What it's actually good for
Digestive enzyme supplements are a broad category that includes lipase (fat digestion), protease (protein digestion), amylase (starch digestion), lactase (lactose digestion), and various other enzymes. The evidence quality varies dramatically depending on the use case. For specific, diagnosed enzyme deficiencies, the evidence is unambiguous: lactase supplements effectively prevent symptoms of lactose intolerance, and prescription pancreatic enzyme replacement therapy is essential and well-proven for exocrine pancreatic insufficiency (as in chronic pancreatitis or cystic fibrosis). Where the evidence weakens considerably is for the general "take with meals for better digestion" use case that drives most consumer supplement sales. A few small, often industry-funded trials suggest broad-spectrum enzymes may reduce postprandial bloating, but these studies have methodological limitations and the effect in people with functioning digestive systems is uncertain. The overall grade is B because the category includes genuinely effective interventions for defined conditions (lactase, PERT), but the typical consumer use case of general digestive comfort is poorly supported. If you suspect an enzyme deficiency, getting tested is far more valuable than empirically supplementing with a broad-spectrum product.