Weight-loss guru’s experiment: From junk food to ketogenic diet

Since then, he has written about diets to control blood sugar, improve gut health and shed fat faster – so for him to be tucking into burgers and chips, fried chicken, frozen pizza and fizzy drinks seems at the very least hypocritical. But, there is a reasonable explanation. The British-doctor-turned broadcaster is fond of self-experiments, and had put himself on what he describes as a “medium-level, ultra-processed food diet” for a documentary called Australia’s Health Revolution.

Initially, he rather enjoyed the novelty of unhealthy eating. “It took me back to the foods of my adolescence,” says Mosley. “And I quite liked eating things I hadn’t tried for a long while. But I didn’t like the way it made me feel. I was hungry all the time, sleeping badly and snoring loudly. It had an impact on my mood; I got a bit depressed and in a matter of days felt more lethargic.”

His GP wife, Clare Bailey, is normally tolerant of Mosley’s self-experiments, even coping with the episode when he swallowed a tapeworm to see how it would affect his body, but after two weeks she called time on this one. By then he had gained three kilos, pushed his blood sugar into the diabetic range, and his blood pressure was raised.

There is a happy ending to this misadventure. Mosley cut out the junk food, put himself on the diet he describes in his latest book, The Fast 800 Keto, and within 10 days had shed the extra kilos and everything was back to normal.

There is nothing new about the ketogenic diet. A low-carb, high-fat, adequate-protein way of eating, it has been used since the 1920s to help control seizures in children with hard-to-treat epilepsy. Decades later, a version known as the Atkins diet took hold, and more recently celebrities such as Kourtney Kardashian have helped keto go mainstream.

Mosley admits he has always been a keto sceptic, but has now changed his mind. “So many more studies have shown a benefit, at least in the short term,” he says. “I’m still not convinced that for most people keto is healthy in the long term. I’m sticking to the Mediterranean diet for that. But it’s like playing golf; you don’t use the same club all the way round. You start with your driver, you use your iron, you use your putter, depending on what stage you’re at and what you want to achieve.”

The new book includes a selection of recipes based on minimally processed foods. Although obesity rates have soared since the 1980s and one by one different macronutrients have taken the blame – too much fat, too many carbs, too much sugar – Mosley believes we are missing the bigger picture. He sees ultra-processed convenience foods – the things he was living on during his self-experiment – as the leading culprit.

The increase in the consumption of these factory foods has been matched by soaring obesity statistics. Now science is starting to make a much stronger case against them. Mosley cites one 2019 Spanish study published in medical trade journal the BMJ, involving nearly 20,000 university graduates who were followed for more than a decade. Those eating more than four servings a day of ultra-processed food were 62% more likely to have died during that time.

Meanwhile, US researcher Kevin Hall has conducted a trial that suggests consuming lots of ultra-processed foods leads to people overeating. He took 20 healthy participants and had them spend four weeks at the National Institutes of Health facility where they could be closely monitored. Each was restricted to a minimally processed or ultra-processed diet for two weeks, then switched to the other diet for two weeks (the study used a food classification system called NOVA, see panel, left). In both diets, the sugar, sodium, fat and fibre were exactly matched, but participants were allowed to choose how much they ate. By the second week on the ultra-processed diet, people were consuming an extra 500 calories a day, which resulted in a weight gain of about a kilogram, as opposed to a loss of about a kilogram when they were eating the minimally processed foods.