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What kind of game is it?
Diet Diary is a simulation game where you choose meals, exercise, and sleep for a pixel-art character each day and guide them to a goal weight. First you set your character's sex, height, weight, age, goal weight, and job. Then you pick "Today's menu" and press "Start diet," and the days advance automatically, one at a time.
Weight changes with the gap between the calories eaten and the calories burned each day (your calorie balance). Your character's body shape follows BMI, so you can see the weight loss, too. Reach your goal and you'll see a "Goal reached!" screen with how many days it took and how your weight changed, which you can share on X or through your phone's share menu.
The English version uses pounds (lb) and feet and inches, U.S.-style meals like burrito bowls and cheesesteaks, and the CDC's adult BMI categories.
Features
Real formulas behind the calories
Resting metabolism (BMR) is calculated with the Mifflin-St Jeor equation, which is widely used in research and nutrition counseling. Daily calories burned combine that with your job's activity level (desk job, on the go, on your feet, or manual labor) and the intensity of your exercise in METs. Weight changes at about 3,300 kcal per pound of body fat (about 7,200 kcal per kg).
For example, a daily balance of −500 kcal works out to roughly 1 lb lost per week. The formulas and sources are explained in detail on the game's "How the Math Works" page.
Days that don't go to plan
Just like a real diet, not every day in the game goes the way you planned.
- The weather is sunny 55%, cloudy 30%, or rainy 15% of the time, and you can't exercise on rainy days
- There's a 15% chance of skipping your workout on weekdays and a 50% chance on weekends
- On weekends you snack a bit extra (150–400 kcal)
- Sleep only 5 hours and you'll get hungry and snack
- Random events happen too: donuts at the office, happy hour with coworkers, a friend asking "Did you lose weight?"
Stress and binges
Skipping breakfast or cutting calories too hard builds up stress. When stress reaches 85 or more, you binge the next day and eat 1,500 kcal extra. It lets you experience one of the hard parts of dieting: pushing too hard with strict cutting can backfire.
Energy-saving mode and muscle
If you keep cutting calories hard, your body goes into energy-saving mode and your BMR slowly drops. On the other hand, sticking with strength training builds muscle and raises your BMR a little. You get a feel for why losing weight slowly with exercise tends to go better than crash dieting.
An example week
Here's one possible week, starting with the default character: a man in his 30s at about the U.S. average height and weight (around 5'9" and 200 lb), with an on-the-go job and a goal 7 lb below his starting weight.
| Day | What happens |
|---|---|
| Monday | Toast for breakfast, a burrito bowl for lunch, grilled salmon for dinner, and a 30-minute walk (the default menu). The day ends with more calories out than in, and weight starts to drop |
| Tuesday | Rain means no exercise, so fewer calories burned |
| Wednesday | A walk on the lunch break burns a few extra calories |
| Thursday | Happy hour with coworkers sends calories in way up |
| Friday | Switching dinner to veggie soup to make up for it. Cutting that hard raises stress |
| Weekend | Workouts get skipped and there are extra snacks. Even so, the week ends in the negative and weight is down a little |
Events happen at random, so the same menu gives different results each time you play.
Tips
- A menu with a daily balance of about −300 to −500 kcal keeps stress low and your weight going down steadily
- Adding strength training raises your BMR and makes the later days easier
- When stress gets high, a snack or a good night's sleep is a valid way to bring it down
- You can change the menu at any time during the game. Watch the chart and adjust
For full instructions, see "How to Play" on the game's site.
FAQ
- Does it cost anything?
- No, it's free. You don't need an account or an app.
- Is the weight I enter sent anywhere?
- No. Your height, weight, and other inputs, along with your game progress, are stored only in your browser.
- Can I stop and continue later?
- Yes. Your progress is saved automatically, and you can press "Continue" next time to pick up where you left off.
- Will I lose weight the way the game says?
- The numbers in the game are estimates based on formulas from public health resources and research. Real weight changes vary with your body and lifestyle. This game is not medical advice or individual health guidance, so talk to a doctor or registered dietitian about real weight loss.