Protein-losing enteropathy (PLE) was first used to describe excessive loss of plasma proteins into the gastrointestinal tract in a case report in the Lancet in 1959. Though steatorrhea was noted as part of the presenting patient's syndrome both clinically and biochemically, treatment was limited to albumin infusions, dietary salt restriction, diuresis, and bowel resection, and all were ultimately unsuccessful in providing any sustained improvement [1]. In the 1960s, a teenager with a chronic history of malnutrition, tetany, and rickets presented for care with edema, diarrhea, and hypoproteinemia. A trial of a gluten-free diet had failed to improve her symptoms. Pancreatic enzymes were present in normal quantities via direct testing, ruling out exocrine pancreatic insufficiency. The clinical team isolated lymph from the duodenal lumen via aspirate and confirmed the presence of only long-chain fatty acids. A subsequent trial of dietary fat restriction to 12 grams daily resulted in improvements in abdominal pain, diarrhea, and serum albumin concentration [2]. This case study and similar contemporaneous cases led to a series of medical trials, including a formal investigation by Jefferies and colleagues in which the authors reported multiple clinical outcomes of dietary long-chain triglyceride (LCT) restriction in two patients with PLE. After two weeks of diet modification, diarrhea resolved in both patients, serum albumin and calcium levels increased, and stool fat content decreased. Notably, both patients demonstrated true, non-edematous weight gain [3]. Another subsequent study described the clinical course of six children one to eight years of age with primary intestinal lymphangiectasia treated for three to eight years with a diet low in LCT and high in medium-chain triglycerides [4]. The study demonstrated a sustained long-term benefit from the dietary intervention with symptomatic relief and improved growth velocity; the authors also confirmed clinical relapse upon diet relaxation.

The overarching principle of dietary fat restriction in the management of PLE has not changed significantly in the years since these investigations were performed; however, the intervening years have provided the astute clinician with additional tools to optimize management, including improved diagnostic tests and a wider availability of nutritional supplements. Given the complexities of pediatric lymphatic disorders, one specific dietary prescription will not fit every patient. However, reduction of dietary LCT intake can positively affect overall calorie intake and nitrogen balance, reduce morbidity and treatment failure of concurrent medical therapies, and improve growth velocity. Ultimately, the goal of dietary therapy is to maximize quality of life, including growth, physical and social functioning, and maintaining a positive relationship with food. A team including a gastroenterologist and a registered dietitian familiar with intestinal physiology can play an integral role in providing the appropriate medical and nutritional education and counseling to patients and families, recommending nutrition interventions necessary for growth and development, and prescribing appropriate laboratory monitoring and nutritional supplementation. In this paper, we aim to describe in detail the principles underlying dietary fat restriction in the management of pediatric lymphatic disorders including PLE, the approach to nutritional and dietary intake assessment with a focus on both consequences of active PLE and dietary restriction, and recommendations for serial clinical, anthropometric, and biochemical monitoring. Clinicians will be equipped to tailor interventions and therapy to their individual patient depending on disease severity and patient factors.