Thursday, September 13, 2018 - 13:15
Fasting practices promote long-term eating habits, gradual weight loss, with optimal nutrition.

The abstinence of energy for short periods of time alternated with periods of feeding has been practiced throughout the history of mankind: either through religious ascetic practices, health sanatoriums retreats, or through seasonal reduced food supply before industrialisation permitted abundance all year around. Recently fasting has emerged as novel approaches to address metabolic health issues, and potentially increase both life and healthspan.

CRON (Calorie Restriction on Optimal Nutrition) is the earliest investigated protocol. It advocates a daily restriction on energy intake by 20-40 per cent of estimated requirements, but without malnutrition. The first randomised controlled human trial demonstrating safety, efficacy and feasibility of CRON was recently completed: the CALERIE study spanned over two years, included 34 non-obese participants following moderate calorie restriction versus 19 controls following ad libitum intake. Surrogate biomarkers of healthspan, indicated significant beneficial effects of calorie restriction, which in time would protect from ageing related disease.

Fasting protocols which alternate restricted with unrestricted feeding phases have demonstrated similar effects.

Intermittent fasting (IF): total abstinence, or significant restricted energy (2100-2500kJ/day) over 1 to 4 non-consecutive days weekly. IF results in a net decrease in energy, because evidence shows that participants don’t seem to overcompensate on feeding days. Health benefits are driven by the resulting weight loss, and also via molecular pathways activated by fasting. In-vitro and animal studies show energy deprivation trigger the expression of regulators of cellular stress responses, resulting in: autophagy (cellular “spring-clean”), increased antioxidant capacity, reduced systemic inflammation, improved insulin and glucose homeostasis, increased fat oxidation, increased brain-derived neuro-growth factor, and stem cells activation. Benefits involving the microbiota are currently being investigated.

Time-restricted feeding (TRF) describes the practice of restricting feeding for a four to eight hour window every 24 hours, and abstinence for the remainder of the day. Energy intake usually matches normal requirements. The regular switch between fasting and feeding metabolisms is what appears to produce the metabolic benefits through pathways described above.

Are IF and TRF fad diets?
“Fad diets” are commonly followed over two to four weeks, including extreme regimens of food groups exclusion, severe energy restriction, often involving a commercial product to curb hunger and mask low energy levels. They commonly promise unrealistically rapid weight loss. Extreme restrictions can result in cravings, micronutrients deficiencies, disordered eating, and eventually in weight rebound because eating behaviours are not changed to healthier sustainable ones. The concept that weight can drop off quickly with a quick fix is contrary to how the body functions.

Conversely, fasting practices promote long-term eating habits, gradual weight loss, with optimal nutrition.  Evolutionarily speaking this may match what human physiology is used to. Considering the molecular effects, fasting may be the key trigger to activate inborn mechanisms for chronic disease prevention.

Personalisation to individual requirements is always key to any nutritional intervention, and should involve well educated professional advice.

Author: Dr Veronique Chachay is from UQ's School of Human Movement and Nutrition Sciences. Dr Chachay's research interests include the nutrient-gene relationship in the context of health and ageing disease, brown adipose tissue recruitment and activation, diet-induced thermogenesis in the management of obesity, the genetic characterisation of individuals following exclusive dietary patterns, as well as the effect of exclusive dietary patterns over time in the context of ageing and longevity.