Monday, February 1, 2010

Prescribing fasting

In our culture of consumption, we rarely hear about the benefits of fasting. Many of us have probably never gone a day without eating (sick days don’t count).

That’s one reason I found this study so intriguing (thanks Stephan for drawing my attention to this).

Not surprisingly, fasting is not a concept touched upon in the medical school curriculum. In fact, it seems that the reverse is modeled. Unless a patient is NPO (nil per os = nothing by mouth) in preparation for surgery (or for some other medical condition), hospitalized patients are fed abundantly with typical hospital food (not to mention juice and gram crackers for snacks).

The study tested “alternate day calorie restriction (ADCR)” in overweight asthma patients. They enrolled 10 overweight asthma patients and assigned them to 8 weeks of this diet intervention, looking at effects of the diet on asthma symptoms, lung function, oxidative stress, and inflammation.

The diet: Every other day, study subjects ate whatever they normally ate. On intervening days, they ate <20% of their normal calorie intake = a canned meal replacement of 320 calories for women and 380 calories for men.

The results:
  • 9 of the 10 subjects adhered to the diet and lost an average of 8% of their initial weight over the 8 weeks. 
  • Asthma-related symptoms, quality of life measures, and pulmonary function tests improved significantly.
  • On days of calorie restriction, energy metabolism shifted towards fatty acid utilization (marked by increased levels of beta-hydroxybutyrate and decreased levels of leptin) - this means subjects were adhering to the diet. 
  • Serum cholesterol and triglycerides decreased. 
  • Markers of oxidative stress decreased, and uric acid levels (an antioxidant) increased. 
  • Markers of inflammation decreased. 
While this study was small and over a short time period, it introduces an important question (and is easy enough to reproduce on a larger scale).

When patients struggle with new and foreign diet changes, I wonder if a first step might simply be prescribing regular days of fasting.

Regardless of any potential health benefits, here is another good reason to fast:
“For now, it seems that some fasting is the best way to remind myself of the millions who are hungry and to purify my heart and mind for a decision that does not exclude them.” 
~Henri J. M. Nouwen


  1. Fasting has been around for many centuries as a religious practice.

    And, as a part of our evolutionary history, our ancestors had to survive through many times of famine, and our bodies are well-adapted to going for long periods with little or no food.

    The 50 Best Health Blogs

  2. Check out the Pima Indians of Arizona and Mexico. The group in Arizona has been subjected to fast food and convenience stores. The Pima in Mexico still live adhering to their traditions of feast and famine. the Pima in Az. have a seriously large and growing population of obese and diabetic adolescents and adults. The Pima in Mexico are slim and healthy.
    Fasting by calorie restriction has been proven to be healthy, but complete elimination of food for one or multiple days is not healthy. Do not forget that the body requires calories to breathe, think and process. We need protein. and we must have water.
    Too many people think of "fasting" as food elimination instead of calorie restriction.
    One should only eat to 80% full anyway. You should always walk away from a meal still feeling a little hungry. not full. Guruji used to say the amount that fits in your hand. Which would make sense bc your stomach is about as big as your fist right?

  3. Karen, thanks for making that distinction between calorie restriction and complete food elimination - that's a good point. In that study I mention in the post, it is calorie restriction (<400 calories/day) that they are studying.

    And thanks for your comment, Jim! In terms of our evolutionary history, I would think people more often experienced calorie restriction during times of famine -- not complete food elimination. As for religious practices, maybe more complete elimination?

    Also, Karen, I'm curious about this idea of fasting on moon days in the ashtanga tradition: 1) do people actually practice this, and 2) is it complete food elimination on moon days or just calorie restriction?

  4. Thanks for this post Christina! This is definitely and interesting topic, and I agree that periodic days of fasting/caloric restriction might be a useful therapeutic tool. I really enjoyed reading Jim and Karen's posts too :)!

    This reminded me of an article in Time Magazine a few months ago about epigenetics (a structural modification in a person's DNA - primarily by methylation and de-methylation of amino acids, to some extent this regulates gene expression). In the article, the authors hypothesized that these epigenetic markers can be inherited along with your genes.

    To investigate this theory, they looked at family records in Norbotten, a small Swedish town that experienced intermittent years of extreme famine vs abundance. They discovered that the grandchildren of boys that survived years of famine (prolonged fasting) lived about 6 years longer than the grandchildren of boys who lived during a period of food overabundance. When they adjusted for socioeconomic status, the survival difference increased to 32 years (instead of 6).

    There are some possible confounding factors, and I didn't see the original scientific article, but is still interesting. Along the lines of Jim's comment - perhaps periods of fasting is somehow an evolutionary advantage? Also relates to the positive impact of caloric restriction, not just for your personal health, but potentially the health of your descendents :).,8599,1951968,00.html

  5. Caitlin, this is fascinating! I'm going read that Times article carefully and look for that study!