How long can the body go without food?

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Just how long can the body go without food? And what are the implications of restricting food intake for long-term health and well-being? 

The length of time a body can be deprived of the fuel and nutrients it needs to function properly varies greatly and depends on many factors. These can include age, race, ethnicity, level of activity, and amount of fat tissue. 

For a baby or a young child, the length of time is shorter because a developing child’s brain and body expend energy at a high rate and need to be fueled on a regular basis. For fully grown adults, the amount of time a body can go without food varies according to the factors above. 

But no matter what the length of time is, going without food can have serious consequences.

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Regardless of the amount of time a body can go without food, the body interprets this restriction of its source of fuel as starvation and will shift into survival mode to ensure vital bodily functions will continue. Dieting for any length of time and diets of any kind are forms of restriction, which can lead to serious physical and mental health complications, including hair loss, organ damage, depression, and eating disorders. So intentionally going without food for any reason for a long period of time, unless medically directed due to a legitimate food allergy, for example, is never a good idea.

So, how long can the body go without food?

How long the body can go without food isn’t a topic that can be studied by scientists in an ethical manner, because restricting food for any reason other than medical necessity, such as due to an allergy, can have fatal consequencesHowever, studies on those who participated in hunger strikes found that time frames participants abstained from eating food ranged from several weeks to several months. 

The longest recorded human fast in a higher weight individual is 382 days, or just over one year. (1) However, this is an old study, covering a short period of time, and research has subsequently found that conventional weight management practices have a high long-term failure rate. (2) In lower weight individuals, the body’s starvation tolerance is probably closer to several months, according to another study. But damage to the body during that period can be fatal. (3) 

Another study reported that, because of the higher amount of fat tissue in female bodies, women are able to last longer in a starvation mode than men. (4)

What happens to the body over time without food?

Food is a source of fuel for the body. The protein, fat, carbohydrates, fiber, vitamins, minerals, and calories in foods are all needed for hundreds of processes in the body. When the body is deprived of the sources of energy and nutrients needed to operate optimally, the body has to lean upon its reserves. If the body is already depleted, existing deficiencies will cause complications to occur more quickly. 

One of the first things that happens when not enough calories are consumed to provide enough energy to fuel the body’s activity level and maintain its present body weight is metabolism will slow down. This won’t necessarily happen with a few skipped meals over a few days, but it will occur if the body is deprived of enough food to sustain itself over a longer period of time. 

The body interprets this lack of fuel as starvation and will adjust its metabolism accordingly to survive. Dieting and diets are, in effect, forms of starvation and can have dire consequences.

Starvation has three phases. (5) 

Phase I

Starts as soon as the last meal eaten has been digested. The body doesn’t have to adapt to long-term food shortage here yet. But the brain needs a steady supply of glucose between meals. This phase is brief, because the body stores little energy as glucose or glycogen, which will be used up within 24 hours. After 12 hours of starvation, about half of the body’s energy is drawn from free fatty acids, rather than glucose. (6)

Phase II

Starts when glycogen stores are fully depleted. In this phase, the body breaks down its fat stores to create new sources of glucose in the liver and kidney and produce ketone bodies to help fuel the brain. (5)

Women with anorexia nervosa (AN) who typically consume less than half the calories needed to meet their daily energy needs show low levels of IGF-1, estrogen, insulin and leptin levels, which are essential for the body to operate properly, and elevated cortisol levels, which are stress hormones and indicate the body is in distress. (7)

When someone goes on a diet, the results are the same as what happens in Phase II of starvation. (8)

Phase III

Occurs when food deprivation is prolonged, fat reserves are exhausted, and the brain can’t rely on ketone bodies any more. This is when the body breaks down muscle tissue to convert amino acids to glucose in the liver to maintain brain function. This is the protein wasting stage, and it can be fatal when protein loss is over 50%. (9)

Signs the body is in starvation mode

Some signs that signal the body is in starvation mode include:

  • Depression:  the body’s production of neurotransmitters has slowed down, resulting in less serotonin, which helps regulate mood
  • Constipation: the body’s GI tract doesn’t have enough food to propel the digested mass through the intestinal tract 
  • Feeling cold: because metabolism is lower, the your body produces less heat to conserve energy for other vital bodily functions
  • Lack of energy: without the Krebs cycle processing food, the body’s biochemical processes don’t produce enough energy
  • Hair loss: as a result of the thyroid slowing down 

Signs of eating disorders

These can all be signs of eating disorders, too. Anorexia nervosa (AN), bulimia nervosa (BN), and binge eating disorder (BED) can involve periods of restricting food–which the body interprets as starvation–in some way, whether by not eating, purging, or exercising excessively. What starts as restricting amounts of food consumed or specific foods, food groups, or ingredients in an attempt to be what is perceived as “healthier,” or to lose weight, which any diet and uniformed healthcare practitioners may recommend, can lead to disordered eating and a full-blown eating disorder. (10)

If you think you or someone you know may have an eating disorder, it’s important to seek help sooner rather than later. Eating disorders do not go away on their own, but recovery is possible.

Disclaimer about "overeating": Within Health hesitatingly uses the word "overeating" because it is the term currently associated with this condition in society, however, we believe it inherently overlooks the various psychological aspects of this condition which are often interconnected with internalized diet culture, and a restrictive mindset about food. For the remainder of this piece, we will therefore be putting "overeating" in quotations to recognize that the diagnosis itself pathologizes behavior that is potentially hardwired and adaptive to a restrictive mindset.

Resources

  1. Stewart WK, Fleming LW. (1973) Features of a successful therapeutic fast of 382 days’ duration. Postgraduate Medicine Journal. 1973;49(569):203-9. https://pubmed.ncbi.nlm.nih.gov/4803438/
  2. Aphramor, L. (2010). Validity of claims made in weight management research: a narrative review of dietetic articles. Nutrition Journal, 9, 30. https://doi.org/10.1186/1475-2891-9-30
  3. Wang T, Hung CC, Randall DJ. (2006) The comparative physiology of food deprivation: from feast to famine. Annual Review of Physiology,68:223-51. https://pubmed.ncbi.nlm.nih.gov/16460272/ 
  4. Henry CJK. (July 2008) The biology of human starvation: some new insights. Nutrition Bulletin, 26, (3): 205-211. https://onlinelibrary.wiley.com/doi/abs/10.1046/j.1467-3010.2001.00164.x
  5. McCue MD. (2010) Starvation physiology: reviewing the different strategies animals use to survive a common challenge. Comparative Biochemistry and Physiology, Part A Molecular and Integrative Physiology, 156(1):1-18. https://doi.org/10.1016/j.cbpa.2010.01.002 
  6. Newsholme EA, Leech AR. (2009) Functional Biochemistry in Health and Disease. Xvi. Wiley-Blackwell; Chichester, UK; Hoboken, NJ, 543. https://www.wiley.com/en-us/Functional+Biochemistry+in+Health+and+Disease-p-9780471931652 
  7. Misra M, Kilbanski A. (2006). Anorexia nervosa and osteoporosis. Reviews in Endocrine and Metabolic Disorders,7(1-2):91-9. https://pubmed.ncbi.nlm.nih.gov/16972186/ 
  8. Walford RL, Mock D, Verdery R, MacCallum T. (2002). Calorie restriction in biosphere 2: alterations in physiologic, hematologic, hormonal, and biochemical parameters in humans restricted for a 2-year period. The Journals of Gerontology, Series A, Biological Sciences and Medical Sciences,57(6):B211-24. https://pubmed.ncbi.nlm.nih.gov/12023257/ 
  9. Devlin, MJ. (September 2011). Why does starvation make bones fat? American Journal of Human Biology,23(5):577-585. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3169094/#R103
  10. Memon AN, Gowda AS, Rallabhandi B, Bidika E, Fayyaz H, Salib M, Cancarevic I. (2020 Sep 6) Have Our Attempts to Curb Obesity Done More Harm Than Good? Cureus, 12(9):e10275. doi: 10.7759/cureus.10275. PMID: 33042711; PMCID: PMC7538029.

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