The Safety in Numbers Effect


Does the chance of a cyclist being involved in a fatal accident increase as the number of cyclists on the road increases? The answer may surprise you. While the raw number of cycling fatalities does increase as the number of cyclists on the road increases, the chance that any one of those cyclists is killed is likely to decrease. This negative correlation between the number of cycling fatalities and the number of cyclists on the road is called the safety in numbers effect.

Safety in mumbers

The graph above illustrates the safety in numbers effect by plotting the number of kilometers cycled per inhabitant along with the number of cycling fatalities for every billion kilometers traveled for various countries. The graph is from a research report published by the OECD (Organisation for Economic Co‑operation and Development) titled “Cycling Health and Safety.” The safety in numbers effect generally holds for pedestrians as well as cyclists.

OECD_LOGO_1The OECD report cautions against thinking that the negative correlation seen in the graph leads to the conclusion that increasing the number of cyclists causes a decrease in the likelihood of cycling fatalities. The report also mentions that there has not been very much research into the possible causes of the safety in numbers effect and goes on to suggest several factors that may be involved.

  • Awareness: The more cyclists there are on the road, the more drivers will be aware of them. The more aware drivers are of cyclists, the less likely they are to hit them.
  • Expectancy: The more cyclists there are on the road, the more drivers expect to see cyclists. The more drivers expect to see cyclists, the more likely they are to actually see them and avoid hitting them.
  • Collective vigilance: The more cyclists there are on the road, the more likely it is that potentially dangerous or threatening situations will be noticed by at least one of them. Those who notice potential threats will communicate this information to the other cyclists who then have a greater chance to avoid the threat.
  • Knowledgeable leaders: The more cyclists there are on the road, the greater the chance that at least one of them will be knowledgeable about route and traffic conditions. The knowledgeable cyclist may lead the others along safer routes.

It may also be the case that safety and the number of kilometers ridden are linked in a causal loop. The safer cycling is, the more people are likely to cycle, and the more people cycle, the more opportunity there is for awareness, expectancy, collective vigilance or knowledgeable leaders to have an effect in reducing fatal accidents.

Hovenring 3

The Hovenring in the Netherlands is the world’s first suspension bridge designed to allow cyclists and pedestrians to safely cross a busy highway intersection.

Another factor that almost certainly plays a role in both increasing the number of kilometers ridden and in reducing fatalities is the presence of a well-developed cycling infrastructure. The Netherlands, Denmark, and Germany, the three countries with the best fatalities to kilometers ridden ratios shown in the graph, also have exceptionally well developed cycling infrastructures.  The Netherlands and Denmark are especially notable in this regard. The United States, on the other hand, has generally lagged behind the rest of the developed world in building well-designed and well-maintained cycling infrastructure.  The better the infrastructure, the more people are likely to use it to cycle safely.


Dutch cyclists

There is an additional factor to consider that is highlighted by the Netherlands which has by far the lowest ratio of fatalities to kilometers traveled of any of the countries shown in the graph. In addition to having an excellent cycling infrastructure, the Netherlands has a long-established cycling culture. As early as 1911 the Netherlands had more bicycles per capita than any other European country. When privately-owned cars became more affordable after Word War II, cycling became less popular as a means of transportation. As the safety in numbers effect would lead you to expect, this was accompanied by an increase in cycling fatalities. During the 1970s widespread demonstrations took place in the Netherlands protesting the number of child cyclists who were killed on the road. The government responded by restricting the use of motorized vehicles in cities and towns, building cycling infrastructure, and embarking on a program of safety education for both cyclists and drivers that placed the Netherlands at the forefront of countries that make serious efforts to incorporate cycling into people’s daily lives. Children in the Netherlands are taught how to cycle safely from a very young age; adults are tested on their ability to share the road with cyclists as part of the process of getting a Dutch driver’s license. According to a press release from the Netherlands Ministry of Transport, Public Works and Water Management, in 2004 the Netherlands was the only European country in which there were more bikes than people, and in 2007 26% of all trips made in the Netherlands were made by bike. As a society the Netherlands has embraced a culture of cycling and this has played an important role in producing both the very large number of kilometers traveled by bike per inhabitant and the very low number of cycling fatalities shown in the graph.

Any or all of these factors – a strong social and cultural history of cycling, the presence of an excellent cycling infrastructure, driver awareness and expectation, cyclist vigilance and leadership – may have a role to play in explaining the safety in numbers effect. The negative correlation between fatalities and the number of kilometers ridden is simple and easy to see, the causal factors that produce this correlation are complex and difficult to tease apart.

(This article has been cross posted to The Info Monkey.)

Cycling and Weight Loss Part 2: Metabolic Homeostasis

scale_caloric_balanceThis is the second 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 part of this series, Riding the Bike to Lose Weight, I pointed out that there is a modifying factor that affects the basic  relationship between caloric intake and weight loss.  The basic relationship is that if you ingest fewer calories than you burn during the course of a day, you will lose weight, if you ingest more than you burn, you will gain weight, and if caloric intake and caloric burn are about equal, your weight will remain stable.  The modifying factor is metabolic homeostasis.

If you’re not familiar with the jargon, “metabolic homeostasis” is incomprehensible and useless gobbledegook.  In the context of thinking about weight loss, “metabolic” refers to the chemical processes that are involved in the breaking down of food in the digestive system and the ways the results of that breakdown process, such as glucose, are used by the body.

A homeostatic system is one that acts to keep itself at an equilibrium point or within an equilibrium range.  A common example is the climate control system in your house or car.  You set the thermostat for a high and a low temperature and the climate control system keeps the temperature of your house or car within this range.  If it gets too hot, the air conditioning is turned on; if it gets too cold, the heat comes on.

The human body is a brilliant homeostatic system in a number of ways.  If the core temperature of the body gets too hot, you sweat to rid yourself of excess heat; if core temperature gets too cold, you shiver to generate more heat.  If blood glucose drops too low, the system reduces glucose uptake at the muscles to maintain glucose supply to the brain.  Cyclists in the heat of battle sometimes wish it didn’t work this way as they go into a bonk and their legs shut down.

caloric homeostasisMetabolic homeostasis refers to the body’s mechanisms for maintaining a balance between caloric intake and caloric burn.  This homeostatic system is more complicated than previously thought and much about it is currently not well understood.    I’ll try to summarize some of the issues that come into play when considering weight loss, exercise and metabolic homeostasis.

One thing that appears to be soundly supported by the available evidence is that the body adapts to a regular, sustained change in the relationship between caloric intake and caloric burn by reducing the number of calories needed to fuel the same amount of activity.  Here’s an example of how this works.  Suppose your caloric intake and burn are balanced; on a typical day your regular activities burned 2000 kilocalories and you ingested about 2000 kilocalories in food during the day.  Your weight would remain stable.  Then you go on a diet and ingest only 1800 kilocalories a day.  At first you would lose weight because the 1800 kilocalories you ingest is less than the 2000 kilocalories you burn each day.  However, if you stayed on this 1800 kilocalorie per day diet for a period of time, your body would adapt to that reduced caloric intake by enabling you to engage in the same activity you were doing every day before you began the diet while only burning 1800 kilocalories.  Once that happens caloric intake and caloric burn are balanced again and you stop losing weight.

Reduction-in-RMR-GraphA slightly more technical way to express this idea is that the basal metabolic rate will change to maintain metabolic homeostasis.  Roughly speaking, basal metabolic rate is the rate at which kilocalories are burned to support normal daily activity.  When the balance between caloric intake and burn is disrupted through dieting or exercise weight is initially lost because fewer kilocalories are ingested than are burned and the basal metabolic rate has not yet adapted to the change.  However, after a period of sustained dieting or exercise the basal metabolic rate adjusts to the reduction in kilocalories ingested (by dieting) or the increase in kilocalories burned (by exercise), a balance between caloric intake and burn is once again achieved, and weight loss stops.

Maintaining metabolic homeostasis through a reduction in basal metabolic rate means that there’s only so far you can go when trying to lose weight by dieting, exercise or both.  If you want to keep losing weight through dieting, you have to continue reducing the number of kilocalories you ingest every day.  If you want to continue losing weight through exercise such as riding the bike, you have to keep increasing the intensity of the exercise.

This is why it was recommended in Riding the Bike to Lose Weight that you continually try to ride harder, longer, faster, stronger every time out on the bike if you want to lose weight.  If the intensity of the exercise remains the same, basal metabolic rate will adapt to it and weight loss will stop.  If the intensity keeps increasing, basal metabolic rate will lag behind and weight loss can continue.

If this were the whole story about metabolic homeostasis it would be simple.  If you enjoy riding the bike, figure out ways to put more time and energy into riding the bike and forget about worrying about calories and weight loss.  You will be doing something you enjoy, you will be thinking about something you enjoy and you will most likely lose weight.  The hope is that when you get to the point where you are putting all the time and energy you can or want to into the bike, your weight will have dropped to a level you like.

Unfortunately, it’s not this simple.  Riding the bike (or any other form of exercise) makes you hungry, makes you want to eat more. In addition, men and women are affected differently by this increase in the desire to eat after exercise.  More on this in the next post in the series.

Aerodynamics Part 3: Shaving Your Legs

The day after I posted Aerodynamics Part 2 about some small and free or relatively cheap things you can do to reduce air resistance and drag I came across this video.

We’ve all heard that shaving your legs makes you faster.  Does it?  Check this out.

Over the 40 km length of their trial runs, differences in how hard the rider is going over relatively short periods of time may well be sufficient to account for the differences they observed and they don’t address how, or even whether, they controlled for differences in effort over the trials with and without leg hair. From what you can see in the video it seems pretty clear they didn’t use physiological measures to control for effort.  Looking at the set-up in the video I would guess average speed was used as a control but without more information no hard conclusions can be drawn.  However, the magnitude of the differences they observed certainly indicate shaving your legs is something worth exploring further if you want to reduce air resistance and drag.

Aerodynamics Part 2: Small Things That Reduce Air Resistance and Drag

PIC372688193Tony Martin won the UCI World Time Trial Championship in 2011, 2012 and 2013, and is the odds on favorite to win it again this year. He is an incredible bike rider and by all accounts an incredibly nice guy; he once caught and passed David Millar in a time trial and apologized to Millar as he went by. The picture is of Martin time trialing in full aerodynamic mode at the 2013 Criterium du Dauphine which is an eight-day race that Martin won on the basis of the insurmountable lead he built by winning the time trial.

If you want to minimize air resistance and drag as much as possible, you ride like Martin rides in a time trial. Unfortunately, this is beyond the reach of many riders for a number of reasons. First, it’s expensive. Between his bike frame, wheel set, skin suit, helmet, etc., Martin is moving well over $10K worth of gear in the photo. Next, an optimized wind tunnelaerodynamic position is difficult to accomplish. Differences in body mass and shape mean that the position that optimizes both aerodynamics and power output is different for every rider. Finding that position takes hours of iterative testing and refinement in a wind tunnel. In addition, a full aerodynamic tuck is difficult to maintain and usually takes many hours of practice to be able to hold for any length of time. Simply strapping a set of aerobars unto your bike isn’t going to do it. Finally, riding in an optimal aerodynamic position is difficult. The position is uncomfortable and the bike is more difficult to control when you’re stretched out on aerobars.

Although going full aero involves a significant investment of time, effort and money, there are a number of simple things you can do that will reduce air resistance and drag that are relatively easy and are either free or cost the price of a new jersey. Taken individually, none of these things will result in a huge reduction in air resistance but small things add up and they can make a noticeable difference over a long ride.

Get Low

The biggest single thing you can do to reduce air resistance without spending any money is to reduce the surface area on the front of your body that is exposed to the wind as you ride forward. It’s easy to do and you don’t need aerobars to do it. Bend at the waist and lean forward. The lower you get the better off you’ll be but almost any degree of forward lean will reduce the area of your torso that is exposed to the wind.

Tour of the Battenkill 2012This is easiest to do if you have road handlebars on your bike. Moving your hands from a position on the flat upper bar on either side of the stem to the brake hoods will bring you down a little bit. Keeping your hands on the hoods and bending your elbows will bring you down more. You can get fairly low with your hands on the brake hoods by bending your elbows to the point where you’re resting your forearms on the handlebars like the rider in the picture. You can usually get even lower by riding with your hands on the drops.

Elbows and Knees

PIC298104874While the exact elbow position for optimal aerodynamic riding depends on the rider’s body size and shape, it’s generally the case that tucking the elbows in is better than bending them out. Many riders, however, tend to bend their elbows out in a variety of circumstances. When you bend at the waist and lean forward to get low, make sure to pull your elbows in rather than bend them out. People also tend to bend their elbows out when they are leaning into a climb, working hard to maintain a strong tempo, gripping the bars tightly, or are just tired. Pay attention to where your elbows are and if they are flaring wide, bring them in.

Knee position is an aerodynamic factor that people sometimes miss because it’s usually not obvious in pictures of riders who are time trialing. Take a look at where your knees are relative to your body while you’re pedaling. If your knees are spread open so that they form a V-shape with your body, your legs are funneling air into your body and increasing the air resistance and drag you have to overcome. Ride with your knees pulled in toward the top tube on your bike. Obviously, you don’t want your knees banging into the top tube but closer to the tube is better than further away. When you do this, don’t accomplish the “knock-kneed” position by flaring your ankles out.

Your Jersey

Wear a tight jersey. If your jersey is loose or baggy, it is catching the wind and increasing air resistance by acting like a sail that is pulling you in the opposite direction. Don’t worry about what you look like. How you look in your exercise clothes may be a big deal for gym bunnies but for riders the big deal is how smart and how well you ride. If you’re overweight, you’re overweight; there are things you can do to change that but wearing a loose jersey isn’t one of them. Don’t worry about it. Ride smart.

???????????????Keep your jersey zipped up. Partially unzipping a jersey allows air to circulate around the upper body to the back where it is trapped by the jersey. It’s like strapping a sail facing the wrong direction on your bike. You would think this would be a no-brainer but you see riders all the time from beginners to pros who have expensive aero gear on their bike and who are trying to go fast with their jersey partially unzipped.


watts and wind resistence_ key pointsThe graph discussed in Aerodynamics Part 1 illustrates that air resistance is negligible when you are going slow but it quickly ramps up with velocity until it becomes the overwhelming force you have to overcome to move your bike forward. While all of the tips and techniques offered in this post have a small effect in reducing air resistance they are all easy to do. They are also either cost-free or cost, at most, the price of a new jersey. Small benefits add up and their combination can make the difference between a ride that is exhausting and a ride that is exhilarating.

Thank You and a Request

Thanks very much to all of you who bought a copy of Nutrition for Cyclists on Although it doesn’t look like I’m going to start out as the Stephen King of the exercise and nutrition publishing world, the book is doing well for a writer trying out self-publishing for the first time.  I expect I owe almost all of that success to the readers of this blog because Tuned In To Cycling is the only place the book has been announced. So, thanks again to everyone who has purchased the book.  I sincerely hope you found useful information that has helped with your rides.

Now comes the request. It is very difficult for first-time authors to get noticed among the hundreds of thousands of self-published ebooks on Amazon. One of the most effective ways, maybe the most effective way, to draw readers attention to a book is a set of positive reviews.  If you’re Stephen King, the quality and number of reviews doesn’t matter very much but for an unknown author positive reviews are often the difference between success and sinking without a trace.

As I’m writing this post, Nutrition for Cyclists has only garnered one review and, unfortunately, it appears to have been written by a person who spent very little time with the book and either didn’t read or didn’t understand what they found there. A lot of work went into Nutrition for Cyclists and I’m hoping it doesn’t get lost in the clutter because of a solitary review written by a reader who missed the point.  If you bought Nutrition for Cyclists, and if you found it to be useful and valuable as a resource for making good decisions about what to eat and drink before, during and after a ride, you would be doing me a great favor if you would write a review on Amazon with some info about why you found the book to be worthwhile.  Thanks.

“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 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.