The other day I was catching up with my friend Kim Leavitt, who is a deep thinker. I told him about the blogging I was doing on fighting obesity, with fasting as the key tool. (By "fasting," "eating nothing" or "a period of no eating" I mean a period of drinking water, carbonated water, tea or coffee—without sugar or other sweetener—but nothing else.) Kim's insightful questions inspired me to distill the logical spine of my views on weight loss down to four propositions:
Eating nothing leads to weight loss.
For healthy, nonpregnant, nonanorexic adults who find it relatively easy, fasting for up to 48 hours is not dangerous—as long as the dosage of any medication they are taking is adjusted for the fact that they are fasting.
Eating sugar, bread, rice and potatoes makes most people feel hungry a couple of hours later. People who have, by and large, quit eating sugar, bread, rice and potatoes can notice this effect on the rare occasions that they do eat a substantial amount of sugar, bread, rice or potatoes. Moreover, if they pay attention, those who have quit eating sugar, bread, rice and potatoes can notice which other foods cause them to feel hungry a couple of hours later.
Two months or so after quitting eating sugar, bread, rice, potatoes—and all the other foods and beverages that make them feel hungry a couple of hours later—a large fraction of people will then find fasting relatively easy.
Let me comment on each proposition in turn:
Proposition 1: "Eating nothing leads to weight loss" is not controversial.
Proposition 2: The best evidence that fasting is not dangerous comes from the experience of those in religious traditions that encourage fasting. For example, the Mormonism I grew up in not only instructed everyone who could to fast for 24 hours once a month, it also encouraged people to fast for longer periods of time for special spiritual purposes. Mormon fasts often involved not drinking as well as not eating. Given the body of experience indicating that even fasts that risked dehydration were usually not that dangerous, nonreligious fasting that encourages the drinking of water should not be dangerous for those in good health who are not pregnant or anorexic. The biggest worry I have about people fasting is that it could easily throw off the dosage of medication they are taking. So anyone taking prescription medication should consult their doctor about medication interactions before fasting. And anyone taking nonprescription medication should think hard about lowering the dose when they fast.
Proposition 3: In talking about sugar, bread, rice, potatoes, and other things that an individual finds from experience make them hungry a couple of hours later, I am consciously being agnostic about the mix of hormones or other internal body mechanisms that make this happen. Following Jason Fung, I have tended to talk as if insulin was central to the mechanism. (See "Obesity Is Always and Everywhere an Insulin Phenomenon" and "Forget Calorie Counting; It's the Insulin Index, Stupid.") Even if I am totally wrong about the biological mechanisms, Proposition 3 can still be verified by experience. Because the data on how hungry an individual feels arrives so quickly, each individual can gather the needed personalized evidence quickly.
Proposition 4: As for Proposition 3 and the effects of various foods, each individual can readily gather the relevant evidence for themselves on how much easier fasting is after going off sugar, bread, rice, potatoes and other foods and beverages that make them feel hungry a few hours later. People who are still eating sugar, bread, rice and potatoes and other troublesome foods and beverages may well find fasting excruciatingly difficult. But I make the testable prediction that a large fraction of those who go off those foods will find fasting relatively easy. To be more specific, physiologically, if one has gone off that set of foods, the hunger from fasting will not be anywhere near as intense. It will be much easier to distract oneself from the hunger with distractions like a good TV show, work, or a hike. Also, it is likely true that the self-discipline developed by going off troublesome foods will come in handy in sticking to the fast through all the reminders of food that surround us in our society.
Conclusion: These four propositions are the core of the argument I have been making in my diet and health posts. If anyone wants to attack the approach to weight loss I have been recommending, I urge them to attack some element of the argument I have outlined above. The clear implication of the above argument is that for a large fraction of people, fasting—combined with avoiding sugar, bread, rice and potatoes—is a powerful, not-too-painful, tool for weight loss.
Addendum: In a comment below, Ani poses and important challenge:
When you say that eating nothing leads to weight loss, you are making the assumption that (i) your metabolism is not affected by the fact that you are fasting and (ii) that once you start eating after fasting, you do not overeat. These might be valid, but have to be stated at least as assumptions, if not as proven facts.
On point (ii), I am assuming a long-enough fast and a short-enough eating window that it is simply not appetizing to eat enough extra during that short period of time to make up for the weight-loss effects of not eating during the previous period of fasting. The avoidance of sugar, bread, rice, potatoes and other troublesome foods and beverages is likely to reduce the required ratio between the duration of fasting and the length of the eating window.
On point (i), my claim that for many people fasting won't be painful includes the claim that for those people, their metabolism won't get so low that they face a serious problem of feeling sluggish or listless. As for the effects of a slower metabolism on weight loss, physics, chemistry and biology put a limit on how efficient one's metabolism can get. One's metabolism might become quite a bit more efficient, so that you don't need to eat much to feel good and keep your weight even. That amount of food might be small enough that you are spending a lot more time fasting than time eating, but enough fasting will keep your weight steady.
In my posts on cancer,
I make the point that an efficient metabolism, while not favorable to being able to eat a lot total, could give one's normal cells a decisive edge over cancer cells that have inefficient metabolisms and therefore a tough time in the absence of abundant food.
Ani also mentions animals. One of the key things about a fasting schedule, combined with avoiding troublesome foods, is that it is much, much easier to execute consciously than attempts at calorie restriction while keeping to a traditional eating schedule. Consciously-chosen fasting plays to our strengths as humans. It is in a different category than, say, fasting during hibernation for animals.
Don't miss these other posts on diet and health and on fighting obesity:
Julia Belluz and Javier Zarracina: Why You'll Be Disappointed If You Are Exercising to Lose Weight, Explained with 60+ Studies (my retitling of the article this links to)
Also see the last section of "Five Books That Have Changed My Life" and the podcast "Miles Kimball Explains to Tracy Alloway and Joe Weisenthal Why Losing Weight Is Like Defeating Inflation." If you want to know how I got interested in diet and health and fighting obesity and a little more about my own experience with weight gain and weight loss, see my post "A Barycentric Autobiography."