Oct 27, 2010
The glycemic index is everywhere. Recent magazine articles, radio advertisements, talk shows and well publicized books are making great claims from its use. Low glycemic meals are being touted as an aid in weight loss as well as an effective manager of diabetes and possibly relevant to the prevention of heart disease.
The varied use of low, mid and high glycemic foods are also being studied and integrated as part of good sports nutrition and enhanced performance. Can you imagine all of the possibilities with the implementation of a few choice foods into our daily nutrition plan? Is it really this simple? Within these last few weeks I've had the opportunity of researching the glycemic index through several of the most current web sites and journals dedicated to research reports and updates. With all of the publicity the index has been receiving, it's time to examine what it is, how it works and how the personal training community can benefit from its day-to-day use.
How It Works
The glycemic index refers to the relative degree to which blood sugar increases after the consumption of food. A food is always measured relative to the effect of pure sugar. High glycemic index foods can raise blood glucose levels very quickly, as well as insulin levels. In contrast, low glycemic index foods do not significantly raise blood glucose levels and insulin levels after eating. Pure glucose is given a value of 100 while other foods are given an index number representing its relative effect on blood glucose levels.
For example, sweet corn is assigned an index number of 55 which means sweet corn raises blood glucose levels 55 percent as much as pure glucose. In general, foods below 55 are considered low glycemic index foods, 55-70 represents mid-glycemic index foods and over 70 are considered high glycemic foods. In the past, it was widely believed that simple sugars dramatically increased blood glucose levels while starches such as potatoes and bread were digested slowly. The results from numerous studies show this is definitely not the case. In fact, one of the biggest surprises comes from potatoes, which reported an average index of 84, making it one of the higher glycemic foods available. Here's a look at how a high, mid and low glycemic value food can alter one's blood glucose response.
For Weight Loss
Most clients who come to trainers for help primarily want to lose weight or shed body fat. Can the application of the glycemic index to our food choices really help us lose body fat? Research has confirmed that one of the most effective ways to lose body fat is by eating 5 to 6 meals daily combined with resistance training and some form of cardio.
Small, frequent meals increase the thermic effect of food as well as prevent the body from going into starvation mode. Research further agrees there should be a larger portion of carbohydrates mixed with more moderate amounts of protein and fat. The glycemic index allows us to more effectively evaluate our nutrition plan focusing on the quality of carbohydrates. For those who incorporate a larger amount of low glycemic foods, they will be rewarded with a slow and steady release of glucose keeping insulin levels in check.
This is of tremendous benefit to those who complain of low energy when cutting back on calories. Since all nutrients are not created equal, low glycemic foods have the added effect of keeping individuals feeling more satisfied for longer periods of time. In contrast, high glycemic foods used early in the day could cause unwanted surges in glucose levels, leaving one feeling energy deprived as well as creating hunger pangs. Lower insulin levels play a critical role in how and when we store fat. These reduced levels make fat easier to burn and more difficult to store.
For Sports Performance
Athletes have long known that eating properly before training and competition can improve performance in measurable ways. Increased carbohydrate intake prior to exercise can be measured through increased muscle and liver glycogen stores as well as aid in the maintenance of blood glucose levels for sustained energy. Glucose levels then provide fuel for the brain, which allow us the luxury of good judgment and enhanced concentration levels while exercising. How, then, can the glycemic index help athletes in their performance?
Despite what may sound logical in applying the glycemic index, researchers have found that what you eat prior to endurance exercise does not necessarily play a role in your ability to sustain an endurance activity. Whether your meal consists of low, mid or high value foods does not seem to matter as much as what you consume to sustain your energy stores during exercise. While high glycemic foods do not play a favorable role in weight loss, they can have an important effect in sports performance.
Following a heavy training session, when muscle glycogen stores are depleted, high glycemic foods can provide a quick release of glucose re-filling energy stores. Within the first few hours following exercise, blood flow to muscles is increased. Glycogen synthesis can be optimized during this critical time by the use of high glycemic carbohydrates. One of the concerns expressed by athletes and coaches over the course of time is that ingestion of carbohydrates in the hour before exercise could cause a dramatic increase in insulin levels, ultimately causing hypoglycemia within a short time after exercise begins.
Recent studies have shown that even though high glycemic foods were taken prior to endurance exercise, the resulting performance was not affected. This is an important finding in that the quality of carbohydrates is less important in meals prior to exercise while potentially being of great significance to aid recovery in the time following exercise. There is still much debate on this subject.
Working With Clients
While there are many ways to utilize the index to benefit our varied client base, remember that different people can have different results and there are many factors which can influence the index of foods like food preparation, age of food, fiber content, protein and fat content, as well as many other variables. It is not a perfect science nor have all testing results been consistent. However, as fitness professionals, the glycemic index provides us with yet another tool to help our clients meet their individual goals.
By offering our knowledge and assistance on this subject, it's possible that we can fine tune our clients' training and nutrition programs to more closely match their energy requirements throughout the various stages of training. Many athletes and dieters have reported marked differences in weight loss and performance results by manipulating their balance of foods to meet their goals. Specific athletes may see a direct benefit from using the glycemic index in their food selection. However, there is insufficient evidence to suggest that all athletes will see equal benefits.
All trainers, coaches and serious athletes should know the difference between high, mid, and low glycemic value foods and when their consumption and appropriate mix will best serve their intended purpose.
Please consult the chart below detailing how various foods stack up on the glycemic index. For a more comprehensive list, go to www.mendosa.com/gilists.htm.
The Glycemic Index of Common Foods