Why shouldn’t you make important decisions on an empty stomach or in the evening? KBSU expert opinion

Expert opinion by Larisa Bugova, Associate Professor of the Department of Faculty Therapy at the KBSU Medical Academy, PhD in Medicine, and endocrinologist.

In everyday life, you often hear proverbs like, «Don’t make decisions when you’re hungry» or «The morning is wiser than the evening.» But what’s the medical, neurophysiological, and endocrinological significance behind these phrases? A person’s ability to think rationally, assess risks, and draw balanced conclusions isn’t simply a matter of willpower or character. It’s a complex biochemical process directly dependent on glucose levels, hormonal levels, circadian rhythms, and overall metabolic health.

As experts note, people often underestimate the influence of basic physiological needs on higher nervous activity. Larisa Bugova, Associate Professor of the Department of Faculty Therapy at the Medical Academy of the Kabardino-Balkarian State University named after Kh. M. Berbekov and a PhD candidate in Medicine, explains how blood sugar levels, hunger and satiety hormones, and the biological clock dictate the quality of our decisions.

According to Larisa Bugova, the brain is the body’s primary energy consumer. Its primary and preferred fuel is glucose. While the brain can adapt under extreme conditions and feed on ketones (fat metabolism products) or obtain energy from amino acids, she emphasizes that a constant supply of sugar is essential for optimal, uninterrupted functioning. Furthermore, many hormones require glycosylation (binding to glucose) for normal functioning, further confirming the critical importance of this nutrient.

The Hunger Trap: Cortisol and Ghrelin

When people use the expression «hungry means angry,» they are describing the body’s classic stress response, explains Larisa Bugova. When there’s a prolonged absence from food, the brain begins to experience an energy deficit and perceives it as a threat. In response, the adrenal glands release the stress hormone cortisol, signaling the brain to mobilize and «feed its own reserves.»

With high cortisol, a person becomes irritable and impulsive, the expert notes. «Objectivity decreases, concentration falters, and apathy sets in. The brain’s main subconscious goal at this point is to quickly get rid of temporary discomfort. This is why, on an empty stomach, people can either make a hasty, erroneous decision or, out of sheer stubbornness and irritation, turn down a lucrative deal simply to end an unpleasant conversation.

Endocrinologists pay special attention to ghrelin, the hunger hormone. Its levels gradually increase during hunger and decline after satiety. However, ghrelin can remain consistently high despite chronic stress, lack of sleep, or strict diets. The constant feeling of hunger it signals literally «eats away» at concentration and cognitive ability.

As Larisa Bugova explains, the body remembers a person’s eating schedule. If a person is accustomed to eating «on the clock,» ghrelin will begin to be released at the usual mealtime, even if the body doesn’t have a pressing need for calories at that time. According to the expert, skipping such a regular meal causes severe nervousness and decreased performance in people who eat a balanced diet.

The other side of the coin: the sugar trap

The solution would seem obvious: just eat. But it’s not that simple, the expert warns. Sugar is considered a pleasure substance, along with nicotine and alcohol. Pleasure is accompanied by the release of the neurotransmitter dopamine. However, too frequent «rewards» to the brain (a constant supply of glucose from food) leads to overexcitation of neurons and their depletion, leading to addiction. For comparison, Larisa Bugova cites serotonin (the happiness hormone), which, unlike dopamine, is not addictive.

The quality of carbohydrates, she says, plays a huge role. Sucrose consists of glucose and fructose. While the brain requires glucose, fructose in large doses is neurotoxic. The liver can safely process about 12 grams of fructose, but modern humans consume about 50 grams per day. Excess fructose, the expert believes, is a factor in the development of depression, memory loss, and cognitive decline.

Larisa Bugova supports this by citing data from an American experiment: for 10 days, schoolchildren were given food without added sugar, but with calorie content and weight maintained (so that the improvement in well-being could not be attributed to weight loss). By the 10th day, the children’s metabolic parameters (insulin, lactate, and sugar levels) had stabilized, and their academic performance, memory, concentration, and overall well-being also significantly improved, as noted by their parents.

Insulin and Leptin: The Invisible Enemies of a Clear Mind

Speaking about the impact of sweets on the brain, Larisa Bugova warns: just one sweet drink a day increases the risk of diabetes by 29%. In response to sugar, the pancreas releases insulin. This not only nourishes cells but also synthesizes fat. Chronic excess sugar leads to insulin resistance, which, according to population studies, is directly correlated with poor cognitive performance and memory impairment. As Associate Professor Bugova notes, citing the work of Dr. Robert Lustig, excess sugar increases chronic inflammation and the formation of free radicals, which damage brain cells.

Furthermore, high insulin blocks the action of leptin, the satiety hormone produced by fat cells and signals the brain to stop eating. Leptin blockage (leptin resistance), according to Larisa Bugova, is accompanied by apathy, lethargy, inactivity, and a paradoxical, constant feeling of hunger. The opposite, genetic condition, leptin deficiency, also occurs, causing children to eat nonstop, leading to obesity developing as early as 2-3 years old, the expert adds.

How do circadian rhythms and daily fluctuations affect productivity?

According to the expert, our brains are governed by strict circadian rhythms, and cognitive functions, attention, and analytical thinking fluctuate throughout the day.

By evening, emotional and neurotransmitter resources are depleted, explains Larisa Bugova. Activity in the prefrontal cortex, responsible for complex analysis and impulse control, decreases.
According to the expert, evening hunger or fatigue compound the natural decline in concentration. If a person also has metabolic problems (excess weight, diabetes, or high blood pressure), their brain operates in strict energy-saving mode in the evening, which inevitably leads to impulsive decisions based on momentary emotions rather than long-term strategy.

Expert Summary: Rules for «Balanced» Thinking

In summary, the endocrinologist formulated several key findings:

It’s best to avoid making important decisions on an empty stomach or late in the evening. During these periods, the expert believes, emotional resources are depleted, and neuronal performance is reduced. The brain perceives hunger as stress, which provokes impulsivity.

Hunger distorts reality. A surge in cortisol and ghrelin impairs judgment. A person seeks to quickly relieve discomfort rather than solve the problem optimally.

It’s not just the fact of eating, but also its quality. As Larisa Bugova emphasizes, if a person eats foods high in added sugar and fructose, they’ll experience a quick dopamine response, but it’s followed by «brain fog,» decreased concentration, and memory loss. «You can make a brilliant deal on an empty stomach if you’re used to it, and you can just as easily make a fatal mistake by gorging yourself on fast carbohydrates,» the expert notes.

Individual sensitivity matters. According to the expert, some people are genetically and metabolically able to easily tolerate hunger. Cognitive decline primarily affects those accustomed to a strict diet, as well as those with obesity, insulin resistance, and diabetes.

A comprehensive approach is necessary. As Larisa Bugova summarizes, brain function is influenced not only by immediate hunger but also by overall physical health: sleep quality, blood pressure, and the presence of metabolic disorders.

The expert’s main advice: if a person is about to sign a contract, have a difficult conversation, or choose a life strategy, they should take care of their metabolic comfort in advance. A balanced diet (complex carbohydrates, proteins, healthy fats), stable glucose levels without insulin fluctuations, and making decisions during peak cognitive activity hours—this is the formula that, according to Larisa Bugova, will help avoid annoying mistakes.