[Full disclosure: I was given a copy of the book by the publisher]The question everyone seems to be asking today is whether or not intermittent fasting (meaning an occasional fasting period of up to a day not a lengthy fast/cleanse) is a viable weight loss strategy.
The answer's rather simple. If a person can happily incorporate fasting of any sort into their lives, and that in turn lowers their weekly available energy intake, then yes, fasting may well be a useful strategy. On the other hand, if fasting challenges your quality of life sufficiently to make the intervention too much to bear long term, well then no, fasting's not for you.
As far as fasting goes, there seem to be three primary schools these days. There's Martin Berkhan's Leangains system (the system popularized without credit in The 8 Hour Diet) which at its base involves fasting for roughly 16 hours a day, there's Brad Pilon's Eat. Stop. Eat. which at its base involves 1 or 2 weekly 24 hour food fasts interspersed with healthful eating, and there's today's featured review of The Fast Diet which takes researcher Krista Varady's work on what she's called alternate day modified fasting (ADMF) and bookifies it for the masses. At its base, ADMF (and The Fast Diet) simply involves ensuring there are two days weekly where calories consumed are in the 500-600 range.
The book was written by non-practicing physician turned journalist Dr. Michael Mosley and his journalist co-author Mimi Spencer and it leads with the theory that because humans evolved during times of severe dietary insecurity, where fasting was the unavoidable norm, that fasting has unique properties that in turn are healthful and protective. And while that may be true, it certainly has yet to be proven as the science is nowhere near conclusive yet just as the authors themselves point out on the second introductory page,
"Scientists are only just beginning to discover...".Putting aside the fact that many of our closest primate relatives do in fact graze all day (chimpanzees for instance), I'm not sure this theoretical line of reasoning really matters in lieu of evidence, though certainly it does provide a reason to consider the possibility that fasting has interesting properties.
Sadly, the cautionary comment that the science of fasting is young was a rarity in this book that takes hyperbole, conjecture, anecdote and hope to truly dramatic levels and even just 5 pages following the "just beginning" statement the state of the evidence has somehow morphed into,
"The scientific evidence was extensive and compelling".Odd that statement in the context of this book given the vast bulk of the book is quite literally built off the personal (and clearly conflicted) anecdotal evidence of Dr. Mosley and Ms. Spencer's own experiences with their diet - one might have thought that were there actually extensive and compelling evidence a medically trained award winning journalist might have preferred to rely on it to tell the story rather than what he ate for breakfast.
When The Fast Diet does venture into evidence based research the bulk of it comes from mice and rats - useful models to start with no doubt, but of course results from rodent studies are not automatically translatable into humans. One of the book's primary theories is that fasting is helpful because it reduces circulating levels of IGF-1 (insulin like growth factor 1) which in the case of a particular strain of mouse, might be implicated in many disease processes including aging and cancer. And while I am by no means an expert in intermittent fasting or IGF-1, it strikes me as odd that in the few studies I found on medline that specifically looked at IGF-1 levels and intermittent fasting in human subjects following the ADMF protocol espoused by The Fast Diet, there wasn't a consistent effect on IGF-1. One study I looked at showed a decrease in IGF-1 only when energy restriction was accomplished by means of a 10 week liquid ADMF diet, while the other, actually showed little change or even a small rise in IGF-1 levels following a full 6 month trial of ADMF dieting by overweight women. But rather than report on the effect one of the longest and largest trials of ADMF dieting in overweight humans that showed no change to circulating IGF-1 Dr. Mosley chose to report on his own personal drop in IGF-1 levels while following his diet - an odd thing considering the randomized trial he didn't cite was in fact conducted by Dr. Krista Varady - the researcher responsible for The Fast Diet's actual regimen and one of the book's most regularly featured personalities.
Dr. Mosley's self reporting doesn't end there. He also happily self reports that his fasting glucose level went down consequent to his fasting....but of course he also happened to have lost 10% of his body weight - an amount more than sufficient to explain his biochemical improvements, and he reports that his memory seemed to have improved as evidenced by his results in an online test he took twice.
Dr. Mosley's section covers other purported benefits of ADMF fasting - most propped up almost entirely by theoretical or non-human based underpinnings with his take being that ADMF fasting staves off Alzheimer's, prevents cancer, improves chemotherapy, lengthens your lifespan, improves your memory, decreases depression, and of course helps you to lose weight and improves your cholesterol.
The next half of the book was written by Ms. Spencer who doubles down on the "evidence" by stating,
"There is evidence from trials conducted by Dr. Michelle Harvie and others that this approach will help you lose weight, reduce your risk of breast cancer, and increase insulin sensitivity",though Dr. Harvie's provided citation refers only to a paper looking at the impact of fasting on biochemical markers and not in fact fasting's actual impact on long term weight management, breast cancer risk or insulin sensitivity. Later on she goes further to describe intermittent fasting's benefits as,
"widely accepted disease-busting, brain-boosting, (and) life-lengthening".But really her section is more about how to actually wield the diet - one which no doubt includes putting up with hunger. Here's how she describes it,
"While hunger pangs can be aggressive and disagreeable like a box of sharp knives, in practice they are more fluid and controllable than you think".Unfortunately there's yet to be long term data to back that up as she herself notes a few pages further in,
"While the long-term experience of intermittent fasters in still under investigation, people who have tried it comment on how easily it fits into everyday life".Now whether that's true or simply the effect of post-purchase rationalization it flies some in the face of Dr. Varady's work with ADMF dieters which showed that folks randomized to intermittent fasting ala The Fast Diet's style for 6 months were far less likely than those randomized to more traditional caloric restriction to want to sustain the intervention (58% vs. 85%).
And it's Ms. Spencer's section that really dives into the nonsensical stating that despite losing weight, and with no recommendation to exercise, by fasting you'll not only not see a drop in muscle mass, you'll see a rise, and that your food preferences will change such that,
"you'll start to choose healthy foods by default, not by design".She also goes on to state that,
"heavier subjects respond brilliantly to intermittent fasting",yet did not provide a reference. And that's rather crucial in a book that relies on personal anecdote rather than published evidence, or at the very least, clinical experience. From what I can gather neither Dr. Mosley nor Ms. Spencer actually work with individuals who struggle with their weights and I don't think it's a given that the experiences of a woman whose starting BMI was 21.4 (or Dr. Mosley's of 26.4) would necessarily be applicable to those who struggle with their weights to begin with.
Putting my many objections to the reporting of hope and theory as fact, one thing bothered me throughout. If the putative benefits of fasting stem from evolving during centuries of dietary insecurity why would fasting's benefits be expected of diets that even on "fasting" days provided 1/3-1/4 of most folks' daily calorie requirements? Seems to me if you are convinced by the early evidence, and indeed there is some, that fasting confers some biochemical advantages then you should in fact fast, rather than eat and call it fasting.
Ultimately here's a diet book based primarily on theoretical conjecture and mouse studies that's propped up almost exclusively by the personal experiences of two professional journalists neither of which were obese to begin with nor working with patients trying to manage their weights, where statements such as,
"studies and experience show that intermittent fasting will regulate the appetite, not make it more extreme"fail to come with citations, and where on the very same page the statement,
"It all points to a healthier, leaner, longer old age, fewer doctors' appointments, more energy, greater resistance to disease"coexists with the butt covering,
"yet science is only just starting to catch up".So if you want to try fasting as a means to control available energy intake - by all means go for it, but as the authors in rare moments of clarity between wild conjectures and unsupported statements point out, the science is still far too young to be conclusive.
Remember, as always, the most important factor to consider when analyzing your diet is whether or not you like your life while you're losing your weight, as whatever weight you lose with an effort you ultimately abandon is almost certainly going to return when you head back to the life you were living before you lost.