Look at this study … When researchers starved cancer cells of the amino acid methionine, they died. But normal cells thrived:

The Effect Of Replacement Of Methionine By Homocystine On Survival Of Malignant And Normal Adult Mammalian Cells In Culture, Proceedings of the National Academy of Sciences, April 1974

In tissue cultures of normal adult and malignant mammalian cells, homocystine has been substituted for methionine in a medium rich in folic acid and cyanocobalamin. Normal adult cells thrive. Three highly malignant cell types from three different species, including man, die.

Normal cells can make the amino acid methionine from another amino acid, homocysteine (in the presence of vitamin B12 and folic acid). But some types of cancer cells die when they are denied methionine.

Here’s another study, using actual human tumors:

Expression Of The Biochemical Defect Of Methionine Dependence In Fresh Patient Tumors In Primary Histoculture, Cancer Research, June 1993

Researchers took fresh tumors directly from surgeries. They found that:

Tumors of the colon, breast, ovary, prostate, and skin (melanoma) were methionine dependent.

And noted:

The effects of methionine depletion by both dietary and enzymatic means have indicated antitumor efficacy.

Methionine is an amino acid. It makes up protein. So, foods high in protein are higher in methionine. Animal proteins contain higher amounts of methionine than plant proteins. In this paper:

A Review Of Methionine Dependency And The Role Of Methionine Restriction In Cancer Growth Control And Life-span Extension, Cancer Treatment Reviews, October 2012

Researchers said:

The application of nutritional methionine restriction and methioninase in combination with chemotherapeutic regimens is the current focus of clinical studies. … In humans, methionine restriction may be achieved using a predominately vegan diet.

Which foods are specifically higher or lower in methionine? Dr. Greger’s video, Starving Cancer with Methionine Restriction, includes this graph that shows fish, chicken, red meat, eggs, and milk contain higher amounts of methionine, while fruits, nuts, vegetables, grains, and beans contain lower amounts: