A week in the food diary: how to read your own numbers
After a week, your diary contains seven numbers, and the first instinct is to compare each one to a target. This is the least useful way to look at them: the real insights only appear in the aggregate.
One day means nothing
Daily energy expenditure is not constant: it changes based on activity, sleep, temperature, and even what you ate the day before. The variation between two consecutive days for the same person is hundreds of kilocalories, and it is not related to what you wrote in your diary.
Therefore, the unit of observation is not a day, but a week. Seven days smooth out fluctuations in expenditure, recording errors, and the difference between "weighed" and "estimated."
Four numbers to extract from the week
Seven-day average. This is your actual diet. It only makes sense to compare this to your calculated target.
The gap between minimum and maximum. Five days at 1,500 kcal and two at 3,000 kcal average out to exactly the same as seven days at 1,930 kcal—but they feel and function very differently. If the gap is more than double, the issue is not in the counting, but in the fact that weekdays are held together by willpower, while weekends exhaust it.
Average protein. The second most important number after calories. A weekly deficit is visible immediately, while a single day's deficit is not.
The number of days you actually recorded. Six out of seven days is data. Four is not data, but an illustration, and you cannot draw conclusions from it.
How to compare with weight
Body weight fluctuates by a kilogram or more per day due to water, intestinal contents, and glycogen stores. Comparing Monday's weight to last Monday's weight is therefore meaningless: you are comparing two random numbers. The mechanism is analyzed separately — why weight changes by a kilogram in a day.
A working method: weigh yourself every morning under the same conditions and compare the weekly average with the previous one. The difference between these two averages is the only metric that shows the trend.
What four typical scenarios mean
| Weekly average | Average weight | What this implies |
|---|---|---|
| Below target | Decreasing | Everything is consistent, nothing to change |
| Below target | Stagnant for three weeks | Either expenditure is lower than calculated, or not everything made it into the diary |
| Around target | Increasing | The same; start by checking your logs rather than cutting your intake |
| Well below target | Decreasing rapidly | The deficit is too large; losing more than 1% of body mass per week also leads to muscle tissue loss |
In the second and third rows, the cause is often the same: unrecorded items. There is a separate analysis on where exactly these hide: typical counting errors. For the case where logs are correct but weight is stagnant, see: weight loss plateaus.
What not to do after the first week
Cut your intake. The first week is for calibration: you are finding out how much you actually eat, not testing a hypothesis. You cannot change anything without knowing your starting point.
Compensate for missed targets. A diary is a measuring instrument, not a balance sheet that needs to be zeroed out. A day that ends 400 kcal below plan does not require compensation the next day.
Get upset about the average. For most people, the first honest average turns out to be 20–30% higher than expected. This is a normal result for a first measurement, not a failure.
After a month, the diary changes its purpose
For the first few weeks, it answers the question "how much." Later, the question changes: which dishes are repeated, where are the calories concentrated, and what can be changed in the diet without losing anything.
Here, it is useful to look at the list of recurring items. Usually, 15–20 dishes account for three-quarters of all meals, and all work on the diet comes down to editing this short list, rather than daily tracking.
By this point, most people stop recording everything and only track what is hard to predict: eating out, homemade dishes with unclear portion weights, and weekends.
Frequently asked questions
- How many days do you need to keep a diary to understand something?
- At least a week, and preferably two. Daily energy expenditure fluctuates on its own, so a single day doesn't show much, while seven days provide an average, the range, and where the bulk of the calories are going.
- Should I calculate the weekly average weight or look at the morning weight?
- The weekly average. Daily weight can fluctuate by a kilogram or more due to water retention and bowel contents, so comparing two individual days is just comparing random numbers.
- Do I need to compensate for a day when I ate more than the limit?
- No. What matters is the weekly average, not an individual day. Trying to "work off" yesterday usually ends in overeating again and does not noticeably affect the weekly result.
Read next
- Why weight changes by a kilogram in a day — Fat cannot be gained overnight: a kilogram of adipose tissue is thousands of kilocalories that cannot be acquired in eight hours of sleep.
- Why the tracker shows a deficit but weight remains the same — The app has shown a deficit for four weeks, but the scale hasn't moved.
- Weight loss plateau: why weight stalls and what to do about it — The weight has stayed at the same number for the third week in a row, even though the diet hasn't changed — and the first instinct is usually the same: to cut even more.
This article is for general information. It is not medical advice, a diagnosis, or a prescription for treatment or a diet, and it does not replace a consultation with your doctor. If you have a health condition, are pregnant, take medication, or follow a diet prescribed to you, decisions about food belong with your doctor.
Figures from regulations, guidelines and studies are given as they stood when this article was prepared and may since have changed; check them against the primary sources. This article is not advertising, an offer, or individual advice, and neither the author nor the site owner is responsible for decisions taken on the basis of it.