Healthy carbohydrates are found in fresh vegetables and fruits, legumes, nuts, seeds and whole, unprocessed grains. They supply energy, vitamins, minerals, water and a wide array of important plant chemicals. They are also the body’s main source of fiber, which helps to balance blood-sugar levels and keeps the digestive system in good working order.
Less nutritious carbohydrates, such as white sugar, white flour, white pasta, white rice and concentrated fruit juices, have been transformed from their natural, whole state into a refined version that keeps longer, looks cleaner, takes less time to cook and often tastes sweeter, but has lost most of its nutritional value. These types of carbohydrate can also upset our blood-sugar balance and create an environment in which cancer cells can thrive.
Glucose and insulin
All carbohydrates are handled the same way in the body: digestion breaks them down into blood glucose (often called “blood sugar”), the main energy source for the body’s cells. The presence of glucose in the bloodstream stimulates the pancreas to release a hormone called insulin to regulate the amount of glucose; our bodies need just the right amount – not too much and not too little – to function optimally.
Insulin allows glucose to enter cells throughout the body, where it is used as fuel. Excess glucose is stored in the liver and in our fat reserves. This is why insulin is often referred to as a storage hormone.
The amount of insulin the pancreas secretes depends on the amount and type of carbohydrate we eat; as we will see below, some carbohydrates trigger sharper releases of insulin than others. It is preferable to keep insulin production as moderate as possible to avoid some of the unhealthy side-effects that sharp fluctuations in blood glucose can cause. A steady level of insulin means less fuel for cancer cell growth, less fat storage and weight gain, steadier energy levels and fewer carbohydrate cravings.
What is IGF-1 (Insulin-Like Growth Factor-1)?
IGF-1 is an important hormone that stimulates cells (including many cancer cells) to grow. It is involved in multiple aspects of metabolism (protein, fat and carbohydrate). IGF-1 is released by the liver when the pancreas secretes insulin into the blood stream. Read more about IGF-1’s role in cancer development and growth here.
Carbohydrates are the main source of glucose (sugar) in our diet, but some are healthier than others, as illustrated in the graphs below.
The orange-colored graph on the right shows blood glucose and insulin rising moderately when a healthy carbohydrate (e.g. an orange) is eaten, and then tapering off gently. This is the sort of blood-sugar curve we should be aiming for. We call these “low-glycemic index” carbohydrates.
Eating a highly refined carbohydrate (e.g. a donut), as pictured in the red-colored graph on the right, causes blood glucose to rise sharply, triggering a hefty secretion of insulin which in turn causes blood glucose to drop well below the “normal” level at which the body functions optimally. We call these “high-glycemic index” carbohydrates.
This sort of overcompensation often triggers feelings of fatigue, headaches, irritability, and sugar or starch cravings. If you “give in” to these cravings by eating a sugary snack, the blood-glucose/insulin surge-and-drop will start all over again. Over the long term, such a “blood-sugar roller coaster” can contribute to weight gain and insulin resistance.
Healthy carbohydrates contain vitamins, minerals, protein, fats, fiber, and a host of important phytonutrients (many of which are thought to prevent and fight cancer.) Unlike refined carbohydrates, they do not cause a rapid rise in blood sugar and insulin as they are digested and absorbed.
- Non-starchy vegetables (not potatoes – these are a tuber, not a vegetable)
- Legumes (e.g. beans, chickpeas, lentils, whole and split dried peas, etc.)
- Fruit (particularly the non-tropical fruits: apples, pears, oranges, grapefruits, peaches, plums, apricots, berries, etc.)
- Whole grains (brown rice, buckwheat, wild rice, quinoa, barley, whole-wheat pasta, whole-grain bread, etc.)
Unhealthy carbohydrates, on the other hand, generally trigger sharp increases in blood sugar, insulin and IGF-1.They include sugar and sugary foods, baked goods made with white flour, as well as some naturally starchy foods such as potatoes (and especially French fries)
Unfortunately, some foods generally thought of as “healthy” (e.g. sports drinks, rice crackers, bagels, corn flakes or oven-baked potatoes) can also cause rapid increases in blood glucose and should be avoided wherever possible.
How can you tell whether a carbohydrate is healthy or not?
Whether a carbohydrate converts quickly or slowly into blood sugar is reflected by its so-called glycemic index (GI) rating. This index has been devised to measure people’s blood-sugar response to various carbohydrate foods.
Mostof the carbohydrates we eat should have a GI rating of 5o or less; occasionally, it’s OK to eat foods with GI ratings between 50 and 70. However, any foods with GI ratings over 70 should largely be avoidced.
Here are the GI ratings of some commonly-eaten foods: (GI)
- White baguette (95)
- White wheat bread (73)
- Sourdough rye bread (48)
- White rice (73)
- Brown rice (66)
- Quinoa grains (53)
- Spaghetti: white or brown (42)
- Barley: hulled (22)
- Kellogg’s Corn Flakes (93)
- Kellogg’s Special K (69)
- Oatmeal: non-instant (42)
- Instant mashed potato (97)
- Navy beans, garbanzos (31)
- Lentils, green (22)
- Gatorade: orange (89)
- Coca Cola (63)
- Carrot juice (43)
These numbers are from the University of Sydney, which keeps a continually updated database of the GI ratings of thousands of foods. It can be consulted free of charge at www.glycemicindex.com. They also publish an excellent online newsletter to which you can subscribe free of charge.
What is insulin resistance?
- If you’ve developed a condition called insulin resistance (or “metabolic syndrome”), the body makes insulin, but the muscle, liver, and fat cells do not use or respond properly to the insulin. It is a state in which your cells are not responding to insulin appropriately, so the sugar in your blood cannot get into your cells. To compensate, your pancreas pumps out more insulin to try to get the sugar out of your blood and into your cells.
- The hyperinsulinimia (high blood insulin) that results is able to maintain normal blood sugar levels and delay the onset of diabetes.
What causes insulin resistance?
- It is estimated that 1 in 4 people (without diabetes) has a genetic predisposition for insulin resistance.
- Whether or not insulin resistance develops depends (in large part) on one’s eating and exercise habits.
- Not being physically active is a major contributor to the development of insulin resistance.
- In addition, gaining weight/body fat (especially around the middle) is a common trigger. And once you have insulin resistance, it’s more difficult to lose weight. So, obesity and insulin resistance form a vicious cycle: obesity contributes to insulin resistance, and insulin resistance contributes to weight gain!
- People who maintain a healthy weight and enjoy regular physical activity rarely develop insulin resistance, even if they have an underlying genetic predisposition.
Keeping blood glucose within a normal range is important. This is because:
- Glucose is cancer cells’ preferred food; high circulating levels of glucose may therefore fuel the growth of cancer cells. Elevated blood glucose levels are associated with increased risks of the following cancers: pancreas, liver, colon and endometrium.
- The presence of glucose in the bloodstream triggers the secretion of insulin, which is known to promote the growth and spread of cancer cells. Elevated insulin levels are associated with increased risks of the following cancers: colon, endometrium, breast and pancreas.
- Insulin secretions are accompanied by secretions in IGF-1, which may further fuel the growth and spread of cancer cells. Elevated blood levels of IGF-I (insulin-like growth factor-1) are associated with increased risks of the following cancers: prostate, breast and colorectum.
Does the sugar in fruit feed cancer?
The level of glucose in the blood is increased when fruit is eaten, but much less than in the case of refined sugars or white flour. This is partly because fruit contains fiber and many other components along with fructose, and these additional components modulate the effect of the fructose. So, for example, although fructose can “make you fat”, it doesn’t increase the level of insulin in the blood, or the level of IGF, the growth hormone that accompanies insulin.
Should cancer patients stay away from sugars?
- Rather than focusing on simply lowering sugar consumption – though this is an important part of boosting our defenses against cancer – we should aim to decrease our overall intake of high-glycemic index carbohydrates, even non-sweet-tasting ones like French fries or white bread. Carbohydrates are essential to life, but to avoid rapid spikes in blood glucose, insulin and IGF-1 levels, choose low- or moderate-GI carbohydrates and eat sweet foods as occasional treats only, rather than as a regular part of your diet.
- Researchers from the University of Toronto reported on women in remission for breast cancer who had been followed for a number of years. Those with the highest levels of insulin at the beginning of the study were twice as likely to suffer a relapse and three times more likely to develop metastases than women whose diet contained less sugars and who thus had lower levels of insulin. (Read more here)
- Numerous cancers (i.e. colon cancer) have been demonstrated to be sensitive to the effect of sugars in the diet, although the association has not been rigorously studied in all of them. Why do you think PET scans use a radioactively-labelled sugar to find tumors…because most tumors love sugar. When tumors metabolize the radioactive sugar they light up on the scan.
On this website, we publish regular recipes cooking videos and practical nutrition advice to show how you can eat a low-glycemic diet and still enjoy tasty treats.
Learn more about the link between Diabetes and Cancer in this article from the American Institute for Cancer Research