Malnutrition is highly prevalent among older adults. Adequate treatment is crucial to maintain health, improve functional status and independency. For severely malnourished patient, tube feeding is often the most effective treatment, but it also implies a risk of developing refeeding syndrome (RFS). RFS is described as fluid and electrolyte shifts particular hypophosphatemia when recommencing nutrition, potentially causing fatal complications. In 2006 National Institute for Health and Care Excellence (NICE) developed guidelines regarding 1) detecting patients at risk for RFS and 2) a treatment plan for refeeding severely malnourished patients. These guidelines have never been validated. Hence, there is a need to explore the use of different refeeding regimens in the treatment of older malnourished patients, in regards to assess safety, as well as the impact of the treatment, on functional status, independency, quality of life and RFS. This will be the first randomized controlled trial (RCT) that challenges the existing NICE guidelines.This study will be divided into two parts. Part I: a cross-sectional cohort study, monitoring occurrence of hypophosphatemia on patients detected as not at risk for RFS according to NICE guidelines. Part II: a double blinded RCT study, with the aim of tube feeding patients at risk for developing RFS, and assigned either to an intervention group or to a control group, comparing the different refeeding regimens. This study will help develop safe and validated refeeding protocols for severely malnourished older patients.