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Fasting: Yay or Nay?

Discouraged and diabetic, Joanne despaired of finding a “lifestyle” solution for her disappointing numbers: from the lab slips in her chart to the numbers on her bathroom scale, none of the news was good. She had tried a week-long fast a year or two previously, and although her initial results were good, her long-term resolve weakened. Months after her fast she was probably eating more than she had before, evidenced by even larger numbers on that pesky scale.

I carefully made a suggestion to her based on my other patients’ experience. “Folks say that their second long fast is easier than their first…and easier to stick with something workable after the fast. Want to try again?” I enjoy learning from my patients, and particularly for fasting patients I offer email support at no charge to them. “Write me if it’s hard in any way, and I’ll see if I can help you stick with it.”

She thought about it and decided to go for it. That was a year ago, 60 pounds ago, a different attitude and metabolism ago: Joanne is definitely glad she took a second chance at it.

Who Doesn't Eat?

Fasting has been more of a religious than a health-conscious intervention over the ages. Whether it’s a month of daytime fasting in Ramadan, or high holy days in the Jewish tradition, fasting has served as a tool for spiritual purification. And then there was the common wisdom, or, as my mother would say, “Feed a cold and starve a fever,” but that’s not medicine, right? Scientific American has decided that to be a misguided mythology  and suggests that we all just feed everything. (Maybe that’s the cause of our obesity epidemic!)

My first serious medical encounter with fasting was in the office of the veterinarian: “Better to give that dog’s digestion a rest:  hold off feeding until she’s hungry and her behavior has returned to normal.” (Remember, it’s your veterinarian who will look at a sick patient and ask—unlike most physicians—“What’s the diet been like?”)

Although I’m sure avoidance of eating has been justified along the way by the “Just eat less” weight loss camp, I checked out of the campsite years ago and hadn’t really considered food avoidance until the brilliant work of Dr. Jason Fung, The Complete Guide to Fasting.  (If you have wanted to fast, but thought it sounded too hard, stop right now and go buy that book! It has the answer to every question a fast might possibly raise for you!)

Dr. Fung describes two terms of fasting in his book. One option is to enter a prolonged fast, 7-10 days, as a great way to kickstart your body’s inherent wisdom about fasting. (As he and others have pointed out, those of us who have survived evolution are those with the genes that allow us to go out and hunt food even after days of not eating. Those of our ancestors who just wilted away during food-free periods: well, none of them were able to reproduce successfully, so none of us really come from those who fainted when they fasted.) A second option, that you can start on its own or after a longer fast, is the plan of intermittent fasting. Let’s talk about each one separately.

Prolonged Fasting

The rationale for a prolonged fast arises from the perspective that obesity and diabetes are inextricably linked through the bond of insulin resistance. Insulin resistance refers to the phenomenon where, in response to dietary carbohydrates our body releases ever-increasing amounts of insulin to allow those carbs to be used. Our body becomes increasingly deaf to that insulin, just like anyone’s response might be to a chronically repeated nag.  Insulin levels drift higher and higher, and elevated insulin levels prevent  us from burning fat for fuel when food itself is scarce. We all have body fat to burn: how on earth can we be fainting from hunger at 4 p.m.? The answer is in the degree of insulin resistance present in our body: resistance drives up the levels, high levels of insulin lock up the fat and throw away the key.

That fat remains locked up until there is no more insulin around, and that happens most efficiently when you go completely without food. Gradually, after one day, three days, or maybe five days: your body stops expecting food, stops releasing insulin, and you are free to burn fat for fuel! Your energy returns, both physical and mental, and you are no longer suffering, even though you are still fasting. Once you get to that point, your entire body is really quite happy with fat as its sole fuel source, at least for a while.  Most of your body hums along quite nicely on fat molecules for fuel. Fat can’t get into your brain, but your liver nicely takes fat and produces ketones which cross readily into your brain: your brain loves ketones. Ketones have been observed to calm seizure activity, heal a traumatized brain, and nourish the brain of patients with dementia.

On the practical side, there is bad news and good news. The bad news comes first, so let’s start there: the greater your level of insulin resistance, the longer it takes to get to that happy-fat-burning state and the more miserable you might be until you get there. (See below for management tips on that flu-like period.) The good news arrives as you burn fat for fuel: your body learns from this experience and the next time you fast, you’ll get there faster. (This seems to be true even if you did not have a lot of insulin resistance to work through: burning fat and generating ketones is a metabolic skill that takes a bit of practice.)

Intermittent Fasting

The option of repeated and shorter fasts also has real merit. Many folks follow a long fast with a commitment to intermittent fasting, for others it is how they want to start. Here’s the best part: very few rules.

Pick the fasting period and frequency that works best for you: fast for 24 hours (dinner to dinner) once or twice a week; fast 12 hours every night; fast for 36 hours once a week: the options are endless! The shortest period of value for fasting is probably 12 hours, but if that’s hard, start with 8 and work your way up! Fasting overnight offers metabolic benefit (reversing insulin resistance) and is good for your brain and immune system as well. Just like the wisdom of my dog’s veterinarian, our bodies too can benefit from a respite from the difficult and expensive task of digestion: give it a rest!

Weight Loss and Fasting

Intermittent fasting is also referred to as time-restricted feeding. Confining your eating period to 8-12 hours a day results in weight loss, whether or not your caloric intake is less. Studies in mice allowed for precise caloric manipulation and equal calorie, unequal hour eating windows had different outcomes: less time with your food, less love handles.  It’s harder to sort out conclusively in humans, but it seems “natural” that when eating is time restricted, most folks unconsciously cut their calories .

And most people do lose weight from fasting, though not everyone. I would say from my experience that if twenty of you try some form of fasting, about ¼ of you will lose weight effortlessly and quickly; about half of you weight loss will come more slowly, and the last ¼ of you require some true problem solving.

Practical Tips for Fasting

Particularly for the longer fast, I find several supportive principles worth reviewing.

  • You must consume electrolytes: salt, potassium, and more. You can do this with electrolyte additives to water (I use NUUN tablets when I row and rely on it for skipping meals as well.  Well-salted bone broth is another good option.
  • If you are taking blood pressure medication or medication to lower your blood sugar, you must be able to monitor and adjust your medications in cooperation with your physician. Both numbers will fall during your fast.
  • A moderate amount of plain tea and/or coffee is fine; some folks have a small serving of either with a bit of heavy cream: don’t substitute half-and-half or milk, it will stall your ability to adapt to fasting!
  • Exercise is best kept gentle to moderate, without strenuous exertion.
  • And finally, if you’re really suffering, two suggestions:
    • First try a bit of L-glutamine, 500-5000 mg can help with irritation in your digestive tract, carb cravings, headaches and weakness. It might stall your adaptation a bit.
    • Second: break your fast, you’ve gone long enough!  Next one will be easier and longer!

One special application for fasting is in the period of time surrounding chemotherapy treatments. Fasting will slow down your body’s metabolism, but will not slow down a cancer cell’s metabolism: there is some good evidence that side effects are reduced and efficacy of the chemo is increased if you are able to fast for 1-2 days before and 1-5 days after a chemotherapy treatment. Ideally, you can do this in cooperation with your cancer doctor! 

Who shouldn’t fast?

Pregnant women, children under the age of 16, and anyone who is already under their optimal weight!

Weight Loss Stalls and Solutions

What about that last ¼ of fasting pioneers who don’t seem to lose weight when they fast, even though they are following good low-carb eating guidelines, and intermittently fasting to follow up? I consider half a dozen causes and I’m sure there are twice that many that I haven’t thought of.

Folks will not lose weight despite following all the rules if:

  • They are perfectly balancing their caloric expenditure with dietary fats: too many “keto bomb” desserts may not add carbs, but they can be the fat you burn on your low carb/high fat diet. As wise folks have said, and I paraphrase: “To lose weight on Low Carb, High Fat, at least some of the fat calories have to come off your belly and not off of your plate.”
  • Their hormones are wacky in some way: their thyroid is not optimally regulated or their stress hormones are through the roof!
  • Inflammation is begging for calories to hold on to, whether it’s from a chronic injury or even just the inflammation from fat tissue. It’s almost a catch-22 if you think that your fat tissue is causing inflammation which causes you to hold on to fat tissue, but…. Even that inflammation can be modulated, with proper use of supplements such as curcumin to quench the fire link  or fish oil for the omega 3’s.

I promise, soon, a whole article about Dr. Catherine Shanahan’s brilliant book Deep Nutrition link, but here’s a highlight from the ensuing discussion: some people think that  excessive dietary omega-6 fatty acids are the cause and culprit in our modern obesity epidemic. A mere hundred years ago, our essential fatty acids were not too imbalanced: we ate more omega-6 fatty acids ever since we started eating grains, but in the 1900's it wasn't too crazy. However, the 20th century changed everything. When we turned vegetables into oils and margarines, and  food into "food products" , we shoved omega-6 fatty acids onto our plates at an alarming rate, displacing and overwhelming the omega-3 fatty acids. We need both, but in about equal numbers. Too many omega-3’s (rare to find that) and we have trouble clotting our blood; too many omega-6’s and we are inflamed, obese, and our brains don’t work well.

  • Two particular sources of inflammation I look for are an overgrowth of unwanted bacteria in the small intestine OR an imbalance or intruder in the flora of the large intestine.
  • Exercise deficiency is never a cause per se of failure to lose weight, but it is possible to leverage your level of activity by adding in a couple sessions of high intensity interval exercise each week. Link!!
  • Inadequate sleep, finally and perhaps most important, has recently been identified as a cause of failure to lose weight. Inadequate sleep might be too short, too shallow, or just altered: sleeping next to an outdoor source of bright light will reduce your sleeptime melatonin levels and could contribute to weight loss failures.

Most Intriguing

Perhaps most intriguing is the research showing that some form of caloric deprivation--fasting, low protein diets, intermittent fasting--are extremely beneficial for our mitochondria, the little power units inside each cell of our body. It seems that fasting, or very low calorie, fasting-mimicking diets not only reverse insulin resistance, as described above, but also just enable some very efficient housecleaning, resulting in a healthier overall body after the fast.

Watch this space: there's a lot more to learn about the benefits of fasting that will be heavily studied, in humans and in worms! over the coming years.

What else? Have you tried fasting? How did it work, or not work for you? 


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