Put that watermelon down! Here have, this Banana instead, it has a lower Glycemic Index...
Not only have I heard such comments from nutritionists and personal trainers countless times over the years, but I was equally guilty of passing on similar advice.
In this blog post:
- What happens to carbs when you eat/drink them?
- Does the "type" of carb matter?
- How does your body burn carbs for energy, and does it matter?
- What happens to carbs that you don't "burn" with exercise?
- What are the potential hidden health risks of glucose circulating in your blood?
- Can eating too much carbs affect your cholesterol? Are carbs the real cause of heart and cardiovascular disease?
- Is there such a thing as "too much protein"?
- Are there guidelines for me to chose which carbs to avoid and which I don't have to worry about?
The Glycemic Index (GI) has been around since the early 1980s, and is calculated from the "rate at which blood glucose rises" in response to the consumption of a certain food or drink. In other words, a tablespoon of sugar has a higher GI vs. oatmeal because it causes a more rapid increase in the amount of glucose in your blood.
But why is that important? What is glucose? Is the GI a good guide to eating healthy? How strict do I need to be? Are there better means out there to guide you? What about other carbohydrates?
Slow down with the questions! I'll attempt to tackle them one at a time...
So what is glucose, why should you care how much of it is in your blood and how quickly it got there?
Glucose is the simplest molecule of sugar found universally, and the most easily absorbed and commonly utilized by humans and animals. Most carbohydrates ingested by human beings get broken down in the digestive tract into glucose , which gets absorbed through the gut wall into the bloodstream.
Note that there are 2 other monosacharides (or simple sugar molecules) other than glucose: these are fructose (found in fruits) and galactose (found in some dairy products). Just like glucose, fructose and galactose are both "simple" sugars; in other words, they get easily and quickly absorbed into the blood stream.
Here's another piece of useful info: fruits typically contain 1g of glucose for every 1g of fructose. In other words, if an apple has 20g of fructose, it will also have 20g of glucose, resulting in a total of 40g of simple fast-absorbing carbohydrate molecules.
Let's start with the sources of glucose in the bloodstream. Later on we'll tackle what happens to it once its there and why that's important to keep an eye on...
There are 3 primary sources for the glucose circulating in your bloodstream:
1. Digestion of carbohydrates ingested
2. Breakdown of glycogen stores in the liver and muscles
3. Gluconeogenesis : creation of glucose molecules from non-carbohydrate compounds
1. Digestion of Carbs Ingested
That's a simple one. When you eat any form of carbohydrate, their breakdown into simple sugars (glucose, fructose, galactose) starts in the mouth and ends in the intestines. This happens to all forms of carbs , whether they're complex starch such as oats or potatoes or simple sugars such as fruits or candy.
Does "all" the carb ingested get broken down in the digestive tract? The answer is no: some of it (such as insoluble fibers or even very starchy vegetables) stays in the large intestine, where it acts as food for the bacteria residing in your colon through a process called fermentation. Another reason for weak digestion of carbs in the overall health of your gut lining: inflammation caused by inflammatory components (such as gluten or soy) can easily disrupt your gut's ability to digest carbohydrates.
Side note: if your colon is predominantly inhabited by bad bacteria, this results in bloating, gas, and other digestive distress. As a result, one good way to address such problems is by severely restricting carbs for a few days to kill off those bad bacteria and then repopulating your colon with good bacteria by taking a good quality probiotic, or eating good quality fermented foods or yogurt.
But anyway, if your digestive tract is healthy and most of the carbs you consume get digested into glucose or other simple sugars, those molecules get absorbed into your bloodstream.
When does it happen:
Every time you consume any carbohydrate-containing food or drink.
2. Breakdown of Glycogen Stores in the Liver and Muscles
You see your liver and muscles have the ability to "store" glucose for future use. Both of these organs have "barrel-like" structures that are able to "package" glucose molecules into more complex molecules called glycogen and save them for future use.
One way of looking at it is as follows: glucose molecules are loose sheets of A4 paper floating around. The liver and muscles grab those papers and put them in folders. When a shortage of glucose is detected, a folder is opened and its A4 sheets are dumped out, releasing glucose in the bloodstream again.
But hold on! This is not a free ride at all: the liver and muscles have a very small storage capacity, so only a very small fraction of blood glucose actually gets converted into glycogen for storage in the liver/muscles.
Note: the liver is capable of storing glucose as glycogen and then releasing that stored glucose into the bloodstream. Muscles on the other hand CANNOT release glucose from glycogen into the bloodstream: muscle glycogen can ONLY be utilized by that muscle itself to contract
Glucose from bloodstream being converted into glycogen. Glycogen being broken down into glucose when needed.
When does it happen:
When immediate need for glucose arises and enough glycogen stores are available in the liver (for general use) and muscles (for local use only).
Gluco (glucose) - neo (new) - genesis (generation) is a chemical process whereby glucose molecules are formed from non-carbohydrate compounds . Gluconeogenesis occurs when there is an extreme shortage of glucose : in other words, when there is no glucose from digested carbohydrates and glycogen stores in the liver and/or muscles are depleted.
90% of gluconeogenesis comes from 3 compounds: (i) lactate, (ii) glycerol, and (iii) certain amino acids.
I won't get into the chemical processes for gluconeogenesis from each of these 3 compounds, but I'll explain what they are:
(i) Lactate: it's a bi-product of energy production in muscles. You may have heard of lactic acid, technically that term is not correct. Muscles produce lactate and Hydrogen atoms, which are then recycled through gluconeogenesis to produce energy. When the rate of recycling can't keep up with the amount of lactate being produced, your muscles accumulate those Hyrdogen molecules and become more and more acidic and eventually shut down.
(ii) Glycerol: is what is typically bound to a fatty acid to form Triglycerides , the main culprit behind cardiovascular disease. So a shortage of glucose can cause Triglycerides to breakdown into glycerol (used for gluconeogenesis) and free fatty acids (which have many healthy uses in the body).
(iii) Amino acids: in extreme glucose shortages, the body is able to breakdown amino acids (the building blocks of protein) and use them for glucose production. This is why it is not advisable to exercise intensely for long periods of time without adequate carbohydrate intake: your body will "eat itself" to generate glucose.
When does it happen:
Extreme situations when no glucose is available from digestion and glycogen stores are depleted.
So what happens to glucose when it hits your bloodstream?
Let's put the second (stored glycogen) and third (gluconeogenesis) sources of blood glucose on the side for a moment: they only occur when glucose is in short supply and is "immediately needed for quick utilization". So technically, you cannot have circulating blood glucose in these situations as it's immediately utilized.
In other words, glucose in the blood from glycogen or gluconeogenesis is "demand-driven": if it's not needed somewhere in the body, it won't even be there.
Glucose from food/drink on the other hand is "supply-driven": if it's consumed and digested, it will enter the bloodstream, whether you need it or not. And "that", my friends, is where you should pay attention!
What happens to that blood glucose then?
1. Energy production
2. Glycogen Storage
3. Fat storage
1. Energy Production
There are 3 main ways for your cells to produce energy, ranked by order of how quickly they can produce energy:
a- The fastest (creatine phosphate pathway) does not use glucose or fat, and will only give you power for 10-second efforts (e.g. sprinting hard)
b-Glycolysis: breakdown of glucose to be utilized for any effort beyond 10-seconds
c-Beta-oxidation: utilization of fatty acids.
Your brain, muscles, heart, and other organs are equipped to produce energy using glucose - so if any of them has a need for glucose and glucose is available in the bloodstream, it will be utilized.
Practical Applications: let's say you're undertaking a very hard AND long effort - in this particular situation:
- Long effort means the creatine phosphate pathway isn't enough since it only provides 10-seconds of effort
- Hard effort means beta-oxidation doesn't work because you need energy quickly , and breaking down fatty acids takes a bit of time -Glucose is the only fuel that works, and comes from a combination of stored glucose (glycogen) and glucose from a sports drink for example. If you don't ingest food/drink that can be converted to glucose quickly, your glycogen stores will get depleted , and once empty (after 90-120min), you experience what many athletes have experienced and fear: the Bonk!
So what happens if you don't "need" that glucose to produce energy?
2. Glycogen Storage
When your body detects glucose in the bloodstream and doesn't need it for energy production, then its first action is to remove it from the bloodstream and "store" it in the form of glycogen in the liver and muscles.
The hormone "Insulin" (released by your pancreas) travels to your liver and muscles and instructs them to remove glucose and store it in the form of glycogen.
Practical Applications: while the body has limited glycogen storage capacity, there are still ways to increase that capacity (to a certain limit!). Frequent "emptying" and "refilling" of glycogen stores will trigger an increase in storage capacity - in other words, your liver/muscles will create more "folders" in which to store floating A4 paper.
So, what kind of exercise can lead to that? Any unfueled effort lasting 45-90min at an intensity that's hard enough to deplete glycogen. Examples include: interval training, tempo runs, crossfit, circuits, etc. (more on that and other sports-related info in Part III).
Again though, to a certain limit! Yes this means you can get away with eating a little more carbs and feel comfortable that it's getting stored as glycogen and not fat, but that capacity remains very limited no matter how hard your train...
So what happens when glucose is not needed for energy and glycogen stores are full? You guessed it! It gets converted to fat.
3. Fat Storage
So you ate that banana before going to bed, you didn't exercise hard before doing so, so your glycogen stores are full. The starch in that banana gets broken down into simple sugars: glucose and fructose and enters your bloodstream.
Your pancreas detects that glucose and secretes insulin, sending a Group BBM message to your liver and muscles and get that glucose out of the blood ASAP!
But here's the problem: your muscle glycogen stores are full , so they can't take any more glucose. Your liver's glycogen stores are full too ! But the liver doesn't give up so easily: it does remove that glucose, but by converting it into fatty acids and releasing those fatty acids into your bloodstream in the form of Triglycerides !
And those triglycerides start accumulating and form "adipose tissue", aka fat storage under your skin.
Ok so does this mean it's impossible to have glucose in your blood except after a meal? Since glucose will either be used, stored as glycogen or stored as fat, there shouldn't be any left in your blood a few hours after a meal, correct?
Well no, not exactly...
... and how sugar is what causes cardiovascular disease, not fat...
Let's revisit something we talked about earlier: every time a simple sugar (glucose, fructose, galactose) enters your bloodstream through your digestive tract, your pancreas will start churning out Insulin - this hormone acts as a messenger to your liver and muscles to remove that sugar by either storing it as glycogen or converting it to fat.
BUT there are 2 exceptions to that rule:
(i) Insulin resistance: if you keep eating foods that cause your Insulin to spike, your liver and muscles become " less responsive" .
It's like an "enough already!" attitude by your liver and muscles. As this resistance develops, less and less glucose is removed from your blood, so it sits there circulating and reacting with other components in your blood (more on that later).
ii) Pancreatic fatigue: when this Insulin Resistance develops, your pancreas has no idea what's going on. It does NOT know that its messengers (Insulin) are being ignored. So what does it do? Send more messengers!
In other words:
Glucose enters blood from digestive tract => pancreas secretes insulin => insulin is ignored by liver and muscles => pancreas secretes "even more" insulin => pancreas gets fatigued and ultimately lowers insulin production => TYPE II DIABETES
Of course, you are at an even higher risk of developing that form of diabetes if you have a family history of this disorder, as you are likely to develop insulin resistance at a faster rate.
Furthermore, if left untreated, the fatigue in the pancreas can become so extreme that insulin production gets almost completely shut down. You reach a point (Type I Diabetes) where the only solution is to get insulin injections, in most cases for life...
SO! Now you have free simple sugars floating around in your bloodstream and it's not being picked up by your liver and muscles - what do they do?
They cause something called "Glycation". Glycation occurs when a simple sugars bind to either a protein or a fat molecule , causing a range of oxidative damages.
What happens is: when a sugar molecule is bound to a protein molecule, the resulting "glycated" molecule is highly damaging to anything it comes in contact with in the body. Some of the common disorders which have been linked to glycation of proteins through countless studies over the past 10 years include:
- Degeneration in nerves (particularly associated with Alzheimer's Disease and deafness)
- Cardiovascular disease
Of particular importance is when cholesterol molecules get glycated by simple sugar molecules: Low Density Lipoproteins (aka LDL, also inaccurately referred to as "bad cholesterol") attach to simple sugar molecules and become glycated. Once this happens, risk of oxidation for these LDL molecules is drastically multiplied.
Then these "oxidized LDL" molecules travel through the arteries and cause inflammation in the arterial cell wall, leading to the formation of "plaque" . Triglycerides floating around are then able to attach themselves to the inflamed arterial walls.
Numerous studies have shown that non-oxidized LDL does not cause plaque to build up in the arteries , but rather "oxidized LDL" does ; and the oxidation of LDL does not occur without the presence of simple sugar molecules in the blood-stream. This also forms the foundation of the linkages between diabetes and cardio-vascular disease:
Diabetes => high blood sugar => glycation of LDL => oxidized LDL => inflammation in arterial cell wall => plaque formation
BUT HOLD ON! There is another BIG problem we omitted to mention:
I said that when LDL molecules are oxidized, plaque forms in the arteries and triglycerides contribute to that problem. So does a "low fat" diet that minimizes LDL and triglycerides in the blood take care of that problem?
Well no, it doesn't, and here's why:
1. Insulin spikes from carbohydrate food/drink "switch off" an enzyme called "Lipase"
2. Lipase (as the name implies) is responsible for breaking down lipids (triglycerides/fats) into free fatty acids to allow the body to use them as fuel for energy
3. With a high carb / low fat diet, insulin is high, lipase is low, and fat molecules not being used for energy start accumulating , whether you like it or not, and float around in your blood waiting to be "glycated" and oxidized.
In addition, the "excess glucose" gets converted to triglycerides and those are added to the existing ones in the bloodstream as well. In other words, even a ZERO fat high carb diet will lead to triglycerides, high LDL, oxidized LDL, plaques and cardiovascular disease.
All this science is great, but how do I apply that to real life???
Let's try to simply it a bit... If you've read all of what I discussed so far, you know that:
1. Insulin spikes are caused by the amount and type of carbohydrates we eat
2. Insulin spikes cause insulin resistance and pancreatic fatigue, eventually leading to Type II Diabetes
3. This causes high concentrations of sugar molecules in the blood
4. A significant portion of that sugar is converted to triglycerides (fat), attached to LDL
5. Those sugar molecules "glycate" proteins and fat, thereby creating corrosive substances inside your body
6. Glycated LDL molecules get oxidized, cause inflammation in the arteries, leading to plaque formation and cardiovascular disease
SO, if you work backwards: to stop (6) from occurring, you need to limit (1) from happening: in other words, your aim should be to minimize Insulin spikes.
What types of food cause insulin spikes - the whole Glycemic Index concept
Simply put, all foods and drinks containing any form of carbohydrate will cause some sort of insulin reaction.
Side note: proteins also cause insulin reactions, a little know fact. Amino acids can also be converted to fatty acids & triglycerides. So yes, too much protein DOES make you fat .
But as you probably already know, some carbohydrates cause a more significant insulin reaction than others . For instance, you would expect table sugar to cause a bigger insulin spike compared to, say, a potato for example.
Historically, the nutrition and diet industry relied on the concept of Glycemic Index (GI) to differentiate among various foods and drinks when it came to insulin impact.
The concept of the GI is simple: Glucose is giving a score of 100. Any item which causes a bigger insulin spike than glucose has a score of more than 100. Anything that causes a lower insulin spike gets a score under 100.
For example: a Mars bar has a GI score of 78, while apples have an average score of 50.
Generally, a score of 55 or less is considered LOW , 56-69 MEDIUM , and 70 or higher HIGH.
But the GI concept is far from perfect: it has fallen to increasing criticism by healthcare practitioners in recent years for a wide variety of reasons, including the fact that it does not take "portion size" into account ...
Take wholewheat bread for example: it carries a GI score of 97! That's almost as high as pure Glucose, and even higher than that Mars bar! In fact, it carries a higher GI score than White Bread (71)! How can that be?
Well portion size is a big factor there: you see wholewheat bread is far less dense (weight/volume) when compared to a glucose, a Mars bar or even white bread.
The Concept of Glycemic Load
Enter the concept of Glycemic Load (GL) : the GL concept was created to address the portion size issue when dealing with GI - it gives foods a score based on a combination of GI and typical portion size . In other words, it measure the impact on your blood glucose of consuming a typical serving of a certain food .
Generally, a score of 10 or less is considered LOW , 11-19 MEDIUM , and 20 or higher HIGH .
Let's pick up that example we used earlier:
A typical Mars bar weighs around 60g and has a GI of 79.
A typical slide of wholewheat bread weight around 45g and a GI of 97.
BUT: the Mars bar would have a GL of 27 (HIGH), while the slide of wholewheat bread would be at 7 to 10 (LOW).
The Concept of Insulin Index
The Glycemic Load is a convenient way of looking at things, but again, it's not ideal. The GI/GL concepts measure the impact food has on the amount of glucose circulating in your blood, but as we discussed at the beginning of this post, the story doesn't end there:
- Your body has a mechanism to deal with glucose entering your blood: insulin is secreted, sending a message to your liver and muscles to remove that glucose and either convert it to glycogen or fat
- So the "insulin response' matters much more than the "blood glucose' after eating
- The insulin response can vary from person to person
- As we discussed earlier, some people can develop insulin resistance, or a "fatigued pancreas" may not be able to produce enough insulin in the first place...
==> so is there a way to measure the "insulin response" created by various foods ?
As a matter of fact, there is, and it's called the Insulin Index (II).
By measuring the insulin response of food/drink, it already presents a significant advantage over the GI/GL concept. Furthermore, I noted earlier that even proteins can cause an insulin response, and the II captures that as well. Also, while the GI is calculated using Glucose as a baseline (score of 100), the II uses white bread as its baseline, with an II score of 100.
Let's take some examples:
- White bread: 100
- Wholewheat bread: 96 (yes, it's nowhere near as healthy as you think!)
- Mars bar: 122
- Potatoes: 121
- Banana: 81
- Apple: 59
- Cornflakes: 75
- Baked Beans: 120
- Cheese: 45
- Beef: 51
- Fish: 59
The high scores for high GI foods (white bread, potatoes) are certainly not surprising. It is somewhat surprising that "healthy and lean proteins" also cause such an insulin response... But don't be alarmed: if you're eating sensible amounts of protein, that insulin response is actually quite beneficial: the rise in insulin caused by a moderate amount of protein actually drives the amino acids from that protein into your muscles to build new muscles fibers, which is always a good thing!
You will find a table with the Insulin Index for common foods here.
So to recap, in Part I of this post, we talked about:
1. What happens to carbohydrates once you consume them.
2. How your body reacts to those carbohydrates, and what happens to the glucose once its enters your bloodstream.
3. How too much carbohydrate consumption can have adverse effects on your health, including fat accumulation, inflammation, and cardiovascular disease.
4. How different foods can cause different insulin reactions, and therefore can have different effects on your health, performance and well-being.
In Part II (coming over the next 2 weeks), we will cover:
1. What are the general benefits of limiting carbs
2. How carbs impact the health of your digestive system
3. What causes sugar cravings and how to deal with them
4. A bit of history on our diet, and the evolution of carb content vs. protein and fight (yes, I will be picking a fight with the food pyramid!)
And in Part III (I promise not to keep you waiting!), we will cover:
1. Eating recommendations for general health
2. Eating recommendations for athletic performance
3. How "strict" do you need to be in your eating habits
4. How you can still enjoy your love for food without risking your long-term health
As always, feel free to ask any questions in the comments section below and I'll be happy to answer them.