CLINICAL NUTRITION

Lesson 2: Protein calorie malnutrition

Biochemical lesions

When tissue depletion has reached a critical level, biochemical “lesions” result. These lesions are not too well known, although the biochemist is beginning to be familiar with the changes in enzyme systems induced by tissue depletion of several of the nutrients. Enzyme systems involved in the release of energy and other metabolic reactions are dependent on vitamins such as thiamine, riboflavin, niacin, pyridoxine, and pantothenic acid. As a result biochemical lesions develop. In some instances, these are measurable by the fact that there is an abnormal diversion of metabolites, such as:

• The accumulation of pyruvic acid in vitamin B1 deficiency
  
  
• The abnormal excretion of xanthurenic acid after a test load of tryptophan in vitamin B6 inadequacy
  
  
• As deficiency proceeds, functional changes develop; for example, impaired dark adaptation in vitamin A deficiency.