Why Keystone Habits Rarely Trigger Other Changes

Before we change anything about our behavior, we usually put a lot of work into deciding what we’re going to change. Should we start with sleep, exercise, drinking, our schedule? Which one is the best? Which one makes the others easier? Underneath the deciding sits the idea that some habits are worth more than others.

It isn't a bad idea. Most of us have had a first change that made the second one easier, but that doesn’t mean it’s always the case.

Do Keystone Habits Trigger Other Changes?

A keystone habit is the one behavior that supposedly pulls everything else along behind it. We start running in March, and by May we're eating better without trying, sleeping properly, and snapping at people less. Researchers who study whether this happens call it spillover, and they've been chasing a solid answer for over twenty years.

Spillover shows up, but it's small, it's unreliable, and it sometimes runs backwards because doing one good thing can leave us feeling we've earned a pass on the next. Asked outright whether one change had ever set off another, 50% of people usually can’t think of a single time when it had. The ones who can describe things that stayed in the same lane, something like how recycling led to composting or how one organic purchase led to another. Something in one corner of life setting off something in a different corner is pretty rare.

The sequence of habits or behaviors we’re trying to change doesn't make much of a difference either. Studies that compared changing everything at once and changing one thing at a time found no winner, and no difference in how many people quit along the way. Whatever makes a change stick, it usually isn't the order we do it in.

Why Sleep Sits Upstream of Diet and Movement

Sleep seems to sit upstream of other habits though. It might be the closest answer we have to “where do we begin.”

Run on four hours of sleep a night for two weeks with a kitchen we can raid, and we'll eat around 300 calories a day more than we would have if we had nine hours of sleep each night. None of it gets burned off because our body doesn't raise its calorie burn to match. Weight gain happens quickly. In the study that produced these numbers, when people’s sleep went back to normal, the eating stopped within days, but the fat kept coming.

Similar effects happen outside a lab. Give people five or six hours a night in their own beds for a week and the eating effect mostly disappears. Instead, nearly everyone in this study reduced how much they moved. Activity dropped precipitously, and everyone started sitting more or lying down.

Hormones and Sleep

The usual explanation for all of this is that short sleep scrambles our hunger hormones, but the lab study checked and didn’t find that to be the case. Ghrelin, the hormone that makes us feel hungry, didn't change. Neither did leptin, which tells us we've had enough, and neither did cortisol. The hormones were doing what they do on any normal night.

So the signal coming from our body hadn't changed. What changed was how our brain responded to it. Imaging studies show that when we're short on sleep, the parts of the brain handling appetite and reward react more strongly to the sight of food. They react most strongly of all to the food we'd normally talk ourselves out of. We aren't hungrier, food is just harder to refuse. It's the difference between walking past the pastry case and stopping in front of it to talk ourselves through it.

The same thing shows up in how the rest of our day goes, and it rarely feels like a decision. We don't really decide to skip the gym. We just don't get up. We take the elevator instead of the stairs, stay at our desk for a call we'd normally walk around for, and push the harder tasks to tomorrow. By the evening, the day has arranged itself around sitting down. Our body isn't withholding motivation from us. It's running on low energy, and we tend to explain that to ourselves as a lack of discipline.

It works in reverse too. Across sixty-five trials involving more than eight thousand people, helping people sleep better reduced depression and anxiety, and the more their sleep improved the more their mood improved with it. Sleep isn't a first domino. It's the state we're in while we attempt to change everything else, which makes it an essential input.

What Carries Over Between Habits

If the habit itself doesn't trigger the next change, something has to explain the gap between the person whose first change turns into three more and the person whose identical change is gone by week three.

The best answer is that it’s not the behavior itself; it's what the behavior proved to ourselves. Convince us we're capable of something and our behavior follows, and it barely matters what the behavior change even is. The impacts on autonomy and competence are what matter the most. The indicator of how well a change will stick and help us with the next change is how capable and how self-directed we end up feeling rather than the habit itself.

In one study, nearly seven hundred unemployed young adults were asked to set goals around sleep, exercise, and drinking. A year later, they were seven percent more likely to be working. Going to bed earlier isn’t a skill we can put on our resume, but it can shift our locus of control, which is how much we experience our own lives as something we can control rather versus something that just happens to us. 

The habits are the shiny object, but how we see ourselves is a large part of whether we make the change or not.

References

1. Bjorvatn, K., Ekström, M., & Garcia Pires, A. J. (2021). Setting goals for keystone habits improves labor market prospects and life satisfaction for unemployed youth: Experimental evidence from Norway. Journal of Economic Behavior & Organization, 188, 1109-1123. https://doi.org/10.1016/j.jebo.2021.06.013

2. Covassin, N., et al. (2022). Effects of experimental sleep restriction on energy intake, energy expenditure, and visceral obesity. Journal of the American College of Cardiology, 79(13), 1254-1265. https://doi.org/10.1016/j.jacc.2022.01.038

3. Dickinson, D. L., Kakoschke, N., & Drummond, S. P. A. (2025). The impact of insufficient sleep on dietary choices and physical activity behaviors: Evidence from a randomized cross-over trial. Scientific Reports, 15, 24513. https://doi.org/10.1038/s41598-025-08289-4

4. James, E., et al. (2016). Comparative efficacy of simultaneous versus sequential multiple health behavior change interventions among adults: A systematic review of randomised trials. Preventive Medicine, 89. https://doi.org/10.1016/j.ypmed.2016.06.012

5. Nash, N., et al. (2019). Reflecting on behavioral spillover in context: How do behavioral motivations and awareness catalyze other environmentally responsible actions in Brazil, China, and Denmark? Frontiers in Psychology, 10, 788. https://doi.org/10.3389/fpsyg.2019.00788

6. Scott, A. J., et al. (2021). Improving sleep quality leads to better mental health: A meta-analysis of randomised controlled trials. Sleep Medicine Reviews, 60, 101556. https://doi.org/10.1016/j.smrv.2021.101556

7. Sheeran, P., et al. (2016). The impact of changing attitudes, norms, and self-efficacy on health-related intentions and behavior: A meta-analysis. Health Psychology, 35(11), 1178-1188. https://doi.org/10.1037/hea0000387

8. Sheeran, P., et al. (2020). Self-determination theory interventions for health behavior change: Meta-analysis and meta-analytic structural equation modeling of randomized controlled trials. Journal of Consulting and Clinical Psychology, 88(8), 726-737. https://doi.org/10.1037/ccp0000501