Chapter 93
Cancer — 20
Figure 6.5. Hazards of aspirin in a randomized trial of over nineteen thousand participants aged sixty-five years and older. Adapted from John McNeil et al., “Effect of aspirin on all-cause mortality in the healthy elderly,” New England Journal of Medicine 379, no. 16 (October 2018): 1519–28, https://doi.org/10.1056/NEJMoa1803955.
Can diet significantly reduce the risk of cancer? Most of the studies in cancer are in experimental models (rather than in real people on certain diets); nevertheless, they demonstrate the increased risk from high-fructose corn syrup. They also indicate the potential benefit of methionine restriction, the advantage of caloric restriction, a ketogenic diet, low glycemic diets to limit tumor growth, and a dietary tryptophan metabolite released by a bacterium. A randomized trial of increased vegetable consumption versus a control diet in 478 men with early prostate cancer did not significantly affect progression. The foods that have the most unfavorable effects on inflammation markers were shown to be associated with a higher risk of colon cancer in a study of more than 120,000 people followed for twenty-six years. Foods that have been linked to lowering the risk of cancer include those with a rich source of isothiocyanates, such as broccoli, brussels sprouts, cauliflower; the lycopenes in tomatoes; high-fiber foods such as legumes and nuts (especially walnuts, which are high in ellagitannins); foods with high antioxidant and flavonoids like berries and pomegranates; and garlic, with its rich allicin content.
The latest estimate for the proportion of cancers attributable to modifiable risk factors is 40 percent, with the main factors shown in figure 6.6.
That compares to more than 80 percent of cardiovascular disease preventable via lifestyle factors.
There are now three drugs—tamoxifen, raloxifene, and anastrozole—that are FDA approved for prevention of breast cancer in women at moderate or high risk. These drugs block production or the effects of estrogen, but at least 15 percent of breast cancers do not have estrogen receptors. The “moderate to high” category of risk is determined by a breast risk calculator based on such rudimentary features as age, family history, age at first period, and age at firstborn child. Surely, we have far better ways to stratify risk of breast cancer, as I’ve reviewed in the section on mass screening with mammography.
Figure 6.6. Proportion of cancer cases with potentially modifiable risk factors. Adapted from Farhad Islami et al., “Proportion and number of cancer cases and deaths attributable to potentially modifiable risk factors in the United States, 2019,” CA: A Cancer Journal for Clinicians (July 2024), https://doi.org/10.3322/caac.21858.