In a competition of the most villainized molecules of all time, and certainly in more recent times, sugar might be at the top of the list. Countless brands now tout themselves as “sugar free,” while health authorities have warned against the dangers of added sugar consumption.

On one diet during my participation in the Nutrition for Precision Health study, I ate nearly 200 grams of sugar daily for two weeks, mostly in the form of sugar-sweetened beverages. It made me wonder: what does the science of sugar suggest about its healthiness (or unhealthiness)? Let’s dive in.

Table of Contents

• TL;DR (Too Long; Didn’t Read)
• Ok, but Why?
  • What is Sugar?
  • Glucose Plays a Critical Role in Human Function
  • How Does the Body Process Sugar?
  • The Issue is Not Sugar Itself
  • How Much Sugar is Too Much?
  • Tactics for Managing Added Sugar Consumption
• Takeaways
• Reader Questions
• References

TL;DR

• Sugar is a molecule that is not inherently good or bad
• An excess of added sugar consumption is highly correlated with adverse health outcomes, particularly metabolic and oral
• Humans do not require any added sugar from the diet to survive and function properly; therefore, a theoretical lower limit to daily added sugar consumption is zero
• Tactics that may help blunt the impact of added sugar (over)consumption include: diluting, combining or co-ingesting with other foods, slowing the pace of consumption, and ensuring there is no residual material left in our mouth

Ok, but Why?

What is Sugar?

In the context of the major macronutrients – carbohydrates, protein, fat, and alcohol – sugar is a carbohydrate. Depending on the structure of the molecule, carbohydrates can be categorized as simple (e.g., sugar) or complex (e.g., fiber, starch).

“Sugar” is the generic, catch-all term for the many simple carbohydrates with similar chemical structures. Sugar can be further categorized by the number of molecules they contain: monosaccharide, or one sugar molecule; disaccharide, or two sugar molecules; and oligo- or polysaccharide, or more than two sugar molecules.

The most common sugar molecules:

Name	Type	Notes
Glucose	Monosaccharide	The body’s primary energy source; also referred to as blood glucose (or blood sugar) as it circulates throughout the body in blood
Fructose	Monosaccharide	An isomer of glucose, meaning it has the same chemical formula but the atoms are just arranged differently;1 also known as fruit sugar as it is naturally occurring in fruit
Galactose	Monosaccharide	An isomer of glucose, meaning it has the same chemical formula but the atoms are just arranged differently;1 also known as milk sugar as it is naturally occurring in milk
Lactose	Disaccharide	Galactose + glucose; primarily found in dairy products
Maltose	Disaccharide	Glucose + glucose; also known as malt sugar and can be found in grains, molasses, and beer, among other foods
Sucrose	Disaccharide	Glucose + fructose; also known as table sugar, but can be found in some root vegetables like carrots and beets

Glucose Plays a Critical Role in Human Function

Like many other molecules over the course of human history, sugar is the latest to find itself in the crosshairs of the ‘health police.’ Companies and brands have responded with zero sugar or artificially sweetened products as consumers are on heightened alert to avoid it at all costs.

However, like the other molecules that have been demonized over the years – cholesterol comes to mind – sugar (i.e., glucose and its isomers) does have a biological purpose, not the least of which serving as the primary energy source for human metabolism.² Notably, the human brain depends almost exclusively on glucose to function and consumes ~20% of all glucose-derived energy.³ Therefore, no glucose; no life.

How Does the Body Process Sugar?

In the simplest terms, all carbohydrates are ultimately broken down (digested) by the body into glucose.⁴ Once digested, glucose is transported to two primary places: A) the liver to be stored as glycogen for future use or B) circulated via the bloodstream (blood glucose) to tissues such as muscle that need them to generate energy.

Through a series of complex and interrelated processes, the body attempts to maintain blood glucose levels within a specific range at all times, which is called glucose homeostasis. In response to food intake, several hormones including GLP-1, insulin, and glucagon, among others, play a role in keeping glucose levels within this range.⁵

Role of GLP-1 Hormone in Glucose Regulation⁶

Cause	Effect
Stimulates (increases) the secretion of the hormone insulin	Blood glucose decreases
Suppresses (decreases) the secretion of the hormone glucagon	Blood glucose decreases

However, in the absence of carbohydrates that break down into glucose, the body has mechanisms to create its own glucose, which is a process called gluconeogenesis (translation: creation of glucose from non-carbohydrate molecules). In fact, some well known diets such as keto are known to significantly restrict carbohydrates. Yet, many people on these diets do just fine (some better than fine).

Thus, these dynamics beg the question: do we necessarily need to eat sugar?

The Issue is Not Sugar Itself

Like other molecules in our diet, sugar is not inherently good or bad. As evidenced above, there are many critical physiological functions that require glucose. Therefore, I would argue the issue with sugar is not whether or not we eat it (we will), but instead the type, quantity, and speed with which we eat.

Type

Generally speaking, the body has to work harder and longer to break down more complex molecules. An analogy is taking apart a 1,000-piece jigsaw puzzle vs. a 100-piece puzzle; it will take more time and effort to break down the former.

The same can be said of sugar. When complex, unprocessed or unrefined carbohydrates like starch and whole grains are digested, the result is a steadier stream of glucose released into the bloodstream. In contrast, simple carbohydrates like sugar produce a spike of glucose released into the bloodstream, which the body has to counteract. You may have seen this referenced as the glycemic index, or the relative impact to blood glucose of certain foods (higher means a larger spike).

Quantity

Additionally, it may not come as a surprise that it is easier to eat a higher quantity of simple sugars due to their ease of digestibility; they simply (no pun intended) do not satiate or “fill us up.” Therefore, what often occurs is that not only are these molecules quick-digesting and cause a glucose spike, but they are often eaten in quantities that exceed what the body can reasonably handle.

Speed

Finally, the third characteristic of sugar is that it often comes in forms that are very easy to eat quickly. For example, it would be far more difficult to eat ten oranges compared to drinking a glass or two of orange juice. The former have fiber that slows down the digestive process, reducing the glycemic impact on our body, while the latter introduces a bolus of sugar that our body has to deal with in an accelerated manner, causing strain on our digestive system.

How Much Sugar Is Too Much?

Spoiler alert: there is no one-size-fits-all answer to this question. We can, however, put some parameters around how much sugar is too much.

Firstly, it is important to define natural versus added sugar. Natural sugar, as the name suggests, is naturally occurring in foods like fruits and vegetables. Added sugar, on the other hand, can be thought of as natural sugar added to foods that don’t typically have sugar. For example, table sugar to coffee or high fructose corn syrup to carbonated water to make soda.

What Do the Guidelines Say?

The American Heart Association (AHA) recommends men and women consume no more than 36 grams and 25 grams, respectively, of added sugar daily.⁸ For its part, the World Health Organization (WHO) guidelines recommend limiting “daily intake of free sugars to less than 10% of their total energy intake” with “a further reduction to below 5% or roughly 25 grams per day would provide additional health benefits.”⁹

To determine whether these recommendations are relevant to our individual situation, it is important to understand the rationale behind them.

Putting Guidelines in Context

At least in the case of the WHO, these recommendations are derived from clinical trials that demonstrated a correlation between higher sugar consumption and adverse outcomes such as overweight, obesity, and dental caries (cavities).¹⁰ However, as you may have heard in other spheres, correlation is not causation. In other words, just because sugar consumption is high does not mean an individual will become overweight, obese or have cavities with certainty. Rather, it is to say that the higher the sugar consumption, the higher likelihood an individual will develop one of these adverse outcomes.

With this in mind, does the same correlation hold in reverse? Said differently, is there a negative impact of very low or no added sugar consumption? The answer to this question appears to be no for two primary reasons:

1. As described above, the body can create its own glucose from non-carbohydrate sources (gluconeogenesis)
2. Despite our best efforts, it is nearly impossible to eliminate all natural sugars from our diet, certainly if it is a healthful one inclusive of fruits and vegetables. Therefore, the body will have at least some carbohydrates from which to derive glucose and use as metabolic fuel

Taken all together, a theoretical lower limit for daily added sugar consumption can be thought of as zero. On the flipside, the risk of added sugar consumption can be considered as a gradient: the higher the consumption, the higher the risk of developing adverse metabolic or oral health conditions, all else being equal.

Tactics for Managing Added Sugar Consumption

Practically speaking, some amount of added sugar consumption is unavoidable, if not desired for the simple joy of eating it. We may enjoy a cold soda on a hot summer day or a dollop of honey in our yogurt. The key is managing the impact these foods have on our body.

Bearing in mind how glucose is digested by the body (described earlier), here are a few tactics to consider when consuming added sugar:

Dilute

To avoid introducing a bolus of glucose to the digestive system, try diluting sugar-sweetened beverages. For example, mix Gatorade with a bottle of water. This will decrease the quantity of glucose the body has to digest at one time, allowing for a more steady release into the bloodstream.

Combine or Co-Ingest

When added sugar is consumed with other foods containing protein^11,12,13, fat^14,15, and/or fiber^16,17,18, the digestive process slows (more specifically, the rate of gastric emptying slows), which similarly dampens the rise in blood glucose levels.

Slow Down

To achieve the same effect without diluting or co-ingesting, consider consuming the added sugar over a longer time period. For example, rather than drinking an entire can of soda or eating a package of candy in one bout, consume them over 15-20 minutes (or longer) instead.¹⁹

Wash It Down

As kids, we may have heard the warning from our parents or dentist to not leave substances, particularly sugar, in our mouth and on our teeth, and for good reason. Dental caries (cavities) form when bacteria in the mouth metabolize carbohydrates (sugars) from the diet, which drops pH and causes tooth decay (demineralization).²⁰ Drinking water can help wash away sugars from the mouth and help return the pH to a more normal state, thereby reducing the risk of cavities.²¹

Takeaways

Taken all together, it is clear that sugar itself is neither good nor bad. Rather, it is the way in which we humans consume sugar that makes is such.

Over a sustained period, diets high in sugar, particularly simple carbohydrates and added sugars correlate with higher risk of metabolic and oral diseases like Type 2 diabetes and cavities. Further, the way in which we tend to eat these types of foods – quickly and in large quantities – exacerbates the impact on our metabolism and body.

That all said, there are many tactics we can employ to enjoy sugar while limiting the impact on our digestive system and oral health.

Reader Questions:

• Have you made changes to your sugar consumption over the course of your life?
• What are your thoughts on the American Heart Association and World Health Organization sugar intake guidelines?
• How do you consciously or sub-consciously alter your behavior when you consume sugar?

References:

1. https://www.khanacademy.org/science/ap-biology/chemistry-of-life/properties-structure-and-function-of-biological-macromolecules/a/carbohydrates
2. Nakrani MN, Wineland RH, Anjum F. Physiology, Glucose Metabolism. [Updated 2023 Jul 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK560599/
3. Mergenthaler P, Lindauer U, Dienel GA, Meisel A. Sugar for the brain: the role of glucose in physiological and pathological brain function. Trends Neurosci. 2013 Oct;36(10):587-97. doi: 10.1016/j.tins.2013.07.001. Epub 2013 Aug 20. PMID: 23968694; PMCID: PMC3900881.
4. Libretexts. (2024, January 17). 4.2: Digestion and absorption of carbohydrates. Medicine LibreTexts. https://med.libretexts.org/Bookshelves/Nutrition/Human_Nutrition_2020e_(Hawaii)/04%3A_Carbohydrates/4.02%3A_Digestion_and_Absorption_of_Carbohydrates
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9. https://www.who.int/news/item/04-03-2015-who-calls-on-countries-to-reduce-sugars-intake-among-adults-and-children
10. https://www.who.int/publications/i/item/9789241549028
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21. https://www.livestrong.com/article/13774844-how-to-eat-sweets-without-damaging-teeth/