Your Body On: Carbohydrates

From biochemistry, Banting, to bread and beyond.

The carbohydrate. An unsuspecting, cyclic molecule consisting of six carbons. Each of these carbohydrates have a water molecule attached to them, thus the name, carbohydrates.

Who would have thought that this particular arrangement of carbon and water would be the hot-topic of the nutritional mainstream media?

Carbohydrates, which are found in foods from sweet, sugary desserts to whole grain pasta, sweet potatoes, legumes and even maple-syrup — are the subject of much debate. Should I eat low-carbohydrates? What are complex carbohydrates? Is the fructose in fruit bad for you? What about the keto diet and diabetes?

Rather than giving one definitive answer, which is almost entirely impossible as nutritional science consistently shows that there is not one single best diet for human consumption — this article will delve into the basics of carbohydrates; from their metabolism to the controversial hormone insulin, fad diets and some common misconceptions about the macronutrient which you likely already had for breakfast.

Why learn the basics of nutritional science? Nutritional education is lacking in our society. People are headline readers, single-study consumers or preachers of individual anecdotes — often leading to master narratives demonizing certain food groups, macronutrients or even food preparation methods (Raw til’ 4, anyone?).

Therefore, the goal of this article is to add a slight angle of objectivity to your nutritional know-how — arming you with the very basics you need to perhaps, better digest, the next popular nutrition article you come across.

What are the primary sources of carbohydrates?

The word carbohydrates may bring about warm memories of fresh baked breads, delicate pastries and rich, creamy pastas. For others, they may think of sweet-potato fries, their favourite potato chips and ice-cream. Others may be even more adventurous in their definition, dreaming up lentils and chickpeas, carrots, potatoes, turnips and fruits such as bananas, apples, strawberries and mangoes.

All of food items above contain primarily the carbohydrate macronutrient, and in varying amounts and of varying complexities.

A food being high in carbohydrates is not always equatable to being high in sugar. Carbohydrates is the umbrella terms for all the different hydrated carbons — where when we differentiate between digestible and non-digestible, we can understand our net carbohydrate intake.

Snack-break: Net carbohydrates = [Total Carbohydrates —(Fibres + Sugar Alcohols])

This means that when we digest a complex carbohydrate, it will take longer to release the individual molecules of sugars, and the fibres will slow down our digestion, increase satiety and allow a slower release of sugar into our bloodstream. Complex carbohydrates, such as whole grains and legumes, also contain protein which will further activate our satiety signals, such as the PPY hormone.

Snack-break: Have you ever heard about fibre lowering cholesterol levels? It’s true! Bile acids contain cholesterol, where insoluble fibre will bind to bile acids and will be excreted instead of reabsorbed back into the body.

In contrast, simple carbohydrates don’t need any breakdown of starch, and contain no fibre — therefore as it states in it’s name, the carbohydrate is absorbed simply as sugar and ready to be used as energy when it enters the bloodstream.

How are carbohydrates digested?

The digestion of carbohydrates begins with enzymes in our saliva, and will continue to breakdown with the acidity of our stomach fluids. After the mixture is turned and churned into our stomach, it’s pH will neutralize as it passes into the small intestine, where most of the absorption into the bloodstream will occur. The carbohydrate will be absorbed as singular sugars — monosaccharides including glucose and fructose.

Snack break: Simple table sugar is composed of the disaccharide, sucrose which is 50% glucose and 50% fructose. It will be absorbed into the bloodstream as these individual components.

When there is an increase in glucose, our pancreas will release the hormone insulin, which allows our insulin-dependant organs, such as muscle, heart and fat tissue to access glucose for energy.

Is the sugar in fruit bad for you?

Fruits contain naturally occurring fructose and glucose carbohydrates.

Let’s contrast glucose with fructose for a moment. Glucose will elicit a release of insulin, however fructose does not. But the latter is more associated with weight-gain, insulin-resistance and metabolic syndrome.

In order to be used for energy, fructose must be metabolized in the liver first, where it will become glucose, free fatty acids or lactate. This will increase blood glucose, and then allow for insulin signalling. Metabolic and oxidative stress can occur when large amounts of fructose are consumed — which occurs when it is consumed in large quantities, such as is soft-drinks and processed sweet desserts.

This means that the small amount of naturally-occurring fructose in fruits is perfectly fine. Also remember that fruit comes with other types of carbohydrates — starch and fibres, and therefore is not associated with the same metabolic concerns as consuming high-fructose corn-syrup.

The bottom line? Skip the soft-drinks, but have the all the fruit with breakfast.

Does insulin make you gain weight?

In normal physiology, it does not.

Our insulin is tightly regulated when we have normal insulin signalling, and as long as we aren’t consuming an excess of energy, insulin will not have any excess energy to store as fat.

This changes when we have insulin resistance, where our bodies compensate by pumping out more insulin to get the same amount of blood sugar down to normal. The hyperinsulinemia in this context can cause weight-gain.

Why does this happen? Read my article which goes more into depth about insulin signalling here.

But, do carbs make you gain weight?

The issue is that weight-gain arises when we consume an energy surplus of any macronutrient — whether fats, protein or carbohydrate.

Weight-gain arises when we consume an energy surplus of any macronutrient — whether fats, protein or carbohydrate.

Once insulin has fulfilled it’s duty in dispersing nutrients to where they need to be, any extra energy will be rearranged into a triglyceride to be put into fat storage. This fat storage around our organs will make insulin-signalling more difficult, causing hyperinsulinemia and weight-gain.

What’s the hype with low-carb diets and diabetes?

Contrary to popular belief — the low-carbohydrate diet can be traced back to centuries ago, and it is far from being a new discovery within the world of food, diet and nutrition.

In what is known as the “pre-insulin” era, researchers and physicians scoured out different dietary interventions which would alleviate the “sweet urine” of those with diabetes.

As early as 1706, John Rollo, a Surgeon-General successfully treated a patient by dietary restriction — achieving a similar pathophysiological response as a carbohydrate-restricted diet. These ideas propagated throughout history, where low-carbohydrate, sugar-free and even “starvation” diets were the mainstay nutritional intervention of those with diabetes mellitus.

Snack break: Type II diabetes is caused by defective insulin signalling- inhibiting our body’s ability to access the glucose energy in our bloodstream, causing high-blood sugar. The insulin resistance is caused by the excess of fat deposits around organs and it’s ensuing systemic inflammatory response. Type I diabetes is an auto-immune disease targeting the insulin-producing beta-cells of our pancreas, rendering them non-functional.

After the isolation and official discovery of insulin by Canadian cardiologist, Frederick Banting, in 1921, the peptide-hormone went almost immediately to pharmaceutical production to begin relieving people for the very first time, of their once unresolvable diabetes.

Insulin led-way to a new course of life for those with diabetes — they could now mimic the normal physiological state of their metabolism, meaning they could skip the starvation or low-carbohydrate diets and could now enjoy their carbohydrates ad libitum as long as they titrated accordingly with their insulin medication. The insulin medication also improved their co-morbidity outlook — reducing nerve damage, blindness and cardiovascular disease risk.

What’s the difference between a low-carb and ketogenic diet?

On a ketogenic diet, we alter our macronutrient proportions to high fat, moderate-low protein and very-low carbohydrates. In doing this, we deplete our glycogens store and tap into our fat stores to derive energy, essentially simulating the same physiological response during starvation. To reach ketosis, we need to keep our net carbohydrate intake usually under 50 g, which would roughly be the equivalent of 2 medium fruits or 1 cup of rice.

When people with diabetes embark on these low-carbohydrate diets, they are essentially going back in time to the early nutritional interventions of diabetes (primarily Type I)— namely the “starvation” or low-carbohydrate diets which were prescribed by the physicians of the 18th century.

The bottom line

Is low-carbohydrate the answer for resolving type II diabetes?

Could reverting back to the low-carbohydrate diet be the ideal way to nutritionally intervene with a person with type II diabetes?

Potentially, but the diet is not yet considered to have strong-enough evidence, thus clinicians are often hesitant to incorporate into their practice. Also let’s remember that diabetes is much more complex than restricting an individual macronutrient.

If a decision is made to go on a ketogenic diet, it is strongly recommended to consult with a Registered Dietitian to understand the diet within within the complexity of diabetes. They can help you navigate several considerations to individualize the diet to your needs.

For example …. Will you be reducing your hypoglycemic medications? What are your lipid levels and cardiovascular disease risk? Are you an athlete? Are you pregnant? Can you afford the diet? Which recipes will suit the diet and your nutrient needs? These are important considerations to make when altering your diet drastically.

Should I go low-carbohydrate to lose weight?

Remember, low-carbohydrate diets will deplete your glycogen stores primarily found in the liver and muscles. Glycogen, the storage form of carbohydrates, is stored alongside with water — therefore, much of the initial rapid weight-loss observed is attributed to the water lost alongside the glycogen.

A recent RCT (n=600) examined the long-term weight loss of those consuming isocaloric deficits of high-fat, low-carb and low-fat, high-carb diets. While the low-carb group lost the most initial weight (due to depleted glycogen stores), the total weight loss amongst both groups remained the same in the long-term.

Therefore — the best diet for weight-loss is one that you can stick to, and nutritional science consistently shows that there is not one best diet for weight-loss.

We cannot crown one diet king and prescribe this to a population — the human body is too complex and specific to each individual. For you, achieving a calorie deficit may be easier on a lower-carbohydrate diet, for others they may feel more satiated incorporating complex carbohydrates.

Which carbohydrates should I focus on to stay healthy?

Focus on complex carbohydrates, which will have a sources of soluble and/or insoluble fibre which can help you feel fuller, improve glycemic levels and help reduce cholesterol levels.

Good sources of complex carbohydrates include:

• Whole grain breads, oatmeal and quinoa.
• Sweet potatoes, broccoli and carrots.
• Legumes, such as chickpeas, lentils and beans.
• Fruits, such as apples, bananas and berries.

The most concerning carbohydrate to avoid are items containing high-fructose corn syrup, which is found in sweetened beverages, breakfast cereals and many processed foods — this fructose-based sweetener has been shown to induce insulin resistance, even when it is not consumed within an excess of energy needs.

A sweet, last word.

In the world of confusing nutritional science and never-ending fad diets, simply breaking down what a carbohydrate actually is can bring us to a somewhat relieving conclusion — if we don’t want to, we don’t need to cut out all carbohydrates.

On the other hand, if we think a low-carbohydrate approach might help us in terms of weight loss or disease management, a Registered Dietitian can help us manage the risk-benefit ratio of doing so.

It’s tempting to delve into the next fad diet in pursuit of the hyped-up health benefits, anecdotal success stories and drastic weight loss based on limited evidence — however let’s consider this: The rise of obesity and type II diabetes is not because somewhere along the way, we stopped consuming a low-carbohydrate diet.

Instead, let’s work to find a way of eating which is sustainable to us — a way of eating which doesn’t focus on the singularity of one macronutrient over another — and rather considers our nutritional goals, lifestyle, cooking skills, current disease management and quality of life.

Kristen is a freelance nutrition writer. She has a B.Sc. in Nutritional Science and is eligible for registration as a dietitian (RD) in Canada.