How High Glycemic Index Foods Impact Your Health
Before we talk about how high glycemic index foods impact your health, let me first clarify the terms glycemic index (GI) and glycemic load. (GL)
Glycemic Index (GI) and gycemic Load (GL) assess how a carbohydrate containing food influences blood glucose levels.
(for a list of GL of foods visit www.mendosa.com/gilists.htm )
The GI is a numerical system measuring how much of a rise in circulating blood sugar a carbohydrate triggers–the higher the number, the greater the blood sugar response. The GI value is based on a portion that contains 50 grams of carbohydrates, which is not a typical portion size. A GI value tells you only how rapidly a particular carbohydrate turns into sugar. It doesn’t tell you how much of that carbohydrate is in a serving of a particular food, which also affects the rise in blood sugar. This disadvantage is addressed by using the GL.
A GI of 70 or more=high, a GI of 56 to 69 inclusive=medium, and a GI of 55 or less=low.
> 70 is HIGH
< 55 is LOW
The GL gives a numerical value indicating how a serving of food affects blood sugar, it multiplies the amount of carbohydrates found in a serving of food with that food’s GI and divides that number by 100. For example watermelon has a high GI (72), but the amount of carbs in a serving of watermelon is low, so it has a low GL (4).
A GL of 20 or more=high, a GL of 11 to 19 inclusive=medium, and a GL of 10 or less=low.
> 20 is HIGH
< 10 is LOW
High Glycemic Impact Foods and Inflammation
Inflammation is the normal and desired way our body responds to injuries. There are two types of inflammation: acute and chronic, also known as silent inflammation. An example of acute inflammation is a toot ache or a skin cut. The characteristics of it are swelling, pain, redness and heat.
Chronic inflammation is not easy to identify (hence the name silent), because it is below the threshold for pain. Silent inflammation is the inflammation we are all concerned about as is at the root cause of most chronic degenerative conditions. This is the inflammation that can be reduced or aggravated by lifestyle factors, including FOOD.
Eating foods with low glycemic load, lowers inflammatory markers and helps you feel fuller for longer.
- According to Harvard researchers, healthy, middle-aged women who ate the meals with the lowest glycemic load had the lowest levels of C-reactive protein, a marker of inflammation in the body.
- In overweight women who had greater levels of C-reactive protein to begin with, eating higher amounts of low glycemic index foods had an even greater impact on their inflammatory markers.
Over time consumption of high GI and GL foods can lead to insulin resistance, which translates into glucose not being effectively cleared from the blood after eating. This extra glucose and extra insulin in the bloodstream causes inflammation.
- High-GI diet appears to increase insulin resistance after a meal. British researchers compared the effects of a high-fat diet, a low-GI diet, a high-GI diet and a high sucrose (table sugar) diet on insulin resistance in middle-aged men with heart disease risk factors. Despite containing the same number of calories, the high-GI diet caused greater fluctuations in blood sugar and insulin levels.
- In a recent study published in the American Journal of Clinical Nutrition, Harvard researchers found than eating more high-GI foods significantly increases the amount of high-sensitivity C-reactive protein (CRP), a marker of inflammation, in healthy middle-aged women – regardless of whether they have other risk factors for heart disease.
- Researchers from Tufts New England Medical Center found greater declines in CRP concentration after consumption of low glycemic load diets in overweight people. In this study, published in the journal Obesity, 34 overweight people were given calorie-restricted diets that had either a high glycemic load or a low glycemic load. Aside from weight loss, the people who ate the low glycemic load diet saw a drop in levels of inflammation in their body.
High GI, Inflammation and Heart Disease
- In the same Harvard study, researchers explain that high-GI carbs may boost heart disease risk by exacerbating pro-inflammatory processes like insulin resistance. Eating lots of rapidly digested and absorbed high-GI carbohydrates increases the risk of heart disease, particularly in overweight women who are already prone to insulin resistance.
- According to research in the May 2009 issue of the American Journal of Clinical Nutrition, long-term intake of grains with different glycemic indexes may affect the extent of inflammation in people with the heart disease risk factors. For example, researchers from Finland found that the glycemic response to rye bread and pasta are lower than that of oat, wheat bread and potato – with the harmful effects of high blood sugar sticking around in the body for more than two hours. The people involved in this study had metabolic syndrome, which means they were already at higher risk of developing heart disease and other inflammatory conditions.
- Numerous studies have shown that overweight adults on low-GI diets have lower levels of CRP and lower blood levels of bad LDL cholesterol than their overweight peers who eat high-GI diets – even if they didn’t lose weight on the low-GI diet.
High GI, Inflammation and Type 2 Diabetes
When it comes to managing weight, blood sugar and inflammation, portion control of carbohydrates – even low-GI/GL carbs – means you’re not only eating a low Glycemic Impact diet, but a lower carbohydrate diet also.
- Another study from Harvard showed that diets high in low-GI whole grains and portion-controlled carbohydrates may have a protective effect against systemic inflammation in diabetic patients.
- In a 2007 report, long-term, epidemiological studies were reviewed and reached the conclusion that low-GI diets reduce oxidative stress and guard against system-wide inflammation that may mark the beginnings of type 2 diabetes.
Glycemic Response and Colonic Health
I couldn’t talk about carbohydrates, inflammation, weight…, and not talk about gut health, as this is one of my core focuses: “heal the gut to heal the body”! Without going into the details to why that is, let’s have a look at the gut and high GI/GL diet.
The colon (AKA large intestine) is a highly active metabolic organ, containing an exceedingly complex society of microbes. The strength of the gut, is determined in part by the rate of colonic fermentation. In simpler terms the microbes present in the large intestine are responsible for breaking down the fiber, the non digestible (by humans) parts of plants, or complex carbohydrates. This fermentation results in the production of several gases and SCFA (short chain fatty acids) which have several physiological and pathophysiological effects in the body. The colonic fermentation appears to be affected by the rise and fall of blood sugar levels after eating high-GI foods.
- In comparing a high-GI meal to a low-GI meal, Swedish researchers found that rates of colonic fermentation (again a sign of a healthy gut) dropped as blood sugar levels peaked.
- In this study, 15 healthy people ate evening meals with varying amounts of non-digestible fiber (the kind found in wheat bran). At breakfast, those who ate more non-digestible, low-GI carbs reported increased feelings of fullness and showed higher rates of colon fermentation.
I hope this article inspires you to start paying attention to the type of carbohydrates you are eating as well as the amount.
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Liu, S, et al.: Relation between a diet with a high glycemic load and plasma concentrations of high-sensitivity C-reactive protein in middle-aged women. Harvard Medical School, Boston, Massachusetts, USA. American Journal of Clinical Nutrition, pages 492-8, 2002.
Brynes, AE, et al.: A randomised four-intervention crossover study investigating the effect of carbohydrates on daytime profiles of insulin, glucose, non-esterified fatty acids and triacylglycerols in middle-aged men. Hammersmith Hospital, London, United Kingdom. British Journal of Nutrition, pages 207-218, 2003.
Kallio, P, et al.: Inflammation markers are modulated by responses to diets differing in postprandial insulin responses in individuals with the metabolic syndrome. University of Kuopio, Kuopio, Finland. American Journal of Clinical Nutrition, pages 1497-1503, 2008.
Pittas, AG, et al.: The effects of the dietary glycemic load on type 2 diabetes risk factors during weight loss. Tufts-New England Medical Center, Boston, Massechesetts, USA. Obesity (Silver Spring), pages 2200-2209, 2006.
Qi, L, et al.: Dietary glycemic load, whole grains, and systemic inflammation in diabetes: the epidemiological evidence. Harvard School of Public Health, Boston, Massachusetts, USA. Current Opinion in Lipidology, pages 3-8, 2007.
Nilsson, AC, et al.: Including indigestible carbohydrates in the evening meal of healthy subjects improves glucose tolerance, lowers inflammatory markers, and increases satiety after a subsequent standardized breakfast. Lund University, Lund, Sweden. Journal of Nutrition, pages 732-739, 2008.
Colonic fermentation: a neglected topic in human physiology education. Jørgen Valeur, Arnold Berstad: Advances in Physiology Education Published 1 March 2010 Vol. 34 no. 1, 22 DOI: 10.1152/advan.00103.2009