Those patients who lose their appetite are likely to lose weight - but the same can be true even if a high calorie diet is being eaten, due to changes in the body.
That's because cancers can produce molecules that change the way the body functions.
For example, cytokines are proteins normally produced by the immune system to help your body fight infections. Cancers are known to produce these in large numbers. This abnormal release leads can cause weight loss by making the body break down proteins and fat.
High energy foods can help people to maintain their weight, but Dr Shaw notes that it is sometimes hard to know what to eat.
Many of her patients eat a lot of soup.
"It's liquid, it goes down easily, it's a prime choice. But, as a dietician, I will often talk to them about the fact that soup is often low in energy, and it's often low in protein.
"So people might be using it as a replacement for a meal, but it's not providing the same nourishment as a meal.'
Other high energy meals such as roasted chicken, or more nutritious soups, are advised.