Methionine

Methionine makes the urine slightly more acidic, which helps prevent struvite crystals from forming.

DL-methionine is the form of the sulfur amino acid methionine most often added to pet food. FDA lists methionine as GRAS when used in animal feeds under good manufacturing or feeding practice (21 CFR 582.5475). AAFCO also sets an upper limit for cat foods. Methionine changes urine acidity, so a cat with bladder stones or another medical condition should have its diet set by a veterinarian.

Source: govinfo.gov

Methionine is added because cats need it and plant ingredients supply little of it. It is a sulfur amino acid that goes into fur and other body proteins. The body can also turn it into cystine. It also makes urine slightly more acidic. Recipes that mix meat with plant protein often add methionine to reach AAFCO minimums.

DL means the ingredient is a mix of two mirror-image forms of methionine, the D form and the L form. The L form is the one found in proteins, and the mix is how methionine is usually manufactured for feed. FDA's GRAS listing for methionine in animal feed covers the ingredient by name. On Pettings, DL-methionine and methionine share one page.

Source: govinfo.gov

Yes, AAFCO sets a maximum. Its cat food nutrient profiles cap methionine at 1.5% of dry matter, and AAFCO's feline nutrition expert subcommittee kept that limit because of work showing an adverse effect of high methionine levels. Minimums are 0.62% for growth and 0.20% for adult maintenance. A food that meets AAFCO profiles stays inside that range.

Source: aafco.org

Pettings gives methionine 4 out of 5 and lists it as an amino acid. It appears on 75 of the 149 dry cat foods we list. That puts it on about half of the dry foods in our list. Each food's page shows how it scores overall.