It’s three in the afternoon. You ate less than two hours ago. The concentration disappeared. The eyelids are heavy. And something in the body begins to ask for something sweet: chocolate, a cookie, a coffee with milk. Whatever. Most people assume that this feeling is normal. In a sense it is, because it happens to them almost every day. But “frequent” is not the same as “inevitable.” Behind that afternoon slump, there is often a precise metabolic mechanism: a glucose peak followed by a sharp fall.

Every time we eat, the digestive system breaks down food into glucose—the body’s basic fuel—and releases it into the bloodstream. The pancreas responds by secreting insulin, the hormone that “opens the door” of the cells so that glucose enters and is converted into energy. Under normal conditions, the process is gradual and orderly: In people without diabetes, blood glucose peaks about an hour after eating and returns to baseline values ​​within two to three hours.

The problem appears when glucose arrives too quickly and in too much quantity. The blood sugar curve rises sharply, the pancreas responds with a strong secretion of insulin, and before long, levels drop suddenly. This oscillation—rapid rise, sharp decline—is what is known as glucose spike or glycemic peak.

“Glucose spikes unbalance our body”explains Linda Jungwirth, a nutritionist specializing in microbiology. “When that happens, a inflammatory process which, if repeated frequently, can lead to chronic inflammation and, in the long term, in conditions such as type 2 diabetes.” The distinction is important: Jungwirth clarifies that talking about diabetes in this context exclusively implies the type 2 diabetes —which is characterized by insulin resistance or insufficient insulin production— and not type 1, which is an autoimmune condition with completely different mechanisms.

For a long time, the topic of glucose was almost the exclusive territory of endocrinologists and patients with a previous diagnosis. Today, however, The conversation expanded and the use of continuous glucose monitors grew, extending to people without diabetes. Although its value in this population still generates debate in the medical community, the greater visibility of glucose data allowed study in real time the effect of lifestyle on blood sugar levels.

Study results associated glucose spikes—described as rapid energy spikes followed by “crashes”—with difficulty concentrating, lower energy and fatigue; So brain fog, sudden cravings, irritability after eating, and drowsiness after lunch—all can have, at least in part, a glycemic explanation.

Other research has also discussed the relationship between glucose peaks and oxidative stress, endothelial dysfunction and inflammation: mechanisms associated with the development of cardiovascular diseases and type 2 diabetes.

Jungwirth describes the mechanism like this: When the body detects too much glucose in the blood, the pancreas secretes insulin to reduce it. That insulin acts like a key that allows glucose to enter the cells and leave the bloodstream. If this process is repeated frequently and intensely, the pancreas overworks and the blood vessels can deteriorate. “The more glucose spikes you have, the longer it takes the body to regain balance, homeostasis”says Jungwirth. “That constant effort to compensate is what, in the long run, can become problematic.”

It is worth clarifying that the review on glucose spikes in people without diabetes concluded that significant health effects are more likely as a result of frequent and prolonged spikes over time, and not isolated episodes, so that an occasional spike after, for example, a birthday party of pizza or pasta with cake, would not be a problem, but the daily pattern would be.

Not all foods raise glucose in the same way. Those who do it the fastest are the Refined carbohydrates and simple sugars: White bread, white rice, cookies, fruit juices, sugary drinks, industrial breakfast cereals, among some of the most popular examples.

That said, food is not the only variable that affects the presence or absence of glucose spikes. A Stanford study (2025) found that Not all starchy foods affect everyone equallysince there was a lot of individual variability in which of those foods produced the highest peak, and those differences were related to the metabolic state of each person. In other words: Potato can generate a huge spike in someone with insulin resistance, and almost nothing in someone without that condition.

He context also affects. Eating carbohydrates alone and on an empty stomach generates more pronounced peaks than eating them accompanied by protein, fiber or fat, which act as buffers. Along the same lines, the speed at which you eat also influences (the slower the better), and the stress and the lack of sleep also, since they raise cortisol, a hormone that increases blood glucose even without eating.

How to calm glucose spikes

The good news is that there are concrete strategies, backed by scientific evidence, that do not involve extreme diets or giving up carbohydrates to moderate peaks. Many of them were popularized by Jessie Inchauspé, a French biochemist – also known as “the glucose queen” – who has been spreading the impact of glucose on everyday symptoms for years.