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Simple or complex?  Good or bad?

Carbs for fuel

The glycemic index.


The most important carbohydrate of all.

Doctor's orders

My carbohydrate prescription.

Carbohydrates - simple vs complex

Carbohydrates are the body's primary fuel source and they offer 4 calories per gram.  Chemically, they are organic compounds that contain carbon, hydrogen, and oxygen.  They're characterized as simple or complex, depending on their chemical structure and speed at which they get digested.  In general, simple carbs are digested and absorbed much quicker than complex carbs, which take longer to break down and absorb.  Because of this, simple carbs get absorbed quickly and lead to a more rapid rise in blood sugar concentration, which in turn can trigger a rapid insulin release.  In too much concentration, insulin, the storage hormone, is linked to obesity, type 2 diabetes and metabolic disease.

Sugars, or simple carbohydrates, are formed by one or two molecules, called saccharides.  Sugars with one saccharide, like fructose (from fruits) or galactose (from milk) are called monosaccharides.  Sugars with two saccharides, like sucrose (table sugar), maltose (vegetables, beer) and lactose (dairy) are called disaccharides.  Simple carbs come in multiple forms, and are not created equal.  This has led to mass confusion regarding which are good and which are bad.  We'll address this in a few minutes.


Complex carbs are carbohydrates that are formed by linking three or more saccharides.  These are called polysaccharides, or starches.  To get absorbed, the body must first break the polysaccharide links in their individual saccharides, and so in general, complex carbs take longer to increase blood sugar concentrations and offer a more sustained source of energy, compared to simple carbs that offer an immediate source of fuel.  

What makes carbs good or bad?  It's not whether they're simple or complex that determines this.  The meaning of simple or complex simply reflects how many saccharides the sugar has.  And in general, shorter ones get absorbed quicker and offer a more immediate source of energy than longer saccharide chains found in complex carbs.  But I wish it was that simple.  Other factors influence the speed in which carbs get absorbed in our bloodstreams.  Here's where the good versus bad carb thing happens.  Simple carbs, like those found in fruits or vegetables, are often villainized as being bad since people associate them with rapid blood sugar spikes and rebound insulin spikes.  The important thing to understand is that although simple, sugars found in fruits and veggies (fructose and maltose for example) are packed and trapped in a fiber filled environment, and although the sugars are simple carbs, they need to be released from the fiber before they can get absorbed.  That process takes less time than complex carbs, but the ensuing increase in blood sugar does not create the dreaded insulin spike we see with the bad simple carbs.  

Bad carbs are those that are simple, refined, and nutrient poor.  They offer a minimum of vitamins and minerals, and they're not trapped in fiber, making them super easy and quick to digest and absorb.  Although they may assist someone who needs a super quick jolt of energy, the insulin spikes they create are not healthy long term.  During the processing of foods, fiber, which traps the vitamins, minerals and slows the breakdown of saccharides, is removed, leaving a nutrient poor, fiber depleted form of the original food.  Those are bad carbs.  They are simple carbs where the nutrition has been stripped away through processing, leaving them in a refined form where their absorption is unnaturally quick, while being void of any nutritional benefit.  Bad carbs, like those in cola, table sugar, high fructose corn syrup and candy are to be avoided if the goal is long term health and prevention of obesity.  These bad carbs offer no nutrition and no satiety, leading to ignorance of our natural satiety signals and to excessive calorie ingestion.

So, the term simple or complex isn't synonymous with good or bad, and this is more related to the lack of nutrition and super quick absorption we see with processed foods.  Fruits are healthy, their carbs are good, and people who eat carbs coming mainly from healthy sources, whether simple or complex, tend to live longer, fuller lives with less chronic medical conditions.  Unfortunately, many foods we eat regularly are made using these bad carbs.  White flour, white bread and white rice are examples of bad carbs.  Wheat grains undergo a series of steps where grains are transformed into a fiber and nutrition-void flour that has extended shelf stability.  We trade nutrition for convenience.  Then we market those foods and normalize their use in every home and at every meal.  White rice is to brown rice what white flour is to wheat grains.  Although white rice originated as brown rice, a complex carb trapped in fiber, the processing of brown rice into white rice yields a long saccharide chain, or complex carbohydrate, that is bad.  

In a nutshell, simple carbs act like paper thrown in a fire, whereas complex carbs are the bigger logs that offer more sustained energy.  Determining whether carbs are good or bad is more determined by the level of processing that the food has been through.  This processing leads to loss of fiber in exchange for shelf life.  Fiber traps vitamins, minerals and slows down the breakdown and absorption of carbs, all advantages that nature built in the foods that grow in the ground.  So when the fiber is removed, or when carbs are processed into their finest forms, like high-fructose corn syrup, the carbs turn bad and can have negative impacts on our metabolic health. 


If you've been following closely, you can now guess that simple carbs can be bad, like those found in candy, and complex carbs can also be bad, like those in those in white rice or white bread.  You should also understand that simple carbs can be good, like those in fruits and veggies, and complex carbs can be good, like those in whole grains and legumes.

Let's recap.  Carbs can be simple or complex, depending on the length of its saccharide links.  Then carbs can be good or bad, depending on the nutrition (fiber, vitamins, minerals, phytonutrients) they contain, regardless of whether they're simple or complex.  Since foods are a combination of 3 macronutrients, including carbs, proteins and fats, try to choose the best carbs possible


Good carbs are:

  • Low or moderate in calories

  • High in nutrients

  • Devoid of refined sugars and refined grains

  • High in naturally occurring fiber

  • Low in added sodium

  • Low in saturated fat

  • Very low in, or devoid of, cholesterol and trans fats

Bad carbs are:

  • High in calories

  • Full of refined sugars, like corn syrup, white sugar, honey and fruit juices

  • High in refined grains like white flour

  • Low in nutrients

  • Low in fiber

  • High in added sodium

  • Often high in saturated fat

  • Sometimes high in cholesterol and trans fats

simpe vs complex
Glycemic index

The glycemic index

Now that you know that carbs are saccharides linked together in short or long chains, like actual links in a chain, you can appreciate that digesting them takes time.  The length of the chain is one factor that will determine how fast we can break down and digest those carbs, but there is also another very important one.  Fiber.  Yup, even simple carbs can take longer to digest and absorb if they're trapped in fiber.  Remember fruits and vegetables?  They contain simple carbohydrates, yet their carbs are good.  How can that be?  Not all simple carbs are bad.  Those surrounded by fiber, that traps vitamins and minerals, are great simple carbs.  And complex carbs aren't all good.  Some complex carbs have had all the fiber, and the nutrition they trap, removed through food processing.  Take white rice for example.  The fiber gets removed through processing, leaving a complex carbohydrate void of nutrition that we can digest and absorb super quickly.

Let's recap.  Carbs can be simple or complex, depending on the length of its saccharide links.  Then carbs can be good or bad, depending on the nutrition (fiber, vitamins, minerals, phytonutrients) they contain, regardless of whether they're simple or complex.  The speed with which they get absorbed in our bloodstream depends on two factors: 1) the length of the saccharide chain and 2) the amount of fiber surrounding them.


When talking about carbs being good or bad, it's impossible to discuss them without mentioning the glycemic index.  This index measures precisely the speed and level with which carbohydrates get absorbed in our bloodstream and raise blood sugar.  Studies have suggested that high glycemic foods coming with bad carbs increase the likelihood of many chronic medical conditions, including obesity, diabetes, heart disease and cancer.

High glycemic index foods will raise blood sugar quicker and higher than foods with a lower glycemic index.  These do this slowly and steadily, causing less of a spike in insulin release.  This rapid increase in insulin secretion is associated with increased risk of suffering from chronic metabolic disease.  It's also important to keep in mind that a food's glycemic index can also be affected by the food it's being eaten with.  For example, eating a mango (higher glycemic index) after eating chickpeas (lower glycemic index) will cause a slower increase in blood sugar than eating the same mango alone.  So eat high glycemic foods containing good carbs when you want short and quicker bursts of energy, like before a workout for example, and eat foods with a lower glycemic index when more sustained energy is desired.  Instead of focusing on the glycemic index of individual foods, consider the glycemic index of your meal as a whole.


Take a look at common foods and their glycemic index ratings, and don't forget to consider the meal in its entirety!  Also remember that the glycemic index isn't a marker of food nutrition, simply a marker of how high and fast the food will raise blood sugar.

Glycemic index (glucose = 100)


White wheat bread* 75 ± 2

Whole wheat/whole meal bread 74 ± 2

Specialty grain bread 53 ± 2

Unleavened wheat bread 70 ± 5

Wheat roti 62 ± 3

Chapatti 52 ± 4

Corn tortilla 46 ± 4

White rice, boiled *73 ± 4

Brown rice, boiled 68 ± 4

Barley 28 ± 2

Sweet corn 52 ± 5

Spaghetti, white 49 ± 2

Spaghetti, whole meal 48 ± 5

Rice noodles† 53 ± 7

Udon noodles 55 ± 7

Couscous† 65 ± 4



Cornflakes 81 ± 6

Wheat flake biscuits 69 ± 2

Porridge, rolled oats 55 ± 2

Instant oat porridge 79 ± 3

Rice porridge/congee 78 ± 9

Millet porridge 67 ± 5

Muesli 57 ± 2



Apple, raw† 36 ± 2

Orange, raw† 43 ± 3

Banana, raw† 51 ± 3

Pineapple, raw 59 ± 8

Mango, raw† 51 ± 5

Watermelon, raw 76 ± 4

Dates, raw 42 ± 4

Peaches, canned† 43 ± 5

Strawberry jam/jelly 49 ± 3

Apple juice 41 ± 2

Orange juice 50 ± 2



Potato, boiled 78 ± 4

Potato, instant mash 87 ± 3

Potato, french fries 63 ± 5

Carrots, boiled 39 ± 4

Sweet potato, boiled 63 ± 6

Pumpkin, boiled 64 ± 7

Plantain/green banana 55 ± 6

Taro, boiled 53 ± 2

Vegetable soup 48 ± 5



Milk, full fat 39 ± 3

Milk, skim 37 ± 4

Ice cream 51 ± 3

Yogurt, fruit 41 ± 2

Soy milk 34 ± 4

Rice milk 86 ± 7



Chickpeas 28 ± 9

Kidney beans 24 ± 4

Lentils 32 ± 5

Soya beans 16 ± 1



Chocolate 40 ± 3

Popcorn 65 ± 5

Potato crisps 56 ± 3

Soft drink/soda 59 ± 3

Rice crackers/crisps 87 ± 2



Fructose 15 ± 4

Sucrose 65 ± 4

Glucose 103 ± 3

Honey 61 ± 3

Data are means ± SEM.

* Low-GI varieties were also identified.

† Average of all available data.

The complete list of over 1000 foods and their glycemic index can be found at:


Believe it or not, fiber isn't just something that "passes through us", coming out unchanged at the other end.  To start it off, fiber is a carb, a complex carbohydrate actually, but it behaves very differently than other carbs.  Within seconds of ingesting sugar, or other carbs, digestion starts in the mouth, then in about 20 minutes, it gets absorbed in the small intestine.  Meanwhile, fiber remains unaltered until it makes it to the colon, or large intestine.  Humans have an enzyme called Glycoside Hydrolases, and they help break down saccharide links in complex carbohydrates.  But we only have 17 of them, and none of them are capable of breaking down fiber.  But guess who is capable?  Our gut bacteria!  In our gut microbiome, there's more than 60000 of these enzymes capable of breaking down fiber for us.  Every single type of fiber requires a unique type of microbe that produces a unique combination of Glycoside Hydrolase enzymes.  The breakdown of fiber by our gut bacteria helps feed them, and then in turn, they produce some of the most healing and powerful chemical compounds in nature: SCFAs (short-chain fatty acids).  These will be reviewed in detail in the section The Microbiome.  You can access it by clicking 

Fiber only exists in plants, and is absent in animal products, and in much the same way there are different types of carbs (simple, complex, refined, etc.), fats (good or bad, saturated, trans, etc.), there are different types of fibers.  The fiber in your Lucky Charms isn't the same as the fiber in your broccoli.  Since there are over 400000 plant varieties in nature, with at least 300000 being edible, and all having different types of fiber, it's impossible to know exactly how many different types of dietary fiber exist in nature.  Each type of fiber tends to feed a different type of bacteria in our gut, and the bacteria that feed off of fiber then return the favor by producing beneficial compounds that make it in our bloodstream.  So fiber doesn't just pass through us.  It feeds our microbiome (the population of micro-organisms in our gut), which in turn produce chemical compounds that affect every organ in our body.  Fiber also adds bulk and facilitates the passage of stools, as well as lowers cholesterol and controls blood sugar.


Fiber types, soluble versus insoluble

Most plants contain a mix of both.  Soluble fiber dissolves in water while insoluble doesn't.  They both offer unique benefits.  Soluble fiber forms a gel-like substance when exposed to water.  You've likely noticed this effect if you've already seen what happens to chia seeds exposed to water.  Soluble fiber, like pectin, psyllium and guar gum have satiating effects (they make you feel full), and improve gut and cardio-metabolic health by lowering cholesterol and controlling blood sugar.  Certain soluble fibers will serve as food for gut bacteria that ferment them and lead to the production of beneficial SCFAs.  These beneficial compounds lead to gut health by improving gut barrier function and by preventing gut inflammation.  Soluble fiber also promotes gut regularity, which help prevent gut issues like diverticulitis, but less than its counterpart, insoluble fiber.

In contrast, insoluble fiber cannot dissolve in water, thus contributing more to gut regularity than soluble fiber.  Insoluble fiber adds bulk to stools and has a more laxative effect than soluble fiber which tends to slow down digestion.  Insoluble fiber has protective effects against colon cancer and diverticulitis.  Insoluble fiber is also not fermentable, so gut bacteria can't use it as fuel and can't produce SCFAs in return.

The bottom line is that fiber adds bulk to food, traps vitamins and minerals, and is calorie-free.  It nourishes our gut bugs that then produce beneficial compounds in return.  We should aim for at least 38 grams per day for men and 25 grams per day for women.  Many experts say that even these amounts fall short, and long living populations eating a mainly plant-based diet reach almost 100 grams per day of fiber.  Studies have shown that larger amounts of fiber intake have better health outcomes, and less disease.  

Doctor's orders

Carbs aren't the enemy!  They're actually our primary and preferred source of fuel.  Where people get confused is when we're mixing up good and bad, simple and complex, added versus refined.  Somehow, people have started thinking fruits are unhealthy and that white bread and white rice are.  

People should be consuming about 45-65% of their calories from carbs, while choosing good carbs from whole plant foods, while minimizing processed carbs.  So on a 2000 calorie diet, that amounts to 250 grams of carbs per day.

In a nutshell, remember that people eating a mostly whole food plant-based diet won't have to worry about carbs at all.  Plant sources of carbs are good carbs, and whether their carbs are simple or complex, their glycemic index is naturally lower than refined or processed carbs, due to the fiber surrounding them.  These carbs have been proven to lower rates of chronic disease, come packed with gut feeding fiber and disease preventing vitamins, minerals and phytonutrients.  So when choosing carbs, don't overthink it.  If your carbs are coming from natural plant sources, eat as much as you can!  Their fiber, polyphenols and resistant starch content pretty much make them impossible to overeat.  Eat as many colors as possible, since each color is attributable to a unique combination of nutrients, and plant variety is the most potent predictor of gut health than even plant quantity.  The best way to ensure you're getting the right amounts and types of carbs is simply eating a variety of fruits, veggies, whole grains and legumes.

All studies show that plant-based diets are the best way to improve quality and quantity of life, and plants are mostly carbs, good carbs, surrounded by fiber and tons of nutrients.  So if a health professional tells you carbs are bad, run the other way.

doctor's orders
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