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Emma Rourke reviews Horizon: Eat, Fast, and Live Longer

14 Aug, 12 | by BMJ Group

There’s a new intervention being trialled. It will help you lose weight, it will delay the potential onset of dementia, and best of all it will enable you to live in the fullest of health for longer. Perhaps the main virtues of this intervention centre on its sheer simplicity: it doesn’t involve putting any chemicals into your body, it doesn’t involve surgery, and it doesn’t cost anything—it may even save you money. All you have to do is deprive yourself of one of life’s great pleasures—food.

The BBC aired Horizon: Eat, Fast and Live Longer earlier this week. During this one hour programme, Michael Mosley visits a number of institutions seeking to understand the ageing process. He meets a variety of experts, all of whom extol the virtues of caloric restriction (CR), and tries methods they advise in attempts to improve his performance on physiological testing. The most extreme of these methods involved 3 days and 4 nights of fasting, wherein Mosley consumed only water, black tea, and a single sachet of powdered soup.  Subsequently, he tried alternate day fasting, where consumption is limited to around 500 calories on one “fast” day and completely unlimited the following “feed” day. He finally settled for a 5 day “feed” period followed by a 2 day 500 calorie fast period.

For a supposedly scientific programme, however, the science was rather scant. The focus was strongly on the insulin-like growth factor 1 (IGF-1) as mediator of the benefits of CR. This signalling pathway has been widely studied and is known to stimulate growth and inhibit apoptosis of cells. Perhaps unsurprisingly given this role, it has been implicated in the pathogenesis of cancer [1]. It has several key functions in the body, including growth and maintenance of the skeletal system [2]. Interestingly, in vivo deficiency of IGF-1 in combination with testosterone correlates with reduced survival [3].

CR (without malnutrition) has been shown to increase lifespan in laboratory animals. In rodents, for example, CR postpones onset of age-related pathology and prolongs lifespan [4]. Is this explained solely by IGF-1 levels? Studies have sought to test the popular oxidative stress theory of ageing, and indeed noted reduced markers of oxidative damage in calorie restricted rodents [4]. This alternative mechanism by which CR may affect ageing is not even touched upon by the programme. As with much human science, it is more complicated than it seems and there is still no consensus on the role of antioxidant levels in CR—there’s something else at play [4]. That something may involve the nutrient-sensing pathways of target of rapamycin (TOR), it may involve the forkhead transcription factor (FOXO), and it may involve sirtuins [5]. In fact, the one thing we can be sure about is that the molecular determinants of lifespan are incredibly complex, and far from fully understood [6].

The programme furthermore neglected many social factors complicit in the ageing process. Humans are not laboratory animals and their environment cannot be so strictly controlled. Nevertheless, somewhat controversial experimentation in humans is ongoing. Accordingly, some may question whether it is responsible for a qualified doctor to so emphatically endorse such an approach in a prime time television slot? “This could radically transform the nation’s health,” he says.

The programme was littered with health warnings—“don’t do this without supervision” and “for some fasting can be dangerous”—but within hours online weight loss forums were overflowing with posts from people saying they’d give it a go. Mosley’s wife, a GP, appears to support his desire to pursue a 5 days feeding 2 days fasting regime, thus reinforcing to the public that this is a safe and worthwhile method.

Perhaps the diet Mosley ultimately adopts is not that radical, and perhaps it doesn’t even represent CR (the level at which CR is defined varies from 10-25% reduction in overall calorie intake in humans). Any attempt to encourage reduced calorie intake in a nation with such high rates of obesity as our own may be commendable, but critics will likely find little new in the advice Mosley dishes out: reduce your calorie intake, reduce your weight, reduce your cardiovascular risk factors. Perhaps that’s the message to hope people take forward from this.


[1] Hematol Oncol Clin North Am. 2012 Jun;26(3):527-42, vii-viii. Epub 2012 Feb 28.

[2] J Bone Miner Metab. 2008;26(2):159-64. Epub 2008 Feb 27.

[3] Steroids. 2012 Jan;77(1-2):52-8. Epub 2011 Oct 20.

[4] Mechanisms of Ageing and Development. 2004;125(10-11):811-26.

[5] Nature. 2008;454(7208):1065-71.

[6] Free Radic Biol Med. 2011 Jul 15;51(2):250-6. Epub 2011 Apr 22.

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  • Jenny Adams

    Great review.Having done just one 4 day fast in past I have absolutely no desire to repeat the process,whatever the benefits! I was hungry all the time and even dreamed about eating.Patients are intrigued by the idea of the shorter ‘semi-fast’ but I bet the ones who need it most will give up after trying it…

  • JC

    yes “the science was rather scant.” does anyone know of any stronger science, ideally involving humans!, to support this?

  • Hah, you’re right, the ones who do need it most are the ones that will struggle most with the whole concept. At least that’s been my experience with clients over the last couple of years. I’ve found that a gradual introduction to fasting, and appropriate eating, is needed for these folk, and lots of support.


  • “Perhaps the diet Mosley ultimately adopts is not that radical”! Is reducing calories for a few hours in your week radical? What do you think about eating 6 meals in 16 hours @ 1 meal every 2.5 hours? When did moderation become radical and excess became normal?

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