The Problem With Intermittent Fasting For Weight Loss
Fasting is without a doubt one of the oldest approaches to weight loss, dating back as far as the times of Hippocrates. Long before the notion of calories, metabolic rates and energy balance, there was the simple practice of fasting as a means to losing the extra pounds. An approach that on the surface sounds like the most logical method for losing weight, and it’s an approach that some 14% of American adults have tried at one time or another in the hope of keeping their waistlines in check. The appeal of intermittent fasting is self-evident, to say the least- there are no calories to count, no carbs to watch, no protein intakes to adjust and for many, no real change in eating habits aside from not eating for a period of time. There is no question that not eating can bring about rapid weight loss, as long as food is adequately restricted and such restrictions are maintained for a certain length of time. However, such weight loss has proven to be temporary for the overwhelming majority of the population and may in fact be a contributing factor to excess weight gain. Equally discouraging is the fact that most of the weight lost is water and lean muscle mass. Water loss is associated with high levels of fatigue while a decrease in muscle mass inevitably leads to a slower metabolism. A slower metabolism that makes it harder for you to burn calories and thus setting the stage for even greater weight gain in the future. Many athletes combine a more moderate form of intermittent fasting in conjunction with exercise in the hope of burning more body fat and in this article we will examine the pros and cons of these protocols as well.
Intermittent Fasting Does Not Always Mean Lowered Calorie Intakes
The first and most significant point regarding intermittent fasting is that temporary food restriction does not usually lead to a decrease in overall calorie intake. A point that many fail to consider when using intermittent fasting as a way of burning more body fat. Eating less does lead to weight reduction over time, but as we will see, a reduction in meal frequency does not necessarily mean that you are eating less calories overall. On the contrary, research continues to show that food restriction makes most of us consume more calories than we ordinarily would- even though the volume of food may be less. We might think that we are eating less, but studies show that our own estimates are woefully inaccurate measures of how many calories we actually consume. Calories are nothing but an abstract idea to even the most schooled in nutritional sciences- as it is an intangible concept that we can neither see nor sense. That being said, it is no surprise that studies find our own estimates of calorie consumption to be consistently underestimated, (off by a margin as wide as 53%) when compared to actual intakes measured in a sequestered and controlled environments.
This inability to accurately self-report makes it hard to discern real eating patterns among the general population under fasting conditions; however we do thankfully have several circumstances where such eating habits can be regularly observed. During Ramadan, millions of Muslims observe a complete fast from food and water from sunrise (Sahur) to sunset (Iftar) for a period of 28-30 days. Dietary practices during the period usually consist of eating one large meal after sunset and one lighter meal just before dawn, however some may consume an additional meal before going to bed.[30,31] The Ramadan fast mimics conditions present in many intermittent fasting protocols and is an excellent starting point for understanding how we deal with voluntary food restriction while still having access to unlimited food resources. Eating only a limited number of meals before dawn and at night, you might expect such restrictions to bring about significant decreases in energy intake, and consequently sizable reductions in body fat. However, this isn’t always the case. In fact, researchers in Tunisia found daily calorie intake among observant Muslims to be similar to, or in many cases ABOVE normal levels during Ramadan, in spite of a decrease in meal frequency.[2,3] Similar findings were found among those fasting in Saudi Arabia and Algeria- but not among Indian Muslims- possibly due to differences in food supply and food choices.[20,21]
As a result, there is no significant change in body weight during Ramadan among those adhering to the prescribed fasting. These observations give us some useful insights into the practical application of intermittent fasting. Interestingly enough, the Tunisian studies found that because people tended to eat more during Ramadan, there was actually a decreased incidence of nutritional deficiencies among those at risk thanks to greater variety of food consume during the period. It was also found that sugary food and drink are consumed in greater quantities when compared to other times of the year, which might explain as well the increase in caloric intake. Any small reductions in overall body during this time of intermittent fasting has been shown to be more a result of dehydration, fluid loss and mobilization of glycogen stores rather than a reduction in fat mass.[1,5] On a positive note, no long term negative effects have been discovered thus far from such practices- but it does disqualify intermittent fasting as an effective method for long term weight loss.
Intermittent Fasting & Weight Gain- Understanding How Fasting Can Make You Eat More
While increased calorie intake among some but not all observant Muslims during Ramadan highlights an interesting behavior among those who temporarily restrict their food intake we have other instances where this tendency is also clearly demonstrated. During the Second World War American researchers needed first hand information on starvation and re-feeding for the Allied famine relief programs to aid to starving populations in Europe and Asia. Eager to do their part to help the war effort, 36 men stepped forward to take part in one of the most comprehensive studies on fasting and weight loss- called the Minnesota Experiment. For the study, volunteers were given less than less than 40% of their normal energy intake (approximately 1,500 kilo-calories) for a total of 168 days- a grueling experiment that would be hard to duplicate today, but the circumstances at the time made it not only possible but in many ways necessary. The results were as expected, with volunteers seeing an average weight loss of 24% less than their initial weights. However, when participants were given access to unlimited amounts of food at the end of the fasting period they ate far more than they ordinarily would. With some consuming as much as 6,500 kilo-calories daily! So much so that not only did they regain their lost body mass, but ended up EXCEEDING their body fat initial levels- a phenomenon aptly termed ‘post starvation obesity.’[6,7,8,9] (Read more about how restricting calories can make you overeat in my article on Food Addiction here)
This behavior isn’t that dissimilar from what we observed among some Muslims during Ramadan, where people tended to eat more calories than they ordinarily would when food access is restricted. Given the prevalence of famine and starvation during the several million years of our existence on the planet, it is not surprising that we would have a natural tendency to compensate for lower energy intakes after periods of restriction as a way of maintaining a healthy body weight under difficult nutritional circumstances. Our bodies have no idea that many of us live in developed countries with little risk of starvation, but such inclinations, forged over millennia are hard to counter. Not to say that such cues to overeat in response to food restriction cannot be overridden. It is of course possible to fast and not overindulge afterwards just as it is possible for some very strong willed individuals to resist the instinctive desire to eat to the point where they willfully starve themselves to death. Such control is indeed possible, but unfortunately rests among an extremely small percentage of the overall population and is not demonstrative of typical behavior.
Intermittent Fasting As A Quick Fix
Can you lose several pounds within the span of a several days by intermittently fasting? Absolutely, studies show that such regimes can bring about as much as a 5% decrease from your starting body weight. However, as in the case of fasting during Ramadan- such restrictions mean a decrease in carbohydrate- which causes a rapid depletion of glycogen along with the water that it is stored with- resulting in an average weight loss of about 5 pounds. This weight loss is temporary and superficial at best and in most cases, the problems associated with prolonged fasting far outweigh the solution- making intermittent fasting questionable as even a short term strategy. The first problem is that fasting results in minimal loss of fat tissue when compared to other dietary regimes and does involve substantial loss of fat free muscle mass when continued for prolonged periods of time. Aside from the loss of strength, physiological function and the cosmetic effect of appearing ‘flabby’, losing muscle mass significantly reduces your overall energy expenditure,  as muscles count for a sizable percentage of the total calories our bodies burn everyday just to stay alive. Therefore any loss of muscle mass translates into a decrease in resting metabolic rate- which is a death knell for long term weight loss. Having a slower metabolism than when you started your weight loss program means you would have to consistently eat less than you started out eating if you wanted to maintain your ORIGINAL body weight and eat even less and less to effect continued weight loss.[11,12,13,14,15,16,17,18,19] Combine a lower resting metabolic rate with a natural propensity to eat more calories when food is available and you have a recipe for weight gain and utter frustration. (Learn more about how losing muscle mass increases your likelihood for regaining weight here.)
Does Intermittent Fasting Make You Burn More Fat
One of the hardest aspects to grasp is the complexity of human biology. The way our body deals with fat loss is one of those complexities and one that makes weight loss a Herculean task for most. Many use intermittent fasting in conjunction with exercise as a way of increasing fat mobilization by training on an empty stomach. In studies conducted on rodents, short term intermittent fasting did indeed increase fat mobilization by increasing blood levels of free fatty acids- a phenomenon that resulted in increased endurance performance.[39,40] However, as promising as this may sound for increasing performance and burning more fat, no such effects have been observed in humans. Quite to the contrary, lower muscle glycogen levels from fasting have been shown to decrease rather than increase endurance performance  with a 24 hour fast impairing exercise time to exhaustion by 20-50%. As a result, even though fasting increases the availability free fatty acids and increases the rate of oxidation during exercise, any positive effects that it may have are cancelled out by a decrease in exercise intensity and duration.[43,44]
Not surprisingly, strong evidence for an increase in fat burning due to intermittent fasting comes again from studies of observant Muslims during Ramadan. It has been well documented that the rate of fat oxidation depends largely on the amount of carbohydrate remaining after a period of food restriction. That being said, the decreased carbohydrate consumption and general increase in dietary fats would lower stored carbohydrate levels and create an environment for increased fat burning. Studies find a much greater role for free form fatty acids as a substrate for energy production during Ramadan- which would thus lead us to think that such a switch would result in lower body fat levels over time, but this is not the case at all. In fact, as other studies have shown, fat levels remain relatively stable- suggesting that the body may adapt to prolonged changes in feeding patterns in order to maintain body composition.
What do we take away from these findings? Namely that weight loss is a complex process that isn’t readily addressed in the long term or effectively in the short term by intermittent fasting. Elevations in hunger that can lead to subsequent overeating, minimal loss of fat tissue and substantial loss of muscle tissue all serve to make intermittent fasting a regime that is not only counterproductive but also does not provide the health benefits of fat loss. Increased fatigue during fasting periods can also reduce physical activity to a degree that can ultimately limit negative energy balance and curtail weight loss.
Intermittent Fasting & Life Expectancy
One of the central arguments for intermittent fasting has been the claim that lower calorie intakes increase life expectancy and as such it should be a part of everyone’s dietary regime for optimal health. Initial studies of mice and rats from the 1930’s did show that intermittently fasted rodents lived nearly twice as long as normally fed ones- an average of 820 days as opposed to 483 days.[23,24] Other studies found that calorie restriction of 25% or more of normal food intakes extended the lives of hamsters, rabbits, fish, flies, worms, fleas and dogs.[25,26,27] With such intriguing findings, it was no surprise that intermittent fasting became a major focus of research for extending human life, and that the health and fitness gurus immediately jumped on the intermittent fasting bandwagon as the ultimate solution for long life and good health. Preliminary results released in 2009 of a landmark study by the Wisconsin National Primate Research Center that started in 1989 showed promising results for calorie restriction in primates, as only 13% of the monkeys on reduced calorie diets had died of age related diseases as compared to 38% of the normally fed monkeys. The calorie restricted monkeys weighed less, had lower rates of cancer, cardiovascular disease and diabetes when compared to their regularly fed counterparts- and such amazing findings went a long way in cementing the idea that such protocols would work for humans as well.
However, while the media clamors for results from studies whose results border on the fringe of sensationalism, the science of the matter isn’t that clear cut- as you can’t effectively extrapolate data from a study until it has been fully completed. Last week a similar study of rhesus monkeys by the National Institute of Aging completely contradicted the initially reported findings from the ongoing Wisconsin studies. The study found absolutely no improvement in survival outcomes among monkeys that were on calorie restricted diets when compared to normally fed ones. Apparently the positive outcomes found in other animals do not carry over to non human primates- but what was important for longevity was husbandry and diet composition- which is hardly a surprise. Human studies on calorie restriction also do not show any increase in life expectancy from intermittent fasting. Early starvation is associated with higher risk of chronic disease in later life, and people suffering from anorexia nervosa do not live longer than those with a normal calorie intake.[33,34] In fact no evidence has ever surfaced of anyone who experienced starvation at any point in their lives living longer than those who didn’t. The most compelling evidence against intermittent fasting and long term calorie restriction comes from a large scale study of 2.3 million Americans found higher death rates among those whose body weights were below ranges considered normal- which is an inevitable side effect of long term fasting. Along with increased hunger, fatigue, irritability, menstrual irregularities and lower testosterone levels.
In the end, the only health benefits of intermittent fasting of any kind appear only when the quality of food is improved- which leads us to believe that it may be a valuable practice from a spiritual standpoint, but does not compare to the benefits of consistent lifestyle changes in terms of long term weight loss.
Please note that all material is copyrighted and DMCA Protected and can be reprinted only with the expressed authorization of the author.
Featured everywhere from the Wall Street Journal to network TV, Kevin Richardson is the international fitness consultant for UNICEF, natural bodybuilding champion, creator of Naturally Intense High Intensity Training and one of the most sought after personal trainers in New York City. Learn more about his award winning personal training services here!
1. Johnstone A.M. Fasting- the ultimate diet? Obesity Reviews 2006
2. Beltaifa L, Bouguerra R, Ben Slama C, Jabrane H, El-Khadhi A, Ben Rayana MC, Doghri T. Food intake, and anthropometrical and biological parameters in adult Tunisians during fasting at Ramadan. East Mediterr Health J 2002
3. Gharbi M, Akrout M, Zouari B. Food intake during and outside Ramadan. East Mediterr Health J 2003
4. Finch GM, Day JE, Razak Welch DA, Rogers PJ. Appetite changes under free-living conditions during Ramadan fasting. Appetite 1998
5. Leiper JB, Molla AM, Molla AM. Effects on health of fluid restriction during fasting in Ramadan. Eur J Clin Nutr. 2003
6. Dulloo AG, Jacquet J. The control of partitioning between protein and fat during human starvation: its internal determinants and biological significance. Br J Nutr 1999
7. Dulloo AG, Jacquet J, Giradier L. Autoregulation of body composition during weight recovery in humans: the Minnesota Experiment revisited. Int J Obes 1996
8. Dulloo AG, Jacquet J, Girardier L. Poststarvation hyperphagia and body fat overshooting in humans: a role for feedback signals from lean and fat tissues. Am J Clin Nutr 1997
9. Keys, A., Brožek, J., Henschel, A., Mickelsen, O., & Taylor, H. L., The Biology of Human Starvation, University of Minnesota Press, 1950.
10. Jequier E. Energy expenditure in obesity. Clin Endocrinol Metab 1984.
11.Chaston TB, Dixon JB, O’Brien PE 2007 Changes in fat-free mass during significant weight loss: a systematic review. Int J Obes (Lond)
12. Elia M 1992 Organ and tissue contribution to metabolic rate. In: Kinney JM, Tucker HN, eds. Energy metabolism: tissue determinants and cellular corollaries. New York: Raven Press
13. Mueller MJ, Bosy-Westphal A, Kutzner D, HellerM2002 Metabolically active components of fat-free mass and resting energy expenditure in humans: recent lessons from imaging technologies. Obes Rev
14. Doucet E, St-Pierre S, Alme´ras N, Despre´s JP, Bouchard C, Tremblay A 2001 Evidence for the existence of adaptive thermogenesis during weight loss. Br J Nutr
15. Heilbronn LK, de Jonge L, Frisard MI, DeLany JP, Larson-Meyer DE, Rood J, Nguyen T, Martin CK, Volaufova J, Most MM,Greenway FL, Smith SR, Deutsch WA, Williamson DA, Ravussin E 2006 Effect of 6-month calorie restriction on biomarkers of longevity, metabolic adaptation, and oxidative stress in overweight individuals: a randomized controlled trial. JAMA
16. Leibel RL, Hirsch J 1984 Diminished energy requirements in reduced-obese patients. Metabolism
17. Leibel RL, Rosenbaum M, Hirsch J 1995 Changes in energy expenditure resulting from altered body weight. N Engl J Med
18. Rosenbaum M, Hirsch J, Gallagher DA, Leibel RL 2008 Long-term persistence of adaptive thermogenesis in subjects who have maintained a reduced body weight. Am J Clin Nutr
19. Rosenbaum M, Hirsch J, Murphy E, Leibel RL 2000 Effects of changes in body weight on carbohydrate metabolism, catecholamine excretion, and thyroid function. Am J Clin Nutr
20. El Ati J, Beji C, Danguir J: Increased fat oxidation during Ramadan fasting in healthy women: an adaptative mechanism for body-weight maintenance. Am J Clin Nutr 1995,
21. Khaled BM, Belbraouet S: Effect of Ramadan fasting on anthropometric parameters and food consumption in 276 type 2 diabetic obese women. Int J Diabetes Dev Ctries 2009
22. Kreitzman S N,Coxon A Y, Szaz K F:Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. Am Soc Clin Nutr 1992
23. McKay C, Cowell M, Maynard LA. The effect of retarded growth upon length and life upon ultimate size. J Nutr 1935
24. McKay C, et al. Retarded growth, life span, ultimate body size and age changes in the albino rat after feeding diet restricted in calories. J Nutr.1939
25. Masoro EJ. Caloric restriction and aggin- an update. Exp Geronot 2000
26. Morley JE, Chahla E, Alkaade S. Anitaging, longevity and calorie restriction. Current Op in Clin Nutr & Metab Care 2010
27. Lawler DF. Influence of lifetime food restriction an causes, time and predictors of death in dogs. J Am Vet Med Assoc. 2005
28. Colman RJ et al. Calorie restriction delays disease onset and mortality in rhesus monkeys. Science 2009
29. Mattison JA, Roth GS, Beasley TM, Tilmont EM, Handy AM, Herbert RL, Longo DL, Allison DB, Young JE, Bryant M, Barnard D, Ward WF, Qi W, Ingram DK, Cabo RD. Impact of caloric restriction on health and survival in rhesus monkeys from the NIA study. Nature 2012
30 Ibrahim WH, Habib HM, Jarrar AH, Al Baz SA, : Effect of Ramadan fasting on markers of oxidative stress and serum biochemical markers of cellular damage in healthy subjects. Ann Nutr Metab 2008
31. Roky R, Chapptot F, Hakkou F, Benchekroun MT, Buguet A: Sleep during Ramadan intermittent fasting. J Sleep Res 2001
32. Lansky D, Brownell KD. Estimates of food quantity and calories: errors in self-report among obese patients. Am J Clin Nutr. 1982
33. Huang C et al. early life exposure to the 1959-61 Chinese famine has long term health consequences.J Nutr 2010
34.Yi et al. Exposure to the Chinese famine in early life and the risk of hyperglycemia and type 2 diabetes in adulthood. Diabetes 2010
35. Nestle M, Nesheim M. Why Calories Count. From Science to Politics. University of California Press 2012
36. Flegal KM, Graubard BI, Williamson DF, Gail MH. Cause-specific excess deaths associated with underweight, overweight, and obesity. JAMA. 2007
37. Cangemi R, Friedmann AJ, Holloszy JO, Fontana L. Long-term effects of calorie restriction on serum sex-hormone concentrations in men. Aging Cell. 2010
38. Trepanowski JF, Bloomer RJ. The impact of religious fasting on human health. Nutrition Journal 2010
39. Dohm GL, Tapscott EB, Barakat HA, et al. Influence of fasting on glycogen depletion in rats during exercise. J Appl Physiol 1983
40. Koubi HE, Desplanches D, Gabrielle C, et al. Exercise endurance and fuel utilization: a reevaluation of the effects of fasting. J Appl Physiol 1991
41. Ladu MJ. Regulation of lipoprotein lipase in muscle and adipose tissue during exercise. J Appl Physiol 1991
42. Loy SF, Conlee RK, Winder WW, et al. Effect of 24-hour fast on cycling endurance time at two different intensities. J Appl Physiol 1986
43. Christensen EH, Hansen O. Zur Methodik der respiratorischen Quotientbestimmung in Ruhe und bei Arbeit. III: Arbeitsfähigkeit und Ernährung. Scand Arch Physiol 1939
44. Hawely JA, Brouns F, Jeukendrup A. Strategies to enhance fat utilization during exercise. Sports Med 1998