Can sugar promote cancer growth, obesity, cardiovascular disease, fatty liver disease, and type II diabetes?
By Wendi Roscoe PhD
In short, the answer is yes, but it is a very specific sugar and the mechanism is dependent on how this sugar is metabolized by our cells.
The idea of sugar promoting cancer is not new. It is also fairly common knowledge that eating a lot of sugar will cause people to gain weight. Most doctors tell their patients that a good diet is essential to good health. But we mostly take this for granted or don’t take it too seriously to heart. The fact is that excessive sugar in your diet can lead to very serious health problems. Many people will eat frozen dinners that have nice pictures of vegetables on the box and they think this is healthy food. Many people also eat a lot of foods such as pancakes (from a box) or buy cookies, granola bars, even flavored rice in a bag and think they are eating very healthy. The problem is that most of the time when you eat foods in a package that have a list of ingredients, then it is likely not healthy, despite the healthy-looking pictures. Many processed or frozen foods have many chemicals and preservatives and sugars in them that will allow them to stay in a freezer for a long time and to keep their color, texture, and flavor.
This article is just about the fructose that is added to many foods. And I want to explain how this sugar (monosaccharide) is metabolized by our cells and how it affects our body physiology.
What are the different types of sugars?
Monosaccharides are simple sugars; the 3 main ones are glucose, fructose, and galactose. They all have 6 carbon atoms, 12 hydrogens, and 6 oxygens (C6H12O6) but they have a different chemical structure and the way our cell use these are different. Our cells use glucose as a primary source of fuel for making energy (ATP….adenosine triphosphate). When we eat complex carbohydrates, such as potatoes, rice, bread or pasta, then we are eating starch. Starch is a polysaccharide made up of only glucose molecules, and it is our cell’s primary source of energy production. When we digest these starches in our digestive system, only glucose is released into our bloodstream, and used either to make energy (ATP) or converted into glycogen (the animal form of stored energy) in our liver or muscle cells, and any extra is converted into triglycerides (fat) in our adipose tissue (the fat cells in our subcutaneous layer, which is under our skin).
If rice and potatoes are just made of sugar (glucose), why can’t we just eat chocolate bars and cake?
First, because when we digest starches, the glucose molecules are released slowly into our bloodstream because of the time it takes for our digestive enzymes to break them down into the individual glucose monosaccharides. Second, chocolate and cake and cookies etc is made from table sugar (sucrose), which is a disaccharide, which is made of both glucose and fructose. Sucrose is approximately 50% fructose and 50% glucose. Other sugars have different amounts of fructose such as honey (50% fructose but in free form, not bound to the glucose as a disaccharide) or high fructose corn syrup (usually 55% fructose and 45% glucose). Third, when we eat simple sugars they are absorbed much more quickly into the bloodstream from the digestive tract because they are already almost completely broken down. This rapid absorption leads to a spike in the release of insulin from the pancreas. I’ll talk about insulin more shortly.
What is different about fructose?
Fructose is the sweetest tasting sugar, which is why the inexpensive high fructose corn syrup (HFCS) is found in so many processed foods. It is also found in fruit but in much lower amounts. For example, a can of tomatoes contains about 2 grams of fructose, whereas a large soft drink can have up to 60 grams. Fructose is not metabolized in the same way as glucose. Fructose is circulated from our digestive tract through the hepatic portal vein to the liver. The hepatic portal vein is a vein that brings all digested nutrients from the digestive tract to the liver before it goes into the general circulation. The liver then processes these nutrients, meaning that it “decides” what will go into the rest of the circulation and what will be converted into stored energy (glycogen or fat). The liver also stores many vitamins and other nutrients that we eat so they can be released into the blood when needed.
Glucose is the main source of ATP in all cells of the body and that is why we have to maintain a certain blood sugar level, which is regulated in part by insulin. Insulin is released in varying amounts depending of what we eat. Insulin is a hormone that signals the cells in our body to take up glucose from the bloodstream so it can be either used to make ATP. If we have an excess of blood sugar then increased insulin will signal the liver and muscle cells to convert the excess into glycogen and fat. Fructose does not stimulate insulin release nearly as much as glucose does. Scientists initially thought this might be a better sugar for diabetics but recent research shows that fructose is in fact worse for diabetics.
How does fructose relate to cancer growth, obesity, cardiovascular disease, fatty liver disease, and type II diabetes?
Fructose from the digestive system reaches the liver before any other cells in the body. The liver converts about 50% of this into glucose or lactate and the rest is primarily converted into triglycerides (fat). Fructose is not used directly by any cell in the body, it is almost 100% metabolized by the liver.
When the liver has to convert excessive amounts of fructose to glucose or fat, it requires much more energy (ATP) than converting glucose to glycogen or fat. This increased ATP use leads to the production of uric acid and depletes the liver of ATP that it may need for other functions. Also, fructose will inhibit fat breakdown in the liver and only promotes fat production. Over several years of excessive fructose intake, the liver will develop fatty deposits, also called fatty liver disease (Tappy and Le, 2010). Furthermore, the fat produced by the liver from fructose will need to be transported through the bloodstream to adipose tissue to be stored.
The liver produces low-density lipoproteins (LDLs) which are made of cholesterol and help transport the triglycerides through the bloodstream. These are the molecules measured in a blood cholesterol test. Excessive fructose intake increases blood cholesterol levels just as much as eating fat! Therefore, fructose-induced LDL production is a major contributing factor to cardiovascular disease (Stanhope and Havel, 2010). Needless to say, all of the triglycerides being stored in the adipose tissue contribute to increased weight gain. It has also been shown that fructose conversion into lactate (which can leave the liver and circulate through the body and can be used by some cells to make ATP) will inhibit fat breakdown in fat cells. This means that you will continue to store fat and it won’t be used for energy, even if you exercise.
When we measure our blood sugar levels we are measuring glucose levels because fructose is rarely found circulating in the bloodstream because it is almost completely processed by the liver into the molecules mentioned above. Insulin release is highly regulated by blood glucose levels. When we eat, our blood sugar level increases, we release insulin, our cells than take up nutrients and make ATP or store them, then our blood sugar level decreases, insulin secretion decreases until we eat again…this is a normal process that is vital to taking up and using the food we eat. When we eat a high amount of fructose, about 50% of it is converted into glucose which is released into the blood stream, which will stimulate insulin release. Normally when blood sugar levels are high, our liver would not continue to make more glucose, it would convert sugar into fat, but when we eat fructose, 50% is STILL converted into glucose and secreted into the bloodstream. When this happens, insulin is of coursed released in response to the higher blood sugar. This, over time, will lead to insulin resistance, and therefore, type II diabetes(Gerrits and Tsalikian, 1993).
Cancer cells grow more rapidly in an acidic environment. This has been shown in lab experiments with cancer cells growing in vitro. There are articles that say eating a more alkaline diet will decrease the likelihood of cancer growth. I do not think that is the actual link. I do think that a lower blood pH could increase the growth rate of existing cancer cells but eating alkaline foods will do no good because of the buffering system of the digestive system and the circulatory system. When we eat foods they first enter the extremely acidic environment of the stomach, they then pass into the small intestine where a large amount of bicarbonate is released from the pancreas to increase the pH level so that intestinal enzymes can function properly. I don’t think eating alkaline foods will have any impact on blood pH because of this process. However, fructose inadvertently decreases the pH of the blood (more acidic) by increasing uric acid production in the liver. So in my opinion, decreasing fructose in your diet will decrease cancer cell growth by decreasing uric acid production, which therefore maintains a more alkaline blood pH level. It is also possible that blood buffering systems compensate for the increased uric acid (which will eventually be eliminated by the kidneys) and perhaps there is no link. This is just speculation on my part, there are no publications which show this specifically, but I think it is a pretty fascinating relationship that should be mentioned. It is also well known that cancer cells will use 10X more glucose than normal cells, so having high blood sugar for long periods of time will increase cancer growth simply because the cancer cells are getting what they need to grow (Yalcin et al., 2009).
Some interesting facts about fructose:
When you eat a meal that is high in saturated fats (animal fats like meat and butter) you will absorb more fructose from that meal into the bloodstream. Eating healthier unsaturated fats, such as olive oil, will not increase fructose absorption.
Fructose eaten by people that have high activity levels will be much less likely to have the long term effects compared to people that are sedentary.
A high fructose diet can affect the normal bacteria that live in the digestive and can lead to digestive problems such as diarrhea or bloating.
Fructose in food doesn’t affect the feeling of fullness the same as glucose. A hormone called ghelin is released when we eat, which makes us feel full; this hormone release can be suppressed by fructose and can contribute to over-eating.
Another hormone called leptin plays a role in breaking down fat to be used for ATP production. High fructose intake will eventually inhibit this hormone and may also contribute to fatty liver disease.
We are genetically programmed to crave salt, fat, and sugar because these used to be so rare in the diet. Now that they are constantly available, we consume much more than our ancestors ever could. Particularly with the technology we now have to produce massive amounts of HFCS which are added to many processed foods.
A high fructose diet will increase the amount of fat that is stored around your organs, compared to normal fat distribution in the subcutaneous layer under the skin. Excessive fats surrounding organs will increase blood pressure and cardiovascular disease.
Foods that contain high amounts of fructose:
Soft drinks
Gatorade
Table sugar
Baked sweets – cake, cookies, pie, donuts etc
Salad dressings
Sweet pickles
Ketchup
Dried fruits – dates and figs are high in fructose
Tomato paste
Honey
Pancake syrup
Jam
Cereals (most cereals are junk food)
Fast foods
Frozen dinners
Ice cream
Many snacks such as granola bars, “100 calorie bars”, energy bars
*Although fruit generally has a much lower amount of fructose and fruits are very healthy, some fruits have higher proportions of fructose than glucose – grapes, pears and apples tend to have more fructose than berries or citrus.
Now you may be wondering what on earth CAN you eat? Humans are supposed to eat plants and animals. Eat lots of different vegetables, fruit, beans, nuts, eggs, oatmeal, chicken, fish, rice, potatoes, etc. If it has a long ingredients list, then you probably shouldn’t eat it.
Reference List
Gerrits PM, Tsalikian E (1993) Diabetes and fructose metabolism. Am J Clin Nutr 58:796S-799S.
Stanhope KL, Havel PJ (2010) Fructose consumption: recent results and their potential implications. Ann N Y Acad Sci 1190:15-24.
Tappy L, Le KA (2010) Metabolic effects of fructose and the worldwide increase in obesity. Physiol Rev 90:23-46.
Yalcin A, Telang S, Clem B, Chesney J (2009) Regulation of glucose metabolism by 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases in cancer. Exp Mol Pathol 86:174-179.