The Problem With Intermittent Fasting For Weight Loss & Why It Won’t Work For You
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 weight 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 also examine the pros and cons of these protocols.
The Problem With Intermittent Fasting For Weight Loss: Eating Less Does Not Mean Less Calories
The first and most significant problem with intermittent fasting for weight loss is that temporary food restriction does not usually lead to a decrease in overall calorie intake. An important 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 people consume more calories than normal, even though the amount of food eaten might be less. While fasting we often have the perception 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 abstraction to even the most schooled dietitian and nutritionist, as it is an intangible concept and as humans, we can neither see nor sense calories. That being said, it is no surprise that research finds almost all self reported estimates of calorie intake 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 how many calories you take in every day, makes it hard to discern real eating patterns among the general population under fasting conditions, since almost all studies on weight loss use self reported data. However there are several circumstances where fasting 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 this period usually consist of eating one large meal after sunset and one lighter meal just before dawn. Although 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 example for understanding how our bodies deal with voluntary food restriction in the presence of unlimited food resources. By eating only a limited number of meals before dawn and at night, you might expect sizeable decreases in energy intake, and consequently significant reductions in body fat. However, this isn’t always the case. On the contrary, researchers in Tunisia found daily calorie intake among observant Muslims to be EQUAL or ABOVE normal non fasting levels during Ramadan, in spite of the decrease in meal frequency.[2,3] Similar findings were found among those fasting in Saudi Arabia and Algeria, but interestingly enough, not among Indian Muslims. A discrepancy possibly due to differences in food supply, food availability and food choices.[20,21]
Consequently, there is no significant change in body weight during Ramadan among those adhering to the prescribed fasting. These observations give us 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 for large populations with access to abundant food supplies.
The Problem With Intermittent Fasting- 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, there are other instances where this tendency also occurs. During the Second World War, American researchers needed first hand information on starvation and re-feeding for the Allied famine relief programs being developed to aid the starving populations in Europe and Asia. Eager to do their part to help the war effort, 36 men volunteered 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 calories) for a total of 168 days. A grueling experiment that would be hard to duplicate today, but the desperate circumstances at the time made it not only possible, but necessary. The weight loss results were as expected, with volunteers seeing an average loss of 24% of their pre fasted body weight. However, at the end of the study, when participants were given access to food, they ate far more than they ordinarily would. With some reportedly consuming as much as 6,500 calories daily! They ate so much that not only did they regain their lost body mass, but ended up EXCEEDING their initial body fat percentages– a phenomenon aptly termed ‘post starvation obesity.’[6,7,8,9]
This behavior isn’t that different from what was observed among some Muslims during Ramadan, as people generally tend to eat more calories than usual after 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 genetically coded tendencies to compensate for lower energy intakes after periods of restriction. These processes served as a way for our ancestors to maintain healthy body mass during the many periods of low food availability. Our bodies today have no idea that most of us in developed countries face little risk of starvation, but our bodies store fat and force us to overeat under any circumstances of prolonged reductions in food intake, just as it has been doing throughout the ages. Not to say that such cues to overeat in response to food restriction cannot be overridden. It is possible to fast and not overindulge afterwards, just as it is possible for some individuals to resist the instinctive desire to eat to the point where they willfully starve themselves to death. Such control over food intake is indeed possible, but unfortunately is exhibited among an extremely small percentage of the overall population, and is by no means demonstrative of typical behavior. Like winning the lottery, we often believe that we are part of that really small number of men and women who can fast and not overeat over a long period of time, but like winning the lottery, the odd are stacked against you. As in three decades of helping hundreds of people lose weight, I have yet to see more than two or three maintain such a regime for more than a few months. The few who are successful are often held up as examples that it can be done, and they themselves frequently believe that lack of willpower is the only thing stopping everyone else from being able to intermittently fast long term. But this simply isn’t the case and so you should not feel badly if you try it but cannot sustain it.
The Problem With Intermittent Fasting: Temporary and Superficial Weight Loss
Can you lose 5 lbs overnight and even more over 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 intake, which is stored in your muscles and organs as glycogen. A combination of glucose and water. Fasting brings about a rapid depletion of glycogen and thus the water that it is stored with it as well. Resulting in an average weight loss of about 5 pounds. This weight loss is temporary and superficial, and in most cases, the problems associated with prolonged fasting 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 fasting is carried out 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.  Since muscles account for a sizable percentage of the total calories our bodies burn everyday. 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 first started your weight loss program means you would have to consistently eat less to maintain your ORIGINAL body weight, and eat even less to keep losing weight.[11,12,13,14,15,16,17,18,19] Combine a lower resting metabolic rate with a natural propensity to eat more when food is available and you have a recipe for weight gain and utter frustration.
Intermittent Fasting Won’t Make You Burn More Fat
The way our body deals with fat loss is complex and can makes weight loss a Herculean endeavor. 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 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 instead of 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] And exercise intensity is key to muscles getting bigger and stronger and muscles getting bigger is key to increased metabolism and fat burning.
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 percentages over time, but this is not the case. In fact, as other studies have shown, fat levels remain relatively stable, suggesting that the body may adapt to prolonged reductions in feeding patterns in order to maintain body fat. What can we take away from these findings? We can see 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 Won’t Increase Your Life Expectancy
One of the other 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 profit minded health and fitness gurus immediately jumped on the intermittent fasting bandwagon as the ultimate solution for long life and good health. Books were printed, dietary guidelines were made and preliminary results released in 2009 of a landmark study by the Wisconsin National Primate Research Center showed promising results for calorie restriction in primates, our closest animal relatives. As only 13% of the monkeys on reduced calorie diets had died of age related diseases 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 intermittent fasting protocols would work for human life extension as well. But, while the media clamoreds for more results from studies whose findings bordered on the fringe of sensationalism, the science of the matter isn’t that clear cut. Not too long ago, a similar study of rhesus monkeys by the National Institute of Aging completely contradicted the initially reported findings from the ongoing Wisconsin studies. This study found absolutely no improvement in survival outcomes among monkeys that were on calorie restricted diets compared to normally fed ones. Apparently the positive outcomes found in other mammals and invertebrates do not carry over to non human primates. That said, what was important for longevity was husbandry (genetics) and diet composition, which is hardly a surprise. Long term human studies on calorie restriction also do not show any increase in life expectancy from intermittent fasting. Early starvation is associated with significantly higher risk of chronic disease in later life, and people suffering from anorexia nervosa, (an easily followed low calorie intake population) 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. Populations that underwent periods of starvation during the Great Depression or Wars never showed spikes in longevity,  and the most compelling evidence against intermittent fasting and long term calorie restriction comes from a large scale study of 2.3 million Americans where earlier and 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 when the quality of food is improved. People who intermittently fast and eat less refined foods, will always be healthier, but no more so than those who eat regular meals at regular hours. Which leads us with the conclusion that intermittent fasting might be a valuable spiritual practice, but falls short compared to consistently eating well and exercising regularly in terms of long term weight loss.
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