All Things Biology

Written by Lily Hunter

Fasting has had differing public profiles over the years, ranging from participation in religious events to diet fads, but what is the effect on the body, and is it possible to go 40 days and nights eating absolutely nothing? It might surprise you to know that the longest documented fast was a whopping 382 days, undertaken over a period of a year by a Scottish man from June 1965 to June 1966. He did maintain a diet of zero calorie drinks over that period, as it is impossible to go more than a week without water, was carefully monitored by a nearby hospital and was given supplements of vitamins, electrolytes and yeast. Not many people have undergone fasts quite as long as his, making it quite difficult to ascertain the effect this extremely long fast would have on the typical body, but he did lose 125kg (dropping from 207kg to 82kg), maintained this weight loss and went on to have children and live another 30 years.

This is not to say that a fast such as this is recommended for anyone, however, the results, especially the maintenance of the weight loss, have been of great interest to the scientific community. A mass study in 2019 tested subjects’ response to Buchinger fasting (250kcal a day with 2-3 litres of water) on a scale of 4–21 days to observe results not only in weight loss but in whole body changes as well (1). After thorough examination and testing, the subjects showed not only an average weight loss of 3.2kg for 5-day fasters and 8.6kg for 20- day fasters, but also a decrease in blood pressure, higher reported emotional and physical well-being, increased ketosis (where your body burns fat instead of carbohydrates), lower cholesterol and blood glucose, higher levels of haemoglobin and some evidence of decreased inflammation. 

This all sounds amazing, but some of the fluctuating results also indicate mild adverse effects. It is worth mentioning for example, that this study saw a decrease in leucocytes  (white blood cells that fight infection), and thrombocytes (cell fragments that form blood clots and prevent bleeding): whilst they did not decrease past the danger threshold in any fast period observed, it does call into question the balance of risk vs benefit in people with lowered immune systems, blood clotting disorders or those vulnerable to infection.

The Buchinger study provides an interesting insight into the effects of fasting on the body and shows promising results, but it definitely also calls for replication studies and further experimentation into all the potential effects fasting before doctors start prescribing it as a cure-all to patients.

Fasting is one of the most effective forms of weight loss, showing some of the highest success rates in keeping weight off after ending the programme. You may have heard about or tried smaller fasts such as intermittent fasting, but are these just as effective? Studies show that intermittent fasting is a pretty effective alternative to restricting calories with “equivalent benefits in body weight reduction, improvements in glucose homeostasis and lipid profiles, and anti-inflammatory effects.” (2) with even better effects in insulin-lowering and metabolic flexibility.

So, essentially, any fasting is good for the body and for weight loss if that is your main goal, and, if we think about it, it’s not that surprising as to why this is the case. We are, after all, just animals, and have fat stores for a reason. I personally think that one of the reasons people who fast see better physical and mental states as a result is because their bodies are now primed to find food in the most efficient way possible once their body is signalling that they need it – something most of us don’t wait to let our bodies tell us anymore. Overall, fasting can do wonders for your body but you need to remember to keep your protein, vitamins, minerals and electrolytes in check and not to undertake it if you have any major medical conditions.

References:

1.             Wilhelmi de Toledo F, Grundler F, Bergouignan A, Drinda S, Michalsen A Safety, Health improvement and well-being during a 4 to 21-day fasting period in an observational study including 1422 subjects. PLoS ONE. 2019 Jan 2;14(1):e0209353. 

2.             Song D K and Kim Y W. Beneficial effects of intermittent fasting: a narrative review. J Yeungnam Med Sci. 2022 Apr 4;40(1):4–11.