Exploring the Science of Intermittent Fasting

For those looking to lose weight, intermittent fasting is a popular weight loss strategy, but is it really as effective as it the claims to be?

Intermittent fasting is a specific strategy to reduce energy intake through fasting which can be achieved through numerous patterns of dietary restriction. Popular forms of IF include alternate day fasting, eating only within a specific time frames of 4-12 hours, restricting calories on specific days of the week like the 5:2 diet and fasting for religious reasons including Ramadan.

A recent meta-analysis (Gu 2022) consisting of 43 randomized control trials with 2483 participants compared the results of individuals following intermittent fasting diets to those who followed their habitual diet or an alternative energy restricted diet (calorie restriction diet) for at least 1 month duration. Key outcome measures of interest included changes in weight, fat mass, waist circumference, fasted glucose, insulin, cholesterol and triglyceride levels.

Compared to a habitual diet, intermittent fasting diet does result in lower weight, lower waist circumference, reduced fat mass, higher lean muscle mass, lower cholesterol levels and lower triglycerides. However, there were there were no difference between weight loss achieved via intermittent fasting other energy restrictive diets.

Indeed, far from being a magic solution to hasten weight loss, the overall results achieved are often much smaller than people expect. Over a 6 month period, following an alternative day fasting pattern for 2 to 3 days a week (Tosti 2022), participants lost an average 5.9kg (range 2.3 to 9.5kg lost) over a 6 month period as a result of reducing overall energy intake over the week by 22.8% for 6 months. This translated to reduced total fat mass by -4.7kg (range 1.5 to 7.9kg lost) and waist circumference was reduced over the same time period by -8.4cm (range 0.6 to 16.2cm reduction). Compliance to an intermittent fasting approach drops after 6 months and weight loss results of 1kg per month can be achieved by a less restrictive approach.

As an Advanced Sports Dietitian and Health Coach, my goal is to empower my clients with the skills, knowledge and tools to make smart food and lifestyle choices in all situations regardless of whether they are at home, on holidays or going through a busy period at the office.

When it comes to weight loss, there are many tools in the toolbox that can be used to achieve the same result. While intermittent fasting may work for some people, for others it isn’t sustainable. The key is finding the right tools that work for your lifestyle that can be applied not just for a few weeks, but for months and years to create long-lasting results.


Gu L, Fu R, Hong J, Ni H, Yu K and Lou H (2022) Effects of Intermittent Fasting in Human Compared to a Non-intervention Diet and Caloric Restriction: A Meta-Analysis of Randomized Controlled Trials. Front. Nutr. 9:871682. doi: 10.3389/fnut.2022.871682

Tosti (2022) When a calorie is not a calorie: metabolic and molecular effects of intermittent fasting in humans; exploratory outcomes of a randomized clinical trial Aging Biology | Article 1 Editorial (agingcelljournal.org)

Dr Gemma Sampson
Advanced Sports Dietitian
Accredited Practising Dietitian
Health Coach

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