Inadequate diet and Malnutrition

Malnutrition and inadequate diet are semantically related In some cases you can replace term "Malnutrition" with "Inadequate diet", this terms are similar.

Malnutrition noun - A state of poor nutrition; can result from insufficient or excessive or unbalanced diet or from inability to absorb foods.

Inadequate diet and malnutrition are semantically related in undernourishment topic. You can use "Inadequate diet" instead a noun "Malnutrition".