It’s a popular diet trend that’s gained much momentum in recent years, yet research is limited and fasting remains controversial. A Kiwi professor specializing in food addiction, obesity and weight management, Prof Doug. Sellman, explains what spurred him to start fasting – and the surprising impact it’s had on his life.

I discovered fasting only five years ago, at the end of a somewhat demoralizing decade of research on food addiction, obesity and weight-loss.

Previously, I’d dismissed fasting as a bit of a fad. And perhaps also because I endured a week of juice ‘fasting’ during medical student holidays 44 years ago, which was quite aversive. I remember feeling bored, irritable, restless, lethargic and hungry for much of the week. I now realize that wasn’t true fasting – fruit and veggie juices contain calories – and thus I missed out on the alerting experience of fasting. Fasting means stopping all, or virtually all, calories for a deliberate period of time, beyond the normal fasting we all do during a night’s sleep. Keeping busy with normal routines is good while fasting, including tea and coffee (splash of milk only).

Before I tried true fasting I’d heard about research showing that fasting increased longevity in rats. I suspected the same might apply to humans, although I wasn’t convinced it would be worth the pain. And then I chanced upon a YouTube video titled “Science of Fasting” and was amazed I hadn’t heard about the long-standing human research already conducted in Germany, Russia and the USA. This set me on a path of reading about fasting, which corrected much of the misinformation I’d picked up about fasting, and I became motivated to try it out for myself. A key piece of information was that fasting increases metabolic rate, in contrast to chronic food restriction which depresses it.

Not wanting to jump into the deep end, I took it slowly and built up fasting-fitness in small incremental steps. This strategy had worked well for me some twenty years previously, when I shed 16 kgs of unwanted fat very slowly over four years to return to the weight I was in my early 20s.

I took it slowly and built up fasting-fitness in small incremental steps.

The experiment began with 12-hour fasting, which meant not eating or drinking calorie-containing drinks after the evening meal until breakfast the next morning. This was surprisingly difficult to begin with as I faced breaking the psychological habit of supper. But after about 10-12 of these mini-fasts, I was ready to take another step and skip breakfast, thus extending the fast out to 16-18 hours before eating at lunchtime. This step wasn’t particularly difficult after I’d established 12-hour fasting. Insulin levels are low at the end of a 12-hour fast, and insulin is strongly linked to appetite, so I didn’t feel at all hungry in the morning. However, the next step to 24-hour fasting proved surprisingly difficult again, at least to begin with, and probably was related to the psychological habit of eating lunch, but also to the initiation of ketosis when metabolism switches from glycogen burning to fat burning. I notice this at about 18-20 hours of fasting. I get a kind of salty taste in my mouth. Again, after about 10-12 times I was reasonably comfortable with fasting for 24 hours. I then tried 36-, 48- and 72-hour fasting and finally completed a 5-day fast during a normal busy week at the University. I felt ready at that stage to start advocating fasting to others as I settled into a pattern of 16-hour fasting every day, with one 24-hour fast a week, and one 48-hour fast a month with comrades in the online group WELOVEFASTING.

Fasting helps to re-orientate thinking about food as nutrition rather than engaging in eating just out of habit or as a recreational activity.

One of the great freeing experiences of regular fasting is breaking a strong psychological attachment to continuous eating that many of us have. Fasting helps to re-orientate thinking about food as nutrition rather than engaging in eating just out of habit or as a recreational activity. Fasting also helped me become more flexible around food and eating, having previously lost weight using a rather strict regime of eating a little less and exercising a little more.

Most people are thinking about fasting as a simple way to lose weight, and I certainly think I could’ve lost my surplus 16kg in half the time if I’d known about fasting. But although fasting is simple conceptually, it nevertheless needs persistence and good healthy eating between the fasts to achieve sustained weight-loss.

A common question is: does fasting offer benefits to those who are at optimum weight?

Fasting helps maintain optimum weight, but more than that, it is refreshing, even 16-hour fasting. The reset in insulin levels is said to be an excellent foil against developing insulin resistance, the forerunner to Type 2 diabetes (in my family). The stimulation in the process of autophagy (metabolic ‘hoovering’) especially after about 18 hours, along with a decrease in inflammation is said to be a foil against a myriad of other chronic modern diseases, including coronary heart disease, strokes, cancers, and Alzheimer’s disease. More research is required to establish these prevention links definitively, but I’m convinced enough by the theoretical and anecdotal evidence that exists to engage in fasting now – time is running out at age 66. Fasting is free, straightforward, and has been in the wisdom traditions of humanity from the beginning of recorded time.

About seven or eight years ago, I developed an irregular heartbeat. My GP reassured me it was common and benign (ventricular ectopic beats). By about three months into regular fasting they had completely disappeared and haven’t returned. Perhaps it was coincidental, but the association with fasting was compelling.

Fasting is not without risks. People under the age of 20 should not generally fast, nor should anyone with a BMI less than 20, or those pregnant or breastfeeding. And people with significant medical or psychiatric problems should consult their GP prior to engaging in fasting.

Prof. Doug Sellman enjoys fasting

Doug Sellman is a Professor of Psychiatry & Addiction Medicine who has been working in the field of addiction treatment since 1985. He was Director of the National Addiction Centre, Christchurch School of Medicine & Health Sciences from its inception in 1996 through to 2017. He has been a professor within the University of Otago since 2006.