Aggressive cancer cells have a big appetite for a nutrient found in protein-rich food, research has shown.
The discovery could pave the way to new treatments for some of the deadliest cancers.
Scientists grew 60 populations of cancer cells in the laboratory to see what kind of "food" they preferred.
The result was the first large-scale "atlas" of cancer metabolism.
One key finding was the role played by the amino acid glycine in cancer cell proliferation.
Rapidly dividing cancer cells appeared to crave glycine, one of the building blocks of proteins.
But less dangerous, slowly dividing cancer cells tended to release glycine rather than consume it.
When fast-dividing cells were deprived of glycine, the pace of proliferation slowed down. Slower-growing cells, meanwhile, were unaffected.
One way of keeping the cells off glycine was to block the enzymes they use to process it.
Analysis of data from breast cancer patients showed that those with the same glycine-metabolising enzymes had poorer outcomes. This suggested that glycine's role in driving aggressive cancer was not confined to the laboratory.
The research, published in the journal Science, points the way to future therapies which suppress cancer cells' ability to "feed" on glycine.
Dr Mohit Jain, one of the scientists from the Broad Institute in Cambridge, Massachusetts, US, said: "The metabolic activities that enable cancer cells to proliferate quickly or slowly are poorly understood. But across 60 cell lines, we clearly see this association between how fast cells are dividing and how much glycine they are taking up."
Glycine is used in the body to help generate muscle tissue and convert glucose to energy. It also contributes to maintaining healthy nervous and digestive systems.
High-protein foods, such as fish, meat, beans, milk and cheese, are all sources of the amino acid.
Glycine supplements in the form of capsules or powder are also sold in health food shops.
The cell lines used in the research came from nine common tumours, including breast, colon, ovarian, skin and prostate cancers.