Some researchers in Belgium just did an interesting study about how yeast cells use sugar. This study helps to explain why yeast cells multiply rapidly when they have plenty of sugar. The results of their study could also explain why some cancer cells also multiply rapidly. However, this study does not mean that sugars and starches in the diet are a problem. In fact, high-carbohydrate diets actually help to protect against many cancers. Rather, the study explains why cancer cells with abnormal sugar metabolism might behave like yeast cells.
Many Cancer Cells Have an Abnormal Metabolism
Since the 1920s, scientists have known that many cancer cells don’t use oxygen to burn sugar, even when plenty of oxygen is available. By the 1950s, it was clear that tumors that are most likely to use anaerobic (no-oxygen) 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. But if people follow that advice, they would actually increase their risk of early death. If people avoid carbohydrates, they will end up eating more fat and more animal protein. High-fat diets increase your risk of heart attacks. Also, diets that are high in animal protein increase your risk of dying of cancer.
Many Cancer Cells Have an Abnormal Metabolism
The Belgian study tells us something that is interesting to cell biologists and to cancer researchers 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 cancers 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 malignant. 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 substance that might build up in a cancer cell, as a result of the cell’s abnormal metabolism, can activate chemical signals that would promote the growth and division of that cell. The Belgian study is interesting because some of the signaling chemicals are practically the same in human cells as in yeast.
How Cells Burn Sugar
To understand the Warburg effect, you need to know how cells burn sugar. Your body’s favorite fuel is a sugar called glucose. Glucose is the main sugar in your bloodstream.
The Glycolytic Pathway
When we eat sucrose (table sugar), the molecule of sucrose will be split into a molecule of glucose and a molecule of fructose. When we digest starch, we break it down to molecules of glucose. Cells eventually convert both glucose and fructose into a compound called fructose-1,6-bisphosphate. After a few more chemical changes, the sugar molecule is split into two pieces. This splitting is called glycolysis.
To split the sugar molecule, the cell must make an investment of energy. The cell’s immediately usable energy is stored mainly in a high-energy molecule called adenosine triphosphate (ATP). To split the sugar molecule, the cell must convert two molecules of ATP to a lower-energy molecule called adenosine diphosphate (ADP). But at the end of the glycolysis 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 (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.
Ferment or Burn the Pyruvate?
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. For example, yeast cells in a wine cask turn the glucose from grape juice into alcohol. Also, muscle cells produce some lactic acid during intense (anaerobic) exercise. 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. 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.
The Really Bad Cancer Cells Are Anaerobic
Warburg knew that many cancer cells prefer to use anaerobic metabolism, even when they have plenty of oxygen. He showed us that the most aggressive cancers were most likely to prefer anaerobic metabolism. 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 burn calories to clean up the mess that the tumor is making. If the body has many cancer cells, the liver will use up a lot of calories to clean up the mess. The result is a rapid weight loss called cancer cachexia (pronounced ka-kex-ia). Cachexia comes from the Greek words for “bad condition.”
What the Belgian Study Teaches Us
The Belgian study could explain why the Warburg effect happens. It involves a set of intracellular signals that are practically the same in yeast cells as in human cells.
When yeast cells have plenty of glucose or fructose, they make a lot of fructose-1,6-bisphosphate. This fructose-1,6-bisphosphate then activates a signaling protein called Ras. Ras encourages the yeast cell to grow and divide faster.
In a normal human cell, the processes for burning sugar are tightly controlled. But in a cancer cell, these controls might be defective. One possible result is an abnormal buildup of fructose-1,6-bisphosphate inside the cell. Unfortunately, this extra fructose-1,6-bisphosphate would activate Ras. The activated Ras would then tell the cell to grow and multiply. This could explain why the cancers that have abnormal carbohydrate metabolism are likely to be more aggressive.
The results of the Belgian study could explain why some defective cells multiply fast. However, it tells us nothing about how our food choices affect our health. To answer that question, we need to look at other kinds of studies.
High-Carbohydrate Diets Help Protect Against Cancer
As T. Colin Campbell, PhD, explained in The China Study, cancer involves two basic problems. The first problem is cancer initiation, which means that one or more cells have become malignant. The things that cause cancer initiation are called carcinogens. Cancer promoters, in contrast, are things that help the existing cancer cells survive and multiply. By avoiding carcinogens, you can reduce the risk that a cancer will start in your body. If you also avoid cancer promoters, then your cancer cells might grow so slowly that you never even know they are there.
Some drugs can promote cancer, either by suppressing the immune system or by encouraging cancer cells to multiply faster. Some foods can also promote cancer. Campbell has explained that animal-source foods are cancer promoters. You can make some cancers in laboratory animals grow faster by feeding them animal protein. You can switch the growth of those cancers off by taking the animal protein out of the diet. In human beings, a high-carbohydrate, plant-based diet works in several ways to reduce your risk of dying of cancer. It might even suppress a cancer with abnormal sugar metabolism.