Monday, August 24, 2009

Food as Fuel During Exercise

Chapter 5 in The Paleo Diet for Athletes focuses on food being used as fuel during exercise. It takes a close look at how the typical American diet differs from that of the hunter-gatherer. The typical western diet varies in these seven areas:

1. Macronutrient balance (carb, protein and fat)
2. Glycemic load
3. Fatty acid balance
4. Potassium/sodium balance
5. Acid/base balance
6. Fiber intake
7. Trace nutrient density

Macronutrient Balance
Americans love their carbs. Our diets have typically been very carbohydrate heavy. Our diets have generally looked like this, protein (15.5%), carbohydrate (49%), fat (34%) and alcohol (3.1%). The hunter-gatherer diet split protein (19-35%), fat (28-47%) and carb (20%-40%). Hunter-gatherer's have a much higher intake of fat, but it was typically the more healthful omega-3 and monounsaturated fat. The types of fat most Americans eat come from fatty beef, fried foods and other junk that is unhealthy for our hearts. While the carbohydrate intake is much lower in the hunter-gatherer diet, the carbs are much higher quality than those of the diet most eat today.

Glycemic Index and Glycemic Load (all info taken from page 85-87 in book)
I remember the first time I heard about the glycemic index. I heard someone talking about it on a NutriSystem commercial. I thought it was just another silly gimmick to sell diet food. Over the past year, I have become a believer in the science behind the glycemic index. Basically, the quality of a carbohydrate can be determined by the glycemic index. It rates how certain foods raise blood sugar levels compared with glucose. White bread, for instance, has a glycemic index of 100. The higher the glycemic index, the faster the food is turned to sugar and the faster your blood sugar rises. Why is a fast rise in blood sugar bad? It causes your energy to spike and then you crash. It won't sustain you through a long day or a hard workout. If a food has a high GI then it digests quickly and is absorbed quickly and realeases glucose in the blood stream quickly. A low GI food is digested slower and releases glucose at a more even rate into the blood stream. This helps keeps energy levels balanced.

The original glycemic index compared equal quantities of carbs (50 grams of carbs per food item). Watermelon has a glycemic index of 72 and a chocolate bar has a glycemic index of 43. Obviously, you would think watermelon is a better choice than chocolate, but according to the glycemic index, it would wreak more havoc on your blood sugar. Why? Because this is measuring 50 grams of carbs from each product. You would have to eat only 3 oz of chocolate to reach the 50 grams of carbs and 1 1/2 pounds of watermelon to reach the 50 grams of carbs. Confusing, right?

To overcome this confusion, the glycemic load scale was developed. It is measured by taking the glycemic index and multiplying it by the carbohydrate content in a typical serving. Much better. Most all refined grains and sugars have high glycemic loads, while fruits and veggies have lower glycemic loads. Meat and seafood have very low carb content so they do not change blood sugar or insulin levels like other foods. Here are some examples of foods and their glycemic index and glycemic load:

Food / Glycemic Index / Glycemic Load
Crisped Rice Cereal /88 / 77.3
Rice Cakes / 82 / 66.9
Table sugar / 65 / 64.9
Cheerios / 74 / 53.4
Corn Chips / 73 / 46.3
Whole Wheat Bread / 69 / 31.8

Boiled Sweet Potato / 54 / 13.1
Banana /53 / 12.1
Pineapple / 66 / 8.2
Grapes / 43 / 7.7
Apple / 39 / 6.0
Peach / 28 / 3.1

Hopefully you can tell a big difference between the first six items and the last six items. Some of the GI's are still higher in the bottom six, but take notice of the glycemic load. That is where you can really tell the quality of your carbohydrate. Go here if you want to figure the index and load of your carbohydrates! GI > 70 is high, GI 56-69 is medium and GI < 55 is low. A glycemic load < 10 is also considered low.

I will talk more about the other differences in the diets of hunter-gatherer's and Americans later this week. Too much information for one post! I hope I haven't confused anyone too much.

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