Two of the latest buzz-words on the media scene are “Intermittent Fasting”. But does Intermittent Fasting for weight loss actually work?

I know what you’re thinking, “Fasting? Really?” This is something nutrition and diet experts have said is the WORST thing you could do.” Well, what if we were wrong? Furthermore if you’re thinking “I cannot go without a meal for 6 hours or more” then you’re also wrong. Most of us do it every single day. We just call it sleeping.

There are lots of anecdotal stories circulating regarding the benefits of intermittent fasting. These stories mention weight loss, diabetes control, decreased cardiovascular disease risk, cancer-fighting and even anti-aging! In this article I wanted to examine the claim regarding weight loss, and more importantly look at the scientific evidence.





In the scientific community, new evidence is found on a daily basis. At the moment intermittent fasting is certainly an up and coming topic. Here is a summary of the research available currently:


  • An intermittent fasting or temporary caloric restriction regimen can result in a weight loss of up to 5% in 6 days [1, 2, 3, 4].
  • Post-fast, average spontaneous energy intake (how much food you want to eat) doesn’t increase as dramatically as expected. On average the spontaneous energy intake only increased by 20% at the first meal post fast. At this meal people tend to choose higher fat, energy-dense meals.
    Following this first high-energy meal, spontaneous energy intake returns to normal. Simplified, this means that if your first meal after the fast ends is high in energy (with good fats and adequate protein) then your hunger level will not be higher than normal. So to maintain your weight losses, the fast should be followed by the introduction of a real-food based, healthy-fat-containing diet.
  • Individuals who undertook complete fasting for at least a 24hour period found that they were able to maintain weight loss up to 1 year after the study was conducted [4]. The study participants reported however that they periodically used the fasting technique to maintain their weight as desired. They also indicated that they were surprised by their ability to complete a total fast. This ties in with one of my take-home points so stay tuned for those below!


  • During the fasting period, hunger levels definitely increase at least initially [2, 3, 4]. This means that more dedication and motivation will be needed in the beginning. As time goes on, however, the literature does indicate that hunger may go away as Wadden et al report “less food eaten results in less hunger” [5].
  • Fatigue is a real side-effect, also at least initially [6, 7,8]. This fatigue may lead to decreased productivity at work and also decreased energy expenditure because of a lowered desire for exercise.
  • Actual composition of the weight loss may be more water, glycogen stores and protein stores instead of actual fat. Losses of lean protein account for the majority of the body weight decreases during total starvation, with body water losses being a close second [9, 10]. Several studies have shown that low-carbohydrate diets can lead to greater weight loss when compared with diets with the same number of calories but higher total carbohydrates [11]. Of the few studies that have looked at the composition of weight loss on low carbohydrate diets, a trend has been shown for favouring fat loss and preserving (or even increasing) lean muscle mass [12]. Perhaps this is something to consider as an alternate weight-loss solution?


  1. A Trial Fast may be of benefit in terms of practicing how to manage hunger. It may also help with learning how to distinguish between psychological hunger and physical hunger. Basically, if you need to abstain from eating that unhealthy food just because it’s the only thing available – you can!
  2. More Regular Fasting may in fact make it easier to maintain a lower body weight and fat percentage when compared to conventional diets.
  3. More Regular Fasting may not objectively be better for the initial process of losing body fat when compared to alternate diets e.g. a lower carbohydrate diet. Lean muscle mass may actually suffer in prolonged fasting.
  4. Intermittent Fasting can work but may not be for everyone, and may not need to be. More importantly, Intermittent Fasting for weight loss is one approach among many effective ones.
  5. Intermittent Fasting is NOT a way to indulge bad eating habits and avoid the consequences. This is probably the most important take-home message!

For more information and clarification, please feel free to comment below or get in touch today.



  1. Johnston AM. Fasting – the ultimate diet? Obes rev (2007) 8, 211–222.
  1. Hoggard N, Johnstone AM, Faber P, Gibney ER, Elia M, Lobley G, Rayner V, Horgan G, Hunter L, Bashir S, Stubbs RJ. Plasma concentrations of alpha-MSH, AgRP and leptin in lean and obese men and their relationship to differing states of energy balance perturbation. Clin Endocrinol (Oxf) 2004; 61: 31–39.
  1. Johnstone AM, Faber P, Andrew R, Gibney ER, Elia M, Lobley G, Stubbs RJ, Walker BR. Influence of short-term dietary weight loss on cortisol secretion and metabolism in obese men. Eur J Endocrinol 2004; 150: 185–194.
  1. Faber P, Johnstone AM, Gibney ER, Elia M, Stubbs RJ, Roger PL, Milne E, Buchan W, Lobley GE. The effect of rate and extent of weight loss on urea salvage in obese male subjects. Br J Nutr 2003; 90: 221–231.
  1. Wadden TA, Stunkard AJ, Day SC, Gould RA, Rubin CJ. Less food, less hunger: reports of appetite and symptoms in a controlled study of a protein-sparing modified fast. Int J Obes 1987; 11: 239– 249.
  1. Lee KA, Hicks G, Nino-Murcia G. Validity and reliability of a scale to assess fatigue. Psychiatry Res 1981; 36: 291–298.
  1. Russell DMcR, Walker PM, Leiter LA, Sima AAF, Tanner WK, Mickle DAG, Whitwell J, Marliss EB, Jeejeebhoy KN. Metabolic and structural changes in skeletal muscle during hypocaloric dieting. Am J Clin Nutr 1984; 39: 503–513.
  1. Johns MW. Daytime sleepiness, snoring and obstructive sleep apnea. Chest 1993; 103: 30–36.
  1. Grande F. Man under caloric deficiency. In: Dill DB, Adolph EF, Wilber CG (eds). Handbook of Physiology, Section 4, Adap- tation to the Environment. Washington, DC: American Physiolog- ical Society, 1964, pp. 911–937.
  1. Gilder H, Cornell GN, Grafe WR, Macfarlane R, Asaph JW, Stubenbord WT, Watkins GM, Rees JR, Thorbjarnarson B. Com- ponents of weight loss in obese patients subjected to prolonged starvation. J Appl Physiol 1967; 23: 304–310.
  1. Westman EC, Mavropoulos J, Yancy WS, Volek JS. A review of low-carbohydrate ketogenic diets. Curr Atheroscler Rep 2003; 6: 476–483.
  1. Volek JS, Sharman MJ, Love DM, Avery NG, Gomez AL, Scheett TP, Kraemer WJ. Body composition and hormonal responses to a carbohydrate-restricted diet. Metabolism 2002; 51: 864–870.