INTERMITTENT FASTING

Intermittent fasting continues to gain traction in modern society.  Experts agree that this eating regimen may result in favorable metabolic changes and, thus, improve human health. Importantly, evidence suggests intermittent fasting regimens, assuming the individual does not have contraindications, are safe in terms of both physical and mental health in normal weight, overweight or obese healthy adults.

Intermittent fasting refers to voluntary abstinence from both energy containing food and drink.  A variety of formats can be applied.  Many intermittent fasting protocols do not specify what to eat or drink, rather they instruct participants when to consume calories. The most popular types of intermittent fasting include:

  • Alternate-day fasting (involving alternating fasting days, that is days with no energy containing foods and drinks, and eating days)
  • Time-restricted fasting (involving unlimited energy intake within specific time frames,followed by regular, extended fasting intervals)
  • Modified fasting regimens (involving consumption of 20–25 % of energy needs on fasting days),
  • Religious fasting (such as Ramadan and other religious fasts). 1

Time-restricted fasting, or periodical fasting, is a very commonly applied approach to intermittent fasting. One example is 16:8 fasting protocol referring to abstention from energy containing foods or drinks for 16 hours followed by eight hours- feeding periods.  Similarly, 18:6 fasting protocol means 6 hours of feeding with 18 hours of fasting. For instance, 16:8 can be simply applied by skipping breakfast and eating just between 11am and 7pm, with following 16 hours of fast.   An example of a modified fasting regimen represents the basis for the popular 5:2 diet.  This involves restriction for two non-consecutive days with unlimited eating during the other five days in week.

Evidence suggests alternate-days fasting protocol from three weeks to 3 months can lead to successful body weight reduction, with decrease in total body fat, as well as blood lipid levels. These benefits can be achieved not only in obese and overweight, but in normal-weight individuals as well.  Whole-day fasting protocols lasting from 3 to 6 months can also reduce body weight and fat with improvements in blood lipids status. 2

While human studies have mostly focused on the impact of intermittent fasting on body weight and fat, animal studies indicated further health benefits. To be more specific, studies on laboratory animals have shown that intermittent fasting beneficially affects various health indices and improves outcomes of a wide range of diseases. These include metabolic disease, e.g. diabetes and cardiovascular disease; cancers and neurological disorders, such as stroke,Alzheimer and Parkinson diseases. 3

Taking a closer look at intermittent fasting protocols, one can easily assume that appetite would be multiplied after an extended period of fasting. Still,research says otherwise. A group of researchers conducted an interesting trial involving obese healthy volunteers. After an overnight fast, participants were divided into two groups: one skipping breakfast, and the other getting a typical breakfast rich in carbohydrates. Three hours later both groups were served with an ad libitum (no restriction in amount) pasta lunch. Lunch intake between the two groups was compared, as well as the level of appetite controlling hormones.The results revealed no difference in quantity of food consumed for lunch. In other words, extended morning fasting did not cause compensatory intake during lunch nor it increased the appetite in the afternoon.4 

While intermittent fasting offers many health benefits, proper precautions should be employed prior to starting any fasting protocol. Without proper attention to liquid intake and electrolytes, fasting can result in dehydration, electrolyte abnormalities, or other stressors.  As mentioned previously, certain medical conditions, such as diabetes for example,requires strict monitoring by a healthcare professional familiar with medication adjustment during the fasting period.  It is always better to seek advice from medical professional, especially when undertaking extended fasting protocols such as alternate day fasting (not consuming food more than 24-36 hours or longer) or in the presence of medical conditions.

  1. Patterson RE, Sears DD.Metabolic Effects of Intermittent Fasting. Annu Rev Nutr. 2017;37:371-393. https://www.ncbi.nlm.nih.gov/pubmed/28715993
  2. Tinsley GM, La Bounty PM.Effects of intermittent fasting on body composition and clinical health markersin humans. Nutr Rev. 2015;73(10):661-74. https://www.ncbi.nlm.nih.gov/pubmed/26374764
  3. Mattson MP, Longo VD,Harvie M. Impact of intermittent fasting on health and disease processes.Ageing Res Rev. 2017;39:46-58. https://www.ncbi.nlm.nih.gov/pubmed/27810402
  4. Chowdhury EA, et al. Effect of extended morningfasting upon ad libitum lunch intake and associated metabolic and hormonalresponses in obese adults. Int J Obes (Lond). 2016;40(2):305-11 https://www.ncbi.nlm.nih.gov/pubmed/26278005