My title comes from the first words in Sumathi Reddy's Wall Street Journal article shown above. Sumathi writes:
Stop counting calories. It’s the clock that counts.
That’s the concept behind time-restricted feeding, or TRF, a strategy increasingly being studied by researchers as a tool for weight-loss, diabetes prevention and even longevity.
Sumathi goes on to detail this approach and the accumulating evidence that it works.
The idea is simple: keep your "eating window" within a day down to a certain number of hours. This is a strategy that Jason Fung emphasizes in his powerful book The Obesity Code, which I try to distill into a blog post in "Obesity Is Always and Everywhere an Insulin Phenomenon."
Sumathi talks about a 12-hour eating window. Some people may get good results from an eating window of this length, but many people will need to restrict their food intake to a shorter window to get good results. Let me give my sense of things this way: in explaining the rise of obesity in the population as a whole, the two things that have the right timing are the rise of sugar and the lengthening of the eating window in a typical person's day. If, 120 years ago, many people ate breakfast at 8 AM and dinner at 6 PM, that is a little over a 10-hour eating window and well within a 12-hour eating window. Now it is common for many people to eat from soon after they wake up to right before they go to bed, somewhere around a 16-hour eating window. The rise in sugar consumption is less speculative; the data are better:
Based on this history, I suspect that for most people, avoiding all sugar and restricting food intake to 12 hours every day from childhood on is enough to avoid becoming obese in the first place. But prevention is much easier than cure. For those who are already overweight or obese, and have become insulin resistant, losing weight and restoring health might require avoiding even sugar-free carbs that are high on the insulin index, and restricting the eating window to something considerably shorter than 12 hours. (On insulin resistance and the insulin index, see "Obesity Is Always and Everywhere an Insulin Phenomenon" and "Forget Calorie Counting; It's the Insulin Index, Stupid.)
Personally, although I think I could keep my weight steady with an 8-hour eating window, I need something shorter in order to lose weight. In my experience, as long as I only eat foods low on the insulin index during the eating window, even going 20 to 21 hours between a 3- or 4-hour eating window each day is not at all painful. Any hunger I experience is mild and non-insistent hunger. What hunger I do experience is usually from thinking about food. And for the most part, I don't think about food because I am hungry, I am hungry because I thought about food for some other reason.
Eating this way for a while has two effects. On the one hand, for the same practices, weight loss gets tougher when your weight it lower to begin with. On the other hand, eating food that is low on the insulin index during your eating window gets a lot easier over time, and assuming you do that, over time it gets easier to go substantial periods with no food—"fasting"—without any substantial disutility. With fasting, "No pain, no gain" takes on a totally different meaning. If you do it right by eating well during your eating window, there is no pain in fasting, and you won't gain any weight while you are fasting!
When I first started on this program, I hated the idea of an "eating window." Both for theoretical reasons (see "Obesity Is Always and Everywhere an Insulin Phenomenon") and my own idiosyncratic reaction to particular rules, I liked the idea of length of time fasting as the thing to shoot for. But after a month or two, I came to terms with the fact that, logically, if you are eating every day, there is a very close mathematical relationship between the average length of the eating window and the average length of time fasting between the eating window one day and the eating window the next.
Of course, if there are some days when you don't eat at all (which can be quite a reasonable thing to do, and is also not as hard as you might guess–see "Obesity Is Always and Everywhere an Insulin Phenomenon"), then that mathematical relationship doesn't hold. When you skip eating for a whole day, it is cognitively easier to think about the length of the fast than the length of the eating window. But during periods of time when you are eating at least once a day, focusing on the length of your eating window is a perfectly good way to think about things.
There are three ideas that I keep reminding myself and others that keep the program I am following from seeming too abstemious and severe.
First, dietary fat is good, not bad. I have a post specifically on this: "Jason Fung: Dietary Fat is Innocent of the Charges Leveled Against It." And the message that dietary fat is good, not bad comes through clearly if you read "Forget Calorie Counting; It's the Insulin Index, Stupid." Knowing that foods such as olive oil, butter, cheese, cream, cashews, macadamia nuts and sugar-free bacon are great goes a long, long way toward making up for the sugar, bread, potatoes and rice that I have given up. Because I also treat meat as fine in moderation, it is easy to get a good restaurant meal.
Second, because foods that are low on the insulin index are quite satiating per calorie (especially those with significant dietary fat), if you have a reasonably short eating window, you don't have to restrict quantity at all. If you overeat much at all, you will feel uncomfortably overfull afterwards, and you are unlikely to want to do that again. By contrast, sugar or other easily-digestible carbs have a way of making you hungry so you want to eat more and more and more; eating any substantial amount of sugar or other easily digestible carbs makes it very, very easy to overeat badly.
Third, though some people try to make systems, I love the fact that I don't need to do things in any regular way. If it is convenient to go for a long time without eating, I can do that. If I want to shift the timing of my eating window, that is fine. If it is convenient to do a longer eating window on some particular day, that is fine. Things average out. Indeed, holding the average length of the fasts fixed, it may well be more effective to have a long fast and a short fast than to have two fasts of equal length. So irregularity may well be a good thing, as long as the overall rigor of your program is reasonably high. Some of this is speculative; the experiments have not all been done. But the theory I discuss in "Obesity Is Always and Everywhere an Insulin Phenomenon" (following Jason Fung's The Obesity Code) gives no reason to think that smoothing out the timing of your eating windows is important. Most people will get encouraging results from eating windows of 4 hours (one big leisurely meal) or 8 hours (two meals as big as you want with healthy things) every day, even if they vary the timing and jump back and forth between the 4-hour and 8-hour eating windows.
Many people worry that if they try a diet, it might backfire. That is, they could end up yo-yoing back up to an even higher weight than where they started. The scary evidence so far that says most diets backfire does not yet include a regimen relying on substantial periods of time with zero food and fairly strictly avoiding all foods that are high on the insulin index during eating windows. In predicting what that evidence will look like when it is systematically gathered, I am reassured by two things:
I am not suffering at all. No intrusive, onerous hunger; plenty of fun food to eat.
Everyone agrees that while you are eating zero food, it will tend to bring your weight down. Hence, it seems to me that some dosage of fasting will do the trick to maintain my weight or to lose weight. I can't guarantee in advance what that dosage will be, but if I am determined to do whatever it takes, what it takes won't be so bad.
For those who don't read Sumathi's article in its entirety, here are some key passages:
1. The findings, published in the journal Cell Metabolism, showed that when eight overweight people who naturally ate for 15-plus hours a day restricted their eating to a 10-hour window for 16 weeks, they lost 4% of their weight. A year later, they reported sticking to the plan, even though they didn’t have to, and had kept the weight off.
“All of them said they slept better, and they felt more energetic throughout the day,” said Dr. [Satchidananda] Panda. “They were actually feeling less hungry.”
TRF studies of mice—which provide the bulk of research on the strategy—have found that the body, when fasting for half a day or more, has more time to produce the components for cellular repair, break down toxins and coloring agents in food, and repair damaged DNA in the skin and stomach lining, according to Dr. Panda. There is also some evidence that TRF
2. “Many patients have gone off of blood-pressure medications,” [Dr. Julie Shatzel] said. “In some cases, I’ve seen the reversal of prediabetes.”
3. “Both improved their glycemia responses,” Dr. [Leonie] Heilbronn said, referring to the effect food has on blood sugar levels. While the men lost weight, she said, it wasn’t enough to account for the improved glucose levels. “There’s something else going on that’s not just driven by weight change,” she said.
4. “I think the real power of TRF is the simplicity of it,” [Dr. Krista Varady] said.
Don’t miss my other posts on diet and health:
I. The Basics
II. Sugar as a Slow Poison
III. Anti-Cancer Eating
IV. Eating Tips
V. Calories In/Calories Out
VI. Other Health Issues
VIII. Debates about Particular Foods and about Exercise
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)
IX. Gary Taubes
X. Twitter Discussions
XI. On My Interest in Diet and Health
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 “Diana Kimball: Listening Creates Possibilities” and my post "A Barycentric Autobiography. I defend the ability of economists like me to make a contribution to understanding diet and health in “On the Epistemology of Diet and Health: Miles Refuses to `Stay in His Lane’.”