Evidence review shows strong associations between common conditions and and diets high in sugar and/or refined grain foods
by Craig Weatherby
Foods that contain significant amounts of carbohydrates—grains, fruits, vegetables, and beans—are rated according to the heights they raise blood sugar (glucose).
And the scale used to rank different foods according to how high they raise blood sugar levels is called the “glycemic index” or GI.
Thus, foods rich in sugars or “simple” starches—such as sweets, pastries, and white breads—raise blood sugar to higher levels and are assigned high GI numbers.
Conversely, the carbs in fibrous, low-GI foods—such as green vegetables—break down slowly during digestion, releasing glucose gradually into the bloodstream.
Recently, a Australian research group reviewed dozens of prior studies and found persuasive evidence that diets dominated by foods with high GI numbers lead to a higher risk of common lifestyle diseases.
The authors include renowned blood-sugar and diabetes researcher Jennie Brand-Miller, Ph.D. (pictured above), co-author of The Low-GI Diet.
GI rankings: What does the number mean?
Some packaged foods now display their glycemic index (GI) number on the label.
This is what the numbers mean:
- 70 or above = High GI
- 56 to 69 = Medium GI
- 55 or under = Low GI
You can look up the GI of most foods here.
Review affirms negative impacts of sweet, starchy diets
The authors of the meta-analysis analyzed the results of 37 “prospective-cohort” studies that involved a total of nearly two million healthy men and women (Barclay AW et al. 2008).
The review’s Aussie authors found that the people who ate the diets highest in foods that spike blood sugar levels (high-GI foods) were more likely to develop diabetes, heart disease, gall stones, and some types of cancer.
According to lead author Alan Barclay of the University of Sydney, “The key message from this study is that the GI of your diet is a powerful predictor of disease risk” (USNSW 2008).
Because GI ranks carbohydrates according to their impact on blood sugar levels, it’s not surprising that they found a link between high-GI diets and greater risk of diabetes.
As Barclay said, “If you have constantly high blood sugar and insulin levels due to a high GI diet, you may literally wear out your pancreas over time. Eventually it may lead to diabetes in older age” (USNSW 2008).
They also found a surprisingly strong relationship between high-GI diets and cancer.
The heightened cancer risk comes from the fact that spikes in blood sugar cause the body to release hormones – insulin and IGF-1 – that stimulate cell growth, deter natural “suicide” among pre-cancerous cells, and thereby increase the risk of developing cancer.
Other research shows that high GI diets tend to raise cardiovascular risks, by lowering HDL (“good”) cholesterol levels and boosting triglyceride levels. (And people with low HDL cholesterol and high triglyceride levels are more prone to gall stones, as the Aussies’ new analysis affirmed.)
Top 10 tips for reducing the GI of your diet
The GI database created by the University of Sydney allows you to search for foods by name, glycemic index, or glycemic load.
To search the database and learn more about the glycemic index, go to the University’s Glycemic Index Web site, from which we derived some of these healthy ideas:
- Include at least one low-GI carb with every meal, from one of four food groups: fruit and vegetables, legumes (beans), whole grain bread and cereals, or low fat dairy or soy alternatives. This will provide enough carbs to fuel your brain and muscles, while helping to keep blood sugar levels stable.
- Favor legumes over grains and potatoes. The legume family includes beans, lentils, string beans, and chickpeas. Their “resistant” starch helps stabilize blood sugar for up to 24 hours.
- Choose breads made with more than 50 percent whole grains. Choose a dense, grainy bread and be sure that the first grain ingredient begins with the word “whole.”
- Replace refined, high GI breakfast cereals with unsweetened muesli, oatmeal, whole grain cereal, or low-sugar granola.
- If you love potatoes, either have one or two tiny potatoes or make your “mashed” with a 50/50 mixture of potato and white cannellini beans. And always include the potato skin, which adds flavor and is high in fiber and antioxidants.
- Pasta is actually okay to enjoy in small amounts, as its carbs rank surprisingly low on the GI scale. (Choose whole grain pasta when you can.) And if you rinse pasta in cold water after cooking, you will turn some of its starch into the “resistant” type found in beans, which helps stabilize blood sugar levels.
- Choose brown rice or lower GI long-to-medium grain white rices such as basmati.
- Avoid packaged, processed foods containing corn starch and refined grains.
- Go for low-GI whole grains such as rolled oats, quinoa, pearl barley, buckwheat, bulgur, whole kernel rye, or wheat berries (whole wheat kernels).
- Choose low GI snacks—raw vegetables are best, followed by fresh fruit, a dried fruit and nut mix, and unsweetened, lower-fat kinds of milk, kefir, or yogurt.
Blood sugar rises and falls when you eat a meal containing carbs. How high it rises and how long it remains high depends on the relative simplicity of the carbs (the GI) and the quantity. The “simpler” a carb is, the more rapidly it is absorbed into the blood as glucose.
(Sugar of any kind—cane, corn, or honey—is almost as simple as a carb gets, although the starches in white bread rivals its potent impact on blood sugar.)
A newer measure call the “glycemic load” or GL combines both the quality and quantity of carbohydrate in one ranking number. It’s the best way to predict how much differing amounts of various foods will impact blood sugar levels.
However, although the GL scale is the most accurate gauge of a food’s per-ounce impact on blood sugar, the GI provides a simpler, hence more useful tool.
By picking low-GI foods in general, your diet will serve to stabilize blood sugar levels and thereby prevent the “insulin resistance” that underlies diabetes, heart disease… and possibly some cancers.
Vegetables are great choices, as they are low in digestible carbohydrates (i.e., sugars and starch) but come packed with nutrients, filling fiber, and anti-inflammatory, antioxidant, anti-cancer agents. You can enjoy them in as much abundance as you wish.
What about root vegetables like pumpkin and parsnips? They have higher proportions of rapidly absorbed carbohydrates—hence higher GIs—than fibrous fare like peppers, green beans, or broccoli.
But unlike potatoes and refined grain foods, root vegetables are still fairly low in rapidly absorbed carbs. So despite having relatively high GI rankings, their glycemic “load” (impact per ounce) is fairly low.
- Barclay AW, Petocz P, McMillan-Price J, Flood VM, Prvan T, Mitchell P, Brand-Miller JC. Glycemic index, glycemic load, and chronic disease risk—a meta-analysis of observational studies. Am J Clin Nutr. 2008 Mar;87(3):627-37.
- The University of Sydney, New South Wales (USNSW). Refined carb diet increases risk of common diseases. March 10, 2008. Accessed online March 13, 2008 at http://www.usyd.edu.au/news/84.html?newsstoryid=2190.