Many studies show that exercise is relatively ineffective for weight loss. (See the article I retitled in my flagging as “Julia Belluz and Javier Zarracina: Why You'll Be Disappointed If You Are Exercising to Lose Weight, Explained with 60+ Studies.”) In this post, I want to give a possible theory about why. I will build on the idea that “Obesity Is Always and Everywhere an Insulin Phenomenon.”
I need the insulin-centric theory I will explore also to explain why exercise seems to be helpful in avoiding weight gain. On that score, exercise that increases muscle mass and more muscle tone means there is more muscle more ready to take up blood sugar when insulin signals that there is a surplus of blood sugar. That means a more modest insulin signal can get blood sugar back in line. The less insulin is needed to get blood sugar back in line, the less the fat cells hear an insulin signal that they should turn blood sugar into fat and store it. Furthermore, if insulin levels don’t go as high, neither the muscle cells nor the fat cells are as likely to develop partial “deafness” to insulin that leads to the insulin-producing cells “shouting.” That is, if insulin never gets too high in the first place, there is no reason for cells like the fat cells and muscle cells to develop insulin resistance, nor for insulin levels to become even more elevated in response.
What about weight loss? Let’s focus only on weight loss people are trying to achieve because they are genuinely overweight to begin with. In the insulin-centric theory, most people who are overweight to begin with became overweight because of elevated insulin levels over a long time. Thus, most people who are overweight have some degree of insulin resistance, and have insulin producing cells that have to do some amount of “shouting” in order to keep blood sugar in line. That makes it hard to get insulin low enough that fat cells will release their fat. The metaphor I use in “How Low Insulin Opens a Way to Escape Dieting Hell” is that levels of insulin that are hard for people with insulin resistance to get below are enough to lock fat inside fat cells. And remember the idea that most people who are overweight to begin with have insulin resistance.
What will happen when people with high enough insulin levels to lock fat inside their fat cells exercise? If they can’t get energy from their stored fat, then their blood sugar levels will get low, leading them to (a) feel tired, (b) get hungry, and (c) burn less energy when they go through the following non-exercise part of their day. Feeling tired may lead to quitting the exercise program. Getting hungry can easily lead to eating enough more to cancel out any energy burned from the exercise. And in subtle ways, activity levels and non-activity-related energy burning can ramp down during the non-exercise part of the day.
I said that getting below the critical level of insulin at which fat starts being released from fat cells is hard for most people who are overweight to begin with. What I meant was that it is hard if they continue to eat three meals a day. Shortening the eating window to 8 hours—say skipping breakfast and not eating after dinner—means that there are 16 hours for insulin levels to get low. For many people this will lead to substantial weight loss. If that isn’t enough, it is possible to experiment with fasting (not eating, but continuing to drink water) for longer periods of time. If you want to try that, read the cautions I have in “Don't Tar Fasting by those of Normal or High Weight with the Brush of Anorexia.”
The key tip for those who want to shorten their eating window or go even further is that going without eating for 16 hours or more is much easier if when you do eat, you are eating foods that have a low index. On that, see “Forget Calorie Counting; It's the Insulin Index, Stupid”and “Why a Low-Insulin-Index Diet Isn't Exactly a 'Lowcarb' Diet.”
The short version is that if you don’t get your insulin levels low enough—which for people who are overweight usually requires changing the timing of your eating as well as what you eat—it will be very hard to lose weight because your body will fight you. (See “Stop Counting Calories; It's the Clock that Counts.”) And that includes if you exercise.
There is accumulating evidence that shortening your eating window and otherwise having periods of fasting is good for your health in many ways. But even if you decide not to try that, and in the three-meal-a-day context exercise doesn’t lead to any weight loss, exercise can still help make you happier, healthier and smarter, and less likely to gain even more weight than you have already. So it is worth exercising no matter what.
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’.”