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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