Sorta. Intermittent Fasting (IF) can help prevent cancer because if done correctly, it lowers caloric intake, which reduces body fat, which we KNOW prevents cancer. Here is what we know:

  • Obesity is the second largest cause of cancer after smoking.
  • Being overweight increases your risk of postmenopausal breast cancer and prostate cancer, the most common cancers in the US.
  • Animal studies have shown that Caloric Restriction (CR) can inhibit tumor growth. (1,2) (Remember, animal studies are just that, done on animals, and only occasionally show the same results in humans. We have cured a lot cancer in mice.)
  • Intermittent Fasting is a type of Caloric Restriction, hence IF should theoretically reduce cancer, but remember, data in humans is sparse.

Should you try IF to reduced your risk of cancer? That depends. Here are my thoughts:

  • You should not try IF or CR if you are under the age of 21 because you are still growing, your brain is developing, and it could be harmful to restrict intake.
  • For the same reasons, you should not try IF or CR if you are pregnant or nursing.
  • I would not recommend IF or CR if you are diabetic or suffering from reflux (GERD) or an other medical condition that requires you to eat small meals frequently.
  • Always eat breakfast. Always.

Still interested in giving it a go? The challenge then is to reduce your total caloric intake but not sacrifice your nutrient intake. If you are considering IF or CR as part of a cancer prevention strategy, remember that you still have to get in 7-9 servings of fruit and vegetables a day which has been shown to reduce cancer. My recommendations would be to try both IF and CR and see which works best for you.  Some suggestions:

  • Make breakfast your largest meal of the day, lunch the next largest, and have a very light dinner with a protein and green vegetables. It may be easier to reduce calories in the evening when you are winding down and less active, then sacrificing calories during the day when you need energy.
  • Try skipping dinner one or two days a week and just having a handful of nuts. Nuts provide a healthy mix of protein and fat and give your metabolism a boost.
  • Do not eat two hours before bedtime. This ensures you are fasting overnight and your breakfast will be just that, a “break” of your “fast”.
  • Remember to continually hydrate throughout the day with water, juice, or tea.

A final thought is to consider a probiotic or ensure you are consuming yogurt or kefir as part of your CR or IF. Medical science is learning more and more about the importance of the bacteria in our gut in preventing chronic disease. While I am unaware of any specific medical studies evaluating the role of probiotics in IF/CR,  I would hesitate to start a dietary regimen that could drastically alter the balance of bacteria in your digestive tract as there could be consequences to your health.

Let me know how IF or CR works for you. Remember that the goal would be to decrease body fat and be as lean as possible to prevent cancer.

1. Thompson HJ, McTiernan A. Weight Cycling and Cancer: Weighing the Evidence of Caloric Restriction and Cancer Risk. Cancer Prev Res; 2011, 4(11); 1736–42.

2. Eslami S. et al.  Annual Fasting; The Early Calories Restriction for Cancer Prevention. BioImpacts; 2012, 2(4), 213-215 .

Dr. Andrew Weil on Intermittent Fasting

Dr. Oz on Intermittent Fasting and the 5:2 Diet