Nutrition for Cyclists

N4C_AmazonFirst of all, an enormous vote of appreciation and thanks to all of the readers of Tuned In To Cycling over the years who have provided helpful comments, support and motivation for me to write a book about cycling nutrition. It’s finally happened. Nutrition for Cyclists: Eating and Drinking Before, During and After the Ride is now available for purchase at

The book grew out of the nutrition posts here on Tuned In To Cycling and, like those posts, combines suggestions and recommendations for what to eat and drink before, during and after a ride with information about how the body responds to endurance athletics.  To help you decide whether or not you’d like to purchase the book, I’m posting the book’s Introduction here which will give you a good idea about what’s in the book and how it relates to the posts that have appeared on Tuned In To Cycling.

If you decide to buy the book and you think it is useful for other cyclists and worth a 4 or 5 star review, I would greatly appreciate it if you would leave a review on Amazon.  Positive reviews are a huge factor in helping a self-published book find an audience among the millions of ebooks published on Amazon.

Here’s the Introduction to  Nutrition for Cyclists: Eating and Drinking Before, During and After the Ride.

Chapter 1. Introduction

Here’s a quote from former U.S. President John F. Kennedy that many cyclists know well.

Nothing compares to the simple pleasure of a bike ride.

Anyone who has spent any time on a bike knows that it’s true . . . . until it isn’t.
Here’s another saying cyclists know well.

Eat before you’re hungry, drink before you’re thirsty.

Short of a catastrophic accident, nothing can turn a pleasant, joyful or exhilarating bike ride into a nightmare faster than failing to provide your body with the nutritional support it needs to carry out the ride. Nutrition for Cyclists is designed to give riders of all experience levels useful information about meeting the nutritional demands imposed on the body by endurance athletics. Good nutrition can help you get the most out of your ride no matter what kind of ride you like to do.

Finally, one more saying that everybody knows.

Give a man a fish and you feed him for a day; teach a man to fish and you feed him for a lifetime.

Nutrition for Cyclists contains recommendations about what to eat and drink before, during and after a ride. That’s the “give-a-man-a-fish” part. However, no book can give you a recipe for what to do in every possible nutrition-related situation that might arise when you’re riding the bike. Even if a book like this were possible, would you want to memorize it so you would be prepared for anything?

Nutrition for Cyclists also contains a good deal of information about how your body works when you’re engaged in athletic activity. That’s the “teach-a-man-to-fish” part. The more you know about how your body processes food and drink, and about what can happen when there is not enough food or drink for your body to process, the better prepared you’ll be to understand what’s happening to you on the bike.

The short-term goal of Nutrition for Cyclists is to get you started with recommendations about eating and drinking before, during and after a ride. The long-term goal is to give you information about nutrition and endurance athletics so that you will be able to make informed decisions about what’s happening to you on the bike and what you can do to make it better.

The information presented in Nutrition for Cyclists is based on research findings reported in peer-reviewed journals in the fields of human physiology, and nutrition and sport science. The internet is awash with assertions, recommendations, and unsubstantiated claims about exercise nutrition. Some of this advice is supported by sound research. Much of it, including a number of widely cited and uncritically accepted ideas, is not. As will be discussed in the next chapter, focusing on information that is well supported by sound research does not mean that everything in Nutrition for Cyclists is “right” or “true”. It means that this information is the best we have given the current state of scientific research on exercise nutrition.

Nutrition for Cyclists grew out of a series of posts on Tuned In To Cycling, a blog I started in the spring of 2008. While Tuned In To Cycling has posts on many cycling-related topics, the posts on nutrition have proven to be the most popular with cyclists from all over the world. Some of the content of this book has been copied verbatim from the posts on Tuned In To Cycling, some of it is a revised or rewritten version of what’s on the blog, and some of it is new. Everything in Nutrition for Cyclists was checked against the current research literature. If a section of the book has been lifted verbatim from the blog, it means that research published between the time the original post was written and the book was published did not demand changes in the information that had appeared in the blog.

For both new readers and followers of Tuned In To Cycling Nutrition for Cyclists provides the convenience of a self-contained source for nutritional information that is organized into sections devoted to what to eat and drink before, during and after a ride. Also, publication as an ebook means Nutrition for Cyclists is conveniently available anywhere you have a Kindle or any other device with a Kindle app.

Carbohydrate Loading

This post is adapted from Nutrition for Cyclists: Eating and Drinking Before, During, and After the Ride, a forthcoming ebook which I will be publishing for Kindle on

Nutrition for Cyclists: Eating and Drinking Before, During and After the Ride can now be purchased on  For information about the book and how it relates to what I’ve posted to Tuned In To Cycling, please check out this post.

eating spaghettiWell-organized and popular century rides often offer an all-you-can-eat pasta dinner the night before the ride.  If you go to the dinner, you’re likely to see people putting away enormous plates of pasta and if you ask them why they’re eating so much spaghetti they’ll tell you that they’re carbo loading for the next day’s ride.  What is carbohydrate loading and is eating a lot of spaghetti the night before a big ride the right way to go about it?

The basic idea behind carbohydrate loading is that glycogen stores in the muscles and liver can be increased over the norm by following specific exercise and dietary regimens in the days before a ride.  The increased glycogen stores should then translate into a longer time before fatigue sets in due to glycogen depletion during the ride. There are three recognized carbohydrate loading methods and I will suggest an alternative approach.

The original and most severe method follows a week-long regimen. On the 7th day before the ride, you exercise to exhaustion.  This exercise bout should last a minimum of 90 minutes.  The next 3 days are a carbohydrate depletion phase during which you train lightly while keeping carbohydrate intake at only 10% of your daily caloric intake.  The final 3 days before the big ride are a carbohydrate loading phase.  You continue to train lightly while jacking carbohydrate intake up to 70% of your daily caloric intake.  It’s important not to increase your total caloric intake from the norm over the 6 days of carbohydrate depletion and loading.  During the 3 day depletion phase you replace calories normally consumed in carbohydrates with calories consumed in fats and proteins. During the 3 day loading phase your replace fats and proteins with carbohydrates.

drink-b4-thirsty-mod-4-customThink about this for a minute.  The depletion phase is an extended period of controlled hypoglycemia, essentially a 3 day bonk.  During that time you can be expected to experience all of the negative effects of bonking including weakness and lethargy, anxiety, depression, hostility, feelings of hopelessness and failure, low levels of emotional control, reduced awareness of your surroundings and confused thinking.  In addition, the immune system will be depressed and you will be more susceptible to contracting an illness that may still be present when the ride comes several days later.

A 3 day bonk is hard.  Very hard.  The second method eliminates the bonk by eliminating the depletion phase. On the 7th day before the ride you have a long exercise session but you don’t exercise to exhaustion.  For the next 6 days you engage in progressively lighter exercise sessions each day.  Some people recommend tapering the level of exercise down to a day of rest on the 6th day.  For the first half of this 6 day period you ingest carbohydrates at a normal 55% – 60% of your daily caloric intake.  For the final 3 days you ramp carbohydrate intake up to 70% of your daily caloric intake, again by replacing fats and protein with carbs.

The third method is the easiest of the three. During the week before the big ride you exercise lightly and eat normally.  On the day before the ride you do a very short, 3 minute high intensity workout.  The workout should be made up of a 2.5 minute session at 130% VO2 max which is roughly equivalent to the fastest pace you can maintain over approximately 4 minutes of all-out running or cycling.  Follow this 2.5 minute effort with a 30 second flat-out sprint.  If done properly, this 3 minute workout is going to hurt.  During the following 24 hours ingest 12 grams of carbohydrates per kilogram of lean muscle mass.  Muscle mass can vary greatly depending on age, gender and degree of muscular development.  Based on a very rough average of 35% muscle mass for men and 27% muscle mass for women the carbohydrate intake over the 24 hour period would total approximately 305 grams for a 160 lb. male and 191 grams for a 130 lb. female.

If followed correctly, all three of these methods should produce a markedly enhanced level of glycogen storage on the day of the big ride.  Neither anecdotal reports (which are basically worthless) nor research studies have reached a clear consensus on how much better or worse one method is relative to the others.  The bottom line is that all three methods are effective if followed properly.

baby spaghetti dumpNow, I’ll suggest a fourth method that is usually not discussed in the literature.  Forget about it. Don’t bother with any of this stuff.

Wait . . . what? Consider the kind of riding you do.

If your ride takes less than 90 minutes, carbohydrate loading is a non-issue because proper eating before, during and after your previous ride should have adequately prepared you for the next ride.

If your ride takes longer than 2.5 or 3 hours, you’re going to have to eat during the ride anyway because even perfectly executed carbohydrate loading isn’t going to provide you with sufficient glycogen stores to last for this length of time.  All carbohydrate loading is doing is delaying the time before you have to start eating.

Wiggins eating_croppedIf your ride takes between 1.5 and and 2, maybe 2.5 hours, carbohydrate loading might allow you to get through the ride without ingesting any carbohydrates. But why would you want to do this? If you enjoy rides that last more than 90 minutes you would be much better served by becoming proficient at eating on the bike to fully supply your nutritional needs during the ride. You get better at what you practice and if you find a way to avoid eating on the bike, you’re not going to get better at eating on the bike.

The fundamental goal of cycling nutrition is to provide full nutritional support for your ride.  A competitive race, a long organized or training ride, and a Sunday afternoon toodle around the neighborhood all make different demands on your body but whatever the ride, you will do it better and enjoy it more if you provide the nutritional support the ride needs.  The simplest and most effective way to do this is to develop the habit of ingesting small amounts of carbohydrate regularly during the ride.  The best way to develop the habit is to practice doing it.

If properly carried out, carbohydrate loading can fully support rides lasting 1.5 to 2 hours, maybe a bit more, if you don’t ingest any other carbohydrates during the ride. It’s not much use for rides lasting less than 90 minutes or more than 2, maybe 2.5 hours.  Eating properly during the ride can fully support any kind of ride you want to do. The choice is yours.

“Superstarch” and the Endurance Cyclist

cyclist with appleA comment from a reader led me to take a look at a slick website hawking a product called Generation Ucan that is marketed as delivering several “scientifically validated” benefits to people engaged in athletic activity.  From the serious beginner to the most highly-paid professional, athletes are notorious for their susceptibility to being taken in by products that claim to improve performance.  The Generation Ucan website has several of the characteristics that are often associated with nutrition scams that make fabulous claims while trying to sell untested or poorly tested junk to gullible people so I decided to take a closer look.

What is it?

waxy-maize-starch_2 (2)Generation Ucan is hydrothermally modified waxy maize starch.  The starch is processed under conditions of higher than normal moisture (hydro) and heat (thermal) which changes the chemical properties of the starch molecules.   One effect of this treatment that is of interest to endurance athletes is that the carbohydrates in hydrothermally modified starch have a low glycemic index.  Generation Ucan calls HMS “superstarch” which is such an obvious and ridiculous marketing ploy that I’ll avoid it.  What they’re selling is hydrothermally modified starch or HMS.

sciencequizlogoThe Generation Ucan website is filled with phrases like “lab tested”, “scientifically proven”, “our science”, and “proof/validation”.  First of all, reputable research scientists virtually never talk about “proof” like this.  We talk about the extent to which the experimental evidence supports or fails to support the conclusion.  The marketing-hype alarm goes off big-time when “science” and “proof” occur together in product marketing.

What scientific evidence does Generation Ucan actually provide?

The website has links to a couple of white papers that talk about research that supports their claims for their HMS.  White papers are documents produced by a company with the aim of selling a product.  Generation Ucan’s white papers reference “internal studies” as evidence that HMS is wonderful.  As evidence to support their claims about HMS, these internal studies are worthless.  Not enough information is given to determine whether the research was carried out rigorously and properly.  The internal studies may provide good evidence or they may not.  There’s no way to know one way or the other.  However, if the science was good, you would expect it would have been published in a top-rated peer-reviewed journal.  There is no indication on the website that these internal studies were submitted to a reputable journal or survived a rigorous peer-review process.  Basically, the white papers contain a lot of unsubstantiated claims tricked up to look like science.

The Generation Ucan website also provides a prominent link to an article in Men’s Health Magazine that promotes the product.  Men’s Health Magazine?  Lol, really?

Buried in the science section of the website they have a link to downloads.  Follow that link and what you mainly find are sales kits.  Sales kits in the scientific evidence section?  There are seven of these sales kits.  There are also two links to their own white papers, and one link to an article in the journal Nutrition about HMS.  Nutrition is a peer-reviewed journal and this article is the only reliable scientific evidence that I found on the Generation Ucan website.

cyclist in labThe article in Nutrition is the real deal although it should be noted that Generation Ucan funded the research project that is reported in the article.  What does it report?  Nine male cyclists engaged in a 150 minute cycling session at 70% VO2(max) – that’s fairly intense – followed by a 100% VO2 (max) time-trial to exhaustion.  Before the exercise session and immediately afterwards the cyclists were given either HMS or maltodextrin.  Maltodextrin is a sweetener often used in candy, soda and many other products.  HMS and maltodextrin are both sources of carbohydrates.

Note that they didn’t call their HMS “superstarch” when they submitted the research for peer review.   If they had, they would have been laughed out of the room.

Ucan insulin dataThe study found that the HMS group had a lower initial insulin spike than the maltodextrin group.  They also found that the HMS group showed a higher level of fat breakdown during the recovery period.  There were no reliable performance differences between the HMS and maltodextrin groups during either the 150 minute exercise period or the time-trial to exhaustion that followed.  There was also no reliable difference between the two groups in the level of fat breakdown during exercise.

The authors of the article note that the increase in fat breakdown during the recovery period after exercise was probably due to the HMS that was given after the exercise period.  Their research doesn’t test this hypothesis but it is plausible given what is known about the effects of HMS and the relationship between insulin and fat burning.   Insulin is prominently involved in the regulation of fat oxidation.  Lower levels of insulin correspond to higher rates of fat burning and vice versa. The study in Nutrition provides good evidence that HMS reduces insulin and reduced insulin typically produces higher levels of fat oxidation.

Keep in mind that this study in Nutrition is the only reliable scientific evidence that is given on a website that heavily stresses the scientific basis for their claims about how wonderful their product is for athletes.  While this isn’t much, it’s more than you often get on websites that sell wonder foods for sports nutrition.  There is some real science here.  The study provided good evidence that HMS reduces insulin levels.  This information could be of interest to people who are looking to lose weight because reduced insulin levels correspond to higher levels of fat burning after exercise.  It’s worth repeating that the study showed no differences in performance between those who exercised after ingesting HMS and those who ingested maltodextrin.

What claims does Generation Ucan make about their product based on this scientific evidence?

snake-oil-salesman-bigThey claim that their HMS produces “optimized performance”, “sustained energy”, “enhanced fat burn”, “speedier recovery” and “no gastric distress”.  The claim about enhanced fat burn is supported by the evidence in the Nutrition article.  The scientific evidence they reference on the website has nothing at all to do with sustained energy, speedier recovery or levels of gastric distress.  As far as “lab tested” or “scientifically proven” these claims are completely unsupported by the scientific evidence the Generation Ucan people provide.  They give you no good reason to believe HMS provides any of these benefits.

The claim about optimized performance is outrageous.  I expect many people looking at the Generation Ucan website uncritically will understand this as meaning that performance is better if you use their HMS than if you use other carb sources during exercise.  The article in Nutrition that is offered as the only reliable scientific evidence given on the website flatly contradicts this interpretation.   There was no difference in performance (or fat burning during exercise) between the HMS group and the maltodextrin group in the study.

lawyerI have no doubt that company lawyers can parse the “optimized performance” statement to mean that Generation Ucan’s HMS produces optimized performance in the sense that it matches the “optimal” performance levels expected after ingesting carbs from candy, soda or energy drinks.  When you have to rely on lawyers to weasel out of charges of false advertising, there’s clearly something wrong.  Anyone with a lick of common sense can see that, at best, the “optimized performance” claim is highly misleading.  At worst, it is pure bullshit designed to sucker you into buying their product.

What’s the take-home message about Generation Ucan’s HMS?  The product is likely to lower insulin levels.  This can be useful to people who want to burn fat.  If this is one of your goals, taking Generation Ucan’s HMS immediately after exercise may be useful.  If you are diabetic, don’t go near this product without consulting your doctor.  As far as supporting performance during exercise, their HMS is unlikely to be any better, or any worse, than many other sources of carbohydrates you can eat or drink on the bike.

What’s the take home message about the Generation Ucan company based on how they present themselves on their website?  Either the people who are trying to convince you to buy their HMS have the scientific training to tell the difference between good science and junk science or they don’t.  If they do, then the science heavy promotion on the Generation Ucan website is purposefully designed to mislead you into buying their product based on unsubstantiated claims that they figure you are either too ignorant or too stupid to recognize for what they are.  If they don’t, what are they doing marketing their product with a website that goes heavy on the science?  In either case, why should you believe anything they have to say?

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  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.

Cycling Nutrition: The Basics – Glucose, Glycogen and Carbohydrates

More information about the basics of fueling the muscles and hydration can be found in Nutrition for Cyclists: Eating and Drinking Before, During and After the Ride which can be purchased on  For information about the book and how it relates to what I’ve posted to Tuned In To Cycling, please check out this post.

While proper nutrition is one of the most important factors affecting long-distance cycling on a day-in, day-out basis, there is so much misinformation out there that knowing what to eat and when to eat it can be Burning glucosedifficult.  Part of the reason for this is that it’s early days yet for nutrition science; much remains to be learned and nutritional theories are often revised as new information becomes available.  Another reason is that the subject of sports nutrition is confused in the minds of many with the subject of dieting.  Unfortunately, dieting in the US is a multimillion dollar industry that is fat with fads and outright foolishness.  Finally, many cyclists seem to have a deep emotional commitment to their cycling-related eating habits and resist change.  In these Cycling Nutrition posts I’ll try to present nutritional information that is based on research found in peer-reviewed scientific journals on nutrition and cycling and endurance sports in general.  In this post we look at the basics of how muscles are fueled that underlie every discussion of nutrition for cyclists. In other posts we examine eating during a ride, eating after the ride, and bonking.

Muscles burn glucose for energy.  The longer you ride or the faster you ride, the more glucose your muscles need for fuel.  When you get on the bike and start pedaling, the demand for glucose for your leg muscles increases and a signal goes out to the body to start supplying the glucose you need.

Glycogen and glucose

Where does the glucose come from?  The body doesn’t store raw glucose.  Instead, it makes glucose from other substances.  Glucose can be derived from breaking down stored fat and protein.  Subcutaneous fat (the excess fat stored under the skin) is an especially good energy source because fat contains roughly twice the number of calories as either protein or carbohydrate.  This means you get more fuel in the form of blood glucose from breaking down a gram of fat than from a gram of either protein or carbohydrate.  Indeed, breaking down stored fat to increase the level of blood glucose is the reason why exercise leads to weight loss.  The problem with relying on breaking down fat to produce glucose is that the process is relatively slow and energy intensive.  Metabolizing (breaking down) fat can be a useful long term source of energy but it is too slow and inefficient to support immediate and short term demands for glucose to fuel ongoing athletic activity.

In order to have fast access to glucose when needed, excess glucose in the blood is stored in a form known as glycogen.  Glycogen can be quickly broken down to supply glucose as needed.  The main storage locations for glycogen in the body are the muscles and the liver.  Liver glycogen is volatile in the sense that it doesn’t last long.  This is because liver glycogen serves as an energy source for the entire body.  When liver glycogen is metabolized the glucose that is produced enters the blood stream and can be used any place in the body where it’s needed.  If you go to bed with with liver glycogen stored at maximum capacity, a large proportion of it will be gone when when you wake up because it was used to fuel the body’s needs while you slept.

Muscle glycogen is more stable in the sense that once stored it remains in place much longer.  This is because muscle glycogen does not enter the bloodstream.  The glycogen stored in an individual muscle can only provide glucose for that muscle.

So, you’re pedaling along burning glucose derived from glycogen stored in your liver and your cycling muscles and everything’s just peachy.  Until you run out of stored glycogen.  The body can store enough glycogen to support approximately 90 minutes of moderate intensity exercise.  What happens when that glycogen is used up?  Where do your muscles get the glucose they need to keep working?  Some of it can come from fat that has been slowly breaking down while you’ve been riding but that won’t be enough to supply your needs.  Once you’ve exhausted your glycogen stores, most of the glucose you need is going to come from what you’ve been eating and drinking during the ride.  This is where carbohydrates enter the picture.

Basic nutrition for any endurance sport such as cycling is primarily about carbohydrates for the simple reason that carbs can be broken down to supply glucose much more quickly and efficiently than either fats or proteans.  While you’re on the bike you need a steady supply of carbs to both fuel ongoing activity and stretch the time before your stored glycogen is completely exhausted.  When you’re off the bike you need carbs to replace the glycogen you burned during the ride you just finished.  For anyone engaged in an athletic activity that lasts for 90 minutes or more, carbs are what basic nutrition is all about.