The Skinny on Intermittent Fasting
In 1971, a 27-year-old, 456-pound man went to his local university department of medicine to get advice on how to lose weight. Their response was startling but simple: stop eating altogether. While most people would look aghast and think the doctors were nuts, this guy was desperate enough to give it a try. His results over the ensuing weeks were so dramatic that he decided to prolong the fasting deprivation—for more than a year! He ate nothing but vitamins, non-caloric fluids, and yeast for a whopping 382 days. He lost 276 pounds and gained himself a spot in the Guinness Book of World Records. What’s more, he did so with no ill health effects. When the doctors checked back in on him five years later, he had gained back only about 15 pounds.
Although parts of the report seem unbelievable, and the period of fasting is obviously extreme, this dramatic anecdote highlights a very important point. Sometimes, extreme situations call for extreme actions. If you are obese and are suffering from any of the many obesity associated diseases, I can assure you that extreme measures are warranted. It also helps us refine the definition of what “extreme” is when talking about weight loss. Cutting out a piece of your stomach and stretch of large intestines is no longer considered extreme but I would argue it is far more risky than not eating for a year.
Types of intermittent fasting diets:
Alternate-day fasting: Subjects eat every other day. For humans, non eating days typically consist of one small meal of around 500 calories, amounting to a dietary energy reduction of approximately 65- 80%.
5:2 diet: A person eats five days of the week and abstains from eating the other two (for example eating on Monday, Wednesday, Friday, Saturday, and Sunday and fasting on Tuesday and Thursday)—save for one small, 500-calorie meal on fasting days (cutting dietary energy by about 65- 80% on those days).
Time-restricted feeding: Calories are not restricted, and dietary composition is not altered. But eating is confined to a window of typically 8, 10, or 12 hours per day.
The theory that drives this weight loss strategy is the fact that for the vast majority of human history humans did not have access to food on a daily basis. Food intake happened in spurts following the harvest season or a successful hunt followed by periods of abstinence. Food was also not all that plentiful and took a tremendous amount of work to acquire. It was less calorie dense as well. People thus ate less and not every day. Remember most of humanity was destitute for much of human history. It is only in recent history that there has been an abundant and seemingly never ending supply of food that is cheap and easy to acquire.
This fact has led to the hypothesis that since our bodies are designed for an environment of scarcity they are therefore ill equipped to deal with a constant intake of calories. By restoring what would be a more natural pattern of intake we can avoid all the metabolic derangements caused by daily over eating.
This certainly sounds like many of the other fads that have a seemingly plausible theoretical foundation but no real scientific support (e.g. paleo, keto, etc). As the body of scientific literature around fasting has grown, results have been cherry-picked and molded into fad diets that promise weight loss, increased energy, better sleep, and a variety of other benefits to human adherents—some with more evidence backing than others. As books of dubious scientific merit extolling the virtues of fasting fill the shelves, serious researchers continue to probe the genetic, immunologic, and metabolic dynamics that occur in fasting animals to separate hype from reality. There happens to be a tremendous amount of research showing the potential for significant health benefits to this pattern of eating.
Mechanistic explanations for the benefits of intermittent fasting include the following:
- The body uses fats for energy during fasting, reducing adipose mass and resulting in a small, long-term reduction in risk after each fasting episode
- Nutritional stress during periods of fasting, at least in part, results in cellular-level repairs, functional optimization, and metabolic rejuvenation that may improve long-term health by reducing cardiovascular risk factors and acting on the metabolism of glucose. In some animal models, intermittent fasting is at least as good as other diets at improving markers of metabolic health.
A Review in 2017 identified nine trials of modified fasting in humans with sample sizes ranged from 10 to 107 adults, all of whom were overweight or obese. The duration of the fasting interventions ranged from 2 to 6 months. Overall, 7 of 9 studies (78%) reported statistically significant weight loss, which ranged from 3.2% in comparison with a control group during a 12-week period to 8.0% in a one-arm trial during an 8-week period. Three of six studies found significant decreases in fasting insulin, and one found reductions in fasting glucose. Three of eight studies found significant improvements in circulating LDL cholesterol or triglycerides. Three of six studies found significant improvements in inflammatory markers, including C-reactive protein, tumor necrosis factor-α, adiponectin, leptin, and brain-derived neurotrophic factor (BDNF).
In spite of the fasting, the subjects did not seem to get too hangry. In fact, there were mean improvements in mood, including reductions in tension, anger, and fatigue, and increases in self-confidence and positive mood.
One thing that is reassuring is that this eating pattern does not cause an increase in calorie intake on non-fasting days; people don’t “make up” for the fasting on the alternate days. In fact there is evidence that people who use intermittent fasting actually eat less on the non-fasting days.
Research has shown that feelings of fullness and levels of the satiety hunger PYY increased. It appears that the body responds to the fasting by lowering the hunger sensation which may account for much of the benefit of this form of dieting.
While the research for intermittent fasting is still in the early phases it is certainly encouraging. All skepticism must be weighed against the alternatives. The question is not whether or not intermittent fasting is effective but whether it is more effective for you and more effective than anything you’ve already tried. If you are like most, you’ve tried everything else and it’s failed.
There are many advantages to this form of dieting that will be hard for scientists to quantify but that are certainly important.
The program is simple to understand. Its not easy but its simple. Nobody is asking you to adjust the types or quantities of food. There is no special shopping, calorie or point counting, or weighing of food.
Save Your Will Power for Later
There is an advantage to not having to open the pantry door. Every time you look at food packaging the food industry owns your subconscious. All of the subliminal and subconscious messages that the marketing and manufacturing of the food has implanted into your brain stimulate strong cravings. This is why you can’t just eat one cookie. To fight those cravings uses up energy and saps your will power. The more energy you use during the day fighting the cravings the less you have at the end of the day (any late night snackers out there?). If you have no plans to eat, you never open the pantry to begin with. If you don’t open the pantry you are using less energy. This leaves more will power for when you need it.
You’re Not a Slave to Your Hunger
You dissociate the hunger signal with the need to eat. If you were to ask most people why they were eating, they would often respond that they are eating because they were hungry. This seems right and normal but if you think for a moment, it is a real problem. If hunger reason enough for you to eat then you are a slave to your appetites. Since many things can trigger hunger aside from the need for energy (e.g. stress, habit, circadian rhythms) you may be eating when you don’t need to. In other words, you many be eating too much. With the intermittent fasting model you become accustomed to not eating. Hunger becomes a sensation like being tired. Every time you’re tired you don’t run to bed, right? So too, every time you’re hungry you shouldn’t run to eat. You sleep when its time and you eat when its time. After a while you’ll notice that the hunger sensation does not bother you as much. It becomes dissociated from the emotional centers of your brain and eating less becomes easier. You’ll even find that you want food less on the non-fasting days.
Desperate Times Call For Desperate Measures
The extremeness of the diet I think is an advantage. It is my opinion that part of the reason people are unsuccessful at weight loss is that they do not recognize the damage the weight does to their body until it is too late. People are in a terrible state of denial. By forcing someone to take such extreme steps it helps them put the dangers of the excess weight in perspective.
It can’t hurt.
This may be the most important reason. The dangers and damage of being overweight are extreme and warrant trying any and everything that may help. While more research is necessary to fully elucidate which version of intermittent fasting is most effective and all the specific benefits it is clear that there is no harm. This may surprise many. Most of the time that I suggest intermittent fasting to people they look aghast at me as if I suggested they cut off a limb to lose weight (this would be effective but is not recommended). Mouth agape, they exclaim ‘but I’ll die’ or something similar. If only they felt the same way about not losing weight. We’ve been brainwashed that because people are starving in China we have to eat more. We should be more concerned about people who are dying here from the opposite. We have been duped to think that ‘breakfast is the most important meal of the day’ (probably by Kellogs). The meals you don’t eat are the most important of the day.
Horne BD, Muhlestein JB, Anderson JL. Health effects of intermittent fasting: hormesis or harm? A systematic review. The American Journal of Clinical Nutrition, Volume 102, Issue 2, 1 August 2015, Pages 464–470.
Patterson RE, Sears DD. Metabolic Effects of Intermittent Fasting. Ann Rev Nutr 2017; 37:371-93.
Klempel MC, Bhutani S, Fit-zgibbon M, Freels S, Varady KA. Dietary and physical activity adaptations to alternate day modified fasting: implications for optimal weight loss. Nutr J 2010;9:35.