The paper I discuss today is not examining why an unhealthy diet may lead to developing cancer, but rather if what you eat plays a role in the ’spreading’ of cancer, which makes it far more likely to kill you.
A new paper by Le et. al., 2009 in BMC Cancer examined this question by testing animals that had tumors implanted in them on either a high fat diet (34.9% : mouse D12492 diet which equates to 60% fat in caloric terms - according to the company documentation) and a normal chow diet (4.25 % fat: 7001 diet, which equates to approximately 12% of their caloric intake - according to the company data sheet - which is the normal amount of fat typically fed a lab mouse). They then used a fairly new technique (which I discussed briefly about in my recent talk at BIL 2009) which allows the detection of metastasizing cancer cells in the blood stream. As I also discussed in my talk the common thinking is that 90% of cancer death is due to the metastasizing cancer cells. These critical cells are not what most cancer research concentrates on, instead the tend to focus on treatments that reduce the primary tumor and not treatments that reduces the deadly metastasizing cells (in the past this could have been due to technical limitations).
What the researchers found was that the high fat diet resulted in a 300% increase in metastasizing cells detected in the blood stream (at two weeks after cancer implementation - but at 4 weeks there were no differences between the two diet groups - but this is of less importance since enough cells had already escaped into the blood stream). Through the blood stream and lymph system is how these cells migrate to a new organ and wreak their havoc. Interestingly, the primary tumor size was the same in both groups throughout the experiment.
To further corroborate this finding they looked at how many cancer cells had escaped to the lungs. In the high fat fed animals there was a four fold increase of cancerous cells found in the lungs compared to the normally fed animals (at 4 weeks after cancer cell implementation).
This study did not examine if a high fat diet leads to increase incidence of cancer (though the Calle and Kaaks, 2004 report in their review paper that being overweight does increase the incidence of cancers in humans) - but rather if a fatty diet leads to increased cancerous cells metastasizing - which probably ends up killing you.
The researchers next wanted to get into the details of what type of fat is bad, and the role of specific fat deposits we carry on our body.
The researchers found that linoleic acid, which is mostly found in polyunsaturated fat, when added to cancer cells in a dish resulted in increases in binding proteins and morphology which are indicators of a potential for great migration/metastasizing propensity. However, oleic acid, (55 -80% of olive oil) found in monosaturated fats, did not result in these same changes.
Next, they tested if the secreted factors from visceral fat (see a previous piece I wrote on visceral fat and longevity) played a role in cancer cell migration. The found the secreted cytokines from visceral fat (which are different than the cytokines released for subcutaneous fat) attracted cancer cells. And the free fatty acids (FFA) from the visceral fat resulted in the cancer cells having less cell to cell (cell-cell) contact - which would allow them to roam about inside your body and visit other organs.
In summary (from paper):
…imaging reveals intracellular lipid accumulation is induced by excess free fatty acids
(FFAs). Excess FFAs incorporation onto cancer cell membrane induces membrane phase
separation, reduces cell-cell contact, increases surface adhesion, and promotes tissue invasion.
Increased plasma FFAs level and visceral adiposity are associated with early rise in circulating
tumour cells and increased lung metastasis. Furthermore, CARS imaging reveals FFAs-induced lipid accumulation in primary, circulating, and metastasized cancer cells.
Problems with the study:
The high fat diet was ‘extreme’ in the terms of around 60% of the calories consumed by the mice came from fat. It would have been nice to test a more typical western high fat diet consumed by humans (e.g. 25-45% fat with a high percentage of the fat coming from ‘bad’ fat).
The second problem is they used a cancer model in which they implant a tumor underneath the skin compared the more clinically relevant model of putting the tumor in the organ of the tumor origin (I also discussed in my recent talk at BIL).
Simple take home message:
Obviously if you have cancer avoid a high fat polyunsaturated diet so your cancer cells are less likely to spread to other organs. In addition right now today you do not know if you have cancer or not - hence you should still avoid the bad fat diet to reduce the probability of cancerous cells escaping the ‘potential’ primary tumor and invading other organs - not to mention the past research that shows obesity is related to increased incidence of developing cancer.
Make sure you have low levels of visceral fat - meaning exercise and eat healthy.
You might also find my piece of the relatively lack of progress in reducing cancer deaths over the last 55 years interesting, and how researchers are realizing many pathways are involved in cancer.