I have argued that cancer cells are often metabolically damaged and can more easily digest sugar and certain amino acids than fat:

• How Fasting Can Starve Cancer Cells, While Leaving Normal Cells Unharmed

• Why You Should Worry about Cancer Promotion by Diet as Much as You Worry about Cancer Initiation by Carcinogens

• Good News! Cancer Cells are Metabolically Handicapped

• How Sugar, Too Much Protein, Inflammation and Injury Could Drive Epigenetic Cellular Evolution Toward Cancer

• Meat Is Amazingly Nutritious—But Is It Amazingly Nutritious for Cancer Cells, Too?

• My Annual Anti-Cancer Fast

• Cancer Cells Love Sugar; That’s How PET Scans for Cancer Work

So it is important to engage with a study that claims that high-fat diets are cancer promoting—at least on the surface the opposite to my claim that high-fat diets—and fasting, which puts body fat in the bloodstream—are hard on cancer.

There are several points I want to make.

First, many high-fat diets are also high in protein. The fat can easily get blamed for the cancer-promoting effects of the protein.

Second, mice are naturally adapted to high-carb diets; because mouse generations are much shorter than human generations mice are likely to be much, much better adapted to the human agricultural revolution than humans are. Fat is a relatively unusual diet component for mice. Thus, healthy mouse cells may be ill-adapted to process fat, while mouse cancer cells explore a wider set of possibilities. By contrast, until a few generations ago, a substantial amount of sugar was quite unusual for humans. Now, cancer cells may adapt to sugar-rich diets better than healthy cells.

Third, that the mouse finding about high-fat diets and tumor growth was limited to cancers with many immune cells is implicitly suggesting that other mouse cancers are not that great at drawing in and metabolizing fat. This may be the weakest of my three arguments for the simple reason that immune cells that become cancerous are probably key to metastasis: cancer cells migrating from one part of the body to another. Metastasis is often what makes cancers deadly. So immune cells becoming cancerous is a big deal.

In any case, high-fat diets in humans tend to lead to lower obesity compared to high-sugar diets. So Kevin Jiang’s Harvard Gazette article ‘A metabolic tug-of-war’ is off base to invoke the relationship between cancer and obesity in humans as something that is related to high-fat diets promoting certain types of cancer in mice. High-fat diets do tend to promote obesity in mice, so relating a correlation between obesity and cancer to a correlation between a high-fat-diet and cancer is more appropriate if the discussion is entirely restricted to mice.

What I worry about with this Harvard Gazette article is that people will read it through the lens of the traditional view that high-fat diets are bad for humans—a view that has not done very well at standing the test of time. To repeat, I think there is decent evidence that high-protein diets cause cancer—especially diets high in animal protein. Don’t blame dietary fat as cancer-causing unless you have carefully held the amount of protein and especially animal protein constant. And while mouse results can illuminate human biology in many areas, the great difference in the diet mice are adapted for compared to the diet humans are adapted for makes mouse evidence suspect when it comes to comparing high-carb to high-fat diets.

For annotated links to other posts on diet and health, see:

• Miles Kimball on Diet and Health: A Reader's Guide