Cycling and Weight Loss Part 3: Exercise Make You Hungry

hungry empty plateThis is the third in a series of posts about losing weight on the bike. Throughout this discussion it’s important to keep in mind that eating has many consequences for health, athletic performance and weight loss.  The “best” diet for losing weight is unlikely to be the “best” diet for maintaining either your health or a high level of athletic performance.

In the first post in the series, Riding the Bike to Lose Weight, we pointed out the fundamental and most important fact about weight loss.  If you burn more calories than you ingest during a day, you will lose weight.  We also said that given this basic fact, if you focus your attention on deriving more enjoyment out of riding the bike, you are likely to lose weight without worrying about losing weight all the time.  You’ll be thinking about something you enjoy, the more you enjoy it, the more you’re likely to do it, and the more you do it, the more calories you’ll burn while you’re doing it.  All this goodness without any time spent being anxious about your weight.

In the second post in the series, Metabolic Homeostasis, we pointed out that the human body is an exquisitely functioning homeostatic system.  The system will adapt to changing conditions such as an increase in calories burned through exercise or a decrease in calories ingested through dieting in order to maintain a balance between caloric intake and caloric burn.  For this reason we recommended that you should always strive to increase the level or intensity of your riding.  Go harder, faster, longer, stronger and you will increase the caloric burn.  It is hard for the system to reach a balance point if the caloric burn is always increasing.

balansiraneThe recommendations from the previous two posts in the series work hand-in-hand.  If you continue to find new ways to get more enjoyment from the bike, you’re likely to continue to increase the time and energy you spend on the bike, and thereby increase the calories burned by cycling which makes it difficult for the system to adapt to a new and sustained level of caloric burn.

In the post on Metabolic Homeostasis we also talked about how reducing caloric intake by dieting leads to an adjustment in the basal metabolic rate in such a way that the same amount of work can be done to accomplish routine daily activities while burning fewer calories.  When caloric intake is reduced, the system seeks balance by reducing the calories it needs.

When we look at the other side of the weight loss equation, caloric burn, how does the system respond when balance is disrupted by burning more calories through exercise?  One way the system adapts is by increasing the demand for food.  Exercise makes you hungry.

The mechanisms that regulate metabolic homeostasis are complex and not fully understood.  One of the factors involved is a hormone called ghrelin.  One variant of this hormone, called acyl ghrelin or acylated ghrelin, plays an important role in regulating hunger.  When levels of acylated ghrelin in the bloodstream are high you feel the sensation of hunger and want to eat.  After eating, levels of acylated ghrelin in the bloodstream drop.

Burning calories through exercise disrupts the balance between caloric intake and caloric burn by increasing caloric burn.  One way in which the body responds is by increasing the level of acylated ghrelin in the bloodstream.  This makes you feel hungry and want to eat.  The system attempts to return to a balance between caloric intake and burn after exercise by increasing caloric intake.

woman frigThe release of acylated ghrelin after exercise leading to feelings of hunger and the desire to eat does not affect everyone equally.  Most women experience this effect but many men do not.  In some cases a prolonged session (e.g., 90 minutes) of fairly intense exercise can reduce the level of acylated ghrelin in the bloodstream for some men.  Anecdotally, we have observed this difference in our family.  After a fairly long and intense ride my wife is often hungry and wants to eat while I have no interest in food for several hours after the ride is finished.

The emerging understanding about how exercise is related to weight loss has led some “experts” to make statements like “exercise is practically useless for losing weight”.  Statements like this are usually designed to draw attention by grabbing headlines or serving as a sound bite.  When you dig a little deeper you find that the reasoning behind the statement is that after exercise people often feel hungry and they ingest enough calories to offset the calories they just burned during exercise.

Well, duh.

pizza eatingIf you pork out on pizza and beer after your ride, you’re probably going to ingest more calories than you burned and you’re not going to lose weight.  This doesn’t mean exercise is useless, it means you have to use some common sense after exercise and not replace all the calories you just burned.

It seems to me that a sensible way to think about the relationship between losing weight and cycling or any other form of exercise is to always keep the basic tenet in mind that you lose weight when you ingest fewer calories than you burn.  Gain knowledge about factors that affect this simple relationship such as metabolic homeostasis, and the mechanisms the body uses to maintain the homeostatic balance between caloric intake and caloric burn such as increasing the levels of acylated ghrelin in the bloodstream and decreasing basal metabolic rate.  Make use of this knowledge when making decisions about when and how to ride and when and what to eat.  Eat to fully support your ride so you will burn as many calories as you can while you’re on the bike.  Enjoy your ride – this is the most important part – enjoy your ride.  Discipline yourself after the ride so you don’t replace all of the calories you just burned.  If the net outcome is that you burn more calories than you ingest, you’ll lose weight.

A Lesson Learned: The Alpe d’Huez and the Col de Sarenne

Kevin-at-Alpe-d'Huez-1_crop_20pct

Me at Alpe d’Huez

One of the stages in this year’s (2013) Tour de France did several things that had never been done before.  First,  riders climbed the classic Alpe d’Huez twice in one day.  They accomplished this by doing something else that had not been tried in the Tour de France.  After the first climb of Alpe d’Huez they descended the Col de Sarenne, looped back around on the D1091 and rode to the finish at the top of Alpe d’Huez the second time.  The Col de Sarenne had never been ridden in the Tour before because it was thought the road was too narrow and too dangerous.

Descent-from-Col-de-Sarenne-1_800px

The descent on the Col de Sarenne

Several years ago my wife and I had the chance to ride for five days in the French Alps.  Our plan was to ride as many of the climbs that are often used in the Tour de France as possible.  With that in mind we climbed and descended Les Deux Alpes, the Col du Lautaret, the Col du Galibier and, of course, the Alpe d’Huez on our first two days.

Like many cyclists, we had been dreaming of these climbs for a long time and were thrilled to have the opportunity to actually do them ourselves.  But after two days we discovered something unexpected.  We were a little bit bored and a little bit disappointed.  The climbs were difficult, but they were not all that difficult.  The roads, for the most part, were wide, well maintained, and filled with cyclists along with cars and trucks that respected cyclists.  The scenery on the climbs was a bit on the bland side.  Often the road getting to the climb (the D1091 in most of these cases) was gorgeous but the climbs themselves presented more or less generic alpine scenery.

View on Col de Sarenne

View on Col de Sarenne

We passed many other roads winding off into the mountains and began talking about alternative routes with people who lived in the area and with cyclists who were familiar with the local road network .  Almost every one of them recommended the Col de Sarenne.

We took their advice, abandoned our original plan, and rode the Col de Sarenne the first thing the next day.  It turned out to be exactly the right thing to do.  The Col de Sarenne is a spectacular climb and descent.  We found it to be markedly more difficult and immensely more interesting than Alpe d’Huez.  The climb was tough, the scenery was breathtaking, the descent was heart stopping.  We loved it.

For the rest of the trip we rode routes that were recommended to us by people who knew the area.  Every single route we took provided us with special cycling experiences ranging from wild and extraordinary scenery, to difficult and enjoyable climbs and descents, to a small, beautiful village at the end of a road deep into a gorge.

Laura at the beginning of the climb up the Col de Sarenne

Laura at the beginning of the climb up the Col de Sarenne

We learned an important lesson on this trip.  If you’re going to be doing some riding in an area with great cycling opportunities, talk to the people who live there and ask for their recommendations about where to ride.  They will certainly tell you about the famous or well-known rides but if you’re lucky they will also tell you about rides you’ve never heard of that may well end up providing your most cherished memories from the trip.

Cycling and Weight Loss Part 1: Riding the Bike to Lose Weight

A champion

A champion

This is the first of a series of posts about riding the bike to lose weight.  Throughout this discussion of losing weight it’s important to keep in mind that eating has many consequences for health, athletic performance and weight gain or loss. We’ll start by focusing purely on weight loss but it is very important to keep in mind that the “best” diet for losing weight is unlikely to be the “best” diet for maintaining your health or a high level of athletic performance.

A lot of people aren’t going to like these posts.  I noted in a recent post that Americans spend about $50,000 on diet industry products and services every 80 seconds, 24/7/365. If you work for 50 years and average $50K a year, Americans spend more on diet stuff in an hour and 10 minutes than you will make in your entire life. 24/7/365.  The people who are spending that money and the people who are raking in the cash from all that stuff are going to be especially unhappy with these posts.  Why?  Because if you’re riding your bike to lose weight, most of that stuff is a waste of time and money.

Many people get into riding the bike as a way to lose weight and others who are interested in the health benefits of riding have weight loss as a secondary goal.  This is a good idea because riding the bike can be a great way to lose weight.

Shoes on scaleThere are a couple of ways to go about this.  One approach is to focus your attention on losing weight.  You buy diet books and scour the internet for info about losing weight.  You pay careful attention to things like how many calories there are per serving size.  You count calories for each meal and snack. You weigh yourself obsessively.  You may fork out money for the advice of a licensed nutritionist.  If you are especially gullible you buy a magic bracelet.

This approach to losing weight is often accompanied by the view that riding the bike is a type of exercise that is going to be used as a weight loss procedure.  Exercise is onerous but you have to do it.  People with this attitude will often want to maximize their weight loss for every minute they have to spend on the bike.  They’ll want to know things like what’s the smallest amount of time they’ll have to spend on the bike to burn X number of calories, what’s the absolute minimum they have to eat on the bike to get through a longer ride and exactly when they should eat in order to survive the ride on this absolute minimum.  They’re always worrying about numbers.  They’re not having much fun.

Happy cyclist_cropHere’s a second approach losing weight on the bike.  Forget about losing weight.  Forget about measuring this and calculating that, about eating so much of this kind of food and so much of that kind of food, about magic bracelets and paying for the advice of licensed nutritionists.   Forget about all of it.  Instead, enjoy riding your bike, ride frequently and consistently, and keep trying to get better at it.  That’s really all you need to do.  You will almost certainly lose weight.

The basic story is very simple.  Your body needs energy to function.  That energy is measured in calories.  The type of calorie that is used when talking about weight loss and nutrition is sometimes called a large calorie or a kilocalorie. One kilocalorie is the amount of energy that is needed to raise the temperature of 1 kilogram of water by 1 degree Celsius.

If you are alive, you are burning calories. Calories are burned when you sleep, when you think, when you go through your normal daily activities and when you ride.  The fuel that provides these calories is glucose.  The glucose is derived either from carbohydrates, proteins or fats that are being broken down in the digestive system from food you have recently eaten or from reserves stored in the body.   If there is not enough glucose in the blood stream to fuel ongoing activity, the system starts breaking down stored reserves to get the glucose it needs.  When stored fat is broken down, people start losing the kind of weight they want to lose.

calorie-balanceLosing or gaining weight depends on the balance between the calories you burn and the calories you ingest during the day.  If the calories you ingest are less than the calories you burn, you will lose weight because the system will turn to its stored energy reserves (which include stored fat) to get the energy it needs.  If the input calories are more than the output calories, you will gain weight because the excess calories will usually be stored as fat.  If input and output are about the same, your weight will be stable.  Thinking only in terms of weight loss (and not health or performance), it doesn’t matter if the calories being burned are coming from carbs, proteins, or fats.  A calorie is a calorie. That’s almost all you really need to know.

Almost but not quite.  There’s one important modifying factor to consider that we’ll look at in more detail in the next two posts in this series.  In order to take this modifying factor into account when you’re riding your bike, you need to try to get better every time you ride.  Every time out try to get a little stronger, go a little faster, ride a little longer.  That’s really all you need to do.

Riding like this will result in weight loss for the simple reason that in most cases when you add the calories you burn during the ride to the calories you burn during the rest of the day the total calories burned is greater than the calories you take in by eating.  If you burn more calories than you take in, you will lose weight.  Simple. And you don’t need to support the diet industry with your hard-earned cash to do it.

People who take the first approach try maximize weight loss by obsessing over how many calories, what kind of calories, when you eat those calories, and all the rest of it.  People who take the second approach try to maximize the enjoyment they get from riding the bike.  They work on spending more time on the bike doing the things they enjoy about riding the bike. When you engage in exercise or athletic activity you’ll burn the calories whether you enjoy what you’re doing or hate it, whether you’re thinking about losing weight or thinking about whatever you think about when you’re having fun.  So, why not give your attention to enjoying yourself and having fun rather than on how much you’ll weigh the next time you get on the scale?

food-nutriiton-bannerWhen you focus on riding the bike because you enjoy it rather than riding the bike as a weight loss procedure all of the questions about calories and weight loss turn into questions about how to be a better rider.  Getting better on the bike usually means increasing your strength and endurance so you can ride harder, longer or faster.  Eating isn’t about minimizing calories anymore, it’s about supporting performance.  As your performance increases and you ride harder, longer or faster, you burn more calories whether you’re trying to lose weight or trying to be a better cyclist.  If you ride hard enough and often enough, you can eat whatever you want because no matter how many calories there are in what you eat, you’ll burn more on the bike and lose weight.

If you don’t really enjoy riding the bike, find another type of exercise that you do enjoy.  If you enjoy something, you’ll want to do it; if you want to do it, you’ll find a way to do it; if you do it, you’ll burn the calories and lose the weight.  Find something energetic that you enjoy, do it frequently and consistently and always try to get better at it and the weight will come off.  It won’t happen overnight, it won’t happen fast, you’ll hit plateaus, but if you keep striving to ride harder, faster, stronger, longer, you will lose weight.

Once you’ve started to lose weight there’s another factor you have to consider which we take a look at in the next post in this series.

Gearing Part 2: Chainrings, Gear Ratios and the Steps from One Gear to the Next

RingsThis is the second of a series of posts on gearing for road bikes.  It’s aimed at riders who are seeking a basic understanding of bicycle gearing.

Chainrings for road bikes come in many different sizes and configurations.  Standard two-chainring setups (commonly called doubles) usually feature combinations of either 53 and 39 tooth rings, or 52 and 39 tooth rings.  Compact doubles usually have 50 and 34 tooth rings.  Triples (3 chainring setups) usually have either 53-39-30 tooth combos or 52-42-32 tooth combos.  In addition to these standard sizes, it is possible to combine different size rings into unique combinations.

Cassettes for road bikes also come in a variety of configurations.  For example, Shimano, one of the premier manufacturers of bike gear, lists 6 basic sprocket configurations for their 10-speed cassettes.  As is the case with rings, it is possible to combine sprockets into unique cassette combinations.

I’ll use a basic setup of a 53-39 standard double and a 12-25 cassette to illustrate some basic yet important things about gearing.  All of the main points made here will hold no matter how your bike is geared.

Here are the gears available with a drive train composed of a 53-39 double and a 12-25 cassette in both gear inches and meters of development.  The numbers were calculated using Sheldon Brown’s outstanding online gear calculator which has been used by cyclists for many years .

Gear Inches

12 13 14 15 16 17 19 21 23 25
39 87.8 81 75.2 70.2 65.8 61.9 55.4 50.1 45.8 42.1
53 119.3 110.1 102.2 95.4 89.4 84.2 75.3 68.1 62.2 57.2

Meters of Development

12 13 14 15 16 17 19 21 23 25
39 7.0 6.5 6 5.6 5.3 4.9 4.4 4.0 3.7 3.4
53 9.5 8.8 8.2 7.6 7.1 6.7 6.0 5.4 5.0 4.6

As noted in Gearing Part 1: The Basics, meters of development is a system that is used more commonly in Europe than in the US.  Because it tells you how many meters the bike moves forward every time the pedals go around once it makes it easier to understand how different gear combinations translate into the work you’re doing on the bike.

rear deraileurThere are several important things that can be shown by examining the numbers in these tables.  First, it seems that many people have the mistaken idea that all of the gears on the small (39 tooth) ring are smaller or easier than all of the gears on the big (53 tooth) ring.  Looking at the numbers in the Meters of Development table shows that this isn’t the case and that there is a large amount of overlap in the gears available on the two rings.  53-25 is the easiest gear on the big ring; it moves you forward 4.6 meters every time the pedals go around once.  This gear is bracketed by the 39-19 gear (4.4 meters) and the 39-17 gear (4.9 meters) on the small ring.  Comparing the numbers in the table for the two rings you can see that the gears from 53-16 to 53-25 overlap with the gears from 39-12 to 39-17.  In other words about 60% of the gears available on one ring are, more or less, also available on the other ring.

Does this mean that you’re getting ripped off because so many gears are more or less duplicated on the two rings?  Not at all.  While the big ring gives you a bigger top end and the little ring gives you a smaller bottom end, the main function rings are designed to provide has to do with the size of the steps between one gear and the next when you shift.  Take a look at the amount of change involved between shifting on the big ring into the 53-12 gear from the 53-13 gear.  That shift moves you forward .7 more meters every pedal revolution.  Now look at the same shift on the small ring;  shifting from the 39-13 to the 39-12 gear moves you forward .5 more meters with every pedal revolution.  It’s the same 1-tooth change on the cassette but it has a bigger effect on the big ring than the small ring.

This is true for almost every shift from one gear to the next on the cassette.  The shift on the small ring is smaller and more refined than the same shift on the big ring.  An exception in the table is the shift from the 17 tooth sprocket to the 16 tooth sprocket.  This shift is listed as an increase of .4 meters for both rings.  However, this is a rounding artifact; if we carried the math out to more decimal places it would show that the change on the small ring is smaller than the change on the big ring.

What’s going on here is that gear relationships are nonlinear.  A one-tooth change does not always equal the same amount of effort that has to be expended to increase (or decrease) your speed.  In general, the bigger the gear you’re in, the bigger the change involved in moving up or down 1 tooth on the rear sprocket.   We saw this when looking at the difference in the 1 tooth change from the 13 tooth to the 12 tooth sprocket on the big and small rings.

The same thing is true when you look at what happens when shifting between gears on the rear sprocket while you stay in the same ring.  Take a look at the change involved in shifting from the 53-25 gear which is the easiest gear on the big ring to the next harder gear on the same ring, the 53-23 gear.  That’s a change of two teeth (from 25 to 23) and you have to put out the effort to go .4 meters further with every pedal revolution.  Now look at the change from the 53-13 gear on the big ring to the hardest gear, the 53-12.  That’s a change of only 1 tooth but you have to put out the effort to go .7 meters further for every pedal revolution.  Half as many gear teeth and 75% more effort.

klracing005_crop-300pxAll of this can seem overwhelming at first.  What?  In order to make effective use of your gears you’re supposed to do some math in your head while you ride?  You could do this, but I don’t think it’s a good way to make use of this information.  I think the best way to get comfortable with how to use your gears to best advantage is to ride your bike with two basic ideas in mind.  First, there’s a lot of overlap between rings so you have several ways to solve the gearing problems you encounter.  Second, gearing relationships are nonlinear so that a shift from one gear to the next on the cassette will have a bigger effect if you’re on the big ring than the small ring.

Keep these two things in mind, stay aware of which gear you’re in, and ride your bike.  It won’t take long until you develop an intuitive understanding of how the smaller, more refined changes that you get when you’re in the small ring compare with the larger and less refined changes you get when you’re in the big ring.  Try different approaches on ascents, descents and flats.  When you’re in the overlapping part of the gear ratios, are you more comfortable with the small changes on the small ring or the larger changes on the big ring?  With this basic understanding of how your gears are related, you can begin to develop a more sophisticated and efficient use of your gears on the road.

A New Strategy in the Tour de France?

Sagan wins stage 7 3Peter Sagan is a polarizing rider.  On the one hand his juvenile attempts to draw attention to himself with last year’s ridiculously self-conscious displays on the bike when he won a race and this year’s grabbing of the podium girl’s ass and his proud display of his “My cock + your pussey = good times”  t-shirt are an embarrassment to himself, his team and his sport.  On the other hand, he is an immensely talented and unique cyclist.  Sagan is a top-tier sprinter who often falls just a bit short of winning against sprinters like Mark Cavendish and Andre Greipel (although he has and can beat either of them on occasion).  However, unlike any other top-tier sprinter in recent memory, Sagan can ride with the leading group over Cat 2, 3 and 4 climbs.

Sagan’s unique combination of sprinting and climbing abilities opens up the possibility of a very different approach to winning the points jerseys in the three grand tours.  Traditionally the sprinters competing for the points jerseys have relied on winning sprint stages behind strong lead out teams.  Sagan’s Cannondale team demonstrated an entirely different approach to locking down the points jersey in the 7th stage of this year’s
Tour-de-France-2013-Stage-7-profileTour de France on July 5th.  Stage 7 featured a Cat 2 climb about half way through the stage, a little more than 100 km from the finish.  Cannondale took the lead and drove the peloton with a hard pace over the climb.  Sagan could do it; Cavendish, Greipel and the other sprinters could not.  The sprinters fell about 2.5 minutes behind Sagan and the Cannondale-led peloton.  Their teams fell back to try and bring them back to the peloton after the climb, but Cannondale set a ferocious tempo and when 90 minutes of chasing did nothing to close the 2.5 minute gap, the sprinters gave up.  The result was that Sagan had no strong competition and he won both the intermediate sprint for 20 points and the stage for 35 more points while his competitors for the points jersey won nothing.

Cannondale may have demonstrated a unique approach to winning the points jersey that is perfectly tailored to the talents of their unique sprinter.  Compete in the sprint stages but don’t build your team for them.  Sagan is a talented enough sprinter to finish in the top 5 on most Cannondale 2sprint stages without the benefit of a strong lead-out team.  Build the team to do just what they did today; control the peloton and ride hard tempo on intermediate mountain stages.  Sagan loses a relatively small number of points to his competitors on the sprint stages  but he gains a massive point advantage on stages that feature any kind of categorized climb that is difficult enough to defeat the pure sprinters.

A team built along these lines with Sagan as the team leader is going to be very difficult to beat for the points jersey in any of the grand tours as long as the other sprinters can’t climb and come to these races with custom built lead-out teams.

Cycling Nutrition: The Value of the Glycemic Index for Cyclists

idiots guide

Information about the glycemic index and many other topics can be found in Nutrition for Cyclists: Eating and Drinking Before, During and After the Ride which can be purchased on Amazon.com.  For information about the book and how it relates to what I’ve posted to Tuned In To Cycling, please check out this post.

The diet industry is big business; in the US it is estimated that people spend in the neighborhood of $35 billion dollars a year on diet-related products.  (To make that number more comprehensible, if you make $50,000 a year Americans spend your yearly salary on diet products approximately every 80 seconds.  24, 7, 365.)  A large part of this industry relies on consumer ignorance and gullibility to enable the promotion and sale of one fad diet idea after another.  One of the ideas heavily promoted in the diet industry is the glycemic index.

Is the glycemic index useful? Yes.  Is it all the diet industry makes it out to be?  Not even close.  For our purposes here, is it useful to cyclists?  I think the best answer here is – marginally.

First of all, what is it?  The glycemic index is an indicator of how long it takes food to be converted to glucose in the blood.  Glucose is the fuel that muscles burn when they are working and on-the-bike cycling nutrition and performance is largely about glucose production and consumption.  Having an idea of how long it will take to get the food you eat while you ride converted into blood glucose has the potential to be very useful.

Will the glycemic index tell you how long it takes for the Powerbar or raisins you ate to be converted to blood glucose in seconds, minutes and hours?  No.  The glycemic index compares the time it takes for a particular food to be converted to glucose in the blood to the time it takes for pure glucose ingested orally to appear as glucose in the blood.  Glucose is arbitrarily assigned a glycemic index value of 100 to serve as a basis for comparison.  Particular foods are then given a glycemic index value, typically less than 100, based on how long they take to be converted to blood glucose in comparison to pure glucose.  A high glycemic index indicates a food is rapidly converted to blood glucose; a low glycemic index value means it takes a relatively longer time for that food to be converted to blood glucose.  The glycemic index doesn’t tell you how long it takes to get blood glucose out of food, it gives you a rough idea which foods are converted to blood glucose more quickly than others.

eating on bikeThis sounds like it should be of great use to the cyclist.  You’re burning glucose constantly on the bike, you need more, you’re eating to get more, the glycemic index will tell you what to eat to get that glucose as quickly as possible.

It’s all good, right? Not really. Why not?

The glycemic index of most food varies with so many factors that the rough idea the glycemic index gives you of which foods are converted into blood glucose faster can be very rough indeed.  Here are some examples.

  1. For many foods, glycemic index varies as a function of how the food was prepared (pasta boiled for 10 minutes has a different glycemic index than pasta boiled for 15 minutes), when it is eaten relative to when it was cooked (potatoes often have a higher glycemic index when eaten after cooking than they do if refrigerated  and then reheated and eaten the next day), how ripe the food is when eaten (generally, the glycemic index of fruit increases as the fruit ripens), or which variant of the food type you are eating (different types of raisins have different glycemic indices).
  2. Glycemic index for a particular food varies depending on what is eaten along with that food.  Fat, protein or fiber eaten along with a particular food usually results in a lower overall glycemic index.  For example, you’ll usually get faster blood glucose from raisins eaten alone than the raisins in a cookie.
  3. Different people will have a different glycemic index for the same food because individuals differ in how efficiently they digest carbohydrates.  In addition, the same person may have a different glycemic index for the same food when that food is eaten at different times of the day.
rough categories

The glycemic index values that are used to define the categories in this image are rough guides.

Considering all of these factors, I think the glycemic index can be modestly useful to the cyclist planning what to eat during a ride.  There are many glycemic index charts for different foods that can be found on the internet.  The specific numbers given in these charts are best thought of as rough estimates.  For the cyclist it’s probably most useful to consider glycemic index in terms of three rough categories: High, medium and low glycemic index foods.  High glycemic index foods will probably provide needed glucose throughout the ride.  On long rides of two hours or more, low glycemic index foods can produce needed glucose later in the ride if the food is eaten early in the ride.  As you get closer to the end of the ride, higher glycemic index foods are more likely to be beneficial while you’re still on the bike.

WARNING:  The nutritional needs of a person engaged in 60 to 90 minutes of moderate to intense exercise or a long ride lasting more than 2 hours are very different from the nutritional needs of that same person going about their daily activities.  High glycemic foods can be very useful while you’re on the bike.  A steady diet of high glycemic foods when you’re not engaged in endurance exercise has been shown to be related to various health problems such as obesity (and all of its related problems), diabetes and, at least in animal studies, a shortened life span.  High glycemic foods eaten while you’re riding will generally help you.  A day-in, day-out diet of high glycemic foods when you’re not exercising will generally hurt you.