Dieting and the “January Effect”: Our Predictable Irrationality

For anybody who hasn’t read Dan Ariely’s book, Predictably Irrational, I highly recommend it. Dan, a professor of psychology and behavioral economics at Duke, is one of the world’s best analysts in the ways we act … predictably irrational. His writing (two follow-up books, along with hundreds of academic papers and articles in popular media outlets) is full of practical examples of how we systematically go wrong.

I was playing with Google the other day and started using Google Trends. Google Trends lets you see the relative popularity of search terms over time. One of things I wanted to see if there was a “January effect” in diet searches. Everyone talks about starting a diet as part of a New Year’s resolution. Does that actually hold up?


When I looked at the trends for the past year, the highest point in “diet” searches was, indeed, in the first week of 2016. As you see from the graph above, the relative number of searches declined gradually during 2016 and spiked in the week of January 3-9, 2016. (The highest point in the Google Trends graphs is always 100, and the other points are relative to that point.)

Then I checked to see if this was an annual thing.


Yikes! This looks like an EKG. As noted by the spike in January 2015, the high point each year occurs in January, and then declines steadily.

This is a really good example of the way in which we are completely predictable in our irrationality. There should not be anything special about the beginning of the year when it comes to dieting. Whether you start a diet should be determined by your weight, your health, or what you doctor says. That should be the same throughout the year, but it’s not. We’re all apparently “turning over a new leaf” or “starting with a clean slate” and we use the beginning of a new year to do that.

That we have reset points makes sense since there are natural biological resets like going to sleep and then waking up to start a new day. These biological resets also act like decision resets, allowing us to not just renew ourselves physically but also emotionally so we can come into a decision fresh. We are much more rational after a reset because we are less emotionally “hot.” Aphorisms like “take ten deep breaths” and “why don’t you sleep on it” have canonized the value of resets in our lives. Each day is potentially a reset, or each week, or each month. For students, it might be the start of the semester. For businesses, the start of a new quarter or fiscal year.

A reset can be a good thing; it can help you kick start a new habit or avoid making an overly emotional decision. On the other hand, attaching importance to artificial resets can come back to hurt you. If you start a diet in the first week in January where the New Year is defined as your reset and you stray from your regimen, the what-the-hell effect often takes over. “I’ve already blown it. I may as well eat whatever I want and start fresh next time.” (Next week? Next month? Next January?) After using the reset to start a good habit, we feel we dirtied our once-clean slate.

Resets are great for improving habits, but once we start, we need to get beyond thinking the slate is either “clean” or “dirty.” Improving habits is difficult. Anytime is a good time to start, though any time we fall short doesn’t have to be a reason to abandon the attempt altogether or wait until the next reset point to start over.