Sound science backs fasting. Calorie counting can’t compete

Fasting is no longer merely the domain of religion — more and more people are fasting for the sake of their body rather than their soul. It is timely, then, that a randomised controlled trial, published last week, has sought to assess if fasting is actually superior to traditional calorie counting as a sustainable way to lose weight.

On the surface, the trial looks extremely robust. Three groups were compared. In one the participants ate their normal diet; in another they ate 75 per cent of their normal intake of calories each day (these were the ‘calorie counters’); in the third group participants consumed 25 per cent of their diet one day and 125 per cent the next (the alternate day fasters).

The study had a one-year follow-up, a standardised diet (the American Heart Association diet) and close supervision of both groups, with time given for participants to adapt to their eating pattern, a period of six months to allow weight loss, and another six months given for participants to maintain their weight. Weight and fat loss were measured using very sophisticated, objective means that tracked precisely the change in body constituents. The cherry on the cake was its acceptance for publication in the prestigious Journal of the American Medical Association.

The study concluded that there was no benefit to fasting as opposed to traditional calorie reduction, when weight loss, fat loss and risk factors for cardiovascular disease (insulin levels, insulin resistance, cholesterol levels) were considered.

High-quality evidence now exists, you might think, against diets such as the 5:2 or other kinds of intermittent fasting. They work apparently simply because they involve a lower calorie intake. Case closed.

Except a closer reading of the paper suggests not. The reason? The participants in the study were put on a flawed diet.

The American Heart Association diet is a high-carbohydrate, low-fat eating plan. The AHA has given its seal of approval to many processed foods that are low in fat and high in sugar. They are marketed as healthy but are not really. A diet high in unrefined, natural carbohydrates would be fine — however, this diet makes no distinction between refined and unrefined.

The recommendation to eat low-fat dairy is now beyond a joke given all the evidence that certain forms of high-fat dairy products may lower the risk of diabetes, a major risk factor for cardiovascular disease.

Evidence for a generally low-fat diet is not credible either. Multiple studies, for instance, have found no association between saturated fat intake and cardiovascular death.

Overall, it cannot be held up as an optimal eating plan (this accolade goes to the Mediterranean diet).

Such a diet also creates problems in a fasting situation. A high-fat, low-carb diet is associated with considerable feelings of satiety when not eating. This satiety seems to be much less when consuming a more carb-rich diet. This may account for the relatively high drop-out rate — 38 per cent — among the fasters. Who knows how often the remaining participants ‘cheated’. A single high-carb meal doubtless left the participants feeling hungry for the rest of the day.

Moreover, we know that fasting tends to sensitive the body to the action of insulin and to increase levels of growth hormone as well as basal metabolic rate, which itself is useful in burning body fat and building muscle.

Introducing a high-carb meal into a fast will simply ameliorate these physiological benefits as the higher insulin secretion will tend to inhibit growth hormone secretion.

Bearing this in mind, the two arms of the study, the alternate fasting day arm and the calorie restriction arm, were essentially testing the effect of increased calorie restriction versus ‘regular’ calorie restriction using a diet that is far from optimal for health. It is no surprise, when considering the endocrine effects at play, that more stringent restriction did not lead to better weight loss, as we know that drastically decreasing calorie intake is associated with a lowered metabolic rate.

I would argue that the study merely proved that strict calorie restriction versus stricter calorie restriction while on a suboptimal diet is of no benefit.

The results cannot be extrapolated to the low-carb, high-fat diet, the Mediterranean diet, the Atkins diet or other evidence-based approaches combined with fasting.

More research is needed on the combination between fasting and these other dietary approaches, their mechanism of action and long-term results, before we can say anything definitive about fasting versus calorie restriction for the purpose of weight loss.

Meanwhile, there is plenty of sound science in support of fasting. Its benefits include lowering insulin resistance and, by extension, increasing insulin sensitivity, which lowers the risks of cardiovascular disease and diabetes. It reduces levels of LDL or ‘bad’ cholesterol. It also induces a process called ‘autophagy’ in which the body digests and disposes of cell remnants, akin to waste disposal, which has been linked to neuroprotection and may theoretically help protect the brain from degenerative disease. Not only that, it reduces inflammatory mediators in the body, which have been implicated in autoimmune disease; preliminary evidence suggests that fasting may have a role in their treatment but research is ongoing.

Fasting has also found use in cancer medicine. A lower incidence of side effects has been noted in patients receiving radiotherapy for brain cancer as well as chemotherapy. (No one is proposing it as an alternative to chemotherapy, radiotherapy or surgery.) New evidence suggests that it may even have a role in reducing breast cancer recurrence.

With such benefits, it is no wonder that more people are fasting for their health. By contrast, those who merely count calories to lose weight tend to put the weight back on (half of them will do so within five years). Calorie counting just doesn’t cut it.


  • davidofkent

    The human body has developed to store and utilise fat without harm to the organs. It has never developed to cope with non-fruit sugar. Even the sugar in fruit should be kept to a sensible level. ‘An apple a day keeps the doctor away’ sounds about right. As for the ludicrous ‘5-a-day’ admonition that nobody follows, it is simply more evidence that government should butt out of our dietary needs.