I successfully avoid all soy (and all other legumes), wheat, and vegetable oil intake. You're on easy mode. It's only hard when you want to find chocolate without soy lecithin, but you can usually go with baking chocolate in that case.
Soybeans and soy sauce are strangely high in polyamines, which makes their frequent intake suspicious. There are various associations with polyamines and cancer, and if there are foods which are uniquely high in polyamine content, they ought to be put under a lens.
• Okamoto, Akiko, et al. Polyamine content of ordinary foodstuffs and various fermented foods. Bioscience, biotechnology, and biochemistry 61.9 (1997): 1582-1584.
☞ https://doi.org/10.1271/bbb.61.1582
⤓ https://www.jstage.jst.go.jp/article/bbb1992/61/9/61_9_1582/_pdf
>Soybeans, tea leaves, and mushrooms were conspicuously rich in spermidine, while oranges contained a large amount of putrescine. Among the fermented foods, soy sauces were rich in putrescine and histamine, while Japanese sake contained plenty of agmatine.
• Jänne, J., H. Pösö, and A. Raina. Polyamines in rapid growth and cancer. Biochimica et Biophysica Acta (BBA)-Reviews on Cancer 473.3-4 (1978): 241-293.
☞ https://doi.org/10.1016/0304-419X(78)90015-X
• Gerner, Eugene W., and Frank L. Meyskens Jr. Polyamines and cancer: old molecules, new understanding. Nature Reviews Cancer 4.10 (2004): 781.
☞ https://www.nature.com/articles/nrc1454
>The amino-acid-derived polyamines have long been associated with cell growth and cancer
• Russell, Diane H. Increased polyamine concentrations in the urine of human cancer patients. Nature New Biology 233.39 (1971): 144-145.
☞ https://doi.org/10.1038/newbio233144a0
>WE have found that patients with various types of solid tumours and leukaemias have considerably increased concentrations of the polyamines such as putrescine (diaminobutane), spermidine and spermine in their urine. Polyamines are small cationic substances, which occur ubiquitously in nature¹. Because enhanced polyamine synthesis and accumulation are characteristic of rapid growth systems²⁻⁶ it seemed possible that they might serve as indicators of rapidly proliferating tumours.
• Thomas, Thresia, and T. J. Thomas. Polyamine metabolism and cancer. Journal of cellular and molecular medicine 7.2 (2003): 113-126.
☞ https://doi.org/10.1111/j.1582-4934.2003.tb00210.x
>Polyamines are aliphatic cations present in all cells. In normal cells, polyamine levels are intricately controlled by biosynthetic and catabolic enzymes. […] Multiple abnormalities in the control of polyamine metabolism and uptake might be responsible for increased levels of polyamines in cancer cells as compared to that of normal cells.