The habit · Decision 11 of 14

Rewards, and what we will not give one for

The app gives rewards for reaching milestones. Every one of them is visible in the menu, earned or not. The list of what is deliberately left out is the part of the design that needed the research.

Last updated .

What the app does
Rewards logging, not eating less. The biggest ones count weeks in which you logged five days, and one of them is for logging a day that went over.
How sure we are Fair , Real, but small, indirect, or thinly measured.
One review found 0.70 kg more weight loss on average when apps add game elements. That is not a prediction for Snapkin. It is small enough that no reward is worth the risks on the eating disorders page.

The evidence for it

The first number is a pooled average, not an upper limit or a promise. The other findings shaped our design choices.

−0.70 kg average extra weight lost with health apps that add game elements, compared with those that do not Nishi et al. (2024) · 17 body-weight trial comparisons · 95% CI −1.18 to −0.22
> 3 days a week of regular logging went together with less weight regained; this was not a randomized test of a minimum amount Peterson et al. (2014) · 220 women, 18 months · moderation P = 0.004
5,526 posts from three food-logging forums, read for what got in people’s way and what felt bad Cordeiro et al. (CHI 2015) · plus 141 people surveyed

How much a reward is worth, which is not much

Nishi et al. (2024) compares health apps with game elements against ones without. The designs and the support around them varied. This is not a trial of our badges. It covers 36 trials, 49 comparisons and 10,079 people, each lasting eight weeks or more.

Average weight difference associated with adding game elements Body-weight analysis: 17 trial comparisons. The entire review covered 36 trials and 10,079 participants across different outcomes.
no difference
Adding game elements, body weight −0.70 kg

Nishi et al. 2024, 95% CI −1.18 to −0.22, over eight weeks or more

−1.4 kg +0.4 kg
The authors rated the body-weight evidence as moderate certainty. The pooled difference was −0.70 kg, with a 95% confidence interval from −1.18 to −0.22 kg. Other analyses found −0.28 kg/m² in BMI, −1.92 percentage points in body fat and 489 extra steps a day. These are averages across different apps and different groups of people. They are not the most you can get, and not a forecast for one person.

Why the rewards are for logging rather than for eating less

Peterson et al. (2014) followed 220 women through six months of treatment and twelve months of follow-up care. How often people logged predicted their weight change only when they logged regularly every week (moderation P = 0.004). The cut-off they report is more than three days a week. The same analysis found no link between how complete each entry was and weight change (P > 0.05).

This study only watched people, so it supports making regular logging easier. It does not prove that incomplete logs work just as well. Our five-day cut-off is a product choice. So the largest group of rewards here counts weeks in which you logged five days. The biggest ones count total days logged, added up over time. The study does not show that a daily streak is needed.

Why almost nothing here is a streak

Cordeiro et al. (CHI 2015) surveyed 141 people who log or used to log their food, and read 5,526 posts on three apps' forums. People described how a few missed entries grew into giving up. We took this as a reason to make it easy to come back after a gap. It is not evidence that one streak design causes harm.

The same paper found that the feedback already feels unfair before anybody adds a game to it. One person described feeling guilty after going over a goal, without feeling equally good when under it.

There are four streak rewards in the app, all of them for logging and none for eating. They measure your best run ever rather than the current one. Breaking a streak costs you the next one. It cannot take away one you already have.

There is also a reward for coming back. You get it when you log again after a week or more without logging. That gap is exactly where people give up, so the app rewards the return and never mentions the gap.

What we refuse to give a reward for, and why

The rule, stated as a rule Nothing in the right-hand column is a feature we have not got round to.

Gets a reward

  • Logging a day at all
  • Weeks in which you logged five days
  • Total days logged, added up over time
  • Your best run of consecutive days, ever
  • Logging a day that went over your target
  • Reaching protein and staying within the calorie target band
  • Logging again after a week or more away
  • Trying different dishes
  • Sharing a meal, or adding one somebody shared with you
  • Every month you have had the app

Never gets a reward

  • A calorie deficit
  • A weight, or an amount lost
  • Staying under the added sugar limit
  • A “perfect” day, week or anything else
  • Eating progressively further below your target
The calorie reward is a range with a minimum as well as a maximum. A day at 60% of your target fails it exactly as a day at 140% does. We state this as our own rule, not as a comparison. Other trackers do reward deficits and weight lost. But the lists of their badges we could find are only in copies of help pages made by other people, and those pages have since been taken down. This page makes no claims about anybody else's product on that basis.

Nothing here is called “perfect.” Messer et al. (2021) surveyed 1,357 people. Those using a calorie app to control their weight and shape were more likely to say the app had harmed them than those using one for health reasons. The harms they named: thinking about food all the time, all-or-nothing thinking about food, anxiety about food, and purging. Plateau et al. (2018), 352 people, found the same split using different questionnaires. In these surveys, the reason for using the app went together with reported harm. That cannot tell who will be harmed, and it cannot prove cause. Avoiding a “perfect day” badge is our precaution. It is not a proven way to prevent harm.

And there is still no reward, streak or celebration on the added sugar limit, which is the promise the eating disorders page already makes. We have not tested whether a streak on a diet limit causes more harm. We avoid it as a precaution. Adding a rewards screen did not change our mind about it.

The one reward that looks odd is deliberate: you get one for logging a day that went over your target. A log with the heavy days missing is not a log. An app that is only pleasant to open when the day went well stops being told the truth.