What is the difference between free sugars and non-free sugars, both chemically and medically?

Question

Background

On this WHO entry I read that free sugars must be limited in our diet. The limit is around 5% of the carbohydrates intake.

Firstly, I'm quite confused with the difference between free and non free sugars. I would guess it is related to mono and polysaccharides. More I supposed glucose would be a great nutrient as we need lot of carbohydrates, and it is ready for glucolysis.

Also the brain needs about 20% of carbohydrates intake - again I can't see why not glucose. In short: I cant understand what's the problem with free sugars.

Question

On this context I wonder:

What is the difference of free and non free sugars? And why not to eat directly glucose?

Answer 1

TL;DR

Free sugars are all instances were sugar can be avoided and is not essential. It is encouraged to cut down the free sugars intake because sugar has many negative health effects:

Sugar

• increases the risk of obesity
• is linked to diabetes
• is linked to fatal cardiovascular disease
• encourages caries
• is linked to the Alzheimer’s disease
• is linked to ADHD

---

There is a wealth of evidence from many different types of investigation, including human studies, animal experiments and experimental studies in vivo and in vitro to show the role of dietary sugars in the etiology of dental caries (21). Collectively, data from these studies provide an overall picture of the cariogenic potential of carbohydrates. Sugars are undoubtedly the most important dietary factor in the development of dental caries. Here, the term ‘‘sugars’’ refers to all monosaccharides and disaccharides, while the term ‘‘sugar’’ refers only to sucrose. The term ‘‘free sugars’’ refers to all monosaccharides and disaccharides added to foods by the manufacturer, cook or consumer, plus sugars naturally present in honey, fruit juices and syrups. The term ‘‘fermentable carbohydrate’’ refers to free sugars, glucose polymers, oligosaccharides and highly refined starches; it excludes non-starch polysaccharides and raw starches.

^{Source: Joint WHO/FAO Expert Consultation, 2003, "WHO Technical Report Series 916 Diet, Nutrition, and the Prevention of Chronic Diseases", Geneva. 2003, p.109, Emphasis Mine}

Semantically, the main difference is that free sugars are refined, and non-free sugars are unrefined. This is not really a chemical difference in the molecule (refined glucose is still glucose), but rather in the process of manufacturing products and foods.

The medical effects of free sugar are the same as of non-free sugar - glucose is glucose no matter what fancy name you give it and where you put it.

But free sugar is mostly a food additive and not essential: Carbohydrates and starches are unavoidable, but adding household sugar or honey to foods as additives is unnecessary:

Free sugars* contribute to the overall energy density of diets and higher intakes of free sugars threaten the nutrient quality of the diet by providing significant energy without specific nutrients, leading to unhealthy weight gain and increased risk of obesity and various NCDs, particularly dental caries which is the most prevalent NCD globally.

^{Source: WHO.gov. Reducing free sugars intake in adults to reduce the risk of noncommunicable diseases}

Other negative health effects of free sugar are summarised here:

Free sugars contribute to the overall energy density of diets, and may promote a positive energy balance (5-7). Sustaining energy balance is critical to maintaining healthy body weight and ensuring optimal nutrient intake (8). There is increasing concern that intake of free sugars – particularly in the form of sugar-sweetened beverages – increases overall energy intake and may reduce the intake of foods containing more nutritionally adequate calories, leading to an unhealthy diet, weight gain and increased risk of NCDs (9-13). Another concern is the association between intake of free sugars and dental caries (3, 4, 14-16). Dental diseases are the most prevalent NCDs globally (17, 18) and, although great improvements in prevention and treatment of dental diseases have occurred in the past decades, problems still persist, causing pain, anxiety, functional limitation (including poor school attendance and performance in children) and social handicap through tooth loss. The treatment of dental diseases is expensive, consuming 5–10% of health-care budgets in industrialized countries, and would exceed the entire financial resources available for the health care of children in most lower income countries (17, 19).

^{Source: WHO. Sugars intake for adults and children. p.1, Emphasis Mine}

Furthermore, eating too much added sugar increases the risk of dying with heart disease (Harvard Health Blog) and is correlated to ADHD development.

In the past decade, we have become increasingly aware of strong associations between overweight/obesity and symptoms of attention-deficit/hyperactivity disorder (ADHD) in children, adolescents, and adults.

^{Source: Davis, Caroline: Attention-deficit/Hyperactivity Disorder: Associations with Overeating and Obesity. 2010}

Last but not least, links between sugar intake and the Alzheimer’s Disease have been found.

The only good news is that the current consensus regarding sugar addiction is that sugar is not addictive for humans:

We find little evidence to support sugar addiction in humans, and findings from the animal literature suggest that addiction-like behaviours, such as bingeing, occur only in the context of intermittent access to sugar. These behaviours likely arise from intermittent access to sweet tasting or highly palatable foods, not the neurochemical effects of sugar.

Source: Sugar addiction: the state of the science

Answer 2

Imagine that your arteries are hallways and that your muscle cells are apartments with doors withing those hallways.

When glucose enters your bloodstream, the body says, "Hey pancreas! There is energy in the hallways, I need insulin!" Imagine insulin like agents who come and unlock the doors. The energy then gets into your muscle cells and you are full of energy.

That's what happens when everything works well.

What happens when too much glucose enters your bloodstream too quickly? The body says, "Hey Pancreas! I need insulin immediately!". Pancreas says, "How much boss?" The body demands, "Millions within minutes!" Pancreas replies, "What?! I can't do that!" So it tries to create as many insulin agents as possible, but it's not enough.

here aren't enough insulin agents to unlock the doors so too much energy ends up in the bloodstream. And we can't have any of that. So the body goes to plan B. It releases some of it through urine and converts some of it to fat. That's Diabetes type 1.

There is another scenario. Energy enters the bloodstream. Pancreas is working great. There are enough insulin agents, but they can't get to the doors. The doors are blocked by garbage so that the agents can't even reach the handle. What is this garbage? It's fat. It piles up on the apartment doors and prevents insulin agents can't get to it. That's Diabetes type 2. (1)

How does too much glucose enter the bloodstream too quickly? When we consume foods that contain carbohydrates which are deprived of all or almost all fiber. You see, fiber are like traffic controllers who control how fast energy is absorbed into the bloodstream.

If the sugar is bound to fiber, then the traffic controllers do its work. If not, then it's like opening the borders and letting everyone run through without any order. This causes chaos in the bloodstream.

Free sugars are sugars which are not bound to fiber the traffic controllers. Non free sugars are sugars bound to fiber and this is sugar which is consumed when you eat whole fruits and vegetables. No juicing!