Dietary Protein, Not Sugar, Promotes the Growth of Cancer

Some researchers in Bel­gium just did an inter­est­ing study about how can­cer cells use sug­ar. The researchers found that one of the byprod­ucts pro­duced as a result of can­cer cells’ abnor­mal metab­o­lism could be pro­mot­ing the growth of the can­cer. In short, the researchers have fig­ured out a plau­si­ble expla­na­tion for some­thing that had been known since the 1920s: most can­cer cells use anaer­o­bic metab­o­lism, even when plen­ty of oxy­gen is avail­able. By the 1950s, it was clear that tumors that are most like­ly to use anaer­o­bic metab­o­lism tend to be the most aggres­sive. Unfor­tu­nate­ly, the reporters who have been cov­er­ing this study for the pop­u­lar press do not under­stand what the study is about or what its results real­ly mean. Many of the reporters have false­ly con­clud­ed that the study shows that some­thing in sug­ar is some­how caus­ing can­cer. As a result, they are urg­ing peo­ple to avoid eat­ing car­bo­hy­drates. Unfor­tu­nate­ly, if peo­ple avoid car­bo­hy­drates, they will end up eat­ing more fat and more pro­tein, and we know that high-pro­tein diets are the real cul­prit in pro­mot­ing the growth of can­cer.

The Bel­gian study tells us some­thing that is inter­est­ing to oncol­o­gists but is of no inter­est to the gen­er­al pub­lic. Since the 1920s, it has been clear that many can­cer cells pre­fer to use anaer­o­bic metab­o­lism, even when they have no short­age of oxy­gen. This pref­er­ence is called the War­burg effect. Sci­en­tists have also known since the 1950s that the can­cer cells that exhib­it the War­burg effect tend to be more aggres­sive. Back in 1956, Otto Hein­rich War­burg, MD, PhD, argued that the can­cer cells’ abnor­mal fail­ure to use oxy­gen was the under­ly­ing cause of can­cer. This idea is called the War­burg Hypoth­e­sis. Sci­en­tists now know that the can­cer cells’ abnor­mal metab­o­lism is a result of the gene muta­tions that caused them to become can­cer­ous. How­ev­er, the Bel­gian study actu­al­ly shows that the War­burg hypoth­e­sis was not far off the mark. The Bel­gian researchers showed how the War­burg effect real­ly might cause the can­cer to be more aggres­sive. A chem­i­cal that is pro­duced in abnor­mal­ly large amounts with­in a can­cer cell, as a result of the War­burg effect, can acti­vate chem­i­cal sig­nals that would pro­mote the growth and divi­sion of that cell.

To under­stand the War­burg effect, you need to know how cells burn sug­ar. Your body’s favorite fuel is a sug­ar called glu­cose. To use glu­cose for ener­gy, all cells (includ­ing human cells) start off by split­ting the glu­cose mol­e­cule into two mol­e­cules of pyru­vate. This split­ting is called gly­col­y­sis. But to split a glu­cose mol­e­cule, the cell must make an invest­ment of ener­gy: it has to con­vert two mol­e­cules of high-ener­gy adeno­sine triphos­phate (ATP), which is the cell’s main store of imme­di­ate­ly usable ener­gy, into two mol­e­cules of low­er-ener­gy adeno­sine diphos­phate (ADP). But at the end of the process, the cell will have two mol­e­cules of pyru­vate and will have con­vert­ed four mol­e­cules of ADP to ATP. So the cell will have a net gain of two ATP mol­e­cules. The gly­col­y­sis process will also con­vert a coen­zyme called nicoti­namide ade­nine din­u­cleotide from its oxi­dized form (NAD+) to its reduced form (NADH). Two mol­e­cules of NAD+ get reduced to NADH for every mol­e­cule of glu­cose that is con­vert­ed to pyru­vate. No oxy­gen mol­e­cules are involved in the process of gly­col­y­sis. For this rea­son, gly­col­y­sis can take place even in a low-oxy­gen (anaer­o­bic) envi­ron­ment.

So what hap­pens to the pyru­vate? The pyru­vate can under­go two dif­fer­ent kinds of metab­o­lism. In a low-oxy­gen envi­ron­ment, many kinds of cells will recoup their lost NAD+ by con­vert­ing the pyru­vate to alco­hol or lac­tic acid. That is why the yeast cells in a wine cask (which is a low-oxy­gen envi­ron­ment) will turn the glu­cose from grape juice into alco­hol. It is also why your mus­cle cells will pro­duce some lac­tic acid when you are exer­cis­ing so intense­ly (sprint­ing or weight lift­ing) that your mus­cles are not get­ting enough oxy­gen. But in a high-oxy­gen envi­ron­ment, many kinds of cells can do aer­o­bic metab­o­lism. They will use oxy­gen to break the pyru­vate down com­plete­ly into car­bon diox­ide and water. Aer­o­bic bac­te­ria can do this. So can the mito­chon­dria inside the cells of plants, fun­gi, and ani­mals.

From an ener­gy stand­point, aer­o­bic metab­o­lism is far more effi­cient than anaer­o­bic metab­o­lism. Aer­o­bic metab­o­lism yields a net gain of 30 to 32 mol­e­cules of ATP for each mol­e­cule of glu­cose, as opposed to the net gain of only 2 mol­e­cules of ATP that the cell gets from anaer­o­bic metab­o­lism of a mol­e­cule of glu­cose. For the body as a whole, anaer­o­bic metab­o­lism is an even worse deal. When a cell does anaer­o­bic metab­o­lism, it pro­duces lac­tic acid. Then, the liv­er must invest six mol­e­cules of ATP to con­vert the lac­tic acid back to glu­cose. As a result, your body has a net loss of 4 mol­e­cules of ATP for every mol­e­cule of glu­cose that under­goes anaer­o­bic metab­o­lism in your mus­cles.

War­burg found that many can­cer cells pre­fer to use anaer­o­bic metab­o­lism, even when they have no short­age of oxy­gen. He also noticed that this pref­er­ence for anaer­o­bic metab­o­lism is stronger in the more aggres­sive can­cers. These find­ings help to explain why so many can­cer patients lose weight so fast. For every mol­e­cule of glu­cose that a can­cer cell uses, the can­cer cell gets a net gain of 2 mol­e­cules of ATP. Mean­while, the liv­er has to invest 6 mol­e­cules of ATP to con­vert the lac­tic acid pro­duced by the can­cer cell back into glu­cose. So besides los­ing glu­cose to the tumor, the body has to use its ener­gy stores to clean up the mess that the tumor makes. If the body’s tumor bur­den is large, the body ends up using a lot of calo­ries to com­pen­sate for the can­cer cells’ use of anaer­o­bic metab­o­lism. The rapid weight loss asso­ci­at­ed with can­cer is called can­cer cachex­ia (pro­nounced ka-kex-ia). This name comes from the Greek words for “bad con­di­tion.”

It is impor­tant for jour­nal­ists and con­sumers to under­stand what the Bel­gian study teach­es us, and what it does not teach us. The Bel­gian study pro­vid­ed an expla­na­tion of why the can­cers that pre­fer to use anaer­o­bic metab­o­lism, even when they have plen­ty of oxy­gen avail­able, tend to be more aggres­sive. How­ev­er, the Bel­gian study teach­es us exact­ly noth­ing about how our food choic­es affect our health. To answer that ques­tion, we need to look at oth­er kinds of stud­ies.

As T. Col­in Camp­bell, PhD, explained in The Chi­na Study, can­cer involves two basic prob­lems. The first prob­lem is the ini­ti­a­tion of can­cer, which means that car­cino­gens, such as radi­a­tion or cig­a­rette smoke, have turned some cells into dan­ger­ous mutants. The sec­ond is the pro­mo­tion of can­cer, which means that some­thing has encour­aged the mutant cells to grow and mul­ti­ply to the point that they cause prob­lems. In his epi­demi­o­log­i­cal work, Camp­bell has found that pop­u­la­tions that eat a high-car­bo­hy­drate, low-pro­tein diets have a remark­ably low rate of var­i­ous can­cers, includ­ing can­cers of the breast, bow­el, and prostate. Camp­bell has also point­ed out that researchers have found that they can switch the growth of cer­tain can­cers in lab­o­ra­to­ry ani­mals on and off, just by increas­ing and decreas­ing the amount of pro­tein in the ani­mals’ feed. In oth­er words, a high-car­bo­hy­drate diet is prob­a­bly use­ful for sup­press­ing the growth of can­cers, even of can­cers with abnor­mal car­bo­hy­drate metab­o­lism.

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