There have been a number of diets to come and go throughout the years, gaining and losing popularity in practice as the fitness climate is always evolving. From If It Fits Your Macros (IIFYM), to carb backloading, to keto, there will always be methods that rise and fall in popularity. Another such popular diet method that has been used with notable success is Intermittent Fasting. Also commonly referred to simply as “IF”, as the name implies, this version of dieting refers to following periods of fasting, where there is little to no consumption of food for periods of 16-24 hours. It definitely is the flip side of the coin when it comes to dieting compared to the traditional 5-6 small meals that many in the fitness worlds have used for years, but there is solid merit and research for its ability to help increase fat burning (1), helping stabilize blood sugar and improving insulin sensitivity (2).
The idea at the core of IF is to reduce the overall calorie intake, transitioning into weight loss. During the restrictive period, IF protocols involve you undergoing a deliberate calorie restriction (0-25% normal intake) for that 16-24 hour period. Following this restrictive phase, the relatively normal energy intake is resumed for 8-25 hour period. The time frame for which one fasts/feasts is dependent on which particular protocol you are following which we will outline below. There are 3 main protocols typically used, and they include “Lean Gains”, “The Alternate Day Diet”, and the “Warrior Diet”.
The first one is the “Warrior Diet”. This protocol was created by Ori Hofmekler and is described as a 20 hour period of fasting and a 4 hour ‘feeding window’. The main goal of this approach is to increase the activity of the Sympathetic Nervous System, which in terms helps translate into stimulating lipolysis (fat burning) and increase the metabolism as a whole (3).
The next approach has an even longer fasting period of a full 24 hours and as you may have guessed is the “Alternate-Day Diet”. This protocol was created by James Johnson, M.D. and follows a full 24 hour rotation of low calorie intake followed by normal calorie intake. The premise of using this version is that it can activate the SIRT1 gene. This specific gene assists with weight loss and fat loos by inhibiting fat storage and increasing fat burning as the body uses fat for fuel on the restricted day (4).
Last but not least, what is regarded as the most common of the IF diets used these days is the “Lean Gains” method. It was originally created by Martin Berhan and the premise of the diet is a 16 hour fast followed by a seemingly more manageable 8 hour feeding window.
Now, while there is quite a bit of promise for the efficacy of using IF a protocol for fat loss, there are a few drawbacks that have been observed in various studies. One of the main issues is that it has been observed that there can be an undesired increased rate of protein breakdown that goes along with the desired fat loss (5). Another negative that has been shown with IF protocols is that there may be decreases in athletic and workout performance along with decreased endurance (6).
Another important note is that IF isn’t for everyone. It is advised that those who are underweight, have a history of eating disorders or other medical conditions shy away from this approach, and first consult your physician. Additionally if you have any medications, diabetes or are pregnant or breastfeeding, you should also talk to your doctor first to make sure it is advisable for you to experiment with.
So, now that we’ve covered the basics of the possibilities of the various IF protocols, if you opt to try it, we advise that you give the “Lean Gains” method a try first as most find it the most practical and sustainable. Simply fast for 16 hours and in your 8 hour feeding ‘window’ aim to eat the calories that you calculated previously to achieve your calorie deficit. You can calculate your basal metabolic rate with one of the many calculators available online and of course use the many resources that are out of the scope of this specific article for structuring the diet further. While this diet won’t be everyone’s cup of tea, at the very least you now have a better understanding of what they are and how they work.
1. Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. Heilbronn, LK and Smith, SR. 1, January 2005, American Journal of Clinical Nutrition, Vol. 81, pp. 69-73.
2. Effect of intermittent fasting and refeeding on insulin action in healthy men. Halberg, N and Henricksen, M. 6, December 2005, Journal of Applied Physiology, Vol. 99, pp. 2128-2136.
3. Resting energy expenditure in short-term starvation is increased as a result of an increase in serum norepinephrine. Zauner, C and Schneeweiss, B. 6, June 2000, American Journal of Clinical Nutrition, Vol. 71, pp. 1511-1515.
4. Changes in hunger and fullness in relation to gut peptides before and after 8 weeks of alternate day fasting. Hoddy, KK and Gibbons, C. March 2016, Journal of Clinical Nutrition.
5. Increased leucine flux in short-term fasted human subjects: evidence for increased proteolysis. Tsalikian, E. 3, September 1984, American Journal of Physiology, Vol. 247, pp. 323-327.
6. The effects of Ramadan intermittent fasting on athletic performance: recommendations for the maintenance of physical fitness. Chaouachi, A. Supplementary, June 2012, Journal of Sports Science, Vol. 30.