What is it?

Intermittent fasting is a term for an eating pattern where an individual undergoes long periods of fasting and short periods of eating. The diet only focuses on eating frequency, and does not specify restrictions on what to be eaten or portion sizes. Based on this, it is hard to label it as a ‘diet’, but more of an eating pattern.

The length of ones fast, where no energy-containing foods or drinks can be consumed, is typically 16 hours, although this can be adjusted by the person running the diet. However, fasts that are less than 16 hours would be too similar to normal eating habits and would not be labelled as a form of intermittent fasting. With a 16:8 fasting to eating ratio, you spend twice the length of time in a fast. With the average person sleeping 8 hours per day, and eating upon wake and before bed, this can be looked at as the opposite of a normal eating routine.

Proposers of the diet view intermittent fasting as a more natural form of eating compared to today’s conventional breakfast, lunch and dinner. From an evolutionary standpoint, going back to hunter-gatherer lifestyles, food availability was comparatively scarce, and extremely large meals would be consumed followed by an extended period of our bodies surviving without frequent food intake. 

The Benefits

  • A proven weight loss method

Quite simply, by forcing you to eat less meals, energy intake will substantially decrease in most individuals. The only counter to this is if one was to dramatically increase meal size to make up for the reduced meal frequency. A review study found intermittent fasting caused weight loss of 3-8% of total body weight in periods of 3-24 weeks, along with a reduced waist circumference of 4-7% [1].

Further to this, another study found intermittent fasting may be more effective for the retention of lean mass, with less fat-free mass lost over 3-12 weeks compared to conventional restriction methods, despite total weight loss being identical [2].

However, research on this diet is currently limited and no conclusions can be made until more data is produced. From a biological standpoint, the difference in fat loss compared to ‘normal’ diets, provided energy intake is the same, shouldn’t be significantly different.

  • Biological changes

Unique changes can occur during intermittent fasting that are not seen with other methods of restrictive eating. Short-term fasting has been shown to increase serum norepinephrine, due to a decrease in glucose availability and storage, which directly increases resting energy expenditure by 3-14% [3]. Growth hormone secretion is also enhanced up to 500% during short-term (2 days) extended fasting (16+ hours), due to increased frequency of growth hormone-releasing hormone release and longer periods of somatostatin withdrawal [4][5]. Whether these biological effects still occur in the long term, (weeks to months) and have benefits on fat loss and muscle retention, are yet to be determined.

  • Simplicity and time management

This is a huge benefit to those that are not dedicating their entire day to body composition goals. Although some magazines spout ‘8 small meals to lose weight’, and other than the fact those claims are nonsense, cooking and/or eating every few hours is not ideal for those that want to be on a diet yet still have lots of free time to maintain a social life.

Focusing on one or two meals per day, in a short window of time, is more convenient for most people and allows you to not be restricted in other important daily activities. You might also be able to sleep in an extra 30 minutes in the morning by skipping the breakfast oats and protein shake!

The Cons

  • Hunger and weakness

It is important to note this side effect is not the case for everyone running the diet, and some people can even experience the opposite effects. However, like any dramatic lifestyle change, your body will take time to adapt to nutritional or physiological alterations. To be clear, this is psychological hunger as opposed to physical hunger.

Your body is used to habitual routines, such as eating frequently throughout the day, and thus subconsciously prepares you mentally for frequent meals. Changing the routine can cause mental ‘shock’ and may indirectly have short-term effects on feelings of satiation and weakness.

To avoid feelings of hunger, at least during the period where you haven’t adapted to the new eating schedule, make sure to stay hydrated and keep yourself busy during the fasting period (preferably keep your distance from the cookie shop!).

  • No calorie counting

This is not an issue for people who just want to get down to a healthy weight and be in decent shape. However, for those who are really serious and looking to be in single digit body fat, calorie counting is often needed as energy intake should be tactfully controlled and manipulated to favour fat loss once plateaus occur.

Thankfully, intermittent fasting and calorie counting (or IIFYM) are not mutually exclusive, and can be implemented simultaneously for the best results.

  • Reduced muscle protein synthesis

Although meal frequency is largely overemphasized as being a key factor in muscle growth or retention, it certainly has significance when potentially going to extremes and consuming just one meal per day.

More frequent protein intakes throughout the day have been shown to maintain an elevated rate of protein synthesis and anabolism from leucine consumption, and can affect the maintenance of lean body mass and muscle strength [6]. A meta-analysis of 15 studies also showed feeding frequency was positively associated with reductions in fat mass and body fat percentage as well as an increase in fat-free mass [7].

This does not necessarily mean the more meals the better (you don’t need 10 meals per day!), but 3-4 meals containing ~25-40 grams of protein is likely superior at increasing net protein synthesis and net anabolism compared to a single meal containing ~100-160 grams of protein. This is due to a maximum anabolic signalling response from one protein feeding, which is roughly 45 grams of protein, or 5 grams of leucine [8].

Who should run this diet?

Intermittent fasting is ideal for someone who has struggled to lose weight by switching to ‘healthier’ food options, and is looking for another method of fat loss. The diet can be ran by those of all experience levels, from those who are severely overweight or those who are healthy but trying to be in better shape for the summer. It really is flexible. As mentioned, as it is not a diet by definition, it can also be ran alongside many other actual diets that focus on meal choices. Think of it as killing two birds with one stone.

The diet should not be implemented by those who struggle to abide by restrictions on when to eat and when not to eat. In addition, those who find it hard to consume large amounts of food in one or two sittings within a short space of time should stick to conventional dieting methods.


  • Barnoskya AR, Hoddy KK, Untermana TG, Varady KA. (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Science Direct
  • Varady, KA. (2011). Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss?. Obes Rev
  • Zauner C, Schneeweiss B, Kranz A, Madl C, Ratheiser K, Kramer L, Roth E, Schneider B, Lenz K. (2000). Resting energy expenditure in short-term starvation is increased as a result of an increase in serum norepinephrine. Am J Clin Nutr.
  • Hartman ML, Veldhuis JD, Johnson ML, Lee MM, Alberti KG, Samojlik E, Thorner MO. (1992). Augmented growth hormone (GH) secretory burst frequency and amplitude mediate enhanced GH secretion during a two-day fast in normal men. J Clin Endocrinol Metab.
  • Ho KY, Veldhuis JD, Johnson ML, Furlanetto R, Evans WS, Alberti KG, Thorner MO. (1988). Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man. J Clin Invest.
  • Loenneke JP, Loprinzi PD, Murphy CH, Phillips SM. (2016). Per meal dose and frequency of protein consumption is associated with lean mass and muscle performance. Science Direct
  • Schoenfeld BJ, Aragon AA, Krieger JW. (2015). Effects of meal frequency on weight loss and body composition: a meta-analysis. Nutr Rev
  • Glynn EL, Fry CS, Drummond MJ, Timmerman KL, Dhanani S, Volpi E, Rasmussen BB. (2010). Excess leucine intake enhances muscle anabolic signaling but not net protein anabolism in young men and women. J Nutr.