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The Myth of the “Insulin or Sugar Crash” during exercise…

28 Mar

I have been discussing this topic recently with a teammate (thanks for the mind fodder Jason!). There is an idea out there that people need to consume “slow burning” sugar (or carbohydrate) during exercise or else your body will experience a “sugar crash” and you will die… (ok-that last part is not really what people think)…but if nothing else, your race will be sabotaged by “quick burning”, “insulin spiking” types of sugar.

I want to tell you all that this IS NOT TRUE and, in fact, THE OPPOSITE IS TRUE about what you should eat during exercise!!!

First, I want to define the difference between a “simple” and “fast” vs. “complex” and “slow” sugar. “Simple” and “fast” do not mean the same thing. Simple means that the sugar is a monosaccharide or disaccharide- ok what the hell does that mean?  It means that the sugar is made of one or two units of something.  For instance, fructose is just one block of fructose and glucose is just one block of glucose.  Sucrose is a disaccharide (or made up of 2 units of something). Sucrose is made up of a block of glucose and a block of fructose stuck together.  According to the National Institute of health, a “complex” sugar is one that is made up of at least three “blocks” of something. (

Maltodextrin is by definition a “complex” carbohydrate because it is a polymer and made up of many “blocks” of glucose pieces stuck together (In turn, starch is a bunch of maltodextrin pieces stuck together and is also, obviously, complex)  Here is why I have to define these terms though- Maltodextrin is a COMPLEX carbohydrate that acts like a “FAST BURNING” sugar…ok that is just crazy but it is true…

So I obviously have to prove it.  How quickly a sugar “burns” or is digested, absorbed and has an effect on your bloodsugar is described through the glycemic index (the higher the score, the more quickly the sugar is digested, absorbed and affects blood sugar).  This index is subject to a lot of influencing factors, including whether or not you are consuming fat, protein and fiber with your carbohydrates- but putting that aside and just looking at the sugars- we get an idea of how quickly these sugars act. Here is a very rough (but hopefully ball park accurate list- it is tough to get this information because the glycemic index is almost always represented in real foods for practical reasons):

Glucose 85-111
Maltodextrin 105
Honey 32-87
Sucrose 58-65
Lactose 46
Fructose 12-25

So you see now that maltrodextrin is a “complex” sugar that “burns fast” and fructose is a “simple” sugar that burns “slow” (However there are other problems with fructose in the way it is processed in the body that go beyond the scope of this article that don’t really make it glycemic index friendly in large quantities- but this is a separate issue).

So getting back to what to consume during exercise.

During rest, you can experience a “spike” in blood sugar and a subsequent rise in insulin that causes a “crash” or mild hypoglycemia (low blood sugar) a bit later.  This is true, DURING REST. See graph below:


BUT…this graph is NOT TRUE when you are exercising or racing!!!!  This is the myth that a lot of people carry around that is insane in the membrane.  We have evolved (if you believe in that type of thing) to fight tigers and ligers and dinosaurs (right?) and that is why we have historically exercised.  To do this our body produces an adrenaline response when we exercise, similar to a “fight or flight” response.  When we exercise today our body thinks we need to fight something or hunt something so it is smart and increases our heart rate for the battle, shuts down our digestive system and shunts blood to muscles, adjusts our pupils so we can see better – and lots of other stuff too- but it also decreases insulin production out of our pancreases so we have consistently high bloodsugar levels for the battle with the dinosaur.   And this is why you will not have an “insulin crash” during exercise!!!  (this is also why you need to worry about sparing your glycogen stores during exercise- because that glycogen is getting broken down to keep blood sugar up but that is a separate discussion for another article as well)

So why does this matter- it matters because sugars that are higher on the glycemic index typically absorb quicker than those lower on the index.  Gastric emptying times (how fast the sugar gets out of your stomach) are shorter.  And this matters A LOT during moderate to hard exercise.  Remember how I said when you are fighting the dinosaur that your body shunts blood from your digestive system to your muscles for the battle??  That is also what happens when you exercise.  So gastric emptying is a BIG DEAL!! It is an even bigger deal if you are racing or exercising hard-  I am sure everyone who reads this has experienced that truth in all its vomiting glory at one point in their lives during a hard interval or race.

Therefore, high glycemic sugar is where it is at for exercising and immediately after exercising (for quick absorption recovery purposes- beyond the scope of this discussion).  Hammer Nutrition is  super researchy with their products and they have found that maltodextrin has the fastest gastric emptying time. Hammer gels use maltodextrin almost exclusively (a little fruit juice too) as their carbohydrate source and that is why I use them – most nutrition companies do not use maltodextrin at this time because it is a more expensive ingredient to use than alternative sugar sources.

Conventional wisdom is currently that one should eat low glycemic index foods during rest and prior to exercise and high glycemic (preferably maltodextrin for during) during and immediately following exercise.

Now if someone tells you to eat whole wheat bread or some crazy sh#t like that during exercise to avoid the “sugar crash” you can call BS on them and know exactly why they are whack….


5 Oct

Very interesting- The NY times is reporting on some recent research on the mental component to athlete limitations.

In short, elite cyclists used a computrainer to establish power and time for an all-out 4,000 meter time trial. The cyclists were then split up and one group was told that they would be racing against a computer generated competitor putting out 2% more power- this group could not match the effort of their virtual competitor. However, the other group was deceived and told that the computer generated cyclist was them at thier established max effort (in fact, the computer image was outputting 2% more power and 1% more speed than the cyclist had ever done before). In this situation the cyclist was able to match the computer image and go faster and harder than they ever had before. Very interesting stuff and a huge clue that our limits are heavily influenced by mental factors.

Interestingly, money did not motivated the cyclists to go faster or harder in similar experiments. Expectations of ourselves seem to motivate us more than anything else previously considered a motivator….

Do Altitude Tents Really Work?? Setting the Stage to Answer a Tough Question….

25 Jul

The Theory of Altitude Tents:

The theory of the altitude tent is relatively simple.  Sleeping in a hypoxic ( which means less oxygen than the “normal” 21% oxygen content of “air”) tent attempts to simulate some of the beneficial physiological responses that are well-established for athletes living in real-world high altitude environments.  Although there are several mitochondrial and metabolic changes that contribute to the benefits of high altitude living, the primary adaptation that people are after is:

Increased Erythropoiesis (what the heck is that?…it really just means making more red blood cells)

             When there are lower oxygen levels circulating in your blood (as is the case at altitude because the air is “thinner” and there is relatively less of every atmospheric gas, including oxygen, as compared to sea level) your kidney actually detects this low oxygen level and releases a hormone called erythropoietin, or EPO.  EPO then circulates in your body and tells your bone marrow to start producing more red blood cells.  More red blood cells result in increased oxygen carrying capacity of blood, hence increasing the oxygen in your blood to maintain the balance that keeps the kidney happy.  This increase of oxygen in the blood also boosts performance in endurance-related sports because more oxygen to muscle means the muscle can do more work, experience less fatigue and have less lactic acid produced for a given amount of exercise.  More oxygen carrying also implies a higher VO2max for those who like buzz words.  This EPO hormone is the same hormone that has made many professional cyclists infamous- the only difference is the injectable one is made in a lab, but it is the same hormone.  Interestingly, the primary legitimate medical indication for EPO use is kidney failure for the reasons described above.  The question remains whether or not a simulated hypoxic tent environment actually replicates this same biological response seen at altitude?

Diagram of Erythropoiesis (making more red blood cells)


Hypoxic Vs. Hypobaric:

A very important distinction to make when assessing altitude tents is the difference between hypoxic and hypobaric.  In the real world, high altitude is a hypobaric state.  Hypobaric means that all atmospheric gases are “thinner” at higher altitudes and therefore less abundant.  While less oxygen is available at high altitude, 21% of the “air” is still oxygen. The way an altitude tent works is different.  An altitude tent works under a hypoxic environment instead of a hypobaric environment.  The air has the same “thickness” as the altitude at which the tent is set up.  The hypoxic tent environment replaces part of the percentage of the “air” that is oxygen with nitrogen.  Hypoxic (and normobaric) means you are breathing less than 21% oxygen but the air is still “thick” like at sea level.  Unlike real altitude, there are lots of gas molecules around in a tent, just a little more nitrogen and a little less oxygen than the normal breakdown of air. The hypoxic vs. hypobaric distinction becomes very important when we look at the potential limitations of altitude tents and reasons why some physiological responses may be different. 

Of note, “normal” air is about 78% nitrogen anyways so nitrogen is very abundant and it won’t hurt you to breathe a little more of it for anyone who may think breathing nitrogen sounds scary. 

Responders Vs. Non-Responders

The term “responder” is a commonly used term in the altitude tent literature. It simply means that some people experience benefits from the tent in similar ways to altitude, while others do not. No one quite knows why it works for some people and not others. It is probably multifactorial and very complex.  There has been a particular interest in studying the association of a particular enzyme genotype, call the angiotensin converting enzyme, in association to whether or not someone is a “responder.”  This angiotensin converting enzyme is just a fancy name for an enzyme in our bodies that contributes to blood pressure control and it is postulated that it also plays a role in how we adapt to altitude, although the mechanism for this theory is not understood.  People inherit different versions of the gene that is in charge of this enzyme and it might make a difference what version of the gene you have. In short, some people may respond while others do not and we don’t really know why, but different gene makeups probably play a significant role.

So do the tents work….???

Ah ha!  So I have done a review of the current published scientific literature on this topic and I will be posting my impressions very very shortly….stay tuned….


Next topic up…Does compression wear really do anything?? Or are you just being duped into buying some really expensive old man tube socks??



A different kind of pro triathlete blog….

8 Jun

So every Pro Triathlete has to have a blog.  But I don’t really find the topics of what I eat for breakfast or my favorite summer smoothie recipe to be all that intriguing (although there is nothing wrong with those blogs of course- I am just not that exciting =)  ).  If I am going to write something, I want to contribute to triathlon content in a way that is different and offer information that is hard to get other places.  I have decided that using what I know best is the best way to get there. 

This blog will talk a little about my races and experiences as a pro triathlete; but I will primarily discuss topics that utilize my background in biochemistry, medicine and research to take hard scientific questions about performance related topics and translate them into information that can be digested by everyone.  A lot of the topics I have chosen are still question marks in the scientific literature and they require thorough literature reviews to get the most current information.  My job is to do comprehensive research on tough topics and then communicate the most up to date key information to you.  Your job is to enjoy!!

Topics on deck: 

Do altitude tents actually work?

Compression Wear- Commercial Gimmick or Simple Science?

Nutrition: Decoding the relationship between glycogen stores and the right race day nutrition.

Mitochondria: The unsung hero of exercise adaptation