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The Glycemic Index of Carbs


Knowing the glycemic response of food is just as important as knowing its micronutrient content, its caloric value and its acid to alkaline ratio. Successful body composition management relies on this knowledge, and for athletes, it is crucial to performance.

In many ways, food is like a drug. It is composed of chemicals, albeit natural chemicals, which influence hormone responses, neurotransmitter activity and in fact, the entire biochemistry of the body. Carbohydrates for example, represent a potential fuel source. But long before they’re converted into ATP or stuffed into fat cells (after conversion into fatty acids) when over-consumed, they must go through a complex digestive process, find their way into the blood stream, swim up river to the liver and then connect with insulin.

The fiber and chlorophyll content of carbohydrates makes them unique, but even more interesting is the fact that although they are advocated as the primary calorie source in the western diet, they possess no known minimum essential value (we’re not talking about the vitamins and minerals they contain). In other words, if you eliminate all the carbohydrate foods (sugar, flour, plant starches & fruit) from your diet forever, you will not die or demonstrate any symptoms related to any known disease, although you may experience some fatigue, depending on your activity level and whether or not you are addicted to refined sugars or bread. Keep in mind that although fiber has proven health value, no research council yet has discovered a minimum requirement for it either.

The human body can make glucose (blood sugar) from other raw materials present in the body without ever receiving it directly from dietary sources. Just pickup any textbook on human physiology or nutritional biochemistry and read it for yourself. Through a process called gluconeogenesis, our bodies can convert the carbon skeletons of amino acids, glycerol, pyruvate and lactate into glucose. Glucose also combines with amino acids to form structural components known as mucopolysaccarides which are crucial to joint and membrane function.

We need dietary fat to supply fatty acids and we need dietary protein to supply amino acids. These macronutrients we cannot live without. This explains how hunting societies have survived without any plant life for extended periods of time, especially the Inuit and the Greenland Eskimo, who traditionally consumed walrus, seal and fish exclusively for months on end (eaten raw or sun-dried) without symptoms of deficiency.

In the absolute sense, we need 2 essential fatty acids, 8 essential amino acids, about 22 minerals and approximately 13 vitamins. All of these can be obtained without eating carbohydrates. And we do require calories for fuel and energy. So where do carbs fit in? After all, the main function of carbohydrates is to serve as an energy fuel, particularly during exercise.

My premise is not to discourage the consumption of carbohydrates such as organic green leafy vegetables, organic multi-colored vegetables, moderate quantities of starch (yams, squash, lentils, legumes) and organic fresh fruit. I do however, advocate a standard which avoids and/or minimizes the use of carbohydrates known to be destructive to health and human performance, such as muffins, buns, bagels, bread and pasta (made from refined, bleached and/or rancid grains & flour), commercial breakfast cereals, sucrose, fructose, corn syrup, French fries, potato chips, etc… Besides quality, I’m also concerned with the amount of carbohydrates each individual consumes, as even “natural carbs” concentrated in naturally occurring sugars and low in water volume (like brown rice, beans and squash) can be easily over consumed to the point of obesity, especially if one is inactive.

What is a Carbohydrate?

Carbohydrates are composed of carbon and water. Classified as one of three primary macronutrients (fats, carbs and protein), atoms of carbon, hydrogen and oxygen combine to form sugar molecules known as monosaccharides. More than 200 monosaccharides or simple sugars have been identified in nature, the most common of which is glucose (dextrose) or blood sugar. Fructose, or fruit sugar, is the sweetest of the simple sugars.

When two monosaccharides join together, they form a disaccharide or a double sugar. Lactose, composed of glucose and galactose, is commonly known as milk sugar. Maltose or malt sugar is present in beer and cereals. It is composed of two glucose molecules joined together. Sucrose is common table sugar, composed of glucose and fructose. Known also as “white death” in its refined form, it is highly addictive and consumed at an estimated national average of 33 teaspoons per day per person. I think its vernacular name is appropriate.

Complex carbohydrates are technically known as oligo or polysaccharides. These carbs contain at least 3 sugar molecules linked together, but more often they contain thousands. Starch and fiber are two common forms of plant polysaccharides. Animal flesh contains no fiber. Fiber is basically a complex form of carbohydrate which resists digestion in the human gut. It passes through our digestive system in two basic forms, soluble and insoluble. Research concerned with gastrointestinal health and medicine demonstrates a very important relationship between intestinal flora, gut bacteria and fiber. When fiber is broken down in the gut through bacterial fermentation, a special metabolite called butyric acid is formed, which influences immune function and even gene expression.

Maltodextrin is a complex carb derived from corn and grain starch. Known also as a glucose polymer, maltodextrin is common to many sport nutrition powders and drinks. It has a very high glycemic index (100) so caution should be applied to its use and timing, especially if you are diabetic, hyperglycemic, hypoglycemic or hyperinsulinemic. It's best to use maltodextrin in relation to physical exercise, like during or after a workout, practice or game, when the demand for carbohydrate replenishment is high.

Glycogen is an animal polysaccharide. It’s kind of like a potato starch. Glycogen is stored in our muscles and liver, and is a major source of carbohydrate energy (glucose) during intense exercise. After we whittle our way through the cell’s small supply of stored ATP and creatine phosphate, glycogen comes to the rescue. It is synthesized from the glucose in our blood, which comes directly from eating carbohydrates, or as mentioned, from endogenous (internal) supplies of glycerol and amino acids.

If the diet is totally carb-free, as observed in some hunter/gathering groups or in the design of a pre-competition bodybuilding diet, glucose can be obtained from the breakdown of protein and the glycerol portion of fat. Eventually we reach a “ketogenic” state. As the body burns fat as a fuel source, ketone bodies accumulate which can lead to acidosis, depending on the quality and form of fatty acids present in the body. A constant glucose level within a narrow range is important, since glucose is the primary energy source for the nervous system and the brain.

All dietary carbohydrates are not equal, as their rate of digestion and absorption varies. Simple sugars, other than fructose, tend to enter the bloodstream quickly, causing a sharp rise in blood-sugar. This produces an elevated insulin response. Complex, long-chain and fiber-rich carbohydrates enter the bloodstream more slowly. A moderate rise in blood sugar occurs, causing a moderate insulin response. Both responses are favorable, but with athletic performance in mind, timing is crucial. Athletes should ingest low-glycemic carbs prior to training and high-glycemic carbs for 2-4 hours after. Once carbohydrate (glycogen) stores are restored, one should then return to low-glycemic carbs combined with healthy fats and high-quality undenatured protein.

The Glycemic Index

The glycemic index of carbohydrates was developed initially for diabetics. Knowing the effect of food on blood sugar is important for monitoring a diabetics glucose levels. Foods that lead to a slow increase in blood glucose have a low glycemic index. Those that induce a rapid rise in blood sugar have a high glycemic index.

The glycemic index measures the extent to which blood glucose increases after eating a 50g portion of carbohydrate. This increase is then compared to glucose, which is given the value of 100. Knowing the glycemic index of different fruits, vegetables and starchy foods is important because a rapid rise in insulin, except after a workout, can ruin your fat-reducing objectives, increase serum cholesterol levels, encourage the onset of fatigue, intensify joint inflammation and set you up for hyperinsulinemia. Athletes need blood sugar stability to perform well. We all do.

Carrots, white potatoes, bananas, bread, rice cakes and white rice cause a rapid rise and fall in blood-sugar. These foods should be avoided before you workout. Pre-workout meals should consist of foods that have a low glycemic index (under 50), such as slow-cooked oats, grapefruits, green apples, cherries and plums, or a yam/protein combination.

Glycemic Index of Selected Whole Foods

Oatmeal 55
Whole-grain pasta 45
Wild rice 55
Baked potato 95
Carrots 85
Yams 50
Kidney beans 30
Spinach 15
Pineapple 65
Grapefruit 25
Yogurt, plain, no sugar 15
Honey 75

You can reduce the glycemic response of food by combining it with an essential fat or a high quality protein, both of which have low glycemic indexes. Fats delay the gastric-emptying time of carbohydrates. This is why I add 2 scoops of Whey Protein Isolate and a tablespoon of The Sport Oil to my morning freshly squeezed grapefruit juice a couple hours before training. Whole grapefruits have a glycemic index of about 25, the juice about 35. Juicing removes most of the fiber, but because grapefruit and orange juice contain mostly fructose, they still have a low glycemic effect.

I prefer grapefruits because of their "zesty" effect early in the morning, and because they also contain HMB, naringenin (which extends the thermogenic effects of ephedrine and synephrine) and good quantities of the carotenoid lutein. Grapefruit juice is alkaline forming, but only when freshly squeezed and consumed raw without pasteurization. The Colgan Institute advocates grapefruit juice mixed with grape juice (50:50) as an ideal medium for enhancing the uptake of creatine monohydrate. Grapefruit juice contains an enzyme that reduces stomach acidity.

Ideally, each one of your six meals per day should consist of the three macronutrients, the quantity of which is modified according to your lean body mass, the frequency and intensity of your workouts and your metabolic rate. After working out, when your metabolic window of opportunity is wide open, indulge yourself with 50-100g of a high glycemic carb matrix, 2-5g of creatine monohydrate, 2-5g of L-glutamine and up to 25% of your total daily requirement of high quality protein, all in a blended liquid slurry.

This approach will encourage glycogen replenishment which 1) aids recovery from exercise 2) dampens cortisol activity, which protects your lean mass, muscle base and immune system from erosion and 3) enhances the IGF-1, testosterone, insulin and growth hormone rectangle. Eat well and prosper!

For a comprehensive list which details the glycemic index of a great variety of foods check out WWW.MENDOSA.COM/GILISTS.HTM