What are the consequences of not eating for several hours?

Fasting or not eating for several hours is physiological and is associated with the circadian rhythm. However, when it is prolonged it has severe repercussions on metabolism.

Written and verified by the doctor Mariel mendoza on November 03, 2021.

Last update: 03 November, 2021

Fast is the term used to describe the fact of not eating for several hours. By definition, it is the amount of time without eating until the next breakfast. There is a daily fast that is associated with the circadian rhythm and usually varies between 10 to 14 hours.

However, fasting can be established from just 4 hours to 40 days without eating, with the possibility of subsisting using energy reserves.

State of metabolism after spending several hours without eating

Fasting is divided into 3 phases that depend on the main source of energy used. There are also 3 sources: carbohydrates (sugars and carbohydrates), lipids or fats and proteins.



First phase

In this case, the energy fuel is glucose and all carbohydrates. The circulating glucose in the blood will be metabolized and then the glycogen stores in the liver and muscle are degraded.

This can supply power for 24 to 48 hours. In these early moments, 25% of glucose is directed to the central nervous system, while the rest is directed to muscle and red blood cells.

After this time, hypoglycemia (decrease in blood glucose) occurs, which may manifest with dizziness, cold sweats, headache, and general tiredness. In addition, the stored triglycerides are degraded, so that fatty acids are metabolized faster.

When the energy supply to the brain begins to be insufficient, the activity of the sympathetic nervous system is increased with the consequent release of catecholamines (adrenaline and norepinephrine) that favor the degradation of lipids and proteins.

Second stage

If we continue without eating for several hours, after hypoglycemia, lipid consumption ensues. The low plasma sugar acts on the hypothalamus, the autonomic nervous system, the adrenal glands and the pancreas.

When triglycerides stored in adipose tissue are degraded, they release fatty acids into plasma, which are converted into a metabolic intermediate that can generate energy in the form of ATP. Or in ketone bodies, which are also energy fuel.

Growth hormone is released that limits glucose uptake by peripheral tissues. In addition, it promotes the degradation of lipids and the synthesis of ketone bodies.

Increases norepinephrine and adrenaline, which inhibit muscle glucose uptake and insulin secretion. The release of glucocorticoids, such as cortisol, which promotes the breakdown of proteins with the release of amino acids to produce more glucose, is also promoted.

By not eating for several hours, the pancreas modifies its behavior and its rate of hormone release, increasing glucagon production.

Third phase

At this point it is no longer considered fasting, but starvation. It is a practically irreversible advanced state. There are no longer reserves of carbohydrates or lipids and proteins continue to be degraded. There is multi-organ involvement, with an increase in volume due to fluid retention (edema).

Symptoms associated with not eating for several hours

After 4-6 hours after the last intake, hypoglycemia manifests itself, with symptoms such as generalized weakness, dizziness, headache and bad breath. In addition to lack of concentration, memory impairment, irritability and bad mood.

By not having food in the stomach, gastric acid irritates the stomach lining causing gastritis. This results in burning and pain in the epigastrium.

The feeling of hunger causes bingeing due to anxiety, in which it is preferred to consume carbohydrates and fats in greater quantity than required. And the metabolism slows down in order to maintain as many reserves as possible.

Delayed intestinal transit causes bloating, constipation, and a feeling of fullness after eating. However, a 12-16 hour fast is not detrimental to health in the long term. In fact, it’s what the intermittent fasting protocol is based on.

Feedback status after fasting

When food is eaten after a period of fasting, the so-called feedback status, as an adjustment mechanism to avoid another episode of hypoglycemia. In this case, triglycerides are the first to be metabolized.

However, glucose goes through an adaptation process. Initially, due to low blood sugar levels, it is only the liver cells that capture glucose, receive it through the portal vein, and distribute it to the brain and peripheral tissues.

This is due to the liver remains synthesizing glucose for a few hours after ingestion, but not with the purpose of releasing it into the blood, but to re-establish liver glycogen reserves.

As the plasma glucose concentration rises, so does the liver uptake rate. Progressively, it will be metabolized through the glycolysis pathway and its excess will be disposed of for the synthesis of glycogen and triglycerides.

The liver builds glycogen stores to use when needed. This is a store of glucose.

Nutritional recommendations for meal times

For an efficient metabolization of the energy contained in the food consumed, not only the amount ingested is important, but also how it is distributed during the day. It is recommended that the daily feeding be with a frequency of 5 times a day.

In addition, energy must be distributed with 20% of the total at breakfast, 10% at each snack, 30% at lunch and 30% at dinner. Snacks would be one between breakfast and lunch, and another between lunch and dinner. This translates to consuming food every 3 to 4 hours.

In terms of quantity, balanced and harmony is recommended in the main meals, with 10-15% proteins, 15-30% fats and 55-75% carbohydrates. All foods in the nutritional pyramid must be included.

Secondly, intermittent fasting is considered healthy if guided correctly. It consists of a 16-hour fast, with a short time interval for ingestion of 8 hours. Then fasting again.



Not eating for several hours may be an option

Many nutritionists recommend eating every 3 to 4 hours. Splitting the food reduces anxiety and maintains the feeling of satiety, which allows you to make more appropriate choices at the next meal.

However, intermittent fasting can be beneficial for your health as long as it is managed properly. Although you have to consider that stopping eating in itself is not a factor in losing weight. It must be accompanied by an appropriate intake plan and prescribed physical exercise.

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