Intermittent fasting dissociates beneficial effects of dietary restriction on glucose metabolism and neuronal resistance to injury from calorie intake. Anson RM1, Guo Z, de Cabo R, Iyun T, Rios M, Hagepanos A, Ingram DK, Lane MA, Mattson MP. Proc Natl Acad Sci U S A. 2003 May 13;100(10):6216-20. Epub 2003 Apr 30.
Dietary restriction has been shown to have several health benefits including increased insulin sensitivity, stress resistance, reduced morbidity, and increased life span. The mechanism remains unknown, but the need for a long-term reduction in caloric intake to achieve these benefits has been assumed. We report that when C57BL6 mice are maintained on an intermittent fasting (alternate-day fasting) dietary-restriction regimen their overall food intake is not decreased and their body weight is maintained. Nevertheless, intermittent fasting resulted in beneficial effects that met or exceeded those of caloric restriction including reduced serum glucose and insulin levels and increased resistance of neurons in the brain to excitotoxic stress. Intermittent fasting therefore has beneficial effects on glucose regulation and neuronal resistance to injury in these mice that are independent of caloric intake.
I have never been that interested in diet as I never had much of a problem with body weight, nor as a physical therapist did I really think it was my job to talk about it, except maybe to suggest that weight loss or gain might be beneficial for a given patient. However, since reading the paper on dietary restriction preserving muscle mass and preventing sarcopenia I have continued to read more on the subject. I had also read about the Warrior diet on wikipedia, concluded it fit my personality pretty well, not eating during the day then eating as much as you want in the evening. This week I read and finished the warrior diet book, and I thought it had some good insights but I was a bit disappointed to learn that the author did a lot of eating during the day rather than abstaining, which isn’t what I have done or wanted to do. Reading the criticisms of the Warrior Diet on amazon.com a lot of people said they liked the concept but the book was padded out and he did a lot of promoting supplements which I’m not interested in either. Someone said they started off on the Warrior Diet, then moved on the the Fast 5 Diet, which it turns out is what I was already doing, didn’t promote supplements and best of all the pdf of the Fast-5 Diet book is available free. I’m not going so far as to say I’d advocate it yet, but I’m on my 15th day and so far I like it.
So what’s the point? Calorie restriction has been shown to extend the lifespan and prevent disease, and muscle loss in a wide variety of fauna, with similar metabolic improvements seen in people, though the prolonging of lifespan in humans has yet to be established. Regarding the animals, some of the caloric reductions were done by just limiting available calories 30% (plus or minus depending on the study) while other papers were limiting calories by feeding the animal every other day. This led researchers to wonder how much of the every other day diet (intermittent fasting) benefits were due to the calorie reduction, and how much of it was due to the spacing out of the food source (fasting irrespective of calorie reduction). Most of the mice on the every other day diet decreased overall calories but the strain used in this paper ate almost double on the feeding days such that overall calorie intake was about the same (~90% as the mice allowed to eat as much as they want everyday).
Both the fasting and the calorie restriction mice had reductions in blood glucose and insulin to a similar degree with a slight edge given to the fasting mice. IGF-1 and B-hydroxybutyrate however increased in the fasting mice, but went down in the calorie restricted mice with the researcher concluding these increases might be neuroprotective, as was the shift towards ketosis, found in the fasting but not calorie restrictive diets. The mice were then injected with kanic acid to their hippocampus to assess if there was an effect with either diet on neuron survival. Both the caloric restriction and intermittent fasting rats had better survival of neurons compared to the mice that ate their fill daily, with the intermittent fasting mice being significantly better.
So based on this study intermittent fasting has some health benefits in addition to and separate from what you get from calorie restriction alone (EVEN IF YOU EAT DOUBLE ON THE NON-FAST DAYS). The question then becomes, what’s the best/easiest/most tolerable form of intermittent fasting. The mice did an every other day fasting diet, which to me sounds miserable. Though, skipping breakfast and lunch per the Warrior and Fast 5 diets sounded fairly miserable to me too, until I tried it, and so far I like, and I definitely feel like I have more energy during the day. It’s still unknown, at least to me, if the once a day diet has similar protective benefits to the every other day diet. I should point out that it likely doesn’t have to be either/or proposition as these researchers had to search for a strain of mice that ate double on the feeding days because most didn’t and calorie reduction went hand in hand with intermittent fasting. Thus far I notice it does seem to reduce my overall calories too, so with the best of both worlds maybe I’ll live to 150 before I have my consciousness uploaded into a robot;) To be continued…
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Chad Reilly is a Physical Therapist, obtaining his Master’s in Physical Therapy from Northern Arizona University. He graduated Summa Cum Laude with a B.S. Exercise Science also from NAU. He is a Certified Strength and Conditioning Specialist, and holds a USA Weightlifting Club Coach Certification as well as a NASM Personal Training Certificate. Chad completed his Yoga Teacher Training at Sampoorna Yoga in Goa, India.