# Where the numbers come from

*Guide · 2026-10-22 · https://undiet.app/guides/where-the-numbers-come-from*

The diet switch chart on the home page draws the mean weight change that published studies reported for each diet. This page lists every study used, the figure as the paper reports it, how it was scaled to the chart, and what an average does and does not say about one person.

## What the chart shows

The diet switch chart on the home page draws, for each diet you tap, the mean body weight change that a published study reported, scaled to a 96 kg start. The light jitter on the line is cosmetic, under 0.3 kg, so it reads like a weigh in series rather than a plot.

The studies are randomised trials where one exists, with a meta-analysis or a second trial as a cross check. The table below names each one, with links to the publisher.

## How a study becomes a line

Each study reports weight at a few time points. We take each as a percentage of that trial’s own starting weight, apply it to 96 kg and draw straight lines between the points.

Nothing is extended past a study’s last measurement. Where a trial stopped before week 30, the line holds flat and the chart says so.

## What an average is not

An average is the middle of a wide spread. In STEP 1 the mean was 14.9% lower at 68 weeks, yet about one in seven people on the drug lost under 5% and about one in three lost 20% or more.

The people in these trials also had counselling, regular weigh ins and a team watching, and in the drug trials a placebo group lost weight too. Their average is not a forecast for anyone reading this page.

Undiet describes what the papers report; it does not advise. Before a diet, a fasting protocol or a medication, talk to your doctor or a dietitian.

## Undiet 90 has no study

[Undiet 90](https://undiet.app/diets/undiet-90) is the rotation program built into the app, and no trial has tested it. Its line is labelled as a model on the chart: the mean of two balanced diet arms, the PREDIMED-Plus Mediterranean group and the low fat group of Bazzano et al. 2014.

When a study of the program exists, this page and the chart will use it instead.

## What happens when you switch

The second period on the chart follows its own study from that study’s first week, starting at the weight the first period ended on. No study tested one diet after another, so this is the honest shape, not a measured one.

Three findings about leaving a program are added on top. After semaglutide stopped in the STEP 1 extension, people regained two thirds of what they had lost within a year; after behavioural programmes end, each kilogram lost comes back at about 0.13 to 0.19 kg a year; and the 1.6 kg of water lost in the first two weeks of a ketogenic diet is modelled as returning when a low carb period ends.

## Reading the table

Each row names the study, who was in it, how long it ran, the figure as the paper reports it, how it was turned into the line, and the caveat we think you should know. Links go to the publisher’s page.

Sample sizes are the number randomised unless the row says otherwise. Where a trial reported only a percentage, the kilograms are that percentage of 96 kg.

## The studies, one by one

- **GLP-1**: STEP 1, n 1,961, 68 weeks. Reported: semaglutide 2.4 mg once weekly: body weight 14.9% lower at 68 weeks vs 2.4% lower with placebo (15.3 kg vs 2.6 kg from a 105.3 kg baseline). On the chart: Weekly means read off the published Figure 1A (observed in trial data, weeks 0 to 68, digitised from the article PDF), applied to 96 kg. Caveat: With placebo controlled injections, dose escalation over 16 weeks, counselling every 4 weeks, a 500 kcal daily deficit and 150 minutes of activity a week. The placebo arm lost 2.4%. [Wilding et al., NEJM 2021](https://doi.org/10.1056/NEJMoa2032183)
- **GLP-1, cross check**: SURMOUNT-1, n 2,539, 72 weeks. Reported: tirzepatide 5, 10 and 15 mg: 15.0%, 19.5% and 20.9% lower at 72 weeks vs 3.1% with placebo. On the chart: Not drawn; listed so the line can be checked against a second source. [Jastreboff et al., NEJM 2022](https://doi.org/10.1056/NEJMoa2206038)
- **Keto**: Foster et al. 2010, n 307, 2 years. Reported: low carbohydrate arm: 9.5 kg lower at 3 months, 12.2 kg at 6 months, 10.9 kg at 12 months, 6.3 kg at 24 months (103.3 kg baseline); the low fat arm lost the same. On the chart: Table 2 kg values divided by the 103.3 kg baseline, applied to 96 kg. Caveat: With weekly group behavioural sessions for 20 weeks and prescribed walking. The low fat arm lost the same amount, so most of this line is the programme, not the carbohydrate rule. [Foster et al., Annals of Internal Medicine 2010](https://doi.org/10.7326/0003-4819-153-3-201008030-00005)
- **Keto, cross check**: Bueno et al. 2013 meta-analysis, n 1,577, 12 months or longer. Reported: very low carbohydrate ketogenic vs low fat diets at 12 months or longer: 0.91 kg more lost on keto (95% CI 0.17 to 1.65 kg). On the chart: Not drawn; listed so the line can be checked against a second source. [Bueno et al., British Journal of Nutrition 2013](https://doi.org/10.1017/S0007114513000548)
- **Fasting 16:8**: TREAT, n 116, 12 weeks. Reported: 0.94 kg lower (1.17%) at 12 weeks on 16:8 vs 0.68 kg lower (0.75%) in the control group; the difference was not significant. On the chart: The reported 1.17% of the 99.3 kg baseline, applied to 96 kg; straight line to week 12, then held flat because the trial stopped there. Caveat: No calorie target, no counselling, daily weigh ins on a connected scale. 141 were randomised and 116 analysed. [Lowe et al., JAMA Internal Medicine 2020](https://doi.org/10.1001/jamainternmed.2020.4153)
- **Fasting 16:8, cross check**: Chen et al. 2023 meta-analysis, n 665, 8 to 14 weeks. Reported: time restricted eating vs control in adults with overweight or obesity, mostly 8 to 14 week trials: 1.28 kg more lost (95% CI 0.52 to 2.05 kg). On the chart: Not drawn; listed so the line can be checked against a second source. [Chen et al., Frontiers in Nutrition 2023](https://doi.org/10.3389/fnut.2023.1079250)
- **Vegan**: Kahleova et al. 2020, n 244, 16 weeks. Reported: 6.4 kg lower at 16 weeks on the low fat vegan diet (93.6 kg baseline) vs 0.5 kg lower in the control group. On the chart: 6.4 kg divided by the 93.6 kg baseline (6.8%), applied to 96 kg; held flat after week 16 because the trial stopped there. Caveat: Ad libitum, with weekly classes. Weight was measured at weeks 0 and 16 only, so the line between them is straight. Run by the Physicians Committee for Responsible Medicine. [Kahleova et al., JAMA Network Open 2020](https://doi.org/10.1001/jamanetworkopen.2020.25454)
- **Low-carb**: Bazzano et al. 2014, n 148, 12 months. Reported: low carbohydrate arm: 5.7 kg lower at 3 months, 5.6 kg at 6 months, 5.3 kg at 12 months (96.3 kg baseline); low fat arm 1.8 kg lower at 12 months. On the chart: Table 3 kg values divided by the 96.3 kg baseline, applied to 96 kg. Caveat: With dietitian sessions, weekly at first then monthly, and one meal replacement a day in both arms. [Bazzano et al., Annals of Internal Medicine 2014](https://doi.org/10.7326/M14-0180)
- **Low-carb, cross check**: DIETFITS, n 609, 12 months. Reported: healthy low carbohydrate 6.0 kg lower vs healthy low fat 5.3 kg lower at 12 months; the difference was not significant. On the chart: Not drawn; listed so the line can be checked against a second source. [Gardner et al., JAMA 2018](https://doi.org/10.1001/jama.2018.0245)
- **Mediterranean**: PREDIMED-Plus, one year results, n 626, 12 months. Reported: 2.4 kg lower (2.7%) at 6 months and 3.2 kg lower (3.7%) at 12 months in the intervention group vs 0.4 kg and 0.7 kg in the control group. On the chart: The reported percentages (2.7% at 26 weeks, 3.7% at 52 weeks), applied to 96 kg. Caveat: Energy restricted, with activity promotion and behavioural support, in adults aged 55 to 75 with metabolic syndrome. Measured at 6 and 12 months, so the line to month 6 is straight. [Salas-Salvadó et al., Diabetes Care 2019](https://doi.org/10.2337/dc18-0836)
- **Undiet 90**: No study. Modelled as the mean of two balanced diet arms, see the two arms. Reported: No study of Undiet 90 exists. The line is the mean of two balanced diet arms: the PREDIMED-Plus Mediterranean group and the low fat group of Bazzano et al. 2014 (2.6 kg lower at 3 months, 2.3 kg at 6 months, 1.8 kg at 12 months from 97.9 kg).. On the chart: Mean of the two arms, each interpolated weekly from its reported time points, applied to 96 kg. Caveat: Not a study of this program. A labelled model, the mean of two balanced diet arms, shown so the chip has an honest line rather than an invented one. [PREDIMED-Plus, one year results](https://doi.org/10.2337/dc18-0836), [Bazzano et al. 2014, low fat arm](https://doi.org/10.7326/M14-0180)
- **No diet**: Control groups of TREAT and Kahleova et al. 2020, n 179, 12 to 16 weeks. Reported: control arms asked to change nothing: 0.68 kg lower (0.75%) over 12 weeks in TREAT and 0.5 kg lower over 16 weeks in Kahleova et al.. On the chart: Mean of the two control arms (0.75% and 0.54%) placed at their mean time point, week 14, applied to 96 kg; held flat after that. Caveat: People in a trial weigh in and know they are watched, which is why even control arms drift down a little. Outside trials, adults gained about 1.5 kg per four years (Mozaffarian et al. 2011, 120,877 people). [Lowe et al. 2020; Kahleova et al. 2020](https://doi.org/10.1001/jamainternmed.2020.4153)
- **No diet, cross check**: Mozaffarian et al. 2011, n 120,877, up to 20 years. Reported: three cohorts followed up to 20 years: an average gain of 3.35 lb (1.5 kg) per four year period. On the chart: Not drawn; listed so the line can be checked against a second source. [Mozaffarian et al., NEJM 2011](https://doi.org/10.1056/NEJMoa1014296)
- **The switch**: STEP 1 extension, n 327. Reported: one year after semaglutide and the lifestyle programme stopped, participants had regained 11.6 of the 17.3 percentage points lost, two thirds of the prior weight loss. On the chart: After a GLP-1 period ends, two thirds of what was lost is added back evenly over the following 52 weeks. [Wilding et al., Diabetes, Obesity and Metabolism 2022](https://doi.org/10.1111/dom.14725)
- **The switch**: Hartmann-Boyce et al. 2021, n 59,081. Reported: after behavioural weight loss programmes end, each kilogram lost was associated with faster regain at 0.13 to 0.19 kg a year; the difference from controls lasted at least five years. On the chart: After any diet period ends, 0.16 kg a year for each kilogram lost is added back, evenly. [Hartmann-Boyce et al., BMJ 2021](https://doi.org/10.1136/bmj.n1840)
- **The switch**: Hall et al. 2016, n 17. Reported: in the first 15 days of an isocaloric ketogenic diet body weight fell 1.6 kg, which the authors attribute mainly to water, with fat mass down only 0.2 kg. On the chart: When a keto or low carb period ends and the next one is not low carb, that 1.6 kg of water is modelled as returning over 15 days. A metabolic ward study of 17 men; the return is a model, not a measured figure. [Hall et al., American Journal of Clinical Nutrition 2016](https://doi.org/10.3945/ajcn.116.133561)

## Programs in this guide

- [Keto](https://undiet.app/undiet/diets/keto.md): A very low-carbohydrate, high-fat approach that pushes the body to run on fat instead of glucose. Structured and demanding, especially at the start.
- [Low Carb](https://undiet.app/undiet/diets/low-carb.md): Reduces carbohydrates (bread, pasta, sugar) without the strictness of keto, leaving room for fruit and veg.
- [Fasting 16:8](https://undiet.app/undiet/diets/fasting-16-8.md): Less a diet than a schedule: eating is kept within a set window (a common one is 8 hours). What you eat is up to you.
- [Vegan](https://undiet.app/undiet/diets/vegan.md): Excludes all animal products. Ethical and health motivations both common.
- [Mediterranean](https://undiet.app/undiet/diets/mediterranean.md): A way of eating built around vegetables, legumes, whole grains, olive oil and fish, with less red meat and sugar. Less a strict plan than a pattern, which is why people stay with it.
- [GLP1 Therapy](https://undiet.app/undiet/diets/glp1-therapy.md): A general tracking entry for anyone using a GLP1 receptor agonist medication for weight management.
- [Undiet 90](https://undiet.app/undiet/diets/undiet-90.md): A 90 day rotation program that cycles structured eating phases with recovery breaks.

More guides: https://undiet.app/undiet/guides.md. Find my diet in five taps: https://undiet.app/find-my-diet. Free on iPhone (https://apps.apple.com/app/id1490849895) and Android (https://play.google.com/store/apps/details?id=be.krnic.undiet).

Undiet describes programs and records what you log. It does not give medical advice.

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