FatOK Help

FatOK estimates the physical fitness for adults from the four points of view:

  1. Health (waist-to-height ratio) [1,2]
  2. Traditional body mass index (the estimate of "thickness or thinness" by weight and height) [3]
  3. US Army Body Fat Standard (the estimate of the body fat percentage by the height and the circumferences of waist, neck, and maybe hips) [4]
  4. Fitness [5] (FatOk uses circumference method [4] to estimate the body fat percentage)

You select your main slimming goal from this list at the first launch of FatOK. For the chosen goal, with the button in the navigation bar, you can see your progress to this goal, the remaining distance to it. When there are enough data, you also see the average change for two weeks in the month before the last measurement. You can change your main goal in the settings (⋯⃝ -> Main goal).

FatOK also shows the caloric intake estimates to maintain and change your body fat percentage [6], [7], [8], [4]. It is handy because these estimates depend on your weight.

In addition to the information in the main goal row, Body Mass Index "thickness or thinness" estimates are shown in Weight entry and Body Mass Index entry of FatOk, after entering the weight and pressing Add.

The Waist entry, as distinct from all others, gives the estimate, which is valid not only for adults but for children also. If you are interested in the waist-to-height ratio only, you may use the Waist entry instead of the Body Fat (%) and save time on measuring your neck.

You may hide some of the entries mentioned above in the settings (⋯⃝ -> Items to show) if you don't use them.

FatOk works in close cooperation with the Apple iPhone Health app. In particular, it stores the weight, waist, height, and body fat percentage in the common Health App database. It allows watching the complete graph of your weight, waist, and body fat percentage with time in the Health App.

Therefore at the first start, FatOK asks your permissions to read and write in the common Health App database the height, weight, waist, and body fat percentage. Since, in general, the estimates are different for men and women and depend on the age, it also asks permission to read the date of birth to calculate the age and sex.

FatOK also asks permission for its notifications. Fat OK notifications will remind you to perform the measurements when two weeks have passed after the previous ones. So they are not intrusive. You may also set the notification time in the notification day (⋯⃝ -> Notification time). The two weeks interval is the minimal time to unambiguously estimate whether you lose or gain your body fat in the case of healthy slimming [9].

Before you begin, check that you entered the date of birth and sex (male or female) in the Health app. Health App does not allow other applications to change these values.

When you run FatOk the first time, start with entering the height if you did not enter it in Health App because the estimates depend on the height.

WARNING: You should be aware the FatOK gives only the estimates (see the formal medical disclaimer). These estimates are approximately correct for the majority of people but not for all. In case of doubt, always seek the advice of your physician or other qualified health providers.

Also, the caloric intake estimation assumes that the level of your weekly physical activity remains approximately constant. Be aware that it may be dangerous for your health to gain or lose weight too quickly. More exactly, a weight loss of no more than 1 to 2 pounds (0.5 to 1 kg) per week is recommended [4]. The estimates that FatOk makes take this requirement into account. Again if you feel that the caloric intake estimates don't work for you or in case of doubt, seek the advice of your physician or other qualified health providers.

You also should be very careful when you continue to lose weight in the "healthy" interval. It is true that the weight of most healthy persons indeed is in the "healthy" interval. However, it does not mean that each of them can reach any point in the "healthy" interval without the damage to her / his health. The same is true for the waist also.

As for the probability rate, a 2010 study that followed 11,000 subjects for up to eight years concluded that the waist-to-height ratio is a much better measure of the risk of heart attack, stroke, or death than the more widely used body mass index [9,1]. Also, a 2010 systematic review of published studies concluded that the waist-to-height ratio might be advantageous because it avoids the need for age-, sex- and ethnic-specific boundary values [10, 11].

In general, FatOK estimates of fitness are approximately valid for adults aged 20 years old or older. The US Military Body Fat Standard and body fat percentage estimates are roughly correct for adults aged 17 years and older. The Waist-to-height ratio estimates are approximately valid not only for adults but for children also.

If you don't have FatOK, you can download it on the App Store.
Download Fat OK

How to measure the body circumferences

The information and images below are from The Army Body Composition Program [4]

Neck measurement (for men and women)

Measure Soldier's neck circumference at a point just below the larynx (Adam's apple and perpendicular to the long axis of the neck). The Soldier should look straight ahead during the measurement, with shoulders down (not hunched), round the neck measurement up to the nearest half-inch.

For men (Figure B-3)

Abdominal measurement. Measure the Soldier's abdominal circumference to the nearest half-inch (through the navel (belly button)). Take measurements at the end of the Soldier's normal relaxed exhalation. Round down to the nearest half-inch.
Circumference measurements for men

For women (Figure B-4)

Waist (abdomen) measurement. Measure Soldier's natural waist circumference against the skin at the point of the minimal abdominal circumference. The Soldier's arms must be at the sides. Take measurements at the end of the Soldier's normal relaxed exhalation, round the natural waist measurement down to the nearest half-inch.

Hip measurement.

Measure Soldier's hip circumference while facing Soldier's right side by placing the tape around the hips to pass over the greatest protrusion of the gluteal muscles (buttocks) as viewed from the side. Ensure the tape is level and parallel to the floor. Round the hip measurement down to the nearest half-inch.
Circumference measurements for women

Support and Feedback


  1. Schneider; et al. (2010). "The predictive value of different measures of obesity for incident cardiovascular events and mortality.". The Journal of Clinical Endocrinology & Metabolism 95 (4): 1777-1785
  2. Ashwell, M., Gunn, P. & Gibson, S., 2012. "Waist-to-height ratio is a better screening tool than waist circumference and BMI for adult cardiometabolic risk factors: systematic review and meta-analysis." Obesity Reviews, 13, pp.275-286.
  3. "BMI Classification". Global Database on Body Mass Index. World Health Organization. 2006.
  4. Army Regulation 600-9. Personnel-General. "The Army Body Composition Program." Headquarters Department of the Army Washington, DC 28 June 2013. (Unclassified)
  5. Natalie Digate Muth. "What are the guidelines for percentage of body fat loss?" December 2, 2009. http://www.acefitness.org/acefit/healthy-living-article/60/112/what-are-the-guidelines-for-percentage-of-body-fat
  6. Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO (1990). "A new predictive equation for resting energy expenditure in healthy individuals". The American Journal of Clinical Nutrition. 51 (2): 241–7.
  7. "Position of the Academy of Nutrition and Dietetics: Interventions for the Treatment of Overweight and Obesity in Adults". Journal of the Academy of Nutrition and Dietics. January 2016 Volume 116 Number 1, 129-147
  8. Richard Weil, MEd, CDE. " How fast is your metabolism?" January 19, 2004. http://www.nbcnews.com/id/3958677/ns/health-webmd_health_resource/t/how-fast-your-metabolism/
  9. https://www.nhs.uk/live-well/healthy-weight/should-you-lose-weight-fast/
  10. https://en.wikipedia.org/wiki/Waist-to-height_ratio
  11. Browning Lucy M, et al. (2010). "A systematic review of waist-to-height ratio as a screening tool for the prediction of cardiovascular disease and diabetes: 0.5 could be a suitable global boundary value.". Nutrition research reviews 23 (02): 247-69

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