Let us think of the bloodstream not simply as a river of life, but also as an archive of our metabolic history. Within it, millions of red blood cells travel continuously through an intricate network of vessels, carrying out one of the body’s most essential tasks: delivering oxygen to living tissues.
These cells move through a medium containing glucose, one of the principal fuels used by our cells. But there is an important point to remember. The glucose circulating in our blood does not come only from sweet foods.
The carbohydrates in our diet — found in foods such as bread, rice, pasta, potatoes, legumes, cereals, and fruit — are broken down during digestion into molecules that can raise blood glucose, the amount of glucose circulating in the bloodstream.
There is another important source. Our liver can produce and release glucose when the body needs it. Even when we are not eating, this process helps maintain the blood glucose concentration required to supply tissues that depend particularly on glucose as an energy source.
Blood glucose is therefore the result of a delicate balance between what we absorb, what our body produces, and what our tissues use. As with so many biological processes, health depends largely on maintaining that balance.
The Chemistry of the Encounter: There is a common misconception that glucose begins attaching itself to our proteins only when metabolism becomes disturbed. In reality, glycation — the spontaneous attachment of glucose molecules to proteins and other molecules — is a continuous chemical process that occurs throughout the body.
Glucose can react with proteins, lipids, and other molecules without the involvement of an enzyme, meaning without the need for a specialized protein to catalyze the reaction.
What changes when glucose levels rise and remain elevated is the rate and extent of these reactions.
Glycation occurs in everyone, even under normal metabolic conditions. But there is a fundamental principle. The greater and more prolonged the exposure to glucose, the greater the extent of glycation.
Hemoglobin in red blood cells provides a particularly clear example. A small proportion of the glucose in the bloodstream binds spontaneously to hemoglobin, the protein that enables red blood cells to transport oxygen, forming glycated hemoglobin, or HbA1c.
Because red blood cells circulate for approximately 120 days, HbA1c provides a record of prolonged glucose exposure. It does not capture blood glucose at a particular moment. Instead, it reflects average glycemia over approximately the previous two to three months, with greater influence from more recent weeks.
In this way, HbA1c allows us to read part of our metabolic history through a small molecular modification of hemoglobin.
The Silent Erosion: If hemoglobin is a relatively short-lived record of our metabolic past, other proteins have a much longer memory.
Among them are collagen and elastin, structural proteins that provide strength and elasticity to many tissues. Some of these proteins are renewed slowly and can remain in the body for years.
When glycation is excessive and prolonged, proteins undergo progressive chemical modifications and may accumulate advanced glycation end-products, commonly known as AGEs. These compounds are formed through a series of reactions associated with glycation and can alter the structure and function of tissues.
Some AGEs can form cross-links between proteins, changing their mechanical properties. Others can interact with cellular receptors and contribute to oxidative stress, an imbalance involving reactive molecules that can damage cellular components, and to chronic inflammation, a persistent inflammatory response that may contribute to tissue injury.
The image of tissues being “caramelized” may be evocative, but the biological reality is much more complex. Our tissues do not literally become caramelized. Rather, molecular modifications accumulate progressively and may alter the structure and function of proteins over time.
The consequences can affect different parts of the body.
- The retina, the light-sensitive layer at the back of the eye, where damage to small blood vessels can contribute to diabetic retinopathy and impair vision.
- The kidneys, whose microscopic filtering units, called glomeruli, can undergo structural and functional changes that contribute to diabetic kidney disease.
- The peripheral nervous system, consisting of the nerves that connect the brain and spinal cord with the rest of the body. Metabolic and vascular disturbances can contribute to neuropathy, meaning nerve damage that may cause pain, tingling, or loss of sensation.
- The heart and blood vessels, where chronic hyperglycemia — persistently elevated blood glucose — contributes to cardiovascular risk in combination with other metabolic disturbances such as insulin resistance, high blood pressure, abnormal blood lipids, and excess visceral fat.
The important point is that vascular damage in type 2 diabetes is multifactorial. Persistent hyperglycemia and the molecular changes associated with it are part of the picture, but they interact with several other metabolic and vascular factors.
The Road Ahead: Science offers us a sensible compass. Health does not require us to eliminate glycation, which is a natural chemical process that cannot be completely avoided. What matters is limiting excessive and prolonged exposure to glucose while preserving healthy metabolic function.
We can influence our metabolic health through everyday choices.
1. The Order of the Meal
Beginning a meal with vegetables and other fiber-rich foods can help moderate the rise in blood glucose after eating, particularly when carbohydrate-rich foods are consumed afterwards.
The overall composition of the meal, the amount and quality of carbohydrates, and the degree of food processing remain much more important than the order of individual foods. This is therefore not a formula for compensating for an otherwise unbalanced diet.
2. Movement After Eating
A walk or light physical activity after a meal encourages muscles to take up and use glucose and can reduce the postprandial glycemic response, meaning the rise in blood glucose that occurs after eating.
It is a simple intervention whose real value lies in making it part of a regular routine.
3. The Small Alchemy of Vinegar
Acetic acid, one of the principal components of vinegar, can modestly reduce the rise in blood glucose after a meal when vinegar is consumed with food.
Its effect, however, is limited and should never be regarded as a means of compensating for an unhealthy diet. The overall quality of what we eat remains vastly more important.
4. Restorative Sleep
Adequate sleep is an essential component of metabolic health. Sleep deprivation and disruption of our daily biological rhythms can impair insulin sensitivity, meaning the ability of cells to respond appropriately to insulin and take up glucose.
Good sleep helps the body regulate energy metabolism more effectively.
Diabetes Has a Threshold. Biology Does Not: Here we encounter a particularly important distinction.
Medicine needs objective criteria and defined thresholds to diagnose diabetes. Under current criteria, diabetes in nonpregnant adults can be diagnosed with an HbA1c of 6.5% or higher, a fasting plasma glucose of 126 mg/dL or higher, a two-hour plasma glucose of 200 mg/dL or higher during a 75-g oral glucose tolerance test, or a random plasma glucose of 200 mg/dL or higher in a person with classic symptoms of hyperglycemia or a hyperglycemic crisis. In the absence of unequivocal hyperglycemia, the abnormal result must be confirmed.
These thresholds are indispensable. They provide medicine with consistent criteria for diagnosis, guide clinical decisions, and allow meaningful comparisons among patients and studies.
But biology does not recognize diagnostic boundaries.
An HbA1c of 6.4% does not mean that the blood vessels are completely protected, while an HbA1c of 6.5% does not mean that vascular risk suddenly changes the following day. Metabolism does not operate like a switch that changes from “normal” to “diabetic” when a particular number is reached.
Risk follows a continuum. An HbA1c of 5.8% does not meet the diagnostic criteria for diabetes, but it does not represent exactly the same metabolic risk profile as an HbA1c of 5.0%. The ADA recognizes that the relationship between HbA1c and the risk of developing diabetes is continuous and curvilinear, extending below the conventional prediabetes range.
This distinction is fundamental to understanding the disease.
We can speak of diabetes as defined by diagnostic criteria and, separately, of metabolic deterioration that may precede the diagnosis by years.
These are two ways of looking at the same biological continuum. One belongs to the necessary language of medical diagnosis. The other reflects the gradual nature of biology.
And this has an important consequence. The body does not wait for HbA1c to reach 6.5% before responding to an unfavorable metabolic environment.
Hyperglycemia is one of the factors involved, but it does not act in isolation. Insulin resistance, high blood pressure, abnormal blood lipids, visceral fat accumulation, chronic low-grade inflammation, and other metabolic factors can interact well before a diagnosis of type 2 diabetes is established.
That is why waiting for a diagnosis before taking care of metabolic health may mean waiting until a biological process that has been developing for some time has crossed a clinical threshold.
A Reflection on the Future: Monitoring HbA1c can be an exercise in metabolic self-awareness. An HbA1c below 5.7% is within the range considered normal under current diagnostic criteria. Between 5.7% and 6.4% lies the range classified as prediabetes, indicating an increased risk of developing diabetes. An HbA1c of 6.5% or higher falls within the diagnostic range for diabetes.
But a single number does not define a person’s entire metabolic health.
HbA1c is a molecular footprint of prolonged exposure to glucose. That exposure depends on a system far more complex than the amount of sugar we eat.
Our structural proteins can have a much longer memory than our red blood cells. Some are renewed slowly and may accumulate molecular modifications over time. That is why taking care of our metabolism today also has consequences that reach into the future.
The blood, by contrast, is constantly renewed. Red blood cells that leave the circulation are replaced by new ones, and each generation carries its own metabolic history.
Reducing sustained hyperglycemia decreases excessive glucose exposure and therefore reduces one of the conditions that promote the formation and accumulation of glycated proteins. We cannot immediately erase the molecular marks of the past, but we can avoid adding to them.
Ultimately, caring for our metabolic health means preserving a delicate balance between flexibility and rigidity, renewal and wear. It means protecting our blood vessels, tissues, and organs from a metabolic environment that, when unfavorable for long enough, can leave an increasingly deep molecular imprint.
This is not about giving up the sweetness of life. It is about understanding that glucose is part of a complex energy economy that the body regulates continuously.
Because true metabolic harmony does not mean eliminating glucose, an essential fuel for life.
It means preventing excessive and sustained exposure from becoming a burden on our biology and mortgaging our future.
Nullius in verba