What happens when you don’t eat?

In this brief guide, we’ll address the query: “What happens when you don’t eat?” Also, we’ll explore in what instances fasting is safe, and when people should avoid fasting. 

What happens when you don’t eat? 

Not eating, also known as fasting, can have various effects on a person’s body, depending on his or her health, and metabolic functions. 

The act of fasting can be done as a way to instill self-discipline, to lose weight, for spiritual/religious reasons, and as a sign of protest. 

Its effects may also vary, depending on the time for which an individual fasts. Intermittent fasting, for example, consists of alternating periods with normal eating schedules, with periods of 24-hour fastings (this approach is also known as eat-stop-eat). 

When fasting, a person’s body undergoes phases. During the first eight hours after a person has eaten, his or her body sources calories from food in the digestive system. 

Various hormones shift and allow the sugars found in foods to be taken in by the cells for their various processes. This is referred to as a fed state

About halfway into the fed state, a person’s body enters what is known as the early fasting state, and during this period, a person’s body begins to use stores of fat known as glycogen, from the liver. 

The early fasting state can last for up to 18 hours after eating, and towards the end, a person’s body will have begun to source calories from protein and fat. 

After 18 hours, the body will have entered the fasting state, which will last up until 2 days after last having eaten. By then, a person’s body will have consumed the energy stored as fat in his or her liver, and begun to source calories from proteins and fat from other areas. 

This can lead to ketosis, a condition in which fat and protein reserves such as adipose tissue and muscles are broken down to nourish a person’s cells. 

Beyond this, there is a danger of a person entering a state of ketoacidosis, which is when the acid concentration in a person’s blood increases, lowering the pH and altering many metabolic functions.

Ketoacidosis is a life-threatening condition that requires immediate medical attention and can occur in diabetic patients whose blood sugar levels spike and crash. 

Specifically, the effects of fasting may include: 

  • Weight-loss – as fasting restricts an individual’s intake of calories, it activates lipid metabolism to begin sourcing energy from adipose (fatty) tissue and protein:
  • Lowered (but also varied) blood sugar levels – as it reduces the intake of instantly available calories (sugars) it can help users reduce insulin resistance.*
  • Irritable moods – Some individuals may experience irritable moods and changes in temperament as a result of being hungry. Also known as being “hangry.”
  • It may Improve cognitive function – a low intake of calories can reduce inflammation, which has been linked to neurodegenerative disorders and cognitive diseases. Though this has yet to be studied definitively and defined in humans. 
  • Increases growth hormone secretion – Human growth hormone is essential for tissue growth, weight loss, and other metabolic functions
  • It is associated with increased longevity – a lower intake of calories is associated with delayed aging, though the exact cellular and metabolic processes have yet to be discerned.

*However, it is important to note that this may not be the case for all patients, and they should consult with a medical specialist to see if this option is both feasible and safe. 

There are many benefits to fasting, but it may not be indicated for all individuals. Below, we’ll review a few circumstances in which fasting may be beneficial, and when it may be contraindicated. 

When is it safe to fast?

Fasting is generally safe, so long as the individuals carrying it out have no underlying medical conditions for which it is contraindicated. Users should, however, be mindful that when fasting, they don’t become dehydrated, and that when they eat, their diet is balanced and meets their nutritional needs. 

Intermittent fasting, along with a diet low in calories and carbohydrates can be used by those looking to lose weight, under medical supervision, of course. 

Users should always consult with a certified medical professional or a nutritional expert to see if fasting is in their best interest, and to avoid malnourishment. 

When should people avoid fasting?

Fasting is contraindicated for children of all ages, pregnant and breastfeeding women, the elderly, and those diagnosed with comorbidities such as diabetes, autoimmune diseases, and other disorders. 

Diabetic patients should be especially cautious, and combine a healthy diet with exercise before embarking on a fasting regime, to avoid dangerously low blood sugar levels and ketoacidosis. 

Those with underlying health conditions should consult with a medical practitioner to see if fasting can provide them with their desired health benefits.  


In this brief guide, we’ve addressed the query: “What happens when you don’t eat?” Also, we’ve explored in what instances fasting is safe, and when people should avoid fasting. 







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