Mental Capacity and Nutritional Decision-Making: The Dietitian Expert's Role

Mental capacity intersects with nutritional decision-making in some of the most clinically and legally complex cases in medicolegal practice. A patient who has lost capacity to make decisions about their nutrition — through acquired brain injury, progressive dementia, or a psychiatric condition — is dependent on others to make those decisions in their best interests. When that process fails, or when the clinical management of their nutritional needs does not meet an acceptable standard, the consequences can be severe.

As a dietitian expert witness, I am instructed in mental capacity and nutrition cases across several contexts: brain injury claims where the patient lacks capacity and requires ongoing artificial nutrition; end-of-life cases where the decision to withdraw or withhold artificial nutrition is challenged; and cases where a patient with fluctuating or limited capacity has been managed without adequate regard to their nutritional best interests.

Mental Capacity and the Decision to Accept Artificial Nutrition

The Mental Capacity Act 2005 requires that all adults are presumed to have capacity unless there is evidence to the contrary. For patients lacking capacity to make nutritional decisions, decisions must be made in their best interests, having regard to the patient's previously expressed wishes, the views of those close to them, and the clinical assessment of what treatment serves their best interests.

In practice, the decision to commence artificial nutrition in a patient who is not consuming adequate oral intake requires consideration of whether the patient has capacity to consent, and if not, what process was followed to establish that the decision was made in their best interests. Where a patient lacks capacity and that process was not followed correctly, or where artificial nutrition was withheld without a lawful and documented best interests process, the clinical team's conduct is legally assessable.

Refusal of Artificial Nutrition in Patients with Capacity

A competent adult patient has the absolute right to refuse medical treatment, including artificial nutrition. The medicolegal complexity arises in the assessment of whether the patient truly had capacity at the relevant time. Capacity is decision-specific and time-specific. A patient with a brain injury or a psychiatric condition may have fluctuating capacity. A clinical team that proceeds as if a patient has capacity to refuse nutrition — or as if they lack it — without a properly conducted capacity assessment documented in the clinical record, is exposed to a finding that they did not meet the required standard.

A dietitian expert can address whether the clinical management of the patient's nutritional needs was consistent with the capacity assessment as documented, and whether the nutritional consequences of the decisions taken were foreseeable and appropriately managed.

PEG Insertion and Dementia

PEG tube insertion in patients with advanced dementia is a specific and contested area of nutritional decision-making. The evidence base is not supportive: systematic reviews have consistently failed to demonstrate that PEG feeding in advanced dementia improves survival, quality of life, or reduces aspiration pneumonia compared with careful oral feeding. In cases where a PEG is inserted without an adequate best interests process, or where the clinical team fails to advise the patient's family about the evidence base, the decision-making process is assessable.

Brain Injury Claims and Long-Term Nutritional Management

In catastrophic brain injury claims involving a patient who lacks capacity, the long-term nutritional management is a significant component of the future care plan. The patient may be dependent on artificial enteral nutrition indefinitely, or may require a modified texture oral diet with ongoing dietetic supervision.

The dietitian expert's role in these cases includes assessing current nutritional management, projecting future requirements as the patient's condition changes, identifying the dietetic interventions that will be required, and costing ongoing specialist dietetic input. These are condition and prognosis assessments requiring familiarity with the long-term nutritional trajectory of catastrophic neurological injury.

Practical Guidance for Instructing Solicitors

Records to obtain: all clinical records relating to capacity assessments during the relevant period; documentation of any best interests meetings and the decisions made; all dietetic or nutrition support team documentation; records of any discussions with the patient or family about artificial nutrition; clinical records relating to any insertion, removal, or modification of enteral feeding devices; and biochemistry reflecting nutritional status throughout the relevant period.

Key instruction questions: Was the patient's nutritional decision-making capacity assessed at the relevant time? Was the decision to commence, continue, or withhold artificial nutrition consistent with a properly documented best interests process? Did the clinical management of the patient's nutritional needs meet an acceptable standard? What are the patient's ongoing and future nutritional needs?