intake easier when appetite is low. ^[1]
• Keep hydration a priority, especially if swallowing is uncomfortable, to reduce fatigue and support treatment tolerance. ^[2]
• Try different temperatures and textures (cool, smooth foods) to ease mouth or throat soreness and improve intake. ^[2]
• If weight is dropping or swallowing becomes very difficult, discuss higher‑calorie liquids and supplements with your care team promptly. ^[4]

Key takeaways

Radiation therapy can contribute to weight loss through appetite loss, fatigue, and swallowing discomfort, particularly in head and neck treatments. ^{[1] [2]} Maintaining adequate calories and protein, using soft foods and liquid supplements, and working closely with your care team and a dietitian can help prevent excessive weight loss and keep treatment on track. ^{[4] [3]}