This article’s topic is glycemic index. Why do you care about glycemic index? Because high glycemic index foods are implicated in human obesity, and because glycemic index is a concept that explains a lot. Why do most of us carry around excess body fat? Why is whole wheat considered nutritionally superior to processed/white wheat? Why is 200 kcal of sweet potatoes and eggs ‘better for me’ than 200 kcal of doughnuts? Why do I crash after eating a huge meal? Why is it okay to drink gatorade and juice and sugar loaded drinks while exercising, but not while watching tv? Why might it be a good idea, for your energy levels, to throw some peanut butter on that piece of bread, or to put some eggs or olive oil on that white rice? In every case, the answer lies partly or entirely in the concept of glycemic index.
My last post, “Weight Management and Carbohydrates”, stated that the most important rules of weight management are:
1. Weight Management = Energy Input - Energy Output
2. Your carbohydrate intake should be varied each day to meet your energy output for the day.
A few people took issue to this view. Not everyone agreesthat ‘energy in – energy out’ can actually be used to manage weight, but that what you eat is the most important factor in weight management.
I still believe that ‘energy in – energy out’ is the first item to address when looking at weight management. As far as what you eat, see rule #2 – “your carbohydrate intake should be varied each day to meet your energy output for the day”.
Why should your carbohydrate intake be varied each day? Because if you don’t need the them (you did not have enough ‘energy out’), carbohydrates can make you fat. Why? Because carbohydrate rich foods are generally calorically dense (so they lead to overeating) and because carbohydrate rich foods generally have a high glycemic index. What is glycemic index and why could that make you fat? That is topic of this article.
There are three important characters for this article:
1. Glycemic Index - Glycemic index (GI) is a relative measure (scale of 0-100) of a food’s (or combination of foods) effect on your blood sugar. A high-GI food will be quickly digested and will result in a rapid and pronounced rise in blood sugar. Low-GI foods take more time to be digested and will have a slower and smaller effect on your blood sugar.
2. Blood Sugar - Your blood sugar is literally the amount of sugar floating around in your bloodstream. It measured as a concentration - the amount of glucose (the primary fuel source for your body’s cells) per volume of blood. Glucose levels (blood sugar) are usually lowest immediately in the morning and rise after eating a meal.
3. Insulin - a hormone released in response to high blood glucose levels. It is released in order to decrease and stabilize blood sugar levels.
So, just a quick example to demonstrate the relationship between these three characters:
You wake up in the morning. Your blood sugar is probably the lowest it will be all day - you are in a fasting state. You arrive at work and you still haven’t eaten anything. Someone brought in doughnuts, you are wicked hungry and they are from your favorite bakery. So you eat two. Your blood sugar increases as digestion begins. Your digestive system is literally turning some of the components of the doughnuts into glucose, which then travels through your bloodstream and is used by your cells as fuel. Since doughnuts have an extremely high glycemic index, they are rapidly digested and cause a large and fast increase in blood sugar. Your body prefers a stable blood glucose level, so insulin is released to encourage a lower blood sugar level. This insulin does its job, and in due time your blood sugar decreases and stabilizes.
Cool, eh? Your body has mechanisms and feedback loops that keep your blood sugar approximately level, regardless of if you are fasting or eating doughnuts. So if my body’s mechanisms are going to maintain an even blood sugar no matter what I eat, I can just eat whatever I want!?
No, it’s not okay to eat whatever you want, whenever you want, because when you threw down those two doughnuts and sent your blood sugar sky high, only to have it brought back to reasonable levels through an insulin response, you did yourself a disservice. The problem is the insulin response.
There are some smart people out there who have brought forth epidemiological and biochemical evidence that a strong insulin response (releasing insulin in response to high blood sugar) is something that should be minimized/avoided as much as possible. Their evidence suggests that, among other things, insulin discourages the use of body fat for energy, and encourages the glucose floating around in your bloodstream to be stored in the form of additional body fat.
Insulin response aside, high GI foods don’t generally make you feel very good. They send your blood sugar and energy levels on a roller coaster ride, they usually are nutrient-poor and do not provide a feeling of health and vitality, and finally, they don’t keep you full for very long. A lot of us have probably experienced the peculiar phenomenon of eating a bunch of Chinese food and then, 60 minutes later, being hungry again. One reason this may happen is because most of what you ate was white rice, a high GI food. If you had eaten a lower GI food, such as brown rice, or more vegetables or meat, you would have been full for longer.
Below is a "Summary Table" comparing the characteristics and effects of high and low glycemic foods. Some examples are also provided, along with their glycemic index (0-100).
All rice is high GI, all cereal, all dessert and all bread are high GI. If you want to eat them, you still should. But consider the lower GI variety:
And what if I want to eat white rice? Or eat a piece of toast? Or a potato?
Then combine them with a low GI food. For example, add some beans or fried eggs to that rice, add some peanut butter to that piece of toast, add yogurt (no sugar added variety) to your cereal, and pour a bit of olive oil over your potato.
To summarize: Try to avoid high GI foods, and favor lower GI foods. Add peanut butter or olive oil to bread or rice in order to lower the combined GI. How much you eat matters too – a small amount of a high GI food is not as bad as a large amount. Minimizing high GI foods will minimize the amount of insulin released when you eat, potentially helping you burn fat and minimize fat storage. Avoiding high GI foods will also help to prevent overconsuming calories. Eating low GI foods will keep your energy levels more stable, is more nutritious, and will keep you satiated for longer.
Remember that avoiding high GI foods will not magically take care of any weight management woes. Energy balance (calories in - calories out) still matters.
I’ve given high GI foods a pretty bad rap here.. High GI foods are not actually all bad guys – they are tricky two-facers. They do have their time and place in your diet – look to my next, and final, post on carbohydrates to discuss this two-face idea and to wrap up all of this carbohydrate talk with a discussion of “Carbohydrate Timing and Endurance Athletics”.