Shahar Madjar, MD, Journal columnist

Roger A Lewis, a physicist from the University of Wollongong, Australia, had an interesting question: what amount of energy input (calories) does he need in order to maintain his weight. There are several websites that attempt to provide an answer to this question. But the answers differed widely and none of them provided a precise solution.

Lewis decided to embark on the “tried-and-tested path of self experimentation …” in order to find “the sweet spot (mostly avoiding sweets) where energy in equals energy out.” He published his results in the Christmas Issue of the prestigious British Medical Journal. The articles in the Christmas issue of BMJ are always presented with a great deal of humor. They also demonstrate methodological rigor.

It helped that the study was conducted during the Covid-19 isolation period. Isolation meant no working lunches, dinner parties, nor restaurant meals. It also meant sticking to a steady, consistent diet. His levels of physical activity have also remained relatively constant. He writes, “Each day was the same: get up, weigh myself, check emails, eat breakfast, Zoom, eat elevenses, Zoom, eat lunch, Zoom, time for a little nap, Zoom, eat dinner, and so to bed.”

He started by cutting his daily caloric intake to 5000 kJouls (1,195 calories). After 11 days at that level of caloric intake, he lost 2.23 kg (4.91 Lb). Over a total of 114 days, Lewis then gradually increased his caloric intake-from 5000 kJ to 7500, 8000, 8500, 9500,10,500, and eventually to 11,500 kJ (2748 calories).

Despite the significant increase in his caloric intake over this period, the data didn’t clearly show whether he was gaining or losing weight. The problem wasn’t a failure to adhere to the diet he designed, nor a malfunction of his bathroom scale. Instead, the culprit seemed to have been a great variability in the data he collected during each day. In desperation, in order to collect more data and to show a consistent trend in his weight, he started to weigh himself several times a day. “On 6 June 2020 (day 88) I weighed myself … at seven time points throughout the day, 35 measurements in all.” His weight along that day varied by more than 2 kg!

These daily fluctuations in weight were not directly related to his dietary intake. He found out, for example, that he lost an average of 0.57 kg during his twice-weekly 5K runs, and 1.07 kg between the time he was going to sleep and the time he was waking up in the mornings.

This shouldn’t have come as a surprise. These daily fluctuation in weight are normal and do not represent any loss, nor gain, in the mass of bodily fat. Instead, these fluctuations are more tightly related to the balance of fluids in our bodies. We gain weight immediately when we take in any amounts of fluids. We lose weight after urinating, having a bowel movement, and while sweating and breathing (yes! The exhaled breath you see form into a small cloud on a cold day is a large collection of tiny water droplets that leave your body). This balance of fluid intake and output is kept meticulously; and whatever fluid comes in, must eventually leave the body.

Despite the great variability in his daily weight, Lewis’ experiment wasn’t a failure. While the daily fluctuations could not be ignored, a general trend started to present itself. The initial phase in which he dramatically restricted his diet resulted in a significant weight loss. And toward the end of the experiment, after he had gradually increased his caloric intake, his weight started to inch up. He stopped the experiment before he was able to return to his original weight, but based on the multiple data points he collected, he was able to calculate the exact caloric intake that would result in an equilibrium of his weight. This number was exactly 10,286 kJ (2,438 Calories), or, as Lewis puts it, “about what my spouse thought before the whole thing began.”

As a bonus, he also calculated that “an extra apple a day will add 5 g [gram] to my weight, or about 2 kg [4.4 Lb] over a year.”

What can one learn from the results of one person’s self-imposed, self-disciplined, self-experimentation? I have learned that losing weight is a matter of numbers and calculations- a matter of basic arithmetic. And I have learned that when it comes to losing weight, frequently recording my weight, ignoring the noise of daily variation, and paying attention to long-term trends is what matters most.

And, coming shortly: “When somebody loses weight, where does the fat go?”