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Several studies have looked at the link between fat intake and survival after the diagnosis of breast cancer, with mixed results. There is little evidence that total fat intake affects cancer outcomes, but diets high in fat tend to be high in calories, too. This may add to obesity (being seriously over weight). Obesity is tied to:

  • Higher risk of several types of cancer
  • Higher risk of cancer coming back after treatment
  • Shorter survival for many types of cancer

There is evidence that certain types of fat, such as saturated fats, may increase cancer risk. There is little evidence that other types of fat, such as mono-unsaturated fats (in canola and olive oil, olives, avocados, peanuts, and many other nuts and seeds) or polyunsaturated fats (including omega-3 fatty acids in fish and walnuts) reduce cancer risk.

In one study, high saturated fat intake reduced prostate cancer-specific survival, and in another, mono-unsaturated fat intake lowered the risk of death from prostate cancer. Excess saturated fat intake is a known risk factor for heart disease, a major cause of death in all populations, including cancer survivors.

Although trans fats have harmful effects on the heart, such as raising blood cholesterol levels, their link to cancer risk or survival is not clear. Still, survivors (especially those at increased risk of heart disease) should eat as few trans fats as possible. Major sources of trans fats are margarines and snack foods that contain partially hydrogenated oils.