Loss Aversion: Why Putting Money On The Line Helps You Stick To A Diet

Losing $50 feels worse than winning $50 feels good. That simple quirk of human psychology explains why casino players chase their losses, why people keep paying for gyms they never visit, and why putting money on the line can be one of the most effective diet tools there is.

The discovery

In 1979, psychologists Daniel Kahneman and Amos Tversky published prospect theory, a description of how people actually make decisions under risk, as opposed to how economics textbooks assumed they did. One of its central findings was loss aversion: losses loom larger than equivalent gains. In many experiments people needed a potential gain of roughly twice the size of a potential loss before they would accept a 50-50 bet. Kahneman received the Nobel Prize in economics in 2002 for this work; Tversky had died in 1996.

A classic demonstration: offer people a coin flip where they lose $100 on tails. Most will not play unless heads wins them something like $200. Mathematically a $150 win is a good bet. Emotionally, it does not feel like one.

Loss aversion on the casino floor

Casinos are a living laboratory of loss aversion, and a few patterns show up again and again:

• Chasing losses. After a bad run, players often raise their stakes to get back to even, because ending the night down feels unbearable. It is the single most expensive habit in gambling.
• The house money effect. Economists Richard Thaler and Eric Johnson described how people who are ahead take bigger risks with their winnings, as if that money were not really theirs. The same person who would never bet $200 of their own will happily risk $200 of "the casino's".
• The break-even effect. Near the end of a losing session, long-shot bets that offer a chance to get back to zero suddenly look very attractive.

All of these mistakes come from the same root: the pain of a loss distorts the next decision. That is also exactly what makes loss aversion useful for building habits.

Why your gym membership is not working

In a well-known 2006 paper titled "Paying Not to Go to the Gym", economists Stefano DellaVigna and Ulrike Malmendier studied thousands of US health club members. Those on monthly contracts went so rarely that they paid more than $17 per visit on average, when a pay-per-visit pass would have cost about $10. Once the money has gone out of your account at the start of the month, skipping a session costs nothing extra. There is no fresh loss to avoid, so the sofa wins.

Turning loss aversion around

The trick is to put the loss after the behaviour instead of before it. Instead of paying in advance and getting nothing back for missing a session, you put money at risk that you only keep if you follow through. Every skipped workout now feels like a fresh loss, and your brain fights hard to avoid it.

The research supports this. In the 2008 University of Pennsylvania trial led by Kevin Volpp, participants who made a deposit contract, risking their own money each month, lost around 14 pounds over 16 weeks, compared with about 4 pounds for people who only had regular weigh-ins. A lottery-style incentive, which exploits our love of a small chance at a big win, worked almost as well. We explain the apps built on these ideas in betting on your own weight loss: DietBet, HealthyWage and stickK.

Five ways to use loss aversion for weight loss

1. The deposit jar. Give a trusted friend $100. Each week you hit your target (workouts done, steps reached, weekly average weight down), you get $25 back. Miss, and they keep that week's share.
2. The anti-charity. Pledge that any failed week sends money to a cause you dislike. Commitment contract sites such as stickK formalise this with a referee.
3. Prepay specific sessions. Book and pay for individual classes with a strict cancellation policy, rather than an open-ended membership.
4. Streaks. Fitness apps that show a long streak harness loss aversion too: nobody wants to break a 60-day run.
5. Team stakes. Letting down a team adds social loss on top of financial loss. See office fitness challenges and friendly wagers.

The limits

Loss aversion is a strong push, not a permanent solution. In the Volpp trial, much of the extra weight loss had disappeared seven months later, after the incentives ended. Stakes work best as scaffolding while you build habits that eventually stand on their own, like the trigger-routine-reward loop in the science of never missing a workout.

And watch for the gambler's mistakes in your fitness life. Missing a session and "winning it back" with a punishing double workout is chasing losses by another name, and it is a fast route to the problems described in why you are gaining weight even if you exercise every day. A loss is a loss. Accept it, and stick to the plan.

This article is general information, not medical advice. Check with a doctor before starting a new diet or exercise programme, especially if you have a health condition.